Nitrogen doi: 10.3390/nitrogen7020054

Authors: Tomáš Ječmen Tomáš Křížek Helena Ryšlavá Kamila Tichá Kateřina Bělonožníková

Riverine detritus is a key nutritional resource for benthic consumers, yet its biochemical quality fluctuates rapidly and is poorly captured by bulk indicators such as elemental analysis. To improve assessment sensitivity, we compared two analytical approaches targeting organic nitrogen. We refined a fluorimetric assay for primary amines using o-phthalaldehyde (OPA), identifying 2 M KCl as an optimal extraction medium that maximizes recovery while minimizing matrix interference. In parallel, we optimized capillary electrophoresis with contactless conductivity detection (CE-C4D) for free amino acid determination using 0.4 M ammonium carbonate. Applied to detritus from multiple river sites and seasons, both methods showed that primary amines and amino acids vary by an order of magnitude more than total nitrogen and exhibit patterns not detectable by elemental analysis, with consistent temporal trends across catchments. Primary amine-based measurements therefore provide a more sensitive and ecologically relevant assessment of detrital nutritional quality than bulk nitrogen metrics. The OPA assay is well suited for routine monitoring due to its simplicity and robustness, whereas CE-C4D enables detailed compositional profiling where amino acid speciation is required. Overall, detrital quality reflects both intrinsic properties and recent hydrological conditions, underscoring the importance of antecedent discharge and precipitation dynamics in its interpretation.

Nitrogen doi: 10.3390/nitrogen7020053

Authors: Abdulkadir Bayır Mehtap Bayır Gökhan Arslan Harun Arslan Abdel Razzaq Al-Tawaha

Aquaponics is a production system that results from the interaction between aquaculture and hydroponics. Whereas the mechanistic view of aquaculture and hydroponics has been explained using a simplistic nitrogen (N) cycle pathway, a new perspective on aquaponics could be obtained through the lens of a meta-holobiont. In this perspective, the symbiotic interplay across levels involving fish, plants, and microbes will be crucial for understanding and engineering aquaponics. With the advent of omics technology, it has become easier to explain the molecular basis of nutrient cycling and system stability. Although most available data are descriptive at present, they provide a foundation for understanding microbial interactions within the system. In this paper, we examine the genomic signatures of the N cycle, focusing on the roles of comammox bacteria and nifH-mediated N fixation. Moreover, the functionality of siderophore-producing microbes in enhancing nutrient bioavailability will be analyzed. Additionally, we explore the molecular mechanisms involved in the synthesis of secondary metabolites and Induced Systemic Resistance. Lastly, we discuss the path to aquaponics 4.0 and bio-digital twin modeling in aquaponics.

Nitrogen doi: 10.3390/nitrogen7020052

Authors: Beniamin-Emanuel Andraș Peter-Balazs Acs Vasile-Adrian Horga Edward Muntean Susana Mondici Ionuț Racz Marcel Duda

Nitrogen is a key determinant of both yield and quality in cereal crops; however, its efficiency is strongly influenced by environmental conditions and genotype. This study evaluated the impact of different sowing densities and nitrogen fertilization regimes on grain quality indices in four triticale (×Triticosecale Wittmack) varieties—Negoiu, Utrifun, Zvelt, and Tulnic—using a split-plot arrangement of the 4 × 3 × 3 type, under the climatic conditions of northwestern Romania. The experiment, conducted over two contrasting growing seasons (2021–2023), employed a split-plot design testing three sowing densities (450, 550, and 650 seeds/m2) and three fertilization levels: basic soil nitrogen fertilization, soil + foliar N-P-K application, and soil + foliar + biostimulant. The results indicated that climatic variability had a predominant effect on grain quality, followed by the genetic characteristics of the varieties and their response to water stress. In the drought-affected 2021–2022 season, the Zvelt variety recorded the highest protein content (14.2%), significantly outperforming the control (13.3%). Supplementary foliar fertilization and the use of biostimulants under drought conditions did not improve quality; in some cases, they led to significant decreases in protein content (from 14.36% to 13.69%) and thousand-kernel weight (TKW). Under optimal precipitation conditions in the 2022–2023 season, supplementary fertilization significantly improved hectoliter weight and TKW (reaching 46.7 g compared to 44.2 g in the soil-only treatments). Higher sowing densities (650 seeds/m2) generally led to decreases in hectoliter weight and TKW in favorable years. These results suggest that nitrogen fertilization can improve triticale quality. In this study, high yields, both quantitatively and qualitatively, appear to be mainly influenced by varieties and climatic conditions, especially water availability during critical growth stages.

Nitrogen doi: 10.3390/nitrogen7020051

Authors: Maria Gabriela Meirelles Helena Cristina Vasconcelos

Atmospheric nitrogen dioxide (NO2) is an important component of reactive nitrogen and plays a key role in the atmospheric nitrogen cycle outside major emission regions. However, its variability under remote background conditions remains poorly characterized, as most observational studies focus on urban or continental environments. This study investigates the background variability of in situ NO2 measurements at a remote North Atlantic island (Azores) over the period 2015–2024 and examines its association with large-scale atmospheric transport regimes. Monthly NO2 concentrations were classified into background Atlantic conditions and months classified under enhanced transport conditions using an objective PM10 percentile-based criterion. Differences between regimes were assessed using non-parametric statistics. Although median NO2 concentrations were slightly higher during months classified under enhanced transport conditions, the difference was not statistically significant. Wind speed analysis for the overlapping period 2018–2024 also indicated higher values during these months, but these differences were likewise not statistically significant. These results indicate that, at a monthly resolution, the influence of enhanced transport conditions on NO2 at this remote marine site is weak and not statistically resolved by the present approach. The findings therefore provide limited statistical support for a transport-driven modulation of NO2 and instead highlight the difficulty of detecting subtle reactive-nitrogen signals in clean marine environments. These findings contribute to improving the interpretation of reactive nitrogen variability in remote marine settings and highlight the value of island observatories for studying the atmospheric nitrogen cycle.

Nitrogen doi: 10.3390/nitrogen7020050

Authors: Most Annica Tabassum Md Mustafizur Rahman Md Abu Hanif

Seed pre-treatment is imperative for breaking the seed dormancy of some perennial species. The addition of soil amendments might be helpful in supporting seed germination and growth by available essential plant nutrients. This research investigated the effects of different pre-treatment and soil amendments on the germination, growth, and physiological performance of radhachura (Caesalpinia pulcherrima L.), an important ornamental and multipurpose woody shrub. Four pre-treatments and five soil amendments were applied in a CRD (Completely Randomized Design) arrangement to evaluate their individual and combined impacts under controlled nursery conditions. The ANOVA result revealed that seed germination indices of radhachura were mostly influenced by soil amendment rather than the seed pre-treatment. Among the soil amendments, vermicompost had a more profound impact on germination speed, Timson’s index and peak value, which had a similar effect to NPK application. Soil organic amendments positively affected growth, with vermicompost exerting the greatest influence on multiple germination traits that may support the early growth of radhachura, while biochar and compost maximized certain root and plant-length traits. Pearson correlations and PCA (first seven PCs explaining 76.2% variation) revealed the strong integration of late biomass, plant length, and root development, identifying vermicompost as key enhancers of multivariate vigor in radhachura seedlings. It might be concluded that C. pulcherrima L. species germination and growth was mostly influenced by soil amendment rather than seed pre-treatment. The study highlights that integrated nursery practices combining appropriate pre-treatment and soil amendments can enhance the germination success of radhachura.

Nitrogen doi: 10.3390/nitrogen7020049

Authors: Ben Crews Austin Fox Gary Zarillo

Eutrophication driven by excess nitrogen (N) and phosphorus (P) remains a pervasive global water-quality challenge, necessitating scalable nutrient recovery strategies that extend beyond conventional treatment approaches. This review synthesizes the emerging literature on algae-based systems as dual-purpose platforms for nutrient mitigation and biomass valorization. We examine systems including seaweed bioextraction, integrated multi-trophic aquaculture, algal turf scrubbers, and wastewater phycoremediation, while highlighting reported nutrient removal efficiencies and operational constraints. Beyond remediation, the spectrum of valorization pathways considered ranges from biofertilizers, feed, bioenergy, and materials to nutraceuticals, cosmetics, biomedical materials, biomanufacturing, and methane-mitigating livestock additives. The review emphasizes the economic and logistical challenges linking remediation-scale biomass production to commercial markets, including the contamination risk, processing intensity, regulatory classification, and scale mismatch. We propose an integrated remediation–valorization framework to guide research, policy, and industry toward nutrient-circular, economically viable restoration strategies.

Nitrogen doi: 10.3390/nitrogen7020048

Authors: Trinh Van Tuan Em Nguyen Van Chuong

The excessive use of inorganic nitrogen (N) fertilizers in rice production poses significant environmental and economic challenges, particularly in intensive farming systems such as those in the Mekong Delta, Vietnam. This study aimed to evaluate the potential of Herbaspirillum seropedicae (H. seropedicae), an endophytic N-fixing bacterium, to enhance soil fertility, improve rice growth, and maintain yield while reducing N fertilizer inputs in Dai Thom 8 rice under field conditions. A randomized complete block design with five treatments, including different nitrogen reduction levels combined with bacterial inoculation, was employed. The results showed that treatments integrating H. seropedicae significantly improved soil properties, including soil organic matter, total nitrogen, and available nutrients, compared to the control. Growth parameters such as plant height, tiller density, and chlorophyll content were also enhanced, particularly in treatments with bacterial inoculation. Yield components, including grain number and filled grains per panicle, were significantly increased, leading to higher grain yield. The highest yield was observed in T5 (5.72 t ha−1), while T3 and T4 achieved comparable yields with reduced N inputs. Additionally, grain quality analysis revealed increased protein content without negatively affecting starch composition. These findings highlight the potential of H. seropedicae as a biofertilizer to improve N use efficiency and reduce dependency on chemical fertilizers. The study provides strong evidence for integrating microbial inoculants into sustainable rice production systems. Among the treatments, T3 (50% N reduction combined with bacterial inoculation) is recommended as the optimal strategy due to its balance between high yield and reduced input costs, contributing to environmentally friendly and economically viable agriculture.

Nitrogen doi: 10.3390/nitrogen7020047

Authors: Tae Seon Eom Tae Wan Kim Sung Yung Yoo

High-temperature stress severely reduces the photosynthetic efficiency of radish (Raphanus sativus L.), a cool-season crop. This study evaluated five nitrogen (N) levels {0 N, 0.5 N, 1 N (234 kg urea ha−1, based on RDA), 2 N, and 4 N} through an open-field experiment under high-temperature stress conditions. Analysis of OJIP transients revealed that high temperatures severely inhibited photosynthetic capacity in the 0 N, 0.5 N, and 4 N treatment groups. These groups exhibited a simultaneous increase in K and J-steps, signifying electron transport bottlenecks and structural damage to the oxygen-evolving complex (OEC). Consequently, energy absorption and trapping decreased, while heat dissipation increased. In contrast, the 2 N treatment maintained superior Fm(maximum fluorescence) and energy flux, demonstrating enhanced photosynthetic resilience. However, despite improved photosynthetic stability, the 2 N group did not show a significant increase in yield compared to the 0.5 N or 1 N treatment groups. These results suggest that photosynthetic protection under heat stress does not necessarily guarantee higher yields, highlighting the need to identify optimal fertilization points for sustainable production. Overall, the findings of this study provide fundamental data for strategic nitrogen management in open-field radish cultivation to mitigate the impacts of increasing climatic instability.

Nitrogen doi: 10.3390/nitrogen7020046

Authors: Emanuela Cojocaru Jerca Adnan Arshad Ionuț Ovidiu Jerca Yuxin Tong Gina Fîntîneru Fatjon Cela Elena Maria Drăghici

Excessive nitrate accumulation in leafy vegetables presents significant health risks, requiring sustainable strategies to optimize yield while minimizing nitrogen-related anti-nutritional factors in controlled environments. This study investigated the effects of varying LED light intensities 236.9 µmol·m−2·s−1 (high), 189.8 µmol·m−2·s−1 (medium), and 117.6 µmol·m−2·s−1 (low) on nitrates (NO3−) dynamics, growth, and biochemical composition in two Lollo Rossa lettuce cultivars, Carmesi and Carnelian, grown in NFT hydroponic systems. Conducted under constant temperature (20/18 °C day/night) and CO2 (625 µmol·mol−1) to isolate light’s influence, the experiment used a replicated design with three replicates per treatment, each including two cultivars. Morphological traits (plant height, rosette diameter, leaf number, biomass, root development) and biochemical parameters (nitrate and sugar contents) were assessed via mean comparisons, trends, and correlations. Results demonstrated that higher light intensity significantly suppressed nitrate accumulation in lettuce through enhanced assimilation and dilution effects linked to increased growth. Nitrate levels dropped to 2091.67 mg kg−1 from 2443.33 mg kg−1 in Carmesi and 2013.33 mg kg−1 from 2515.00 mg kg−1 in Carnelian. Negative correlations were observed between nitrate content and growth parameters: nitrates vs. fresh biomass (r = −0.89); nitrates vs. plant height (r = −0.79). Concurrently, it boosted carbohydrate content (Carmesi: 3.03 °Brix; Carnelian: 3.08 °Brix) and promoted vigorous growth, with Carmesi achieving superior metrics under high light (height: 22.12 cm, rosette diameter: 29.87 cm, fresh biomass: 206.88 g, root biomass: 19.58 g) compared to low light (17.45 cm height, 183.42 g biomass). Carnelian exhibited similar trends but prioritized root elongation. These findings underscore light’s role in regulating nitrate transporters and assimilation enzymes (e.g., nitrate reductase), offering a low-cost approach to reduce nitrate risks, enhance nutritional quality, and improve yield in controlled horticultural systems (CHS).

Nitrogen doi: 10.3390/nitrogen7020045

Authors: Sofia Vitsa Panagiotis Sparangis Nikolaos Katsenios Christoforos-Nikitas Kasimatis Christos Kyriakou Ioannis Zafeiriou George Papadopoulos Aspasia Efthimiadou Dionisios Gasparatos

Nitrogen (N) fertilisation, as well as selection of the best cultivar and sowing date, have a significant impact on growth, plant physiology, and yield of wheat. In this study, three parameters (application of N fertilisation, early/late sowing time, and cultivars) and their interaction were examined to investigate their impact on agronomic characteristics of durum wheat and N soil content. Fertilised plants had the highest values of dry weight (15,265 kg/ha) and yield (5530 kg/ha) compared to the control. N fertilisation contributed to the increase in chlorophyll and stomatal conductance values in all measurements, while photosynthetic and transpiration rates were not affected by N application at the final measurement. Late-sown plants presented higher seed yield, even though a positive impact in dry weight (14,747 kg/ha) and 1000-seed weight (53 g) was observed in early-sown plants. The Levante cultivar reported the highest values of number of tillers (3), while yield (5399 kg/ha) and 1000-seed weight (60 g) were higher in the Simeto cultivar. The soil N content remained stable and was not significantly affected by the cultivar and sowing time. The results of this study indicate that the combination of fertilisation regime, cultivar, and sowing time influences growth and yield of durum wheat under the specific conditions of this Mediterranean environment.

Nitrogen doi: 10.3390/nitrogen7020044

Authors: Saira Sulaman Sule Orman

Wheat productivity and grain quality are strongly influenced by nutrient management and soil moisture availability. Nitrogen (N) and potassium (K) regulate biomass production, physiological stability and grain protein development. However, their efficiency varies under water-limited conditions. This study aimed to evaluate how soil moisture modulates nitrogen–potassium efficiency, nutrient partitioning, physiological responses and grain quality development in wheat. The current experiment was planned to assess the impact of varying but combined levels of N and K fertilizers on wheat crop growth and yield components as well as nutrient uptake and grain quality under different irrigation levels (i.e., normal irrigation Field Capacity (FC) 100%, partial water deficit FC75%, moderate water deficit FC50%, severe water deficit FC25%). The results of the study showed that increasing N-K supply enhanced biomass, chlorophyll contents, nutrient accumulation and grain quality under full irrigation, with N2K2 showing the highest growth, yield and quality traits. Under moderate deficit, N2K1 maintained a relatively stable yield and physiological performance, whereas severe moisture limitation markedly reduced nutrient uptake, grain development and fertilizer efficiency despite a higher NK application. Progressive reductions in irrigation also altered nutrient distribution among leaves, straw and grain, indicating moisture-regulated remobilization during grain filling. Maximum increments in values for plant height (27%), total biomass (108%), grain yield (183%), grain NPK content (38%, 6.3%, 26%), grain protein (38%) and wet gluten (38%) were noted in the N2K2 treatment at FC100%, but these parameters showed up to 80% reduction under the same treatment of N-K at FC25%. It is concluded that wheat response to N–K fertilization was moisture dependent and fertilizer rate alone did not ensure productivity under severe water deficit. Therefore, integrating nutrient supply with irrigation management is essential to sustain productivity and grain quality.

Nitrogen doi: 10.3390/nitrogen7020043

Authors: Xuequn Yan Xinwei Xiong Jingfen Pan Lu Yin Xiao Liu Yanglei Jia

Nitrogen metabolism is fundamental to all organisms, with ammonium transporters (Amt) playing a pivotal role in transmembrane ammonium transport. Brachiopods, as “living fossils”, offer unique insights into the evolutionary adaptation of marine invertebrates. This study systematically identified and characterized the Amt gene family in the brachiopod Lingula anatina. Five canonical Amt genes were identified, with nonrandom chromosomal distribution and evidence of lineage-specific duplication events. Phylogenetic analysis revealed that these Amt proteins cluster into three well-supported clades, showing closer affinity to Caenorhabditis elegans, reflecting conserved ancestral features predating protostome radiation. Structural predictions showed that LanAmtA and LanAmtB retain the canonical 11-transmembrane helix (TMH) topology with an extracellular N-terminus, while LanAmtC features a unique 12-TMH architecture with an intracellular N-terminus, resembling certain vertebrate Amt-related proteins. Critical functional residues involved in ammonium selectivity and transport were preserved across all paralogs. Expression profiling revealed non-redundant spatiotemporal patterns: LanAmtA1 and LanAmtB2 dominate early embryogenesis, with LanAmtB2 becoming the major isoform in late developmental stages; LanAmtC exhibits constitutive high expression across adult tissues. Collectively, our findings demonstrate that the L. anatina Amt family expanded via local duplications, evolving structural stability, regulatory diversity, and functional specificity. This study provides a comprehensive molecular framework for understanding the evolutionary adaptation of nitrogen-handling mechanisms in basal lophotrochozoans and sheds light on how intertidal organisms cope with dynamic environmental conditions.

Nitrogen doi: 10.3390/nitrogen7020042

Authors: Md. Mosaraf Hossain Md. Abdul Kader M. Jahiruddin Shamim Mia Ahmed Khairul Hasan Abu Zofar Md. Moslehuddin

Understanding the factors controlling nitrogen use efficiency (NUE) in paddy soil is essential for optimizing the application of relatively costly nitrogen (N) fertilizer for rice cultivation. Therefore, an experiment was conducted to assess the seasonal variation in NUE among three Aus, five Aman, and three Boro rice varieties at the Bangladesh Agricultural University (BAU) farm during the Aus, Aman, and Boro cropping seasons. In addition, the variation in the NUE of rice was assessed among eight soil series throughout Bangladesh during the Boro season. The experiment included N control and N application at the recommended rates. The results showed that BRRI dhan48 outperformed the other varieties in the Aus season, with the maximum agronomic efficiency (AE). In contrast, BRRI dhan65 was better in terms of physiological efficiency (PE), whereas BRRI dhan42 showed the lowest AE. Throughout the Aman period, BR11 exhibited the best AE and PE. During the Boro season, BRRI dhan29 and BINA dhan-6 demonstrated the maximum AE, PE, and apparent recovery efficiency (ARE). Grain yield, nitrogen response, AE, and ARE were markedly higher in the Boro season than in the Aus and Aman seasons. Among the eight locations, the highest grain yield of BINA dhan-7 in the Aman season was recorded in the Noadda soil series, followed by Barisal and Sara, with an AE extended from 11 to 19 kg grain kg/N applied, PE from 31 to 61 kg grain kg/N uptake, and ARE from 21% to 41%. These findings highlight the significant variability in NUE among rice varieties, seasons and soil series, suggesting the importance of variety, location and season-specific N management.

Nitrogen doi: 10.3390/nitrogen7020041

Authors: Juan Aviñó-Calero Silvia Sánchez-Méndez Luciano Orden Ernesto Santateresa Francisco Javier Andreu-Rodríguez José Antonio Sáez-Tovar Encarnación Martínez-Sabater Cristina Álvarez Alonso María Ángeles Bustamante Raúl Moral

The large-scale use of compost in arable cropping systems is often limited by the large quantities required to meet the crop’s nutritional needs. Palletization can increase the nutrient density of organic fertilizers and improve their logistical feasibility by reducing storage, transport and application costs. This study evaluated the agronomic and environmental performance of compost pellets derived from pig slurry solids and olive pomace, using them as an alternative nitrogen source for wheat (Triticum aestivum L.) cultivated under Mediterranean conditions. A field experiment was conducted during the 2022–2023 growing season, with four treatments arranged in 24 m2 replicated plots: an unfertilized control (C); pelletized compost (PSCOP); fresh pig slurry (PS); and mineral fertilization based on monoammonium phosphate and urea (IN). Excluding the control treatment, all fertilized plots received a uniform nitrogen rate of 150 kg N ha−1. Soil chemical properties and nutrient availability (Pext, NH4+-N and NO3−-N) were evaluated at the beginning and end of the experiment, while wheat yield and grain quality were assessed at harvest. Greenhouse gas (GHG) emissions were monitored throughout the cropping season to evaluate environmental impacts. The results showed that the wheat yields achieved with PSCOP were comparable to those obtained with PS, although they remained lower than those achieved with mineral fertilization. Grain quality was not adversely affected by the application of PSCOP. Furthermore, PSCOP resulted in lower GHG emissions than mineral fertilization, with values closer to those observed in the unfertilized control. These findings suggest that pelletized organic fertilizers such as PSCOP may be a promising way to enhance nutrient circularity and reduce reliance on synthetic fertilizers and maintain crop productivity and limit environmental impact in Mediterranean agricultural systems.

Nitrogen doi: 10.3390/nitrogen7020040

Authors: Katalin Juhos Szilvia Zsuzsanna Huszárszky Andrea Veres Mădălin Radu Ciprian Bolohan Costel Mihalașcu Andrei Măruțescu Max John Newbert Vasileios P. Vasileiadis

Cover crops (CCs) provide key ecosystem services, including nitrogen (N) retention and increased soil organic carbon (SOC), although their short-term benefits may be limited in dry continental climates. This study assessed a conservation system combining CC and non-inversion tillage (MT+CC) over a full crop rotation (sunflower–winter wheat–corn–sunflower) in south-eastern Romania, compared with plough-based tillage (PT). A randomized block design was conducted on a clay loam Luvisol, and N retention was estimated annually from soil mineral N and the biomass and N content of CC and weeds. MT+CC increased N retention during the first three years (+20.30 kg ha−1 before corn; +26.67 kg ha−1 before sunflower), but this advantage declined, and in year four PT showed higher N retention due to intensive weed growth. MT+CC reduced corn and sunflower yields, likely because of water competition and temporary N immobilization, but increased winter wheat yields. After four years, SOC was significantly higher under MT+CC (1.42%) than PT (1.37%), while total N remained unchanged, resulting in a higher C:N ratio. Consequently, in continental climates, CC use has a limited N retention potential, and excessively late CC sowing and termination is risky in crop rotations dominated by high-N-demand spring crops.

Nitrogen doi: 10.3390/nitrogen7020039

Authors: Jana Maková Renata Artimová Soňa Javoreková Samuel Adamec Oleg Paulen Alena Andrejiová Ladislav Ducsay Juraj Medo

The application of nitrification inhibitors (Nis) with nitrogen fertilizers is increasingly used as a management strategy to improve nitrogen use efficiency in crop production systems. To evaluate the effects of Ni dicyandiamide (DCD) and 1,2,4-triazole (TZ) on the rhizosphere microbiome and strawberry yield (Fragaria × ananassa Duch.), a two-year field experiment was conducted with three treatments: unfertilized control (C), mineral nitrogen fertilizer (N) applied in two doses (40 + 40 kg N ha−1 year−1), and a single nitrogen application (80 kg N ha−1 year−1) combined with nitrification inhibitors (N + Ni). Soil microbiota were assessed using cultivation-based methods and metabarcoding of 16S rRNA and ITS2 regions. Total bacterial counts on complex media increased from 5.85 to 6.15 log CFU g−1 in the N treatment, while remaining 5.89 in N + Ni. Microscopic fungi increased in fertilized treatments during spring but decreased in July of the second year. Microbial community composition differed among treatments, although sampling time explained a larger proportion of variability than fertilization. Relative abundance of Gemmatimonas decreased under N + Ni, whereas Nitrososphaera increased. Fungal Shannon diversity decreased in N + Ni, while prokaryotic diversity did not differ significantly. Despite similar levels of mineral nitrogen measured before harvest, strawberry yield increased significantly in the N + Ni treatment in the second year, reaching 109% higher values than the control and 80% higher than the N treatment. This may indicate that the fertilization regime including nitrification inhibitors influenced nitrogen availability earlier in the growing season.

Nitrogen doi: 10.3390/nitrogen7020038

Authors: Liem Thanh Tran Chuong Van Nguyen

Baby maize (Zea mays L.) is widely cultivated across Asia due to its short growth cycle and adaptability to diverse agroecological conditions. However, its production is frequently constrained by low soil fertility, leading to the excessive use of chemical fertilizers, which in turn contributes to environmental degradation. Endophytic bacteria with the ability to fix atmospheric nitrogen and solubilize inorganic phosphate represent a sustainable alternative for improving nutrient availability. This study aimed to isolate and characterize endophytic bacteria exhibiting dual nitrogen-fixing and phosphate-solubilizing capabilities from baby maize roots. A total of ten bacterial isolates were obtained and screened using nitrogen-free Burk medium and NBRIP medium. Among these, strain CMB2 demonstrated superior functional traits. Molecular identification based on 16S rRNA gene sequencing confirmed that the isolate belongs to Bacillus stercoris. In vitro assays revealed that B. stercoris CMB2 exhibited significant nitrogenase activity, as determined by the acetylene reduction assay, and strong phosphate-solubilizing ability, indicated by a clear halo zone and a high solubilization index. These findings suggest that B. stercoris CMB2 is a promising multifunctional endophytic bacterium for enhancing nutrient availability under controlled conditions. Further validation under greenhouse and field conditions is required to assess its potential for improving plant growth and nutrient uptake in baby maize.

Nitrogen doi: 10.3390/nitrogen7020037

Authors: Julián Andrés Castillo Vargas Anaiane Pereira Souza

Nitrogen (N) utilization by ruminants affects production efficiency, feeding costs, and environmental N losses in confined production systems. Palm kernel cake (PKC), an abundant agro-industrial by-product in tropical regions, has been increasingly used in ruminant diets, although its effects on nitrogen dynamics remain inconsistent. In this study, we systematically reviewed and meta-analyzed the effects of dietary PKC inclusion on N intake, excretion, absorption, and retention in confined cattle, goats, and sheep. Eleven studies published between 1995 and 2025, comprising 44 treatment means and 322 experimental units, were included in the meta-analysis. A random-effects model was applied, and the ruminant species was used as a moderator, defining a significant level at 0.05. Overall, the pooled effects indicated that species significantly influenced N intake (p < 0.01) and N absorption (p < 0.01). Species also showed a tendency to influence N in feces (p = 0.062) and manure N (p = 0.073), whereas N in urine (p = 0.194) and N retention (p = 0.170) were not affected. In subgroup analysis, PKC inclusion reduced N intake in goats (Standardized Mean Difference (SMD)) = −0.792; 95% CI (Confidence Interval) = −1.428 to −0.155; I2 (Heterogeneity) = 76.7%) and cattle (SMD = −1.576; 95% CI = −2.250 to −0.902; I2 = 65.7%), N in urine in cattle (SMD = −0.478; 95% CI = −0.806 to −0.150; I2 = 0%), N absorption (SMD = −0.873; 95% CI = −1.517 to −0.229; I2 = 77.1%), and N retention (SMD = −0.875; 95% CI = −1.338 to −0.412; I2 = 64.1%) in goats. Conversely, PKC had a positive effect on N absorption in sheep (SMD = 1.137; 95% CI = 0.016 to 2.258; I2 = 72.4%). Overall, this study highlights the species-dependent responses of N dynamics to PKC inclusion, emphasizing the importance of species-specific dietary strategies when using agro-industrial by-products to improve nitrogen utilization efficiency and potentially mitigate N losses in confined ruminant systems.

Nitrogen doi: 10.3390/nitrogen7020036

Authors: Karina Batista Mayne Barboza Sarti Laíze Aparecida Ferreira Vilela Luciana Gerdes Cristina Maria Pacheco Barbosa Gabriela Aferri

Maize–tropical grass intercropping has been adopted during the dry season as a strategy for soil cover; however, a knowledge gap remains regarding adequate nitrogen (N) supply and the efficiency of this system in degraded pasture areas. The objective of this study was to evaluate dry biomass, grain yield, and macronutrient concentrations in maize–tropical grass intercropping as a function of N rates applied as side-dressing in the dry season. The experimental design consisted of a randomized complete block design in a split-plot arrangement with four replications. Main plots comprised maize monoculture, maize intercropped with Urochloa ruziziensis (Congo grass), and maize intercropped with Megathyrsus maximus cv. Aruana (Aruana Guinea grass). Subplots consisted of N rates (0, 50, 100, and 150 kg ha−1). Maize–Aruana intercropping showed a positive linear response to N rates for grain yield; specifically, the nitrogen rate of 150 kg ha−1 resulted in a 71.71% increase in grain yield compared to the lack of nitrogen supply. Conversely, maize monoculture showed a negative linear response, where the highest N rate (150 kg ha−1) resulted in a 68.83% reduction in grain yield compared to the lack of nitrogen supply. Despite yield potential being capped by seasonal water deficits and frost events, the intercropping systems maintained essential growth dynamics. Aruana grass provided a protective effect for maize development under stress. The findings demonstrate that N side-dressing in the maize–Aruana intercropping system in a minimum of 71.83 kg ha−1 is an adequate strategy to enhance grain yield and biomass production.

Nitrogen doi: 10.3390/nitrogen7020035

Authors: Georgios Giannopoulos Ioannis Anastopoulos Vasileios A. Tzanakakis Eduardo Vázquez Pantelis E. Barouchas Anne Boos Dimitrios Kalderis Fotis Sgouridis Vassilis Aschonitis George Arampatzis

Despite a growing interest in biochar for olive orchard fertility management, little is known about its effects on nitrogen (N) dynamics and greenhouse gas (GHG) emissions in Mediterranean soils, particularly when comparing neutral (pH 6.7) and alkaline (pH 8.2) soils using farmer-accessible flame-curtain pyrolysis biochar. In this 60-day soil mesocosm study, we hypothesized that biochar amendments in fertilized soils would enhance soil N availability and potentially reduce N2O emissions, with effects modulated by soil pH. Treatments included: control, urea fertilizer, and urea plus biochar (5% w/w). Urea fertilization significantly increased soil ammonium (NH4+) and total oxidized nitrogen (NO3− + NO2−) in both soils, and co-application of biochar further increased these pools, particularly in the neutral soil (NH4+: + 91% and + 62% in neutral and alkaline soil, respectively). Biochar addition consistently reduced cumulative carbon dioxide (CO2) emissions in both soils, supporting its role in stabilizing soil organic carbon. However, impacts on nitrous oxide (N2O) emissions were soil-pH-dependent: biochar slightly reduced N2O emissions in neutral soil, though nearly doubled N2O emissions in alkaline soil, highlighting that biochar’s efficacy for GHG mitigation is context-specific. These findings underscore biochar’s potential to improve soil N availability and reduce carbon losses but reveal clear limitations for N2O mitigation in alkaline soils, necessitating site-specific application strategies that explicitly consider soil pH when targeting climate benefits in Mediterranean olive production.

Nitrogen doi: 10.3390/nitrogen7020034

Authors: Mathew Edung Etabo Pablo Lacerda Ribeiro Britta Pitann Karl Hermann Mühling

Drought will likely become more frequent and intense in Europe due to climate change, which may worsen Mn2+ and P deficiencies found in high pH soils. In this context, research investigating the effectiveness of ammonium-based nitrogen fertilizers treated with nitrification inhibitors (NIs) in alleviating Mn2+ and P deficiencies in such soils has been done. However, studies considering the impact of drought periods and soil texture on this topic are lacking. Therefore, we carried out a study addressing this research gap. Maize plants were grown in a greenhouse experiment, and the experimental setup comprised three factors consisting of soil texture (sand and silt loam), soil moisture (sufficient and drought), and DMPP application (with and without DMPP). The measured variables were bulk and rhizosphere soil pH, Mn2+ availability, maize biomass yield, and shoot concentration of selected macro- and micronutrients. DMPP increased shoot biomass production by 60% in silt loam under drought but not in sand soil texture. In addition, DMPP increased Mn2+ and P shoot concentrations by 38% and 21%, respectively, in the silt loam soil texture under drought. In contrast, DMPP did not alleviate the negative impact of drought on plant biomass production, Mn2+ and P shoot concentration in the sand soil texture. In conclusion, DMPP application is effective in alleviating Mn2+ and P deprivation in high pH soil subjected to drought. However, this effect was soil texture-dependent and observed in the silt loam rather than in the sand soil texture.

Nitrogen doi: 10.3390/nitrogen7010033

Authors: Fang Zhang Shiqing Peng Biao Chen Yanjin Shi Xiaohong Wang Dan Xing

Mulberry (Morus alba L.) is a woody plant primarily cultivated for silkworm breeding, with significant economic and ecological functions. Its nitrogen use efficiency directly affects leaf yield, quality, and environmental adaptability. The main inorganic nitrogen forms available for plant uptake in soil are ammonium nitrogen and nitrate nitrogen, and plant uptake and assimilation of these two nitrogen sources often exhibit species-specific preferences. This review systematically summarizes the research progress on nitrogen uptake preferences in mulberry, confirming that this species generally shows a preferential uptake of nitrate. Specifically, when supplied with nitrate or a mixed nitrogen source dominated by nitrate, mulberry exhibits better performance in growth and development, photosynthetic efficiency, and accumulation of secondary metabolites. This review further discusses the physiological characteristics and underlying regulatory mechanisms responsible for this preference, and analyzes key factors affecting nitrogen uptake preferences, including soil properties, environmental stresses, and microbial interactions. It should be noted that while controlled experiments have yielded important insights, the applicability of these findings under complex field conditions still requires further validation through field trials. Finally, future research directions are prospected, including in-depth dissection of molecular mechanisms, field validation, plant-microbe interactions, and nutritional strategies for stress resistance, aiming to provide a theoretical basis for efficient cultivation and precise nitrogen management of mulberry.

Nitrogen doi: 10.3390/nitrogen7010032

Authors: Phan Tran Hai Dang Nguyen Van Chuong

Baby maize (Zea mays L.) is a high-value horticultural crop widely cultivated due to its short growth cycle and strong market demand. However, intensive production systems often rely heavily on chemical fertilizers, leading to reduced nutrient use efficiency and potential soil degradation. The present study investigated the potential of the Priestia megaterium Thr45 to enhance soil fertility, improve crop performance, and optimize fertilizer management in baby maize cultivation. A field experiment was conducted using a three-factor factorial design consisting of bacterial inoculation, different urea application rates, and different KCl rates. Soil chemical properties, plant growth parameters, yield components, and nutrient composition of edible cobs were evaluated. The results showed that inoculation with P. megaterium Thr45 significantly increased available phosphorus and exchangeable potassium in soil compared with the non-inoculated control. Inoculated plants exhibited higher chlorophyll content, greater leaf development, and increased plant height during early growth stages. Bacterial inoculation also significantly improved yield components, including ear number, ear yield, edible cob yield, and plant biomass. Furthermore, the nutritional quality of baby corn was enhanced, as reflected by increased protein and mineral (N, P, and K) concentrations in edible cobs. Significant interactions between bacterial inoculation and fertilizer treatments indicated that the beneficial effects of P. megaterium Thr45 were closely associated with nutrient management practices. Notably, comparable yield and nutritional quality were achieved under reduced nitrogen and potassium fertilizer inputs when combined with bacterial inoculation. These findings highlight the novel potential of P. megaterium Thr45 as an effective biofertilizer for improving nutrient availability, maintaining high productivity, and supporting sustainable baby maize production with reduced chemical fertilizer inputs

Nitrogen doi: 10.3390/nitrogen7010031

Authors: Matthew T. Streeter Elliot S. Anderson

Standing tile inlets are commonly used to drain unwanted surface water from croplands but can exacerbate pollution by facilitating the transport of nutrients to waterways. Blind inlets have increasingly been viewed as a beneficial alternative to standing inlets since they control erosion and capture particulate nutrients. However, conventional blind inlets do little to limit dissolved nutrient transport, and modified blind inlet (MBI) designs have been proposed that incorporate woodchips—a medium that facilitates denitrification. While initial investigations have highlighted MBIs’ remediation potential, their ability to meet prescribed drainage standards has not been well-documented. In this study, we designed and installed MBIs composed of pea gravel and woodchips in two eastern Iowa fields under row crop cultivation. Flow and nitrate were continuously monitored using in situ equipment directly downstream of the MBIs (February 2023–June 2025). Observed flows were very ephemeral, consisting of ~25 distinct events at both sites, with no flow recorded in between. During several wet weather events, flow rates exceeded the MBIs’ design requirements, confirming their sufficient drainage capacity to prevent in-field ponding. Nitrate concentrations varied considerably, with long-term averages of 11.6 and 19.1 mg/L and overall loadings of 4.94 and 7.10 kg during our 28-month study. We also measured phosphate and sulfate during select wet weather events, and discrepancies in concentrations between inlets and outlets suggested that groundwater was often present alongside surficial drainage in our monitoring setup. We believe our results argue for increased adoption of MBIs in conservation and further quantification of their remediation capabilities.

Nitrogen doi: 10.3390/nitrogen7010030

Authors: Aayushi Rambia Malinda S. Thilakarathna

Compost-based biostimulants (CBB) have emerged as a promising tool in sustainable agriculture, offering an eco-friendly approach to improving soil health, crop productivity, and environmental resilience. Derived from the controlled biodegradation of organic waste, CBB contains a diverse array of beneficial microorganisms, humic substances, and bioactive compounds that act synergistically to stimulate plant growth and soil biological activity. Mechanistically, CBB enhances nutrient acquisition by increasing plant-available nitrogen and phosphate solubility, promoting root development through phytohormone synthesis, and improving stress tolerance by modulating plant defense pathways and antioxidant activity. Additionally, their application enhances soil structure, microbial diversity, and carbon sequestration, making them integral to climate-smart agriculture. Despite their growing relevance, several challenges impede the widespread adoption of CBB. Variability in compost quality, lack of standardized production protocols, limited field-scale validation, and inconsistent regulatory frameworks hinder reproducibility and commercialization. Addressing these gaps requires interdisciplinary research that integrates microbiology, biochemistry, agronomy, and data science to better understand how microbial metabolites interact and optimize formulation strategies. Future research should prioritize the standardization of composting methods, long-term multi-crop field evaluations, and integration with precision agriculture tools for real-time soil monitoring. Policy harmonization, quality assurance frameworks, and farmer education are also vital for ensuring safe and effective use of CBB.

Nitrogen doi: 10.3390/nitrogen7010029

Authors: Alejandra Taco Jesse Potts Bruce Schaffer Pamela Moon Xingbo Wu Yuncong Li

Nitrogen (N) management is a critical factor influencing growth and physiological performance of vanilla. However, quantitative information on N requirements for Vanilla × tahitensis remains limited. This study evaluated six N application rates (0, 2, 4, 8, 16, and 32 g N plant−1 yr−1) on tissue N partitioning, leaf chlorophyll index (LCI), vegetative growth, and biomass under controlled container conditions. Plants were arranged in a randomized complete block design (RCBD), and final analyses were conducted on destructively sampled plants (three plants per treatment; total n = 18). N concentration increased in all tissues with increasing N supply, but responses differed among tissues. Stem N concentration exhibited the greatest proportional increase at high N rates, whereas leaf N increased more gradually. Growth traits and LCI followed curvilinear patterns, with intermediate N rates generally associated with improved vegetative performance. Quadratic models estimated optimal N rates between 13 and 21 g N plant−1 yr−1, with predicted leaf N concentrations of 1.5–2.2%. However, confidence intervals indicated substantial uncertainty for variables with low model fit. LCI was strongly correlated with leaf N concentration, supporting its use as a nondestructive indicator of plant N status. Because the study was conducted under controlled conditions, field validation is required before broader recommendations are made.

Nitrogen doi: 10.3390/nitrogen7010028

Authors: Chuong Van Nguyen Tri Le Kim Tran

Rhizosphere nitrogen-fixing bacteria play a critical role in sustainable crop production by enhancing nitrogen availability and improving soil fertility. This study aimed to isolate and characterize native rhizospheric nitrogen-fixing bacteria (NRNFB) associated with baby maize (Zea mays L.) roots and evaluate their nitrogen-fixing potential. Thirty root samples were collected, and ten bacterial isolates (V1–V10) were obtained using selective media. Morphological, biochemical, and physiological analyses identified strain V3 as the most promising candidate, exhibiting strong growth on nitrogen-free Burk medium and high oxidase, catalase, and urea hydrolysis activities. The strain demonstrated broad environmental tolerance, including salinity up to 4% NaCl, temperatures ranging from 15 to 45 °C, and pH values between 5.0 and 8.0. Molecular identification based on 16S rRNA gene sequencing revealed 100% sequence similarity with Peribacillus simplex LT4 (strain LT4). Nitrogenase activity analysis showed a peak during the exponential growth phase, accompanied by increased nitrogen accumulation in the culture medium, confirming active biological nitrogen fixation. These findings highlight the physiological adaptability and functional efficiency of strain LT4, supporting its potential development as a biofertilizer for sustainable maize production systems.

Nitrogen doi: 10.3390/nitrogen7010027

Authors: Sayanti Kar Souvik Paul Rohit Kumar Singh Saba Parveen Kaizar Hossain Abhishek RoyChowdhury

Ammoniacal nitrogen (NH3-N) is a major pollutant in municipal, industrial, and agricultural wastewaters and is a key driver of eutrophication and aquatic ecosystem degradation. This review paper assessed the potential of water hyacinth (Eichhornia crassipes) as a sustainable phytoremediation option for removing ammoniacal nitrogen from wastewater. This paper focused on the plant’s biological characteristics, nutrient uptake pathways, and adaptability to varying environmental conditions. Specific mechanisms examined include direct root uptake of ammonium, internal translocation, and microbial-assisted nitrification and denitrification within the rhizosphere. The influence of pH, temperature, salinity, retention time, and plant density on removal efficiency was also assessed in this study. Across laboratory, pilot, and field-scale studies, water hyacinth achieved ammoniacal nitrogen removal efficiencies ranging from 74% to 97% under favorable conditions, alongside significant reductions in biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total dissolved solids (TDS). Integration with constructed wetlands, microbial systems, and hybrid treatment approaches further enhanced nitrogen removal and process stability. This paper also highlighted opportunities for biomass valorization through biogas, bioethanol, and compost production while identifying challenges related to salinity sensitivity and biomass management. Overall, water hyacinth emerges as a cost-effective, nature-based solution for decentralized wastewater treatment, with strong potential to support sustainable water management and circular bioeconomy initiatives.

Nitrogen doi: 10.3390/nitrogen7010026

Authors: María Guadalupe Peralta-Sánchez Fernando Carlos Gómez-Merino Eréndira E. Hernández-Andrade Libia Iris Trejo-Téllez

Nitrogen (N) is a key macronutrient that influences the uptake and partitioning of other essential elements in plants. In this research, we evaluated the effect of different N concentrations in the nutrient solution (0, 4.2, 8.4, and 12.6 mg L−1) during the flowering stage on the concentration and accumulation of macronutrients in organs of Mexican marigold (Tagetes erecta L.) ‘Inca’. After 40 days of treatment, plants were separated into leaves, flowers, stems, and roots to determine the concentrations of N, P, K, Ca, Mg, and S, as well as their accumulation based on dry biomass. Nitrogen supply significantly affected dry biomass production and its partitioning among organs, promoting biomass allocation to leaves and flowers while reducing relative root biomass at higher N concentrations. Nitrogen concentrations and accumulation increased in leaves, stems, and flowers as N supply increased, whereas an inverse relationship was observed in roots. When applying 8.4 and 12.6 mg N L−1, phosphorus displayed enhanced concentrations in leaves and stems, although root tissues did not change the concentration of this nutrient. When N was supplied at up to 8.4 mg L−1, the concentration of potassium rose in aboveground organs but decreased at the highest dose, while its accumulation in roots was reduced under high N concentrations tested. Calcium exhibited greater accumulation in the aboveground organs, particularly at 12.6 mg N L−1. Magnesium concentration and accumulation increased in aboveground organs with increasing N supply, whereas its accumulation in roots decreased. The highest concentrations of sulfur in leaves and stems were observed at 8.4 mg N L−1, and its accumulation in the aboveground organs tended to stabilize at the highest dose. Effect size analysis (partial ηp2) revealed that N supply explained a large proportion of the variance in macronutrient concentration and accumulation in aerial organs, whereas responses in roots were generally weaker and nutrient specific. Overall, our data indicate that intermediate N levels (8.4 mg L−1) boost a more efficient nutritional balance in the aboveground organs, while the highest dose predominantly enhances Ca and Mg accumulation. Understanding how these plants respond to nitrogen can help improve the quality of Mexican marigold crops and make better use of fertilizers.

Nitrogen doi: 10.3390/nitrogen7010025

Authors: Yugang Guo Tianyu Hao Xiang Fan Jianhao Song Yankai Feng Jingyue Xiao Yuefeng Xu Chuxin Zhu Chunjuan Lyu Zhongke Bai Xinrui Xu

China has implemented extensive land restoration programs and now leads the world in artificial forest area. However, such plantations often face degradation, largely due to soil nutrient deficiency. In contrast, near-natural restoration tends to result in better soil quality, ecosystem integrity, and stability. This study focuses on three near-naturally restored sites on the Loess Plateau—a critical part of China’s National Ecological Security Barrier System, which has undergone substantial ecological restoration in recent decades. Using soil stoichiometry to assess nutrient balance and land sustainability, we investigated two forest types (Betula platyphylla, BP; Larix principis-rupprechtii, LP) and a mixed shrubland (Ostryopsis davidiana and Cotoneaster multiflorus, OD–CM). Soil profiles were sampled at 20 cm intervals from the surface to bedrock. We measured soil carbon (C), nitrogen (N), and phosphorus (P) contents, along with key environmental factors. The results show the following: (1) The two forest lands exhibited similar C and N levels, which were 1.23–1.26 and 1.40–1.51 times higher, respectively, than those in the shrubland. (2) Lower C/N (BP: 25.05; LP: 23.46) and higher N/P (BP: 4.83; LP: 5.00) in the forest lands indicated lower nitrogen limitation versus the shrubland (C/N: 28.55; N/P: 3.44). (3) Key influencing factors varied across land restoration types, indicating that the vegetation community’s composition mediates nutrient cycling through nutrient uptake and litter input. (4) Relative to plantations in the same region, near-naturally restored lands had 3.47–5.64 times higher C content and 1.51–2.51 times higher N content. Moreover, near-natural communities exhibited higher C/N (21.68–30.56) and C/P (85.92–132.97) compared to plantations (C/N: 8.8–13.1; C/P: 9.16–31.2), reflecting more efficient nitrogen and phosphorus utilization. Thus, near-natural land restoration enhances soil carbon sequestration, nitrogen fixation, and nutrient use efficiency on the Loess Plateau, supporting its promotion as a superior land management strategy for enhancing land sustainability and ecosystem services in this area.

Nitrogen doi: 10.3390/nitrogen7010024

Authors: Asmaa A. Mohamed Mohamed Allam Roberto Mancinelli Emanuele Radicetti Bahy R. Bakheit

Optimizing nitrogen fertilization and planting date is essential for improving forage maize productivity under semi-arid conditions. This study evaluated the effects of nitrogen application rates and planting dates on growth, forage yield, and quality of maize (Zea mays L.) in Upper Egypt. A two-year field experiment (2024–2025) was conducted at the Experimental Farm of Assiut University using a strip-plot design arranged in a randomized complete block design with three replications. Four planting dates (15 April, 15 May, 15 June, and 15 July) were assigned horizontally, while three nitrogen rates (167, 238, and 309 kg N ha−1) were applied vertically. Growth traits, fresh and dry forage yield, dry matter percentage, crude protein content, and protein yield were recorded at 60 days after sowing. Results showed that planting date, nitrogen rate, and their interaction significantly affected most measured traits in both seasons. Sowing in mid-May consistently produced the highest plant height, chlorophyll content, fresh and dry forage yield, and protein yield. Increasing nitrogen application enhanced biomass production and forage quality, with the highest values generally recorded at 309 kg N ha−1. The strongest yield response to nitrogen occurred when maize was sown at the optimal planting date, indicating that nitrogen utilization was closely linked to favorable environmental conditions. Phenotypic correlation and multivariate analyses revealed strong associations among vegetative growth traits and forage yield, with a single dominant factor explaining more than 91% of the variation in yield-related traits across seasons. Overall, the results demonstrate that synchronizing planting date with appropriate nitrogen fertilization is critical for maximizing maize forage yield and quality under semi-arid conditions. Mid-May sowing combined with adequate nitrogen supply represents an effective management strategy for forage maize production in Upper Egypt, while further research is needed to optimize nitrogen-use efficiency and long-term sustainability.

Nitrogen doi: 10.3390/nitrogen7010023

Authors: Haimanot Beruk Tarekegn Yoseph Georg Cadisch Tewodros Ayalew

Biological nitrogen fixation (BNF) is crucial for enhancing soybean productivity while reducing reliance on mineral nitrogen fertilizers. The accurate estimation of BNF via the δ15N natural abundance method depends on reliable B-values, which represent plants that derive all their nitrogen from fixation. This study aimed to assess the B-values and symbiotic efficiency of Bradyrhizobium-inoculated soybean varieties using δ15N natural abundance techniques. Eight strains and five soybean varieties were evaluated in sterilized sand culture using a factorial completely randomized design under lath-house conditions. Plants were analyzed for δ15N, shoot N concentration, shoot N content, and symbiotic efficiency (SE). The applied treatments showed highly significant effects with strong interactions, reflecting substantial genotypic variation in symbiotic performance. Strain SD-53 produced the lowest δ15N values (−0.24 to 0.14‰) and the highest SE, with several strain–variety combinations surpassing N-fertilized controls. Shoot N concentration and content ranged from 0.96–3.16% and 9.90–52.73 mg plant−1, respectively, and SE varied from 29.07 to 136.29%. δ15N showed strong negative correlations with SE and plant N traits. The study identified SD-53 as a promising inoculant candidate and generated the first regional soybean B-values (−0.24 to 0.14‰ for each tested variety and a mean of −0.08 ± 0.14‰) for Ethiopia. These values provide an important baseline for %Ndfa calculations and support future field validation and inoculant formulation.

Nitrogen doi: 10.3390/nitrogen7010022

Authors: Nina Hodalova Koshi Yoshida

In recent years, dietary changes towards reducing animal-based proteins was recognized as a nitrogen pollution-mitigating strategy. This is because producing animal protein generates higher nitrogen emissions compared to its plant-based alternatives. In Japan, there is a switch towards an animal-based diet, potentially leading to degraded water quality. While national-scale studies are common, watershed-level scale dietary changes are not researched, even though nitrogen pollution is often localized. This study aims to evaluate whether dietary and feed self-sufficiency changes can reduce nitrogen load and improve water quality in the Kasumigaura watershed. Firstly, nitrogen load was quantified and spatially distributed. Then, the estimated nitrogen concentration was compared with observed data. Finally, the impact of dietary and feed self-sufficiency changes on nitrogen load and water quality was assessed. Results estimated that nitrogen loading for year 2020 was 4403 tons/N/year, correlating with previous research. Results further showed that switch from livestock to legume protein would significantly improve water quality, up to 0.27 mg N/L. On the other hand, increasing feed self-sufficiency would negatively affect the water quality, up to 0.32 mg N/L. The results emphasize the importance of dietary patterns in mitigating nitrogen pollution. This method can be generalized on other watersheds.

Nitrogen doi: 10.3390/nitrogen7010021

Authors: Alina Șimon Ovidiu Adrian Ceclan Felicia Chețan Alin Popa Marius Bărdaș Laura Șopterean Ana-Maria Vălean

Mineral fertilization is crucial for maximizing wheat yield, ensuring optimal nitrogen and phosphorus supply according to plant development, pedoclimatic conditions, and previous crops, with a balanced N:P ratio being decisive for productivity. This study, conducted at ARDS Turda during 2020/2021–2024/2025, evaluated the long-term effects of nitrogen and phosphorus fertilization on the yield, grain protein content, and foliar disease incidence of winter wheat grown after maize and soybean. The experimental design was polyfactory, in randomized blocks, including 25 variants and 6 repetitions, according to the uninterrupted protocol used since 1967, winter wheat being cultivated after maize for grain and soybean. Phosphorus (0–160 kg P2O5 ha−1) was applied in autumn, while nitrogen (0–160 kg N ha−1 after maize and 0–120 kg N ha−1 after soybean) was split 50% in autumn and 50% in spring. Results indicate that wheat yield is strongly influenced by nitrogen–phosphorus interactions and climatic conditions, with nitrogen increasing yield by 450–2700 kg·ha−1 and maximum yields of 7600–7828 kg·ha−1 achieved at N120 with higher phosphorus rates. Grain protein content (14.96%) was high at N120 dose, while foliar disease incidence and severity were low at minimal fertilization and rose with intensified mineral nutrition.

Nitrogen doi: 10.3390/nitrogen7010020

Authors: Bonface O. Manono Jacinta M. Kimiti Damaris K. Musyoka

Nitrogen leaching from land and farms is a major global issue that pollutes water, damages ecosystems, and accelerates climate change. This review synthesizes evidence from the literature on how interactions among landscape characteristics, sources of nitrogen input, and temporal dynamics shape leaching vulnerability. It identifies conditions under which nitrogen is most likely to be transported through soil systems into aquatic environments. This review reveals that leaching vulnerability is strongly conditioned by soil hydraulic properties and topographic position. Coarse-textured upland soils exhibit substantially greater nitrate mobilization than finer-textured, hydrologically buffered lowland soils. Fertilizer formulation and application timing further modulate loss potential, with late-season mineral nitrogen inputs disproportionately contributing to subsurface export relative to demand-synchronized applications. Most of the nitrogen leaching occurs outside the active growing period, when vegetative uptake is suppressed and drainage intensity is highest. Farmers can lower nitrate runoff by using targeted fertilization, cover crops, and nitrification inhibitors, while landscape-scale features like controlled drainage and vegetative buffers provide additional downstream filtration. The effectiveness of regulatory approaches is amplified when aligned with economic incentives and regionally calibrated nutrient thresholds. Advances in high-resolution observation platforms and process-based predictive tools offer new capacity for anticipatory management, although widespread deployment is limited by financial and institutional constraints. Collectively, these insights support the development of more targeted and sustainable nitrogen management strategies.

Nitrogen doi: 10.3390/nitrogen7010019

Authors: Haimanot Beruk Tewodros Ayalew

Estimating indigenous rhizobial populations is crucial for understanding soil rhizobia abundance, determining the potential need for inoculation, and evaluating the performance of introduced inoculant strains. However, in southern Ethiopia, information on the population abundance of soybean-nodulating rhizobia is limited. To address this gap, the present study was conducted to evaluate the population abundance of indigenous soybean-nodulating rhizobia and to assess the influence of cropping history and soil properties on rhizobial abundance. The study was conducted across five sites suitable for soybean cultivation in southern Ethiopia: Arsi-Negelle, Boricha, Dore, Hawassa, and Wondo Genet. The study sites represented a range of cropping systems, including sole maize, sole tobacco, sole haricot bean, maize–potato intercropping, and crop rotation. Composite soil samples were collected from a depth of 0–20 cm, and rhizobial abundance was determined using the most probable number (MPN) technique. Indigenous rhizobial populations ranged from 0 to 1.7 × 101 cells g−1 of dry soil. Overall, the population levels were low, suggesting that inoculation with effective rhizobial strains would likely improve nodulation and biological nitrogen fixation. Relatively higher rhizobial population densities were observed at Arsi-Negelle under haricot bean cropping history. Statistically significant positive correlations were found between rhizobial abundance and cation exchange capacity, organic carbon, and organic matter. In general, native rhizobial populations across all study locations were below levels considered sufficient to support effective soybean nodulation and nitrogen fixation, indicating the need for inoculation to enhance soybean productivity in the study areas.

Nitrogen doi: 10.3390/nitrogen7010018

Authors: Aryanis Mutia Zahra Apiradee Uthairatanakij Natta Laohakunjit Pongphen Jitareerat Nattapon Kaisangsri Arak Tira-Umphon

The application of plasma-activated water and biostimulants offers a sustainable approach to supporting plant growth under reduced-nutrient conditions by supplying bioavailable nitrogen. This study investigated the growth and postharvest performance of hydroponically grown cos lettuce (Lactuca sativa L.) supplied with three Hoagland-based nutrient treatments: half-strength solution prepared with tap water (HS), half-strength solution with plasma-activated water (HS+PAW), and half-strength solution with plasma-activated water containing 1 mL L−1 milk protein hydrolysate (HS+PAW+MPH). Plants treated with PAW, particularly those in the HS+PAW+MPH, exhibited increases in growth, biomass accumulation, and mineral composition, with reduced nitrate content compared to controls. At harvest, lettuce under HS+PAW+MPH exhibited nearly double fresh yield and enhanced dry matter, protein, lipid, phenolic, and flavonoid profiles as well as increased antioxidant capacity, indicating improved nitrogen utilization and nutritional quality under reduced nutrient input. Postharvest quality was evaluated by packing samples in polypropylene bags and storing them at 10 ± 1 °C and 95–98% relative humidity for 21 days. The HS+PAW+MPH treatment substantially suppressed respiration and production of ethylene, limited weight loss and color change, and better preserved pigments, bioactive compounds, and antioxidant stability compared to HS and HS+PAW, indicating HS+PAW+MPH as a sustainable nutrient management approach for hydroponic systems.

Nitrogen doi: 10.3390/nitrogen7010017

Authors: Raveendrakumaran Bawatharani Miles Grafton Paramsothy Jeyakumar

The Overseer model is widely used in New Zealand as a precision-agriculture-related tool for estimating nitrate (NO3−) leaching losses in agricultural systems. This study evaluated the accuracy of the Overseer model in predicting nitrate (NO3−) leaching through a two-year lysimeter experiment conducted at Woodhaven Gardens, New Zealand, under beetroot and pak choi cultivation. Seven distinct nitrogen (N) fertilizer treatments were applied to assess model performance. In year 1, Overseer overestimated NO3− leaching by an average of 45.2 kg N/ha (15.7%), and in year 2, the model overestimated by 35.2 kg N/ha (43.5%). A sensitivity analysis highlighted soil texture, impeded layer depth and crop residue incorporation as key drivers of leaching variability, underscoring the need for improved model calibration. Overseer performed reasonably well under lysimeter conditions, with a strong linear relationship (Pearson’s correlation coefficient r = 0.89, p < 0.0001) between measured and predicted values and explaining 77% of the variance (R2 = 0.77) in the observed data. The model predicted a baseline leaching loss of 39.4 kg N/ha/year even when measured losses were zero. Overseer demonstrates moderate reliability in predicting NO3− leaching under vegetable cropping systems but exhibits notable limitations in handling crop-specific N dynamics, soil hydrology, and fertilizer timing.

Nitrogen doi: 10.3390/nitrogen7010016

Authors: Yanying Han Minghang Hu Wenqiang Huang Zheng Wu Lingchen Tong Shaobing Zhang Yanhui Ye

Water and nitrogen supply are key factors limiting the establishment of alpine plant seedlings and the efficiency of ecological restoration on the Tibetan Plateau. As an endemic shrub to Tibet, the morphological and physiological response mechanisms of Piptanthus nepalensis (Hook.) D. Don to coupled water and nitrogen stress remain poorly understood. This study employed a pot experiment with a completely randomized two-factor design, incorporating five water gradients (0–100% field capacity, FC) and five nitrogen levels (0–4 g·plant−1 urea). The aim was to elucidate the regulatory mechanisms of water/nitrogen coupling on Piptanthus nepalensis growth, physiology, and morphogenesis. The results indicated the following: (1) A significant water/nitrogen coupling effect was observed, with optimal water/nitrogen combinations producing pronounced synergistic effects. Principal component analysis (PCA) revealed that the first two axes cumulatively explained 99.32% of the morphological variation. The W3N3 treatment (40–60% FC water + 2 g·plant−1 nitrogen) exhibited optimal growth traits and maximum leaf elongation, establishing the optimal water and fertilizer management threshold for this species. (2) Confronted with two starkly contrasting stresses—drought (W4, W5) and waterlogging (W1)—plants adopted convergent “conservative” morphological adaptation strategies (significantly reduced leaf length and width) to lower metabolic expenditure. (3) Photosynthetic physiological analysis revealed that under extreme water deficiency (W5) or waterlogging (W1) stress, intercellular CO2 concentration (Ci) paradoxically increased, indicating a shift in photosynthetic suppression mechanisms from stomatal limitation to non-stomatal limitation (metabolic injury). (4) The Mantel Test confirmed that photosynthetic physiological traits significantly drove morphological trait variation (p < 0.001), establishing a close feedback loop between “physiological function and morphological structure”. Conclusions: Moderate water deficit (40–60% FC) combined with moderate nitrogen fertilization (2 g·plant−1) effectively alleviates non-stomatal limitation and releases morphological constraints, thereby promoting rapid growth in Piptanthus nepalensis. This study reveals the phenotypic plasticity and convergent adaptation mechanisms of Piptanthus nepalensis under water/nitrogen co-stress, providing precise water and fertilizer management guidelines for vegetation restoration in degraded ecosystems of Tibet.

Nitrogen doi: 10.3390/nitrogen7010015

Authors: Rafael M. Amaral Berman E. Espino Floridalma E. M. Francisco Oswaldo Navarrete Carlomagno S. Castro

Estimating nitrogen (N) and the corresponding crude protein (CP) content in forage crops is essential for optimizing fertilization and livestock nutrition. However, standard methods such as the Dumas and Kjeldahl techniques are destructive, costly, and impractical for field use in certain regions of developing countries. This study evaluated four non-destructive approaches—morphometric measurements, Pantone® color scales, smartphone-based RGB analysis (ColorDetector app), and SPAD chlorophyll readings—for predicting N and CP in Megathyrsus maximus (Mombasa grass). A total of 120 samples were collected under three nitrogen fertilization levels and assessed using linear mixed-effects models with cross-validation. Morphometric variables showed poor performance (R2 < 0.01), indicating low correlation with nutrient content. Pantone-based RGB models provided slightly better predictions (R2 ≈ 0.30) but were limited by subjectivity and discrete data. SPAD-based models demonstrated moderate predictive accuracy (R2 ≈ 0.53; RMSE ≈ 0.46%). The highest accuracy was achieved with smartphone-derived RGB data, where full RGB models reached R2 = 0.60 and RMSE = 0.45%. Based on these results, a practical green color scale was developed from RGB values to support real-time, in-field nitrogen and crude protein assessment. This study highlights smartphone imaging as a scalable, low-cost, and accurate tool for non-destructive estimation of nitrogen and crude protein in tropical forages, offering an accessible alternative to laboratory methods for producers and field technicians.

Nitrogen doi: 10.3390/nitrogen7010014

Authors: Amrita Saju Ivona Sigurnjak Erik Meers

Recently, the EU approved RENURE-criteria materials to be used as substitutes for synthetic N fertilisers. Several studies have been performed on the agronomic efficacy and potential environmental impacts of different bio-based fertilisers (BBFs) from biomass recovery, including the RENURE-criteria materials. But information is lacking about their effectiveness under abiotic stress conditions like salinity and drought. The predictions for climate change-induced increased drought and soil salinisation for the European soils have also increased, making it inevitable to understand BBF performance in these impending situations. Two RENURE-criteria top-priority materials (ammonium nitrate (AN) and ammonium sulphate (AS) and another commercially used BBF—an evaporator concentrate (CaE)) were evaluated in a pot trial growing spinach under salinity and drought stress with a reference ‘no stress’ condition to examine crop growth, nutrient uptake, and nitrogen fertiliser replacement value (NFRV). Agronomically, BBFs performed at par with the synthetic fertiliser (SF) under unstressed and salt-stressed conditions, whereas, under drought stress, BBFs outperformed the SF treatment. AS exhibited the highest yield and nutrient uptake, displaying an NFRV of 3.1 and 1.8 under no-stress and salt-stress conditions, respectively. Salt stress did not negatively impact the crops grown in this trial, potentially due to the higher potassium content in the system, which alleviated the possible negative impacts of high sodium. This study delves into the agronomic response, without evaluating crop physiological changes, and, hence, should be taken as a preliminary step into further investigation of observed elemental interactions (that could be potentially driving stress mitigation) while also examining the crop physiology during the duration of stress.

Nitrogen doi: 10.3390/nitrogen7010013

Authors: Bashiri Iddy Muzzo

Pasture-based ruminant systems link nitrogen (N) nutrition with ecosystem N cycling. Grazing ruminants convert fibrous forages into milk and meat but excrete 65 to 80% of ingested N, creating excreta hotspots that drive ammonia volatilization, nitrate leaching, and nitrous oxide (N2O) emissions. This review synthesizes ecological and ruminant nutrition evidence on N flows, emphasizing microbial processes, biological N2 fixation, plant diversity, and urine patch biogeochemistry, and evaluates strategies to improve N use efficiency (NUE). We examine rumen N metabolism in relation to microbial protein synthesis, urea recycling, and dietary factors including crude protein concentration, energy supply, forage composition, and plant secondary compounds that modulate protein degradability and microbial N capture, thereby influencing N partitioning among animal products, urine, and feces, as reflected in milk and blood urea N. We also examine how grazing patterns and excreta distribution, assessed with sensor technologies, modify N flows. Evidence indicates that integrated management combining dietary manipulation, forage diversity, targeted grazing, and decision tools can increase farm-gate NUE from 20–25% to over 30% while sustaining performance. Framing these processes within the global N cycle positions pasture-based ruminant systems as critical leverage points for aligning ruminant production with environmental and climate sustainability goals.

Nitrogen doi: 10.3390/nitrogen7010012

Authors: Felicia Chețan Cornel Chețan Alina Șimon Ovidiu Adrian Ceclan Diana Hirișcău Raluca Rezi Alin Popa Marius Bărdaș Camelia Urdă Roxana Elena Călugăr Paula Ioana Moraru Teodor Rusu

Agronomic systems that can guarantee consistent and sufficient crop yields must be developed and implemented in order to address the problems presented by climate change, especially the increase in average annual temperatures and the unequal distribution of precipitation. Over the course of five successive growing seasons (2019–2024), a Poly-Factorial field experiment was carried out at the Agricultural Research and Development Station (ARDS) Turda, Romania, which is situated in the hilly region of the Transylvanian Plain. The study investigated the combined effects of soil tillage system (conventional tillage—CS; no-tillage—NT) and fertilization strategies (N48P48K48 at sowing vs. N48P48K48 at sowing + N40.5CaO10.5MgO7 applied in early spring at the growth resumption) on the quantitative and qualitative performance of winter wheat (Triticum aestivum L.). Results showed a modest yield difference of 206 kg ha−1 between the two tillage systems, favoring conventional tillage. However, the application of additional early-spring fertilization resulted in a significant average yield increase of 338 kg ha−1. Yield variability across the five years ranged from 262 to 1797 kg ha−1, highlighting the strong influence of climatic conditions on crop performance and emphasizing the need for adaptive management practices under changing environmental conditions.

Nitrogen doi: 10.3390/nitrogen7010011

Authors: Kashaf Sumera Anwar Fahad Shafiq Abida Kausar Shahbaz Khan Muhammad Ashraf Syed Ahmed Shah

The increasing demand for sustainable agriculture requires innovative strategies to enhance nitrogen use efficiency while minimizing environmental losses associated with conventional fertilizers. This study aimed to develop and compare ammonium chloride- and ammonium nitrate-modified nanobiochar as controlled-release nitrogen carriers and to elucidate their effects on nitrogen retention, soil properties, and physiological nitrogen utilization in spinach (Spinacia oleracea L.). Nitrogen-modified nanobiochar was synthesized using ammonium chloride (NB-AC) and ammonium nitrate (NB-AN) at three nitrogen rates (0.03, 0.06, and 0.12 g N g−1 NB) and applied to soil at 1% (w/w). Soil properties, nutrient dynamics, and plant growth and physiological traits were analyzed after 15 and 30 days. Nitrogen modification significantly improved soil nitrogen retention and nutrient availability compared with unmodified nanobiochar. The highest nitrogen loading treatments (NB-AC3 and NB-AN3) notably improved spinach growth, photosynthetic efficiency, pigment content, nitrogen metabolism enzymatic activities, and accumulation of key metabolites (soluble sugars, flavonoids). Nitrogen-release assessments indicated a pronounced controlled-release with reduced nitrogen leaching and greater retention, particularly under NB-AN3. Overall, this study demonstrates that nitrogen-modified nanobiochar functions as an effective nitrogen carrier that enhances nitrogen utilization and growth. These findings provide mechanistic insights into its potential as a sustainable alternative to conventional nitrogen fertilizers.

Nitrogen doi: 10.3390/nitrogen7010010

Authors: Sabina Yeasmin Md. Sabbir Hosen Zaren Subah Betto Md. Kutub Uddin Md. Parvez Anwar Md. Masud Rana A. K. M. Mominul Islam Tahsina Sharmin Hoque Sirinapa Chungopast

This study evaluated the effects of applying fecal sludge-based co-compost (CC) integrated with chemical fertilizers on soil nutrient status, organic carbon (OC) storage, and economic returns in paddy soils. Ten integrated nutrient management (INM) treatments were tested, i.e., BRRI recommended dose of fertilizer (RDF), CC 5.0 t ha−1, RDF + CC 2.0 t ha−1, RDF + CC 1.5 t ha−1, RDF + CC 1.0 t ha−1, RDF + CC 0.5 t ha−1, 75% RDF + CC 2.0 t ha−1, 75% RDF + CC 1.5 t ha−1, 75% RDF + CC 1.0 t ha−1, and 75% RDF + CC 0.5 t ha−1. Two rice varieties were cultivated over two consecutive seasons—winter rice (boro) and monsoon rice (aman)—in the experimental field. Soil samples (0–15 cm) were collected before and after the seasons and fractionated into labile particulate organic matter (>53 µm) and stable mineral-associated organic matter (<53 µm). Bulk soils and CC were analyzed for OC, nitrogen (N), phosphorus (P), potassium (K), sulfur (S), and heavy metals, while the fractions were analyzed for OC and N. Across both seasons, 75% RDF combined with 2.0 t ha−1 or 1.5 t ha−1 of CC consistently showed the highest OC, total N, and soil C stock, with moderate P, K, and S levels. Sole RDF produced the lowest OC and N. Among fractions, stable OC was the highest in the 75% RDF + 2.0 t ha−1 CC treatment, statistically similar to 75% RDF + 1.5 t ha−1 CC, and the lowest under RDF alone. Economically, sole RDF yielded the highest profit, while full RDF + CC achieved competitive returns. Reduced RDF + CC treatments (75% RDF + 1.5 or 2.0 t ha−1 CC) offered slightly lower returns but improved soil sustainability indicators. Overall, applying 75% RDF + 1.5 t ha−1 CC provided the most cost-effective balance of nutrient enrichment, soil C stock, and profitability. This CC-based INM approach reduces chemical fertilizer dependency, enhances soil health, and promotes sustainable waste management, supporting environmentally resilient rice production.

Nitrogen doi: 10.3390/nitrogen7010009

Authors: Jiangyu Chang Pengli Yuan Zhongze Si Yuqi Niu Hafeez Noor Yongkang Ren Linghong Li Pengcheng Ding Aixia Ren Min Sun

Sustainable nitrogen (N) management is critical for enhancing wheat production in the water-limited environment of China’s Loess Plateau. This study investigated the effects of four N rates (0, 120, 180, and 240 kg N ha−1) and two sowing methods, furrow sowing (FS) and drill sowing (DS), on wheat yield, grain quality, and water-use efficiency (WUE). Results indicated that N application significantly improved all metrics. The optimal N rate for yield was 180 kg N ha−1 (N180), producing yields equivalent to the higher 240 kg N ha−1 rate (N240). Compared to the N0 control, the N240 treatment under FS in 2022–23 increased grain yield by 25.4% and WUE by 11.9%, while under DS it increased yield by 23.6% and WUE by 11.1%. However, in the following year (2023–24), the greatest benefits under FS came from N180, which increased yield by 19.3% and WUE by 11.5% over the control. Higher N rates markedly elevated grain quality: N240 resulted in the highest steamed bread score and concentration of volatile compounds. Nitrogen application also intensified soil water use, particularly before anthesis. In 2022–23, the highest N240 reduced soil water at maturity by 16.6% (FS) and 15.9% (DS) and increased total water consumption by up to 7.8% compared to N0. Yield was strongly correlated with soil water depletion in the 0–200 cm layer during the reproductive period. While N240 optimized quality, the N180 rate combined with improved sowing methods (FS or DS) provided the best balance, drill sowing was crucial agronomic practice for enhancing nitrogen-use efficiency (NUE), achieving high yield, superior WUE, and acceptable quality. We therefore recommend an N rate of 180 kg ha−1 with improved sowing as a sustainable practice for dryland wheat production on the Loess Plateau.

Nitrogen doi: 10.3390/nitrogen7010008

Authors: Gilmara da Silva Rangel Thais de Souza Pastor Vinicius Rodrigues Ferreira Tayná de Oliveira Costa Regiane Carla Bolzan Carvalho Murilo de Oliveira Souza Ana Paula Candido Gabriel Berilli Savio da Silva Berilli

Nitrogen is the nutrient most required by plants and plays a central role in agricultural productivity due to its involvement in essential nutrients. This study evaluated the effects of different nitrogen sources on the physiological and morphological development of yellow passion fruit (Passiflora edulis Sims) seedlings. The experiment followed a randomized block design with six treatments (water, urea, ammonium sulfate, potassium nitrate, calcium nitrate, and magnesium nitrate), six replicates per treatment, and two plants per plot. An equal amount of nitrogen was supplied to all treatments, while the urea treatment excluded the additional macronutrients present in the other fertilizers (S, K, Ca, and Mg), allowing us to assess whether the benefits were exclusively attributable to the nitrogen source. The results indicated that ammonium sulfate and calcium nitrate promoted better root system development, while ammonium sulfate also improved shoot growth and physiological characteristics. Multivariate analysis revealed that CP1 explained most of the variability between treatments, highlighting the contribution of these sources compared to the control. Overall, fertilization with ammonium sulfate produced the best results, indicating that it is a more efficient nitrogen source for seedling development.

Nitrogen doi: 10.3390/nitrogen7010007

Authors: Mohamed Tamoudjout Hamid Msaad Soukaina Lahmaoui Ahmed El Moukhtari Cherki Ghoulam Mohamed Farissi

Water deficit is a major constraint limiting the growth and yield of faba bean (Vicia faba L.). A pot experiment was conducted under controlled conditions to evaluate the effect of inoculation with Rhizobium leguminosarum bv. viciae BIHB 1148 (strain F14) and Pseudomonas alkylphenolica PF9 (strain L13) on faba bean drought resilience. Two irrigation regimes were applied: well-watered (80% of field capacity) versus water-stressed (40% of field capacity). Strain F14 was used to ensure effective biological nitrogen fixation, while strain L13 was applied in co-inoculation to evaluate its biostimulatory effects. The control plants received nitrogen in its chemical form. Results indicated that water deficit significantly (p < 0.001) reduced plant growth, nodulation, and photosynthesis-related parameters, and increased hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels, which are key markers of oxidative stress. However, co-inoculation with strains F14 and L13 significantly enhanced shoot and root biomass, as well as most agro-morphological traits. It also stimulated (p < 0.05) the antioxidant activities of superoxide dismutase (3-fold), guaiacol peroxidase (12%), and catalase (104%), and increased proline content (119%), which led to lower levels of MDA (54% decrease) and H2O2 (55% decrease), improved membrane stability, water status, and enhanced photosynthesis. Overall, co-inoculation of faba bean with Rhizobium leguminosarum bv. viciae BIHB 1148 and Pseudomonas alkylphenolica PF9 offers a promising and sustainable approach to improve plant resilience under water deficit.

Nitrogen doi: 10.3390/nitrogen7010006

Authors: Hanaa A. Muhammad Bakhtyar A. Othman Galawezh B. Bapeer

Freshwater resources are on the verge of depletion due to the rapid increase in population, lifestyle changes, and especially during climate change in Iraq. Therefore, treating domestic wastewater correctly will significantly contribute to keeping the balance of water purity and its usage. To fulfil this, the Sustainable Project Appraisal Routine (SPeARTM) program, which leverages Multi-Criteria Decision Analysis with operational sustainability indicators, is used to compare the relative sustainability performance of the novel Modified Sequencing Batch Reactor by visualising the results of the degree of its sustainability compared to the Moving Bed Biofilm Reactor and the conventional Sequencing Batch Reactor system. Although selecting the most sustainable treatment depends on specific treatment goals, available resources, site conditions, and stakeholder preferences, this study considers the equal weighting of sustainability assessment across environmental, social, and economic indices to inform sustainable decision making. The results show that integrating both conventional treatment plants into the novel modified treatment plant demonstrates a comparatively more balanced and stable sustainability performance under the assessed operational conditions. As at a design capacity of 100 m3·day−1, the MSBR achieved a higher organic and nutrient removal efficiencies relative to the conventional SBR and MBBR systems while operating at an intermediate energy demand (187.7 kWh·day−1) compared with the SBR (121.7 kWh·day−1) and the MBBR (211.8 kWh·day−1). Thus, it can compensate for the weaknesses and combines the strengths of the sustainability indices of the two systems, which supports the Modified Sequencing Batch Reactor as a comparatively favourable option for wastewater treatment within the assessed sustainability framework.

Nitrogen doi: 10.3390/nitrogen7010005

Authors: Aikaterini Molla Alexios Lolas Elpiniki Skoufogianni

Sustainable fertilization strategies are increasingly required to enhance crop performance while reducing dependence on synthetic inaputs. In this study, the effectiveness of sea-derived organic amendments, Posidonia oceanica compost and mussel shell powder, was evaluated in Salvia officinalis (sage) cultivation. A pot experiment was conducted in Istron Kalou Xoriou (Crete), using three nitrogen rates (0, 40 and 80 kg ha−1) in combination with four rates of mussel shell powder (0, 50, 100 and 200 g/pot). A total of 9 treatments were set up, each replicated 3 times, resulting in 27 pots. Growth parameters (plant height, total and leaf fresh-dry weight), nitrogen content in plant tissues, nitrogen uptake, and nitrogen use efficiency (NUE) were assessed across three harvest periods. The results indicated that both P. oceanica compost and mussel shell amendments significantly improved soil properties and plant performance. The treatment receiving 200 g/pot of mussel shell powder combined with 80 kg ha−1 fertilization (PH200) consistently produced the highest values for biomass (223.99–383.58 g/plant), nitrogen plant concentration (1.967–2.117%), and nitrogen uptake (1.762–3.248 g/plant). The application of mussel shells effectively increased soil pH, thereby enhancing nutrient availability and promoting nitrogen assimilation. Furthermore, NUE values showed a progressive increase with rising amendments rates. Overall, sea-derived organic amendments demonstrated strong potential as sustainable fertilization materials, contributing to sage productivity improvement while supporting circular management of coastal waste resources.

Nitrogen doi: 10.3390/nitrogen7010004

Authors: Prince Junior Asilevi Patrick Boakye Emmanuel Quansah Alex Kwao Ablerdu William Ampomah

Burgeoning air pollution is a pressing public health concern. However, due to the scarcity and sparsity of ground-based monitoring, its impact remains uncertain. This work demonstrates how satellite-derived NO2 observations can identify persistent pollution hotspots and seasonal patterns in a data-scarce urban region. This work leveraged TROPOMI satellite data and Google Earth Engine to evaluate tropospheric NO2 hotspot patterns in the Greater Accra Region of Ghana from 2019 to 2023. TROPOMI data revealed persistent NO2 hotspots in urban and industrial areas, with overall peak concentrations reaching up to 3.3 × 1015 mol cm−2. Seasonal analysis showed elevated NO2 levels during the dry season, with a mean concentration of 2.3 × 1015 mol cm−2, while lower levels were observed during the rainy season. Increased emissions and reduced dispersion influence this pattern due to stable atmospheric conditions. Google Earth imagery confirmed that the highest NO2 concentrations were associated with the Heavy Industrial Area, highlighting the presence of extensive industrial facilities such as refineries, factories, and quarries. This integration of satellite observations with high-resolution geospatial tools provides a robust methodology for NO2 source attribution, emphasizing the need for targeted emission control measures in industrial zones to mitigate air pollution and associated health risks.

Nitrogen doi: 10.3390/nitrogen7010003

Authors: José Fidel Rodríguez-Tuz Francisco J. Solorio-Sánchez Luis Ramírez-Avilés Juan Carlos Ku-Vera Carlos Fernando Aguilar-Pérez Magnolia Tzec-Gamboa Fernando Casanova-Lugo

The identification of forage species with Biological Nitrification Inhibition (BNI) capacity is a promising strategy to inhibit soil nitrification and reduce nitrogen (N) losses. This study evaluated the BNI capacity of five Urochloa genotypes (Camello, Cayman, Marandú, Mulato II, Talismán) and their impact on biomass yield and nitrogen uptake (NU). The BNI capacity, biomass yield, N content, and NU of five Urochloa genotypes were compared. Significant differences in BNI capacity were observed between genotypes (p < 0.009). Cayman and Marandú presented the highest BNI values (87.41 and 87.21%, respectively), higher than those of Mulato II, Talismán and Camello (78.20, 81.77 and 82.63%, respectively). Regarding biomass yield, Cayman and Marandú stood out with 3093.5 and 2911.7 kg DM ha−1, respectively. Talismán and Camello showed higher N concentrations in the biomass (1.64 and 1.63%). In terms of NU, Cayman recorded the highest efficiency (47.32 kg N ha−1), surpassing Marandú, Camello, Talisman and Mulato II (42.83, 42.77, 41.53 and 37.23 kg N ha−1, respectively; p < 0.0001). BNI capacity influences biomass yield and nitrogen uptake. The Cayman genotype is positioned as a promising forage alternative for the development of more efficient and sustainable livestock systems by promoting more efficient N use.

Nitrogen doi: 10.3390/nitrogen7010002

Authors: Takuji Ohyama Hideo Hasegawa Naoki Harada Yoshihiko Takahashi Norikuni Ohtake Yuki Ono Igor A. Borodin

N is the most crucial nutrient for plant growth and yield. Soybeans require a large amount of N for growth and seed production because of their high protein content. Soybean plants fix N2 by root nodules in association with soil bacteria, rhizobia, but both the fixed N and the N absorbed from roots are essential to obtain a maximum seed yield. However, excess or inappropriate N fertilizer application represses N2 fixation and reduces seed yield. A basal deep placement of lime nitrogen promoted soybean seed yield without inhibiting N2 fixation activity in Japan. This study aimed to evaluate whether this technology can be applied in the Far East of Russia. The effects of deep placement of lime N with a wide row (75 cm) on the growth and seed yield of four Russian varieties were investigated. Without N fertilization, the average seed yield in wide rows was 2.77 t/ha, which was not significantly different from that in narrow rows (2.39 t/ha). Deep placement of lime nitrogen with wide rows increased total mechanical seed yield by 38%, 53%, 17%, and 6% in Primorskaya 4, 13, 81, and 86, respectively. The effect of basal urea application in narrow rows varied among cultivars. Soil analysis and the N composition in xylem sap indicated that the Russian field is richer in soil N than that in Niigata, and the contribution of N derived from N2 fixation was lower than that in Niigata. The effects of row spacing and N fertilization on seed yield varied by variety; therefore, it is necessary to evaluate each variety to determine the optimal row spacing and N fertilization. The field experiment indicated that the deep placement of lime N promoted seed yield of Russian cultivars. This technique may be applied in soybean cultivation in a large field if the appropriate machine is available.

Nitrogen doi: 10.3390/nitrogen7010001

Authors: Nicolas Braga Casarin Cássio Carlette Thiengo Carlos Alcides Villalba Algarin Maria Clara Faria Chaves Gil Miguel de Sousa Câmara Valter Casarin Fernando Shintate Galindo José Lavres

Understanding how supplemental nitrogen (N) interacts with biological N2 fixation (BNF) in modern soybean cultivars is essential for designing fertilization strategies that avoid unnecessary N inputs. We investigated N partitioning among soil, fertilizer and symbiotic sources in soybean grown in a greenhouse pot experiment on a tropical Oxisol. Plants were inoculated with Bradyrhizobium and subjected to four N managements: no external N, soil-applied 15N-urea (20 kg N ha−1), foliar 15N-urea (2 kg N ha−1, 0.7% w/v), and the combination of soil + foliar N. Using 15N isotope dilution, we quantified N derived from the atmosphere (NDFA), fertilizer (NDFF) and soil (NDFS) at organ and whole-plant scales, and related these fractions to nodulation, nitrogenase activity and yield. In the absence of external N, NDFA exceeded 97% in all organs, indicating a strong reliance on BNF and efficient internal N remobilization during grain filling, accompanied by higher leaf nitrate reductase activity. Soil and soil + foliar N markedly increased NDFF and NDFS while suppressing nodulation (particularly at V4) and reducing nitrogenase activity, yet they did not improve grain yield or vegetative biomass. Foliar N alone had only modest effects on N partitioning and did not enhance yield. Under these tropical soil conditions, symbiotic fixation and internal N remobilization were sufficient to meet grain N demand, highlighting the limited agronomic benefit and potential ecological cost of supplemental N during reproductive growth.

Nitrogen doi: 10.3390/nitrogen6040118

Authors: Jaume Arnó Alexandre Escolà Leire Sandonís-Pozo José A. Martínez-Casasnovas

This study explores the potential of Precision Agriculture (PA) to optimize top-dressing nitrogen (N) fertilization in rainfed barley under drought conditions in Central Catalonia (Spain). Efficient N management is critical in Mediterranean dryland winter cereal systems, where water scarcity and environmental regulations limit fertilization strategies. Two plots (2.93 ha and 1.80 ha) were zoned using soil apparent electrical conductivity (ECa) and elevation data obtained with the VERIS 3100 ECa soil surveyor. An on-farm experimental design tested four N dose rates (0 kg N/ha, 32 kg N/ha, 64 kg N/ha, and 96 kg N/ha) across two management zones per plot. Yield data were collected using a combine harvester equipped with a yield monitor and were mapped using geostatistical methods. A linear model (ANOVA) was used to analyze barley yield (kg/ha at 13% moisture), with nitrogen rate and soil zone (management class) as explanatory factors. Results showed low average yields (~1200 kg/ha–1300 kg/ha) due to severe water stress during the 2022–2023 season. Non-fertilized plots (N0) and those receiving moderate (N64) or high fertilization (N96) achieved the best performance, with the latter likely enhancing crop N uptake during the post-stress recovery period. In contrast, low fertilization (N32) proved less effective. Marginal return analysis supported variable-rate N application only in one plot, whereas under drought conditions, a no-fertilization strategy proved more suitable in the other. Ultimately, additional trials conducted under more favourable climatic scenarios are necessary to assess and validate the effectiveness of Precision Agriculture-based fertilization strategies in rainfed barley.

Nitrogen doi: 10.3390/nitrogen6040117

Authors: Ivana Varga Marina Bešlić Manda Antunović Jurica Jović Antonela Markulj Kulundžić

For successful potato production, maintaining a proper balance of mineral nutrients is crucial, as high yields cannot be achieved in fields lacking essential elements. The exact amount of fertilizer should be determined based on the expected yield, crop nutrient requirements, soil analysis, cultivation technology, and specific growing conditions. N (N) plays a crucial role in potato tuber growth. It is involved in the synthesis of proteins that are stored in the tubers and helps prolong the lifespan of the leaf canopy. On average, potato crops require a N supply of 80–120 kg/ha. Based on several studies, N fertilization significantly increased potato tuber yield, while dry matter content showed a slight decline. This indicates that higher N rates can enhance yield but potentially decrease tuber quality. To achieve high tuber yields while preserving desirable dry matter and starch content, the optimal N rate is approximately 100–120 kg N/ha. Although higher N inputs (>150 kg N/ha) may temporarily boost vegetative growth, they ultimately delay tuber maturation, reduce dry matter and starch accumulation, and increase production costs due to inefficient fertilizer use. Excessive N fertilization accelerates soil degradation and contributes to environmental pollution (soil acidification, NO3− leaching, NH3 emissions, NO, N2O, and NO2, leading to additional long-term ecological burdens. Therefore, minimizing N losses through sustainable soil management is essential for maintaining both farm profitability and environmental protection. Integrating N fertilization with biofertilizers—such as beneficial bacteria that colonize roots, enhance nutrient uptake, and stimulate root development—can improve yields while reducing reliance on costly synthetic fertilizers. This supports both soil fertility and crop productivity.

Nitrogen doi: 10.3390/nitrogen6040116

Authors: Wataru Shiraishi Shion Nishimura Morihiro Maeda Hideto Ueno

Drip fertigation (DF) is a sustainable agricultural management technique that optimizes water and nutrient usage, enhances crop productivity, and reduces environmental impact. Herein, we compared the effects of DF and conventional fertilization (CF) with a basal fertilizer on yield, soil inorganic nitrogen dynamics, N2O emissions, and nitrogen leaching during facility-grown eggplant cultivation. The experiment was conducted in a greenhouse from September 2023 to May 2024, with treatments arranged in three rows and three replicates. Soil, gas, and water samples were collected and analyzed throughout the growing season. The results revealed that the DF treatment produced yields comparable to those obtained with the CF treatment while significantly reducing nitrogen and phosphorus inputs. DF effectively prevented excessive nitrogen accumulation in the soil and reduced nitrogen loss through leaching and gas emissions. N2O emissions were significantly lower by more than 60% under DF than under CF. Precise nutrient management in DF suppressed nitrification and denitrification processes, mitigating N2O emissions. DF also significantly reduced nitrogen leaching by more than 70% compared with that in CF. These findings demonstrate that DF effectively enhances agricultural sustainability by improving nutrient use efficiency, reducing greenhouse gas emissions, and minimizing nitrogen leaching during the cultivation of facility-grown eggplant.

Nitrogen doi: 10.3390/nitrogen6040115

Authors: Nasratullah Habibi Zarir Sharaf Mohammad Yousuf Fakoor Shafiqullah Aryan Abdul Basir Mahmoodzada Amruddin Fakhri Shah Mahmoud Faqiri

Nitrogen deficiency is a major constraint on maize (Zea mays L.) productivity in Afghanistan, where poor soil fertility limits yields. This study investigated the effect of urea fertilizer on maize growth, physiology, and yield under semi-arid conditions in Balkh Province with a Calcisols soil type, focusing on maize cultivated for grain production. A field experiment was conducted in 2019 using a randomized complete block design with three replications and four nitrogen levels: 0 (control), 38.4, 76.8, and 115.2 kg ha−1. The region consists of fertile alluvial plains suitable for crop cultivation, though maize productivity is constrained by soil nutrient limitations, especially nitrogen deficiency. The soil at the experimental site is silty loam in texture, moderately fertile with alkaline pH (8.1), low organic matter (0.5%), and limited available nitrogen (15 mg kg−1). Growth traits (plant height, leaf number, leaf area, SPAD value), physiological parameters (leaf area index, crop growth rate, biomass), and yield components (cob length, cob diameter, seed number, 100-seed weight, biological yield, and Brix content) were recorded. Results showed that nitrogen application significantly improved all traits compared to the control. The highest values for plant height (260.2 cm), cob length (31.67 cm), biological yield (216.6 t ha−1), and Brix content (8.6%) were observed at 115.2 kg ha−1, although 76.8 kg ha−1 produced nearly similar results. Correlation analysis revealed strong positive associations between SPAD values, vegetative traits, and yield. The findings indicate that 115.2 kg ha−1 urea is an efficient and practical nitrogen rate for enhancing maize productivity under Afghan conditions.

Nitrogen doi: 10.3390/nitrogen6040114

Authors: Wataru Shiraishi Nobuki Morita Yo Toma Hideto Ueno

Sustainable recycling of organic residues and industrial byproducts is crucial for soil fertility and environmental sustainability. This study evaluated the effects of clinker-tea-waste compost (CTC) on rice growth, nutrient uptake, and soil chemical properties in a low-fertility paddy field over two years. In 2017, CTC was applied at 12, 18, and 22 Mg ha−1, while chemical fertilizer (CF) served as control. In 2018, all treatments received equal CF to assess residual effects. The results showed a limited immediate nitrogen supply in 2017, with no significant differences in rice growth, yield, or soil ammonium nitrogen (AN) among treatments. However, significant residual nitrogen effects emerged in 2018, with higher soil AN concentrations, nitrogen uptake indices, and rice yields in plots with higher CTC rates than in 2017. Si availability from clinker ash was evident immediately after application in 2017, correlating positively with rice stover Si content and CTC application rate. However, its residual effect disappeared in 2018 when CTC was discontinued. These findings demonstrate the complementary nutrient supply of CTC, with delayed nitrogen availability from tea residues and short-lived silicon release from clinker ash. This study highlights the potential of CTC for enhancing soil fertility and crop productivity in rice cultivation systems.

Nitrogen doi: 10.3390/nitrogen6040113

Authors: Tilila Baganna Assmaa Choukri Mohamed Sbahi Khalid Fares

Water scarcity is an increasingly critical global issue, particularly in arid regions like Morocco. Innovative approaches, such as the use of alternative water sources like landfill leachate, offer promising solutions. In this study, phosphate washing sludge was used to treat landfill leachate with the aim of producing irrigation-quality water and recovering nitrogen from the resulting sediment. A total of 40 L of raw leachate was treated with three concentrations of phosphate washing sludge (25%, 37%, and 50%). This volume was processed at the laboratory scale as a proof of concept for potential larger-scale applications. After 24 to 36 h of mixing and agitation, the mixture underwent sedimentation, yielding clear supernatants and nitrogen-rich sludge pellets. These pellets showed a significant increase in organic matter content, from 6.4% to 13.5%, representing an enhancement of 110.9%, thus demonstrating partial leachate depollution and organic matter enrichment. Microbiological analyses revealed a 98.9% reduction in fecal streptococci. The supernatants met irrigation water standards in terms of pH and electrical conductivity, and phytotoxicity tests on maize seeds confirmed their suitability for irrigation. Additionally, the recovered nitrogen-rich sediment presents a valuable input for composting and soil amendment.

Nitrogen doi: 10.3390/nitrogen6040112

Authors: Cleiton Farias de Oliveira Romildo da Silva Neves Thiago Filipe de Lima Arruda Sabrina dos Santos Costa Railene Hérica Carlos Rocha Araújo Ronaldo do Nascimento Alexandre Paiva da Silva Francisco Vaniés da Silva Sá Josinaldo Lopes Araujo Rocha

Nitrogen (N) is the most widely used nutrient in agriculture in the form of urea, yet it is one of the least efficient in terms of application due to losses through volatilization and leaching. The combination of urea with micronutrient sources, especially in the form of nanoparticles, is a promising technology for reducing these losses. Two greenhouse experiments were conducted with the objective of evaluating the influence of coating urea with zinc oxide nanoparticles (NPZnO) and iron oxide nanoparticles (NPFe2O3), associated with elemental sulfur (S°), on the leaching of mineral nitrogen and the production of dry mass and accumulation of N in young corn plants. The coating (0.26% w/w) of urea with elemental sulfur (S°) and NPZnO and NPFe2O3 reduced N losses through leaching (−21.3%) and delayed the nitrification process of N in the soil (−71.8%). This coating increased the efficiency of nitrogen fertilization in young corn plants, boosting the production of dry mass in leaves (+39.4%), stems (+68.8%), and roots (+61.6%), as well as the absorption of N in the above-ground biomass (+64.1%), compared to conventional urea. The use of urea coated with NPZnO and NPFe2O3 associated with S° is an environmentally sound solution for supplying N and micronutrients such as Fe and Zn in a more efficient and sustainable manner, especially in sandy soils with low organic matter content, which are common in the semi-arid region of Brazil.

Nitrogen doi: 10.3390/nitrogen6040111

Authors: Joaquín Herrero Adrián Ramírez-Santos Encarnación Díaz-Santos Gloria Torres-Cortés

The extensive use of synthetic nitrogen fertilizers has sustained global food production for more than a century but at high environmental and energetic costs. Improving nitrogen use efficiency (NUE) has therefore become a key objective to maintain productivity while reducing the ecological footprint of agriculture. This review synthesizes current knowledge on the biological foundations of NUE enhancement, focusing on the role of microbial biofertilizers and biostimulants. The main mechanisms through which plant-associated microorganisms contribute to nitrogen acquisition and assimilation are analyzed. In parallel, advances in genomics, biotechnology, and formulation science are highlighted as major drivers for the development of next-generation microbial consortia and bio-based products. Particular attention is given to the current landscape of commercial biofertilizers and biostimulants, summarizing the principal nitrogen-fixing and plant growth-promoting products available on the market and their agronomic performance. Moreover, major implementation challenges are discussed, including formulation stability and variability in field results. Overall, this review provides an integrated perspective on how biological innovations, market evolution, and agronomic optimization can jointly contribute to more sustainable nitrogen management and reduce dependence on synthetic fertilizers in modern agriculture.

Nitrogen doi: 10.3390/nitrogen6040110

Authors: Susana Cayunao Andrés Pérez-San Martín Emilio Jorquera-Fontena Vanessa Huerta-Mendoza Germán Tortosa Marysol Alvear Juan Ortíz Segun O. Oladele Gustavo Curaqueo

The rapid expansion of the salmon industry has generated increasing amounts of waste sludge with negative environmental impacts. Sustainable alternatives, such as using stabilized sludge in agriculture, are needed to mitigate these effects. At the same time, fruit production has grown globally, with hazelnut (Corylus avellana L.) emerging as a crop of high economic importance. However, the effect of salmon sludge application on hazelnut orchards is poorly understood. This study evaluated the application of thermally stabilized fish farming sludge (DS) compared with a slow-release mineral fertilizer (MF) intwo hazelnut varieties, ‘Barcelona’ (B) and ‘Tonda di Giffoni’ (TDG). Growth parameters including trunk cross-sectional area (TCSA), cumulative growth, shoot growth rate, leaf mass area (LMA) and chlorophyll index (SPAD), as well as soil physicochemical properties and enzymatic activities (fluorescein diacetate, β-glucosidase, acid phosphatase) were assessed. No significant differences (p > 0.05) in physiological parameters were found between DS and MF. However, the DS application increased soil pH by up 18%, electrical conductivity by ~48% at peak values, and enzymatic activities by 44% (acid phosphatase in B variety), 38% (β-glucosidase in TDG) and 169% (FDA in TGD), suggesting a great organic matter contribution and enhanced soil metabolic activity. Additionally, the B variety showed superior physiological performance, while TDG exhibited higher enzymatic activity. Overall, these findings provide a preliminary assessment of DS as a sustainable supplement to mineral nitrogen fertilization in hazelnut orchards, supporting both soil quality improvement and circular economy strategies in agriculture and aquaculture.

Nitrogen doi: 10.3390/nitrogen6040109

Authors: Romana Praženicová Andrei Larkov Kateřina Hanzelková Anton Korban Tomáš Křížek Veronika Hýsková Tomáš Ječmen Jakub Hraníček Denisa Vlčková Alena Gaudinová Petre Dobrev Radomíra Vanková Helena Ryšlavá Kateřina Bělonožníková

In traditional horticulture, fermented nettles (FN) enhance plant growth and resilience. However, their precise mode of action remains unclear. This study aims to characterize the bioactive profile of FN and to evaluate their potential as biostimulants beyond organic fertilizers. For this purpose, FN samples were prepared from Urtica dioica L. harvested in different seasons and analyzed by mass spectrometry (ICP-MS, LC-MS/MS, and GC×GC-MS), electrophoresis, and spectrophotometry to quantify macro- and micronutrients, nitrogen compounds, phytohormones, antioxidant capacity, enzyme activities, and microbial viability. The results show that FN are rich in essential nutrients (N, K, Ca, Fe, and Zn), hydrolytic enzymes (proteases, glycosidases and phosphatases), and phytohormones (auxins, cytokinins, gibberellins, abscisic acid, and salicylic acid). FN contain volatile compounds with potential antimicrobial effects, in addition to strong antioxidant properties. The monitored parameters support the dual role of FN as fertilizers and biostimulants, suggesting that FN act synergistically through nutrient enrichment, enzymatic degradation of macromolecules, hormonal signaling, and microbial priming. Based on our data, particularly because of the highest microbial viability and enzyme activities, the summer FN seem like the most suitable option. Moreover, the seasonal variability in composition highlights the importance of timing the harvest to optimize FN efficacy in sustainable agriculture.

Nitrogen doi: 10.3390/nitrogen6040108

Authors: Débora Tomazi Pereira Ignacio Moreu Badia Julia Vega Fabian López Palica David López Paniagua Nathalie Korbee Félix L. Figueroa

The red macroalga Porphyra plays a key role in Integrated Multi-Trophic Aquaculture (IMTA) systems, acting both as a biofilter and as a source of bioactive compounds (BACs) with nutritional and photoprotective value. This study evaluated how nitrogen source and concentration influence its physiological, photosynthetic, and biochemical responses under ultraviolet radiation (UVR). Gametophytes were cultured for four days under two nitrate sources (artificial and fishpond effluents) at 3 and 5 mM concentrations and exposed to PAR (120 µmol·photons·m−2·s−1) and UVR (9 W·m−2 for 6 h·day−1). Morphological responses, photosynthetic performance, and BACs were quantified. Nitrate uptake increased with nitrate concentration, while growth rate remained unaffected. Samples grown with fishpond effluents, particularly at 3 mM, showed darker pigmentation and higher phycoerythrin and mycosporine-like amino acid (MAA) contents, indicating enhanced nitrogen assimilation and photoprotective capacity. Conversely, 3 mM artificial nitrate in the water promoted the highest electron transport rate and lowest non-photochemical quenching, suggesting greater photosynthetic capacity. Polyphenols and antioxidant activity showed no significant differences among treatments, indicating similar stress status. Overall, it is suggested that fishpond effluents acted as a natural biostimulant, enhancing biliprotein and MAA synthesis without compromising physiological stability, reinforcing its potential for sustainable IMTA-based production of high-value photoprotective compounds.

Nitrogen doi: 10.3390/nitrogen6040107

Authors: Sergii Krysenko

Nitrogen is an essential element required for bacterial homeostasis. It serves as a building block for the biosynthesis of macromolecules and provides precursors for secondary metabolites. Actinomycetes have developed the ability to use various nitrogen sources to ensure their survival in ecological niches with fluctuating nutrient availability. A complex nitrogen metabolism of Actinobacteria allows the utilization of various compounds as N sources, including ammonium, nitrate, urea, amino acids, amino sugars, and amines. One such adaptation is the ability to acquire nitrogen from alternative amine sources like monoamines or polyamines putrescine, cadaverine, spermidine, and spermine, ensuring both nutrient availability (C and N sources) and resistance against high polyamine concentrations. Actinobacterial nitrogen degradation, including the catabolism of amines, is not only important under low nitrogen availability, but also required to survive under high concentrations of these compounds. The purpose of this review is to summarize the knowledge on nitrogen degradation and, more specifically, catabolism of amines in Actinobacterial survival and its role in nitrogen metabolism. Applying critical analysis of the recent available literature and sequencing data, this work aims to explore strategies of pathogenic and non-pathogenic Actinobacteria to survive in the presence of different nitrogen sources, and their impact on primary and secondary metabolism. The knowledge about nitrogen degradation pathways in Actinobacteria including mono- and polyamine catabolism collected in the scope of this review paper is brought in connection with possibilities to combat pathogens by using their capability to metabolize polyamines as an antibiotic drug target. This might offer new directions for target-based drug design to combat Actinobacterial infections.

Nitrogen doi: 10.3390/nitrogen6040106

Authors: Sayali S. Kulkarni Ganesh L. Khande Jayavant L. Gunjakar Valmiki B. Koli

Nitrogen (N2), constituting the majority of Earth’s atmosphere, remains indispensable for biological systems and underpins modern agriculture and industry. Traditionally, the Haber–Bosch process has been essential for synthesizing ammonia (NH3) from N2 under high temperature and pressure, but it contributes significantly to global CO2 emissions. Recently, carbon-free electrocatalytic nitrogen reduction (e-NRR) has emerged as a promising, eco-friendly, and cost-effective approach for green NH3 production under mild conditions using renewable energy, offering a sustainable alternative to the fossil fuel dependent Haber–Bosch process. This work explores NRR by contrasting the limitations of Haber–Bosch with the advantages of electrocatalysis. Despite progress, electrochemical N2 reduction to NH3 production remains challenging due to low activity, poor selectivity, stability, efficiency, and detection issues. Developing efficient e-NRR electrocatalysts is crucial to enhance activity, suppress hydrogen evolution reaction (HER), boost NH3 yield, and improve Faradaic efficiency. This review highlights the role of layered double hydroxide (LDH) catalysts in e-NRR, summarizing the fundamental process, reaction pathways, and synthesis strategies. Ammonia detection methods, key metrics, and potential contamination issues are compared to inform standard NRR measurement protocols. Lastly, we summarize key findings to synthesize and improve LDH electrocatalysts for NH3 production and a sustainable, carbon-free N2 economy.

Nitrogen doi: 10.3390/nitrogen6040105

Authors: Jerzy Mirosław Kupiec Sebastian Szklarek Magdalena Urbaniak Arnoldo Font-Nájera Elżbieta Mierzejewska-Sinner Agnieszka Bednarek Jakub Wójcik Joanna Mankiewicz-Boczek

Agricultural pollution, such as contamination from manure storage or leaking livestock buildings, often spreads through the catchment, affecting groundwater and surface water. An effective solution is the construction of permeable organic barriers. This study evaluates the efficiency of an innovative bioactive barrier in removing nitrogen compounds (NO3− and NH4+) and polychlorinated biphenyls (PCBs). Two types of barriers were tested: a horizontal deposit under a manure storage point and a vertical deposit in the leachate flow path. The bioactivity of the barrier was confirmed by the presence of bacterial genes involved in nitrogen transformation and PCB degradation. Results showed a 70% reduction in NO3− (368.4 mg·L−1) and 43% reduction in NH4+ (42.4 mg·L−1). Genetic analysis identified bacteria capable of complete denitrification, resembling Pseudomonas stutzeri. The analysis also indicated that higher summer temperatures and pH levels fostered microbial communities capable of nitrogen transformation. Cluster analysis revealed that the vertical deposit zone was crucial for nitrogen removal. Additionally, the vertical barrier achieved a 53% reduction in PCBs, with Pseudomonas aeruginosa-like bacteria identified as PCB degraders.

Nitrogen doi: 10.3390/nitrogen6040104

Authors: Asmaa A. Mohamed Mohamed Allam Emanuele Radicetti Roberto Mancinelli Bahy R. Bakheit

Maize is the third most important cereal crop in the world due to its exceptional productivity and adaptability. The study was performed to evaluate the effects of potassium sulfate fertilizer on growth, physiological traits, yield, and its components of three single crosses of maize over two growing seasons. A field experiment was conducted at the agronomy experimental farm, Assiut University, Egypt, using a strip-plot design with three replications. Treatments included four potassium sulfate rates (0, 60, 120, and 180 kg ha−1) and three maize hybrids (SC2031, SC2036, SC168). The results revealed significant combined analysis of variance for potassium sulfate levels and hybrids on most of the studied traits. The hybrid SC2036, when fertilized with 120 kg K/ha, is especially suitable for achieving high productivity under the tested agro-environmental conditions. The path and principal component analysis results highlight that ear diameter and leaf number are the most influential traits for grain yield improvement for all tested crosses. Traits such as chlorophyll content and 1000-grain weight contributed mainly through indirect path effects. The path analysis also underlines hybrid-specific differences in how yield components affect grain yield per plant. These results highlight that the integration of nutrient management, hybrid selection, and multivariate analysis provides a comprehensive strategy for improving maize productivity.

Nitrogen doi: 10.3390/nitrogen6040103

Authors: Aurora Moreno-Lora Samir Sayadi-Gmada M. Milagros Fernández-Fernández Elisa M. Suárez-Rey

Nitrate pollution from agricultural activities is a major cause of surface and groundwater degradation across Europe. In Andalusia, southern Spain, approximately 26% of the regional territory is affected by this type of contamination. To mitigate and prevent nitrate pollution, a regulatory framework has been implemented, establishing specific restrictions and recommendations for agricultural practices and nitrogen fertilization management in designated areas. However, the effectiveness of these measures is often constrained by limited awareness of the issue, insufficient understanding of existing regulations, and a general lack of training in nitrogen fertilization management among farmers. To address these challenges, a specialized training program on crop fertilization was developed for agricultural professionals. This initiative aimed to raise awareness of the environmental impacts of nitrate pollution, disseminate information about relevant legislation, and strengthen technical knowledge related to nitrogen fertilization planning and management, thereby enhancing on-farm decision-making. This study analysed the impact of this training activity on the level of awareness and knowledge regarding nitrate-related issues in Andalusia.

Nitrogen doi: 10.3390/nitrogen6040102

Authors: Maria Maleva Galina Borisova Anastasia Tugbaeva Alina Malakheeva Olga Voropaeva Alexander Ermoshin Anna Betekhtina

The increasing biogeochemical imbalance of nitrogen (N) heightens the importance of studying rhizosphere bacteria, which aid crop nutrient uptake, and their responses to N deficiency. The aim of the study was to assess variety-specific responses of the tomatoes and their associated rhizobacteriome to low N availability. Three determinant varieties of Solanum lycopersicum L. were cultivated in pot-scale experiment during 10 weeks on low-fertility substrate (sod-podzolic soil:peat:clay:sand, 1:1:1:2, v/v), half of which were supplemented with ammonium nitrate (60 mg N kg−1 in total). A comprehensive methodology was employed, including 16S rRNA metagenomic Nanopore sequencing, quantitative assessment of N-cycling bacteria, and analysis of plant growth, photosynthetic pigments, total N in biomass, and fine root architecture. Results demonstrated that N deficiency significantly reduced plant biomass and photosynthetic pigments. The rhizosphere contained a diverse community of N-transforming bacteria (38 identified genera), whose composition and relative abundance were strongly influenced by both tomato variety and N fertilization. Nitrogen application increased the abundance of N-fixers and altered alpha-diversity in a variety-dependent manner. Significant correlations were found between the abundance of key bacterial genera (e.g., Stenotrophomonas, Rhizobium) and N parameters in plants and substrates. The study concludes that the response of the tomato rhizobacteriome to N availability is variety-specific, which is important for the development of microbiome management strategies for enhancing N use efficiency.

Nitrogen doi: 10.3390/nitrogen6040101

Authors: María Inmaculada Rodríguez-García María Gema Carrasco-García Paloma Rocío Cubillas Fernández Maria da Conceiçao Rodrigues Ribeiro Pedro J. S. Cardoso Ignacio. J. Turias

This study aims to evaluate and compare the performance of Autoencoders (AEs) and Sparse Autoencoders (SAEs) in forecasting the next-hour concentration levels of various air pollutants—specifically NO2(t + 1), PM10(t + 1), and SO2(t + 1)—in the Bay of Algeciras, a highly complex region located in southern Spain. Hourly data related to air quality, meteorological conditions, and maritime traffic were collected from 2017 to 2019 across multiple monitoring stations distributed throughout the bay, enabling the analysis of diverse forecasting scenarios. The output variable was segmented into four distinct, non-overlapping quartiles (Q1–Q4) to capture different concentration ranges. AE models demonstrated greater accuracy in predicting moderate pollution levels (Q2 and Q3), whereas SAE models achieved comparable performance at the lower and upper extremes (Q1 and Q4). The results suggest that stacking AE layers with varying degrees of sparsity—culminating in a supervised output layer—can enhance the model’s ability to forecast pollutant concentration indices across all quartiles. Notably, Q4 predictions, representing peak concentrations, benefited from more complex SAE architectures, likely due to the increased difficulty associated with modelling extreme values.

Nitrogen doi: 10.3390/nitrogen6040100

Authors: Marie Lambropoulos Sebastian Raubitzek Georg Goldenits Hans Sandén Kevin Mallinger

Early seedling survival is a key determinant of reforestation success under increasingly variable climatic conditions. Fertilizers used to mitigate nutrient limitations are believed to mitigate early establishment stress, but their effectiveness under heterogeneous field conditions remains uncertain. This study specifically tests whether an amino-acid-based nitrogen fertilizer can provide a more efficient and ecologically sustainable Nitrogen source compared with conventional mineral formulations. Using a dataset of 6238 seedlings from seven operational Austrian reforestation sites, we quantify amendment performance and examine interactions with relief, soil depth, water availability, and management practices. We apply CatBoost to identify influential predictors of mortality and summarize results across repeated evaluations. Further, for the reported settings, we can reliably predict tree seedling mortality for three out of four seedlings, with an average model accuracy of 76.4% and an AUC of 0.82 across sites. The arginine-based fertilizer increased survival probabilities by up to 15% on moist, deep soils but showed no consistent benefit under shallow or drought-prone conditions. The results highlight the potential of amino-acid-based N supply as a more ecologically aligned alternative and support operational decisions on when and where fertilizers may improve oak establishment under changing climatic conditions.

Nitrogen doi: 10.3390/nitrogen6040099

Authors: Tong Li Longxin Luo Zhi Li Ziquan Feng Qi Zhang Shuo Ma Xinyi Li Huaina Gao Minmin Zhou Shang Wu Yali Zhang Han Jiang Yuanyuan Li

Nitrogen assimilation is vital for apple growth, yield, and quality, with nitrate reductase (NIA), nitrite reductase (NIR), glutamine synthetase (GS), and glutamate synthase (GOGAT) serving as key regulatory enzymes. This study systematically identified these four gene families in apple (Malus domestica) through genome-wide analysis and examined their expression patterns under nitrate treatment. In total, 13 genes were identified, 2 MdNIAs, 1 MdNIR, 7 MdGSs, and 3 MdGOGATs, with gene lengths ranging from 2577 to 27736 base pairs (bp); MdGLT1A had the longest coding sequence (6627 bp). The encoded proteins contained 355–2208 amino acids, with predicted isoelectric points (pIs) between 5.55 and 6.63. Subcellular localization analysis predicted distinct compartmentalization: MdNIA1A in peroxisomes; MdGS1 in the cytosol; MdNIR1, MdGS2, and MdGLU1 in chloroplasts; and MdGLT1 in mitochondria/chloroplasts. Functional site prediction revealed multiple phosphorylation and glycosylation sites, with ATP/GTP-binding motifs present only in certain MdGOGAT proteins. Protein interaction analysis suggested close associations among these genes and possible interactions with NRT2.1/2.2. Chromosomal mapping showed their distribution across eight chromosomes, while promoter analysis identified diverse cis-acting regulatory elements (e.g., ABRE and G-box). Under nitrate treatment (0–12 h), these genes exhibited distinct expression dynamics: MdNIA1A and B were rapidly induced (0–6 h) and maintained high expression; MdNIR1 peaked at 6 h and then declined; MdGS1.1B was activated after 6 h; and MdGS2A, MdGLU1, and MdGLT1A/B peaked at 6 h before decreasing. Therefore, these results elucidate the structural and functional divergence of nitrogen assimilation genes in apple and provide a basis for understanding nitrogen utilization mechanisms and developing nitrogen-efficient breeding strategies.

Nitrogen doi: 10.3390/nitrogen6040098

Authors: Mubashir Husnain Pablo L. Ribeiro Britta Pitann Karl Hermann Mühling

Climate change is expected to increase the frequency of extreme soil moisture events, such as winter waterlogging followed by spring drought, particularly in temperate regions of Europe, North America and Northeast China. While N2O emissions from paddy soils under waterlogging and subsequent drainage have been widely studied, knowledge of upland arable soils under wheat cultivation remains limited. We hypothesized that: (1) in upland soils, combined waterlogging and drought reduces N2O emissions compared to continuous waterlogging, and (2) plant presence mitigates soil nitrate accumulation and N2O emissions across different moisture regimes. A greenhouse experiment was conducted using intact upland soil cores with and without wheat under four moisture treatments: control (60% water-holding capacity, WHC), drought (30% WHC), waterlogging, and waterlogging followed by drought. Daily and cumulative N2O fluxes, soil mineral nitrogen (NH4+-002DN and NO3−-N), and total nitrogen uptake by wheat shoots were measured. Prolonged waterlogging resulted in the highest cumulative N2O emissions, whereas the transition from waterlogging to drought triggered a sharp but transient N2O peak, particularly in soils without plants. Wheat presence consistently reduced N2O emissions, likely through nitrate uptake, which limited substrate availability for incomplete denitrification. Moisture regimes strongly affected nitrate dynamics, with drought promoting nitrate accumulation and waterlogging enhancing nitrate loss. These findings highlight the vulnerability of upland soils in regions prone to seasonal moisture extremes. Effective management of soil moisture and nitrogen, including the promotion of plant growth, is essential to mitigate N2O emissions and improve nitrogen use efficiency under future climate scenarios.

Nitrogen doi: 10.3390/nitrogen6040097

Authors: Bridget Kumi Stephen Worrall David Sawtell Ruben Sakrabani

This review examines the current status and future potential of plasma-induced acidification (PIA) as a sustainable method for managing nitrogen-rich organic waste streams such as livestock slurry and digestate. Conventional acidification using sulfuric or nitric acid reduces ammonia (NH3) emissions but raises concerns related to safety, cost, and environmental impacts. Plasma-assisted systems offer an alternative by generating reactive nitrogen and oxygen species (RNS/ROS) in situ, lowering pH and stabilizing ammonia (NH3), as ammonium (NH4+), thereby enhancing fertiliser value and reducing emissions of NH3, methane (CH4), and odours. Key technologies such as dielectric barrier discharge (DBD), corona discharge, and gliding arc reactors show promise in laboratory-scale studies, but barriers like energy consumption, scalability, and N2O trade-offs limit commercial adoption. The paper reviews the mechanisms behind PIA, compares it to conventional approaches, and assesses its agronomic and environmental benefits. Valorisation opportunities, including the recovery of nitrate-rich fractions and integration with biogas systems, align plasma treatment with circular economy goals. However, challenges remain, including reactor design, energy efficiency, and lack of recognition as a Best Available Technique (BAT). A roadmap is proposed for transitioning from lab to farm-scale application, involving cross-sector collaboration, lifecycle assessments, and policy support to accelerate adoption and realise environmental and economic gains.

Nitrogen doi: 10.3390/nitrogen6040096

Authors: Antun Šokec Goran Fruk Mihaela Šatvar Vrbančić Kristijan Konopka Tomislav Karažija Marko Petek

Nitrogen (N) deficiency in apples (Malus × domestica Borkh.) leads to characteristic physiological symptoms, including leaf and fruit discoloration. Fertigation, i.e., the application of dissolved fertilizers, can significantly improve the growth and fruit quality of apples while optimizing nutrient uptake through a more precise and better timed application than conventional fertilization. This study therefore investigates how different fertilization treatments affect the N concentration of different age categories of apple leaves. Apples of the variety ‘Braeburn’ were grown hydroponically on the low-vigorous rootstock M9. Four fertilizer treatments were used: (1) Hoagland solution (HS); (2) HS nitrogen excluded; (3) HS iron excluded; and (4) HS magnesium excluded. Through vegetation, leaf samples were taken from three shoot positions representing different leaf ages (young, semi-young and old) and then chemically analyzed. The lowest N concentrations across all leaf ages and sampling moments were found in the treatment with N excluded (1.69–2.07% N), while the highest values occurred in the treatments where iron (2.00–2.49% N) or magnesium (1.98–2.37% N) were excluded. The seasonal changes in N concentration reflect interactions between the leaf age and the sampling moment. These results show that the N concentration of apple leaves strongly depends on the type of fertilization.

Nitrogen doi: 10.3390/nitrogen6040095

Authors: Abishek Ravichandran Santhi Rangasamy Maragatham Subramaniam Gopalakrishnan Myleswami Dhinesh Vadivel Poovarasan Thangavel Naveenkumar Arumugam Vinothini Nedunchezhiyan Dineshkumar Chandrasekar

Precision application of fertiliser nutrients based on soil-available nutrients is a vital means of increasing castor (Ricinus communis L.) productivity. Fertiliser application based on the targeted yield model under inorganic fertilisers alone and Integrated Plant Nutrition System (IPNS) differ from the blanket recommendation practices. Field experiments were conducted in two locations to validate the Soil Test Crop Response (STCR) targeted yield model developed for hybrid castor on non-calcareous Alfisol. The main objective was to determine the effect of inorganic fertilisers and organic manures on microbial populations, enzyme dynamics in soil, and productivity of castor. Experimental field data revealed that combined application of inorganic fertilisers along with 12.5 t ha−1 farmyard manure increased the soil microbial population and enzyme activity in the rhizosphere soils of castor. Castor responded positively with an increase in highest targeted yield level. The highest yield of 2726 and 2695 kg ha−1 were attained in the treatment T8 (STCR-IPNS −2.75 t ha−1) in both locations, and Treatment T5 (STCR-NPK alone −2.75 t ha−1) was on par with T8. The IPNS treatments showed higher percent achievement than the NPK treatments alone. Root length and dry matter production increased significantly with the application of a higher dose of fertiliser along with farmyard manure. Root dry matter production significantly contributed towards the castor seed yield. More soil-beneficial microorganisms and enzyme dynamics were observed in the IPNS treatment.

Nitrogen doi: 10.3390/nitrogen6040094

Authors: Luiz Eduardo de Morais Fernandes Fontes Guilherme Cristyan Garcia Penha Ana Carina da Silva Cândido Cid Naudi Silva Campos Alek Sandro Dutra Márcio Dias Pereira Charline Zaratin Alves

Biological nitrogen (N) fixation is a well-established practice in various legumes, such as soybeans. However, it has not been widely studied in cowpeas (Vigna unguiculata L. Walp). In this context, it is important to understand how the application of nitrogen-fixing bacteria, either alone or in association, can benefit the crop’s nitrogen demand. This study aimed to determine whether co-inoculation of Bradyrhizobium and Azospirillum favors nodulation and isoflavone production, and increases the nitrogen content, in cowpea crops. The experiment was set up using a randomized block design on two cowpea varieties, with seven treatments consisting of a control and the isolated application of Bradyrhizobium japonicum and Azospirillum brasilense, as well as different co-inoculation doses (75, 150, 225 and 300 mL per 50 kg of seed for each inoculant). There were four replications. Thirty days after emergence, the number of nodules and the dry masses of the nodules, roots and shoots of the plants were assessed. N content and isoflavone content in the fully developed third trifoliate leaf from the apex of the plants were also assessed. Statistical differences were observed between treatments for all analyzed variables, with higher values generally observed for co-inoculation treatments. Co-inoculation of B. japonicum and A. brasilense in cowpea seeds can be a viable and efficient practice. A dose of 75 mL of each inoculant favored nodule formation, root development and N content, as well as contributing to isoflavone production in the cowpea crop.

Nitrogen doi: 10.3390/nitrogen6040093

Authors: Bilal Ahmad Mir Zubair Ahmad Parrey Preedhi Kapoor Parul Parihar Gurmeen Rakhra

Background: In this study, hydroponic experiments were conducted to examine the roles of sulphur (S), calcium (Ca), and nitric oxide (NO) in alleviating salt stress (20 mM NaCl) in tomato (Solanum lycopersicum L.) seedlings. Methods: Analyses included Na+/K+ contents, inorganic nitrogen (nitrate, nitrite, ammonium), nitrogen- and ammonium-assimilating enzymes (NR, NiR, GS, GOGAT), sulphur-assimilating enzymes (ATPS, OASTL), protein content, ROS (O2∙−, H2O2), and in vivo NO visualization were conducted. Results: We observed that salt stress increased Na+, reduced K+, disrupted nitrogen and sulphur metabolism, elevated ROS, and decreased NO, causing oxidative stress and reduced enzymatic activity. Supplementation with potassium sulphate (40 µM), calcium chloride (30 µM), and sodium nitroprusside (SNP; 40 µM) mitigated these effects, enhancing enzymatic activities, restoring Na+/K+ balance, improving protein content, and lowering ROS. The protective role of NO was confirmed using inhibitors L-NAME (500 µM) and cPTIO (100 µM), which reversed SNP’s benefits and aggravated stress damage. Conclusion: Overall, S, Ca, and NO were found to synergistically improve salt stress tolerance by modulating ion homeostasis, nitrogen and sulphur metabolism, and oxidative balance, offering nutrient- and signal-based strategies to enhance tomato resilience under salinity.

Nitrogen doi: 10.3390/nitrogen6040092

Authors: Armstrong Ighodalo Omoregie Muhammad Oliver Ensor Silini Lin Sze Wong Adharsh Rajasekar

Nitrogen eutrophication represents a significant environmental challenge in Chinese aquatic ecosystems, exacerbated by rapid agricultural intensification, industrial expansion, and urban development. This review consolidates existing knowledge on the drivers and impacts of nitrogen pollution in Chinese aquatic ecosystems, with a focus on environments such as lakes, rivers, and coastal waters. The primary sources of nitrogen enrichment are excessive fertilizer application, livestock manure discharge, industrial emissions, and untreated industrial and municipal wastewater. These inputs have led to severe ecological consequences, including harmful algal blooms, hypoxia, loss of biodiversity, and deteriorating water quality, threatening ecosystem health and human well-being. The review also examines mitigation strategies implemented in China, encompassing regulatory policies such as the “Zero Growth” fertilizer initiative, as well as technological advancements in wastewater treatment and sustainable farming practices. Case studies highlighting successful interventions, such as lake restoration projects and integrated watershed management, demonstrate the potential for effective nitrogen control. However, persistent challenges remain, including uneven policy enforcement, insufficient public awareness, and gaps in scientific understanding of nitrogen cycling dynamics. This review aims to inform future efforts toward achieving sustainable nitrogen management in China by synthesizing current research and identifying key knowledge gaps. Addressing these issues is crucial for safeguarding China’s aquatic ecosystems and promoting global nutrient stewardship.

Nitrogen doi: 10.3390/nitrogen6040091

Authors: Thibaut Cugnon Marc De Toffoli Jacques Mahillon Richard Lambert

Crops nitrogen supply through the in situ mineralization of soil organic matter is a critical process for plant nutrition. However, accurately estimating the contribution of mineralization remains challenging. The complexity of biological, chemical, and physical processes in the soil, influenced by environmental conditions, makes it difficult to precisely quantify the amount of nitrogen available for crops. In this study, we created a database by collecting results from 121 mineralization monitoring experiments carried out between 2015 and 2021 on different experimental plots across Wallonia, Southern Belgium, and assessed the efficiency of predictive mineralization methods. The most impactful analytical parameters on in situ mineralization (ISM), determined using LIXIM program, appeared to be potentially mineralizable nitrogen (PMN) (r = 0.79). PMN, estimated by anaerobic soil incubation, also allowed the effective consideration of the after-effects of grassland termination and manure inputs. A multiple linear regression (MLR) combining PMN, POxC, pH, TOC:N, and TOC:clay significantly improved the prediction of soil nitrogen mineralization available for crops, achieving r = 0.87 (vs. r = 0.58 for the current method), while reducing dispersion by 41% (RMSE 56.35 → 33.13 kg N·ha−1). The use of a more flexible Bootstrap Forest model (BFM) further enhanced performance, reaching r = 0.92 and a 50.8% reduction in dispersion compared to the current method (RMSE 56.35 → 27.76 kg N·ha−1), i.e., about 16% lower RMSE than the MLR. Those models provided practical and efficient tools to better manage nitrogen resources in temperate agricultural systems.

Nitrogen doi: 10.3390/nitrogen6040090

Authors: Zhifeng Xun Mingzhu Zhao Xueya Zhao Mi Wang Yujing Liu Xueying Han Yiming Zhang Yanhua Wu Zhi Quan

Urban lawns are a predominant form of vegetation in sports grounds and greenbelts. Nitrogen (N) fertilization is widely used to sustain lawn productivity. However, it also promotes nitrous oxide (N2O) emissions, a potent greenhouse gas. The microbial mechanisms underlying N2O emissions from fertilized lawn soils remain poorly understood. In this study, we conducted a controlled incubation experiment with four N application rates [0 (N0), 100 (N100), 200 (N200), and 300 kg·ha−1·yr−1 (N300)] to investigate N2O emissions and associated microbial processes in urban lawn soil. Biological inhibitors combined with high-throughput sequencing were used to quantify the inhibitor-sensitive fraction of fungi and bacteria contributing to N2O emissions. Our results showed that N fertilizer significantly increased N2O emissions, with the highest emission observed under N200. The fungi inhibitor-sensitive fraction accounted for ~45% of total N2O emissions, significantly higher than that of bacteria (~31%). Dominant fungal phyla included Ascomycota, Basidiomycota, and Zygomycota, with N fertilization significantly increasing the relative abundance of Ascomycota and decreasing that of Basidiomycota. Redundancy analysis revealed strong positive correlations between Ascomycota abundance and N2O emissions across N treatments. At the genus level, Pyrenochaetopsis, Myrothecium, and Humicola were positively associated with N2O production and identified as key functional taxa. These findings demonstrate that moderate N fertilization can disproportionately stimulate fungal-driven N2O emissions in urban lawns. The results provide a scientific basis for optimizing N fertilization strategies in green spaces, with implications for N policy and sustainable landscape management.

Nitrogen doi: 10.3390/nitrogen6040089

Authors: Wahyu Astiko Mohamad Taufik Fauzi Lolita Endang Susilowati Lalu Zulkifli Fahrurozi

Suboptimal land conditions, characterized by limited nutrient availability and poor soil physical properties, restrict the growth and productivity of maize–soybean intercropping systems. Bioameliorants containing beneficial microorganisms, such as mycorrhizae, offer a sustainable strategy to enhance soil fertility and nutrient uptake efficiency. This study evaluated the effects of different bioameliorant compositions on nitrogen availability, plant growth, and yield in maize–soybean intercropping on suboptimal land. A randomized complete block design with four replicates tested five treatments: F0 (control, no bioameliorant), F1 (10% compost + 10% rice husk charcoal + 10% manure + 70% mycorrhizal biofertilizer), F2 (15% each of compost, manure, charcoal + 55% biofertilizer), F3 (20% each + 40% biofertilizer), and F4 (25% each component). Results showed that the balanced F4 bioameliorant markedly improved nitrogen availability, soil health, and yields in maize–soybean intercropping on sandy soils. These findings highlight its potential as a sustainable strategy to enhance productivity, reduce reliance on chemical fertilizers, and strengthen agroecosystem resilience on suboptimal land. The optimized F4 formulation therefore represents a practical approach to improving nutrient availability and plant performance in maize–soybean intercropping systems under marginal soil conditions.

Nitrogen doi: 10.3390/nitrogen6040088

Authors: Bronc Finch Lance Blythe

Bermudagrass (Cynodon dactylon) forage production recommendations are often developed in natural environments with available water limitations, often resulting in highly variable responses and lower average responses. As farmland ownership changes and agriculture and irrigation technologies become more affordable the amount of irrigated hay production has increased. While much of the agronomic management does not differ between rain-fed and irrigated environments, nutrient use and uptake dynamics may. This requires a reevaluation and potential adjustment of current recommendations to allow for increased yield potential of irrigated production systems without detrimental impacts on the system. The objective of this study was to identify the need for further investigation of nitrogen application rates for forage bermudagrass production under irrigated conditions. Nitrogen applications of 0 to 280 kg N ha−1, in 56 kg increments, were applied at spring green-up and following the first and second harvests. Dry matter biomass, crude protein, and total digestible nutrients increased with increasing nitrogen application rate, while yield and profit maximizing rates both exceeded the typical recommended rate for bermudagrass hay production. The responses noted for increased nitrogen application rates indicate the need for further investigation of N requirements of non-moisture-limited hay production.

Nitrogen doi: 10.3390/nitrogen6040087

Authors: Štefan Tóth Peter Mižík Božena Šoltysová Katarína Klemová Štefan Dupľák Pavol Porvaz

The scope of this research was to quantify the mid-term impact of different soil tillage on carbon/nitrogen agronomical key context under optimal growing conditions of the European moderate continental climate. A large-scale on-farm experiment was established in winter wheat/soybean two-crop long-term cultivation without fertilization on fertile Luvic Chernozem. Four treatments were conducted: (T1) ‘Deep Loosening’ with tillage depth of 50 cm, (T2) ‘Plowing’ to 30 cm, (T3) ‘Strip-Till’ with tillage depth of 20 cm, and (T4) ‘No-Till’; the tillage frequency at T1 and T2 was reduced and applied to soybean only, therefore, once per 2 years during the trial period 2020/21–2024/25. Unlike the crop yield, which decreased with tillage intensity decreasing (21.38 > 19.30 > 18.88 > 18.62 t/ha in dry matter cumulatively; T2 > T3 > T1 > T4), the carbon/nitrogen key agronomical parameters either increased (root nodules count/weight: thus confirmed convergent, occasionally reverse indicators; soil compaction: penetrometric resistance) or differed in varying patterns and extent (soil chemical indicators). In fertile Chernozem soils, tillage and indicators have different importance within the nexus studied; plowing still gives the most stable yields. To improve nitrogen fixing, farmers’ practices need to balance yield vs. soil health, including eliminating soil compaction.

Nitrogen doi: 10.3390/nitrogen6030086

Authors: Sabina Yeasmin Mojakkar Noman Zaren Subah Betto Tamanna Rahman Sanjida Parven Sarly A. K. M. Mominul Islam Md. Parvez Anwar

This study aimed to assess the effect of organic amendment-based integrated nitrogen (N) application on major soil macronutrients, carbon (C) accumulation, crop productivity and N use efficiency (NUE) of different rice-based cropping patterns. This experiment was composed of various organic amendments ((i): control (no organic amendment, application of 100% N from urea); (ii): 25% N from compost + 75% N from urea; (iii): 25% N from cowdung + 75% N from urea; iv: 25% N from vermicompost + 75% N from urea) and rice-based cropping patterns ((i) rice–rice–rice, (ii) rice–fallow–rice–mustard, and (iii) rice–vegetables–rice). Organic amendments and soils (0–20 cm) were collected from farmers’ fields and were analyzed for major nutrients: N and organic C (OC), phosphorus (P), potassium (K) and sulphur (S). Soil OC accumulation potential, system productivity and partial factor productivity of N were also calculated. The results indicate that organic amendment application significantly enhanced soil OC (0.957–1.604%) compared to control (0.916–1.292%), with vermicompost attaining the highest OC content and OC accumulation potential (up to 24.15%), especially in the rice–vegetables–rice pattern. Vermicompost also predominantly increased N (22–62%) and S (51–78%) level in soils, while cowdung significantly amended P levels (155–178%) and contributed steadily to improved K levels in soil. Overall, nutrient improvements and soil fertility were highest under the rice–vegetables–rice system, followed by rice–fallow–mustard–rice and rice–rice–rice. System productivity was maximum in the rice–vegetables–rice pattern (up to 85.7 t ha−1), with remarkable enhancements in NUE when organic amendments were applied. Cowdung and vermicompost both matched or exceeded the performance of chemical fertilizer in these cases. These results demonstrate the advantages of integrated N management and diversified cropping to improve nutrient cycling, soil health and sustainable productivity in rice-based agroecosystems.

Nitrogen doi: 10.3390/nitrogen6030085

Authors: Juan J. Patiño-Cruz Erick H. Ochoa-Chaparro Eloy Navarro-León Celia Chávez-Mendoza Ezequiel Muñoz-Márquez Alexandro Guevara-Aguilar Sandra Pérez-Álvarez Esteban Sánchez

Efficient nitrogen assimilation in crops remains a key challenge for sustainable agriculture. This study investigated the physiological effects of foliar application of iodine on Lactuca sativa L. cv. Butterhead, comparing two different chemical forms—nanoparticulate iodine (INPs) and potassium iodide (KI)—selected to contrast a conventional ionic source with a nanoformulations of growing interest in plant nutrition. Plants were treated under passive hydroponic conditions with INPs and KI at concentrations of 40, 80, and 160 µM. The results showed that INPs at 40 µM significantly increased total biomass and soluble amino acid accumulation compared to the control, with no signs of phytotoxicity. In contrast, KI treatments significantly increased nitrate reductase activity, suggesting a role in the activation of the nitrogen pathway. However, neither form consistently outperformed the other across all evaluated variables. Yield and total chlorophyll content remained statistically unchanged between treatments, indicating a complex and form-dependent response. These findings highlight the differential physiological effects of iodine formulations on nitrogen-related metabolism and provide preliminary evidence for their potential integration into precision fertilization strategies focused on biochemical efficiency and metabolic modulation.

Nitrogen doi: 10.3390/nitrogen6030084

Authors: Francesco D’Amico Teresa Lo Feudo Ivano Ammoscato Giorgia De Benedetto Salvatore Sinopoli Luana Malacaria Maurizio Busetto Davide Putero Claudia Roberta Calidonna

The World Meteorological Organization/Global Atmosphere Watch (WMO/GAW) observation site of Lamezia Terme (code: LMT) in Calabria, Italy, has been measuring nitric oxide (NO) and nitrogen dioxide (NO2) (together referred to as NOx) for a decade; however, only a limited number of studies have evaluated their variability at the site, accounting for short measurement periods. In this work, nine continuous years (2015–2023) of measurements are analyzed to assess daily, weekly, seasonal, and multi-year tendencies, also accounting for local wind circulation, which is known to have a relevant impact on LMT’s measurements. For the first time, a multi-year evaluation of LMT data also considers the local wind lidar record to integrate conventional measurements with additional information on the transport of NOx at low altitudes. The study also considers data on local tourism and vehicular traffic to assess correlations with LMT’s measurements, thus providing new insights on NOx variability at the site. The analysis showed peaks in early morning NOx concentrations attributable to rush hour traffic, while in the evening NO2 peaks are present with minor NO counterparts. Weekly cycles have yielded the most statistically significant results of any other similar evaluation at the sites, with all combinations of parameters, seasons, and wind corridors indicating tangible differences between weekday (WD, Monday to Friday) and weekend (WE, Saturday and Sunday) concentrations. The analysis of multi-year variability has shown a slightly declining tendency; however, sporadic bursts in concentrations limit the statistical significance of downward trends.

Nitrogen doi: 10.3390/nitrogen6030083

Authors: Riad O. Eissa Lordwin Jeyakumar David B. McKenzie Jianghua Wu

Biochar has been widely used in agriculture to improve soil quality, support soil remediation, enhance carbon sequestration, and mitigate climate change. Podzolic soils, such as those in Newfoundland, are typically acidic, low in organic matter, and poor in nutrients, which can limit their agricultural productivity. Applying biochar alongside nitrogen fertilization presents a promising strategy to enhance soil fertility, nutrient uptake, and forage productivity. This study evaluated the effects of spruce bark biochar (SB550) and nitrogen fertilization on soil properties, nutrient uptake, and Festulolium forage growth under greenhouse conditions in podzolic soils of Newfoundland, Canada. Five biochar rates (0%, 2%, 5%, 8%, and 10% by soil volume) were combined with two nitrogen levels (0 and 60 kg N ha−1). Soil analyses included pH, soil organic matter (SOM), cation exchange capacity (CEC), and nutrient availability (Ca, Mg, K, P, S, Zn, Mn, and B). In contrast, forage nutrient uptake, biomass production, and quality were assessed. Results showed that biochar significantly increased soil pH, SOM, CEC, and nutrient availability for key elements such as Ca, Mg, and K, while reducing potentially harmful elements such as Na and Mn. The Festulolium nutrient uptake and biomass improved, with dry matter and root biomass increasing by up to 32%. The combined application of biochar and nitrogen further amplified these benefits. This study highlights the potential of biochar as a sustainable soil amendment for improving soil properties and forage productivity in podzolic soils. The findings suggest that biochar, particularly with nitrogen, can significantly enhance soil fertility and agricultural productivity, making it a viable strategy for sustainable forage production in Newfoundland.

Nitrogen doi: 10.3390/nitrogen6030082

Authors: Mehmet Hadi Suzer Ferit Kiray Emrah Ramazanoglu Mehmet Ali Cullu Nusret Mutlu Ahmet Yilmaz Roland Bol Mehmet Senbayram

Sustainable nitrogen (N) management in arable crops requires the real-time assessment of crop growth and N uptake, particularly in water-limited environments. In the present study, we conducted two large-scale field experiments with rainfed and irrigated wheat in South-East Turkey to evaluate the effectiveness of drone- and satellite-based spectral indices, in combination with neural network models, for estimating biomass and nitrogen uptake. Four N fertilizer rates in the irrigated fields (N0: 0, N6: 60, N12: 120, and N16: 160 kg N ha−1) and five N rates in the rainfed fields (N0: 0, N2: 20, N4: 40, N5: 50, and N6: 60 kg N ha−1) were tested. Highest fresh biomass was 57.7 ± 1.1 and 15.9 ± 1.0 t/ha−1 for irrigated and rainfed treatments, respectively, with 2.5-fold higher grain yield in irrigated (8.2 ± 1.2 t/ha−1) compared to rainfed (2.9 ± 0.9 t/ha−1) wheat. Drone-based spectral indices, especially those based on the red-edge region (CLRed_edge), correlated strongly with biomass (R2 > 0.9 in irrigated wheat) but failed to explain crop N concentration throughout the vegetation period. This limitation was attributed to the nitrogen dilution effect, where increasing biomass during crop growth leads to a decline in the concentration of nitrogen, complicating its accurate estimation via remote sensing. To address this, we employed a two-layer feed-forward neural network model and used SPAD and plant height values as supplementary input parameters to enhance estimations based on vegetation indices. This approach substantially enhanced the predictions of N uptake (R2 up to 0.95), while even simplified model version using only NDVI and plant height parameters achieved significant performance (R2 = 0.84). Overall, our results showed that spectral indices are reliable predictors of biomass but insufficient for estimating nitrogen concentration or uptake. Integrating indices with complementary crop traits in nonlinear models provides acceptable estimates of N uptake, supporting more precise fertilizer management and sustainable wheat production under water-limited conditions.

Nitrogen doi: 10.3390/nitrogen6030081

Authors: Cristina L. Franco-Lagos Eloy Navarro-León Erick H. Ochoa-Chaparro Celia Chávez-Mendoza Ezequiel Muñoz-Márquez Alexandro Guevara-Aguilar Marina I. Terrazas-Gómez Esteban Sánchez

Foliar application with iron is a promising strategy for improving nitrogen nutrition and productivity in horticultural crops. In this study, the effect of the foliar application of iron oxide nanoparticles (IONPs) compared to conventional iron sources on physiological, biochemical, and productive parameters of Spinacia oleracea L. was evaluated. Plants were treated with different concentrations (0, 25, 50, and 100 ppm) of IONPs, ferric sulfate (FS), and iron chelate (IC). Biomass, yield, nitrate reductase enzyme activity, soluble protein and amino acid contents, SPAD values, and photosynthetic pigments were analyzed. The results showed that IONPs, particularly at 50–100 ppm, promoted significant increases in biomass (50% more than the control), yield (47%), and nitrate reductase enzyme activity (NRmax) (246%) compared to the control (0 ppm) without negatively affecting pigment levels or leaf physiological condition. Likewise, increases in soluble protein and photosynthetic pigment levels were observed, reflecting improved nitrogen assimilation and photosynthetic efficiency. These findings suggest that IONPs represent an efficient and safe alternative to traditional Fe sources, contributing to the development of sustainable agricultural systems aimed at improving the nutritional value and productivity of leafy crops.

Nitrogen doi: 10.3390/nitrogen6030080

Authors: Vaibhav Shrivastava Ikhlas Laasri

Circular agriculture reclaims nutrients from waste streams to reduce fertilizer imports, mitigate environmental impacts, and close material loops. This review evaluates the agronomic performance of nitrogen, phosphorus, and potassium products recovered from wastewater, crop residues, and manure compared with conventional fertilizers. A structured literature survey identified 85 pot and field trials published between 2010 and 2024, covering ammonium salts, struvite, ashes, compost, digestate, biochar, hydrochar, and biostimulants. Ammonium sulfate and nitrate consistently matched synthetic yields (95–105%) due to their solubility and immediate N availability, while aqueous ammonia showed variable results depending on application timing and soil pH. Struvite and phosphorus-rich ashes performed best (90–100%) in neutral to slightly acidic soils, whereas organo-mineral phosphate fertilizers (85–95%) were less effective in alkaline soils. Potassium-rich ashes and waste mica were effective (80–95%) in soils with moderate cation exchange, though mica underperformed (60–75%) in coarse soils. Biochars and hydrochars improved soil water retention and nutrient exchange, yielding 90–110% of synthetic performance, while biostimulants increased yields by 8–20%. Recovered products demonstrate agronomic equivalence while offering co-benefits for soil health, waste management, and circular economy goals. Future work should prioritize long-term field validation, techno-economic analysis, and regulatory integration to enable large-scale adoption.

Nitrogen doi: 10.3390/nitrogen6030079

Authors: Alshfa Kh. A. Elgaber Emad H. E. Yasin Mohammed Mustafa Abdulrahman Maina Zubairu Kornel Czimber Awad G. Osman Elsiddig A. E. Elsheikh

Laboratory experiments were conducted to investigate the effects of NPK fertilizer, soil type (silty clay and sandy loam) with no history of pesticide application, temperature (28 and 40 °C), and maize residue on the half-life of atrazine herbicide. NPK fertilizer was applied at 375 mg N, 187.5 mg P, and 187.5 mg K per 600 g soil, while maize straw was added at a rate of 12 g per 600 g soil. Atrazine was applied at four concentrations: 0.0678, 1.69, 3.39, and 5.08 mg g−1 soil. The residual concentration of atrazine was measured using gas chromatography over a 150-day period. The results showed that atrazine degradation was highest in Algeraif soil at 40 °C (87%), followed by Algeraif soil at 28 °C (68%) and Gerif soil at 28 °C (54.2%). The addition of NPK and maize straw significantly enhanced atrazine degradation, with degradation reaching 97% at a concentration of 0.0678 mg g−1 soil after 150 days. The lowest half-lives, compared to the control, were 125, 39, 25, 19, and 14 days in Gerif soil (28 °C), Algeraif soil (28 °C), Algeraif soil (40 °C), NPK, and maize straw, respectively, at an atrazine concentration of 5.08 mg g−1 soil. In conclusion, the addition of NPK fertilizer and maize straw significantly enhanced atrazine degradation, reducing both its concentration and half-life in soil.

Nitrogen doi: 10.3390/nitrogen6030078

Authors: Rohini Mattoo Suman B. Mallikarjuna Naveenachar Hemachar

Nitrogen in all of its forms sustains Earth. In every known terrestrial and aquatic habitat, nitrogen controls microbial activity, plant productivity, trophic dynamics, and animal and human growth. This review has tried to show how nitrogen cycling is influenced by both terrestrial and marine ecosystems in addition to by changes spurred on by the climate. The availability, transformation, and final fate of nitrogen throughout the various ecosystems are influenced by these interconnected biochemical and biophysical processes, which are fueled by microbial communities. Predicting and reducing human impacts on the changing ecosystem requires an understanding of these complex interconnections. Anthropogenic and climatic changes alter the structure and function of soil microbial communities, as well as the main metabolic processes of the nitrogen cycle, such as nitrification, denitrification, nitrogen fixation, and ammonification. The mechanisms by which anthropogenic stress alters nitrogen cycling processes, the effects on ecosystem function, and possible mitigation techniques for a balanced nitrogen cycle are all discussed in this review.

Nitrogen doi: 10.3390/nitrogen6030077

Authors: Haibin Chen Shengquan Fang Gengen Lin Yuanbin Shangguan Falian Cao Zhibiao Chen

In southern China, the long-term irrational utilization of land resources has caused severe damage to the ecology and environment of the entire region. Serious issues such as soil degradation and water erosion have led to the decline of soil quality and productivity. In this study, the spatial distribution characteristics of soil carbon, nitrogen, and phosphorus in Zhuxi watershed, Changting County, southern China, were analyzed by coupling geostatistics with GIS. The analysis generated several important results: (1) The concentrations of soil organic matter (OM), alkali-hydrolyzable nitrogen (AN), and available phosphorus (AP) are at moderate levels, and AP exhibits local enrichment in the downstream farmland, while the concentrations of total nitrogen (TN) and total phosphorus (TP) remain at low levels. (2) The optimal theoretical model for AN is an exponential model, while other nutrients follow spherical models. Except for AP, which has a nugget effect exceeding 75%, the nugget effects of other nutrients range between 25% and 75%, indicating that their spatial distribution is moderately correlated. According to Kriging interpolation results, the distribution of OM, TN, and AN shows a clear trend of decreasing from northeast to southwest, followed by a gradual increase, which is generally consistent with the direction of rivers. The trends of TP and AP are more irregular, generally decreasing from downstream to upstream. (3) OM, TN, and AN exhibit a negative correlation with the degree of soil erosion, indicating that soil erosion is associated with the loss of carbon and nitrogen nutrients. However, the impact on phosphorus is relatively insignificant.

Nitrogen doi: 10.3390/nitrogen6030076

Authors: Wacław Jarecki Joanna Korczyk-Szabó Milan Macák Anita Zapałowska Puchooa Daneshwar Miroslav Habán

Organic fertilisers release nutrients more slowly than mineral fertilisers, which is why combining organic and mineral fertilisation gives good results in crop cultivation. In the conducted pot experiment, the reaction of oats to compost fertilisation with or without additional nitrogen mineral fertilisation was examined. The following treatments were used: A, control (no fertilisation); B, compost (sewage sludge 80% + sawdust 20%); C, compost (garden and park waste 80% + sawdust 20%); D, compost (sewage sludge 40% + garden and park waste 40% + sawdust 20%); E, compost B with nitrogen fertilisation (30 N kg ha−1); F, compost C with nitrogen fertilisation (30 N kg ha−1); and G, compost D with nitrogen fertilisation (30 N kg ha−1). The study results indicated that the composts used had an altering impact on the soil’s chemical composition by the end of the experiment. Overall, the lowest levels of nutrients were recorded in the control group, indicating that the composts increased soil fertility. Oat plants were better nourished (SPAD—soil–plant analysis development) after fertilisation with sewage sludge composts than garden and park waste composts. However, the most favourable results were obtained in the treatments where organic fertilisation (composts) was combined with mineral fertilisation (nitrogen). All fertilisation treatments significantly enhanced plant height and the number of panicles in the pot compared to the control. The highest values for the number of grains in the panicle, thousand-grain weight, grain mass from the pot, and protein content in the grain were observed after applying organic–mineral fertilisation. Therefore, fertilisation with composts, especially composts combined with mineral nitrogen, can be recommended for oat cultivation.

Nitrogen doi: 10.3390/nitrogen6030075

Authors: Bhagya Deegala Sanjita Gurau Ram L. Ray

Optimal application of nitrogen fertilizer is critical for soil characteristics and soil health. This study examined the effects of three rates of nitrogen fertilizer applications, which are lower rate (Treatment 1 (T1)-241 kg/ha), recommended rate (Treatment 2 (T2)-269 kg/ha), and higher rate (Treatment 3 (T3)-297 kg/ha), and their impacts on soil temperature, soil moisture and soil electrical conductivity at two different depths (0–30 cm and 30–60 cm) in maize cultivation at the Prairie View A & M university research farm in Texas. Soil moisture, soil temperature, and electrical conductivity (EC) sensors were installed in 27 plots to collect these data. Results showed that EC is lower at surface depth with all fertilizer application rates than at root zone soil depths. In the meantime, EC is increasing in the root zone soil depth with the increase in fertilizer rate. This study indicated that the moderate application (269 kg/ha, T2) which is also recommended rate, showed better soil health parameters and efficiency in comparison to other application rates maintaining stable and moderate electrical conductivity values (0.2 mS/cm at depth 2) and the highest median moisture content at the significant root zone depth (about 0.135 m3/m3), reducing nutrient leaching and salt accumulation. Also, a humid, warm climate in southern Texas specifically affects increasing nitrogen losses via leaching, denitrification, and volatilization compared to cooler regions, which requires higher application rates. Plant growth and yield results further confirmed that the recommended rate achieved the greatest plant height (157.48 cm) compared to T1 (153.07 cm). Ear diameters were also higher at the recommended rate, reaching 4.65 cm ears than in Treatment 3. However, grain productivity was highest under the lower fertilizer rate T1, with wet and dry yields of 11,567 kg/ha and 5959 kg/ha, respectively, compared to 10,033 kg/ha (wet) and 5047 kg/ha (dry) at T2, and 7446 kg/ha (wet) and 4304 kg/ha (dry) at T3. These findings suggest that while the moderate fertilizer rate (269 kg/ha) enhances soil health and crop growth consistency, the lower rate (241 kg/ha) can maximize productivity under the humid, warm conditions of southern Texas. This research highlights the need for precise nitrogen management strategies that balance soil health with crop yield.

Nitrogen doi: 10.3390/nitrogen6030074

Authors: Júlio José Nonato Tonny José Araújo da Silva Alessana Franciele Schlichting Luana Aparecida Menegaz Meneghetti Niclene Ponce Rodrigues de Oliveira Thiago Franco Duarte Salomão Lima Guimarães Marcio Koetz Ivis Andrei Campos e Silva Patrícia Ferreira da Silva Adriano Bicioni Pacheco Edna Maria Bonfim-Silva

Soil water availability can become one of the decisive factors for crop production. The technology of coinoculation with plant growth-promoting bacteria capable of performing biological nitrogen fixation and producing plant hormones may be an alternative that minimizes the effects of variations in soil water availability. In this context, the objective was to evaluate the phytometric and productive characteristics of cowpea coinoculated with Azospirillum brasilense and Bradyrhizobium japonicum subjected to soil water availability stress. The experiment was carried out in a greenhouse in a completely randomized block design with four replications in a 4 × 4 factorial arrangement: not inoculated; inoculated with B. japonicum; and coinoculated with B. japonicum + A. brasilense and N fertilizer, associated with soil water tensions of 15, 30, 45, and 60 kPa. Statistically, the lowest soil water tension, 15 kPa, and the coinoculated and nitrogen fertilizer treatments resulted in greater development of plant height, stem diameter, and number of leaflets. The shoot dry mass was significantly different for only the soil water stress treatments, which showed a decrease in mass accumulation from 15 kPa to 50.22 kPa. Regarding the SPAD index, soil water tension showed a decreasing linear adjustment 24 days after plant emergence (DAEs), with the lowest value of 51.38 at a tension of 60 kPa. At 39 DAEs, the adjustment was polynomial, with the lowest tension index of 59.62 kPa, corresponding to 44.14. The treatments with the use of inoculants had a significant effect on the SPAD index, in which coinoculation with Bradyrhizobium and Azospirillum brasilense resulted in values equal to those of nitrogen fertilizer and greater than those of uninoculated treatments or those inoculated with Bradyrhizobium. Water tension influenced the total water consumption, and at a tension of 18.13 kPa, the lowest accumulation occurred, equivalent to 2.20 g of dry matter for each liter of irrigated water. Statistically, the lowest soil water tension, 15 kPa, resulted in higher numbers, lengths, and widths of pods. In relation to the length of pods, the uninoculated, inoculated with Bradyrhizobium, and coinoculated with Bradyrhizobium and A. brasilense treatments were superior to nitrogen fertilization. Coinoculation and nitrogen fertilization influenced phytometric characteristics. The productive characteristics of cowpea decreased as the soil water tension increased. These results highlight the importance of leveraging biological solutions, such as coinoculation, to mitigate the adverse effects of water stress on crop yields. In addition, by optimizing these practices, farmers ensure greater resilience in bean production, thereby guaranteeing food security in the face of changing environmental conditions.

Nitrogen doi: 10.3390/nitrogen6030073

Authors: Qinglin Sa Jian Zheng Haolin Li Yan Wang Zifan Li

To explore fertilization strategies that achieve both high yield and emission reduction in greenhouse tomato production, a two-season experiment was conducted in autumn 2023 and spring 2024 under equal nitrogen input. Seven treatments were established: conventional fertilization (CK1), biogas slurry alone (CK2), 0.5% biochar + biogas slurry (T1), 2% biochar + biogas slurry (T2), dicyandiamide + biogas slurry (T3), 0.5% biochar + biogas slurry + dicyandiamide (T4), and 2% biochar + biogas slurry + dicyandiamide (T5). The effects of each treatment on tomato root traits, yield, irrigation water use efficiency (IWUE), partial factor productivity of nitrogen (PFPN), and soil N2O emissions were systematically evaluated. An analytic hierarchy process (AHP) was applied for comprehensive assessment. The results showed that fertilization treatments significantly affected tomato root traits (p < 0.05), with T5 exhibiting the best performance in root length, average diameter, total surface area, total volume, and root activity, all significantly higher than CK1. T5 also achieved the highest yield in both seasons, with increases of 8.13% (autumn 2023) and 10.19% (spring 2024) over CK1. Moreover, T5 showed superior IWUE (475.38 kg ha−1 mm−1) and PFPN (405.92 kg kg−1). In terms of environmental performance, T5 significantly reduced soil N2O flux, with the largest reduction reaching 16.16%, particularly during the peak emission stages in the flowering and fruit-setting periods. The AHP-based comprehensive evaluation confirmed that T5 had the highest overall weight with satisfactory matrix consistency. In conclusion, compared with conventional fertilization, the integrated T5 treatment increased tomato yield by up to 10.19% and reduced cumulative N2O emissions by up to 16.16%, highlighting its potential as a feasible fertilization pathway and technical reference for low-carbon and sustainable agriculture.