Nitrogen

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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 F_m(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. Full article

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). Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article