Nitrogen

Feeds rich in protein are the dominant nitrogen input in intensive aquaculture, yet only part of dietary nitrogen is retained as animal biomass; the remainder enters water and sediment through uneaten feed, feces, dissolved wastes, mucus, sloughed tissue, and branchial ammonia excretion. This review aims to integrate nutritional, physiological, microbial, and disease-related evidence into an evidence-graded framework that positions ammonia nitrogen as a reactive node linking feed, host, water, sediment, and pathogen risk. To assemble this evidence, we conducted a structured narrative search of Web of Science and PubMed for records in English or Chinese published from 2006 to July 2026, with no restriction on publication type, and classified evidence as direct, indirect, or conceptual. The strongest evidence shows that dietary protein supply, amino acid balance, digestibility, and feeding regime regulate nitrogen retention and ammonia output, while microbial ammonification, nitrification, denitrification, dissimilatory nitrate reduction to ammonium, anammox, and assimilation determine whether reactive nitrogen is regenerated, retained, or removed. Experimental studies further show that ammonia impairs oxidative balance, mucosal barriers, immunity, and disease resistance. In contrast, evidence that pathogen infection quantitatively alters nitrogen retention, ammonia excretion, organic nitrogen release, and sedimentary ammonium regeneration remains limited and largely indirect. Accordingly, ammonia nitrogen is framed as a measurable reactive node rather than a unique source or a universally validated causal loop. Practical management should combine precision nutrition with water, biofloc, sediment, and disease surveillance, while future factorial studies and isotope tracer studies should quantify the complete nitrogen budget under pathogen challenge. Full article

This study aimed to investigate the effects of different nitrogen (N) fertilizer rates and sowing dates on grain yield, protein content, grain N uptake, and nitrogen recovery efficiency (NRE) in spring and facultative wheat (Triticum aestivum L.) cultivated in northwestern and central Romania from 2018 to 2020. The experiment was designed as a split–split plot study with two spring sowing dates (SDs): an optimal date (1–15 March) and a delayed date (postponed by two weeks). All treatments received a basal autumn fertilizer supplying 36 kg N ha⁻¹ and 92 kg P ha⁻¹. In spring, three N treatments were evaluated: no additional N (N₃₆), 72 kg N ha⁻¹ (N₁₀₈), and 105 kg N ha⁻¹ (N₁₄₁), with the supplementary N top-dressed at the booting stage. The results showed that delayed sowing significantly altered grain N uptake dynamics and reduced NRE, even under standard fertilization regimes. Specifically, delayed sowing reduced grain yield by 7.52% to 28.39% compared to optimal sowing, while adverse climatic interactions in delayed setups reduced the mean NRE to as low as 16.43%. These findings indicate that conventional N application strategies may be suboptimal under variable sowing conditions and highlight the importance of adaptive N management to improve both agronomic performance and environmental sustainability. Full article

Efficient nitrogen (N) management is essential for sustaining crop productivity while minimizing environmental impacts associated with nitrogen losses. However, the high spatial and temporal variability of soil nitrogen dynamics and crop nitrogen status makes field-scale monitoring challenging, while conventional soil and plant sampling methods are labor-intensive, destructive, and provide limited spatial coverage. Recent advances in remote sensing technologies and machine learning (ML) offer promising alternatives for high-throughput, non-destructive monitoring of crop nitrogen status and related nitrogen dynamics in agroecosystems. This review synthesizes current progress in the use of proximal and remote sensing platforms, including unmanned aerial vehicles (UAVs), satellites, and ground-based sensors for assessing crop nitrogen status and inferring soil nitrogen availability. We examine spectral, thermal, and structural indicators, together with emerging sensor-fusion and time-series approaches. We also evaluate ML algorithms, including emerging foundation model approaches, for estimating crop nitrogen status and inferring soil nitrogen indicators, highlighting their performance, limitations, and transferability across environments. Particular emphasis is placed on field-scale applications in heterogeneous and water-limited systems, where nitrogen-water interactions critically influence crop responses. Finally, we discuss current challenges, including data scarcity, model generalization, and operational constraints, and outline future directions toward integrated, real-time decision support systems for precision nitrogen management. Overall, this review provides a comprehensive framework for leveraging remote sensing and data-driven approaches to improve nitrogen monitoring and enhance nitrogen use efficiency in diverse cropping systems. Full article

Rice production in coastal tidal floodplains is severely constrained by periodic tidal submergence, making modern semi-dwarf varieties unsuitable. While local landrace cultivars are widely grown for their adaptability, their adaptation mechanisms and response to nitrogen management under tidal ecosystems remain poorly understood. This two-year on-farm study (aman seasons, 2021 and 2022) evaluated landrace rice cultivars against a modern check (BR23) under different nitrogen-management practices: urea super-granule deep placement and prilled urea application. Landraces adapted better to tidal submergence than BR23, exhibiting greater plant height, culm strength, biomass, and nutrient accumulation. Cultivar effects explained most of the variation in grain yield (38–40%), followed by nitrogen management (18–21%). Deep placement of urea super-granule significantly enhanced growth, yield, and nutrient uptake compared to prilled urea. Shorna showed the highest grain nitrogen uptake (48.23 kg ha⁻¹), agronomic efficiency (20.81 kg grain kg⁻¹ nitrogen), and partial factor productivity (71.91 kg grain kg⁻¹ nitrogen). Bhushiara achieved the highest grain harvest index (0.54) and nutrient harvest indices, indicating efficient nutrient partitioning to grains. During grain-filling, nitrogen and phosphorus efficiently remobilized to the grains, while potassium remained mostly in the straw. Ultimately, pairing resilient landraces like Shorna, Bhushiara, Dudmona, and Lalmota with optimized nitrogen management, specifically urea super-granule application, substantially improves productivity, nutrient efficiency, and climate resilience. This study provides some of the first comprehensive evidence on how genotype-specific adaptation and deep-placed nitrogen interact to support sustainable rice production in Bangladesh’s coastal floodplains. Full article

Acidic soil stress can limit sunflower productivity by reducing nutrient availability, impairing root development, and affecting early plant establishment, while foliar nutrient application and seed pretreatment may provide additional support under recommended nitrogen fertilization. This study evaluated the potential of selected nutrient-based products to mitigate acidic environment stress in sunflower through a field experiment and a complementary laboratory germination test. The field experiment was conducted in 2025 at Ivankovo, Croatia, on acidic soil (pH KCl 4.47), under a recommended nitrogen fertilization dose of 85 kg N/ha for sunflower production. Foliar treatments included Barrier, Bioplex, Borealg, and Bor-feed, while the control was left without additional foliar treatment. Seed yield, yield components, seed oil and protein content, and oil and protein yield were determined. In parallel, sunflower seeds were pretreated with the same products and germinated under controlled conditions in aqueous solutions with pH values ranging from 3.5 to 8.5. Germination, seedling morphology, fresh biomass, total phenolic content, antioxidant activity, and free proline content were analysed. Under field conditions, foliar treatments significantly affected plant height, head diameter, seed mass per head, seed oil and protein content, and seed yield. Barrier produced the highest seed yield (5.3 t/ha), oil yield (2.8 t/ha), and protein yield (0.8 t/ha), whereas Bor-feed had the highest seed oil content (54.36%) but the lowest seed yield (2.5 t/ha). In the laboratory experiment, average total germination was 92%, with maximum values of 96–97% depending on treatment and pH. Barrier most strongly promoted root, shoot, and total seedling length, while Borealg increased root, shoot, and total fresh mass. Biochemical responses depended on seed pretreatment and pH, with the highest antioxidant activity recorded in Bioplex at pH 7.5 and higher proline accumulation generally observed in untreated seedlings. The highest antioxidant activity was recorded in Bioplex seed pretreatment at pH 7.5 (5.34 mM Fe(II)/g FW), while the highest free proline content was observed in the control at pH 5.5 (7.87 mM/g FW) and pH 3.5 (7.79 mM/g FW), indicating a stronger stress response in untreated seedlings. The present study indicates that selected foliar products and seed pretreatments may support sunflower productivity and early growth under acidic stress conditions, with Barrier showing the most consistent positive response. Full article

Nitrogen is integral to all living systems, but its diverse forms are interconverted dynamically through reductions and oxidations that constitute the nitrogen cycle. Ecosystems gain combined nitrogen by bacterial and archaeal reduction in atmospheric N₂, while combined nitrogen is lost to the atmosphere as nitrogenous gases through denitrification. We sought to characterize the diversity and activity of free-living nitrogen-fixing bacteria or diazotrophs in natural prairie grasslands and the activity of the other steps of the nitrogen cycle through metatranscriptomics. DNA and mRNA were obtained from prairie sites that did not contain any leguminous plants to avoid symbiotic nitrogen fixation. Both 16S rRNA gene and nifH amplicon pools were sequenced to characterize the diversity of diazotrophs, and the expression levels of N-cycle genes were quantified by RNAseq. Nitrogen fixation without and with added carbohydrates was quantified by measuring the incorporation of ¹⁵N₂. The soil samples contained a diversity of diazotrophs, as reflected both by 16S rRNA gene and nifH gene sequences. Carbohydrate amendment of soil samples led to substantial ¹⁵N₂ incorporation, showing that members of the resident microbiota were able to fix nitrogen. However, we did not detect ¹⁵N₂ incorporation in unamended soil samples, pointing to a lack of in situ fixation. The very low levels of nitrogenase gene transcripts supported this finding. In contrast, transcripts for nitrification and denitrification genes were expressed, pointing to a gap in the nitrogen cycle. The prevalence of diazotrophs with undetectable nitrogen fixing activity suggested the absence of available carbohydrates to provide the energy needed. The apparent imbalance in the nitrogen cycle would not be sustainable, so other possible mechanisms of acquiring combined nitrogen should be explored. Full article

Forage sorghum is widely used in the southern Great Plains because of its drought tolerance, high biomass productivity, and suitability for multi-cut hay systems; however, information on nitrogen (N) management for forage production and quality in the region remains limited. This study evaluated the effects of N rate and application timing on forage sorghum biomass production and quality at two Oklahoma locations during 2021 and 2023. Biomass production increased with N fertilization at both locations, but response functions differed between sites, with a quadratic response at one location and a linear response at the other. Split N applications primarily altered seasonal biomass distribution by increasing second-harvest regrowth contribution, although total seasonal biomass increased only at the highest split N rate treatment. Forage quality was affected more strongly by harvest timing than by N rate or application timing, with second-harvest forage exhibiting lower fiber concentrations and greater total digestible nutrients. Nitrate concentrations in the forage increased with N rate but remained well below livestock toxicity thresholds. Overall, these results indicate that forage sorghum N management in multi-cut systems should balance sufficient early season N supply to maximize initial biomass production with continued N availability to sustain regrowth productivity and improve seasonal forage distribution. Full article

Despite the pivotal importance of soil microbial communities in regulating the terrestrial carbon (C) cycle and ecosystem functioning, their vertical patterns and their responses to long-term nitrogen (N) deposition, in terms of microbial biomass and relative abundance, still remain unclear, particularly for fungi versus (vs.) bacteria and Gram-positive (GP) vs. -negative (GN) bacteria, where they traditionally have contrasting biological characteristics. In this study, we investigated the responses of GP and GN bacteria, total bacteria (TB), and fungi (TF) and their relationships with four nutrient ratios to 10 years of N addition with three N addition rates (control, N2, and N10 representing 0, 2, and 10 g m⁻²yr⁻¹, respectively) across a 100 cm soil profile (0-10-20-30-40-70-100 cm) in a semiarid grassland, both in terms of absolute biomass and relative abundance represented by the amount and percentage of phospholipid fatty acids (PLFAs) (e.g., GP bacterial PLFAs: total PLFAS) of specific microbial groups, respectively. Our results showed that N addition has significant negative effects on the biomass of these four microbial groups across the whole soil profile, while N addition significantly decreased the relative abundance of GN bacteria and increased those of TF and GP bacteria. Additionally, N addition significantly decreased the biomass of TF and GP bacteria in 0–10 cm soil, and of TB and GN bacteria in 0–10, 40–70, and 70–100 cm soils, with the significant increase or decrease mainly occurring at the N10 rate. Our results also showed that the biomass of these four microbial groups decreased with soil depth regardless of N addition, but that of TB and GN bacteria decreased faster than that of TF and GP bacteria did, and further caused the relative abundance of TF and GP bacteria to increase with soil depth. Significant Pearson correlations among the biomass and relative abundance of these microbial taxa with soil pH, total phosphorus, NH₄⁺-N, and NO₃⁻-N were mainly found in 0–10 cm soil. C:N and NH₄⁺-N: NO₃⁻-N ratios increased with increasing soil depth, while C: phosphorus (P) and N:P ratios decreased. N addition significantly increased C:P and NH₄⁺-N: NO₃⁻-N ratios and decreased N:P ratios, especially under the N10 rate. Among these four nutrient ratios, N:P significantly explained the highest variations in F:B (76%) and GP:GN (38%) across the whole soil profile. Together, these results underline the different responses of soil microbial relative abundance and biomass along the soil profile under long-term N addition. They also suggest a relationship between soil microbial diversity and biomass relationships, and how this links to nutrient ratios in the subsoil needs to be investigated in future. Full article

Balanced fertilization is essential for improving the growth and productivity of Sapindus mukorossi plantations. In this study, a three-year “3414” fertilization experiment was conducted in a six-year-old plantation of the new S. mukorossi cultivar ‘Yuanhua’ to evaluate the effects of nitrogen, phosphorus, and potassium fertilization on vegetative growth, fruit yield, yield stability, and gross output value. Fertilizer levels were set at 0, 300, 600, and 900 kg N ha⁻¹, 0, 250, 500, and 750 kg P₂O₅ ha⁻¹, and 0, 200, 400, and 600 kg K₂O ha⁻¹. NPK fertilization promoted tree height, ground diameter, crown width, and fruit yield compared with the unfertilized control. Among the 14 fertilization treatments, N₁P₁K₂ produced the greatest mean annual increment in tree height, N₁P₂K₁ produced the greatest ground-diameter increment, and N₂P₂K₁ produced the greatest crown-width increment. Fruit yield was highest under N₂P₂K₂ in 2021 and 2022 and under N₂P₂K₁ in 2023. The highest three-year mean yield was obtained under N₂P₂K₂, reaching 1278.93 kg ha⁻¹, and the highest yield stability index was observed under N₂P₂K₂ and N₂P₁K₂. Gross output value showed a pattern consistent with fruit yield, with N₂P₂K₂ producing the highest values in 2021 and 2022 and N₂P₂K₁ producing the highest value in 2023. Among the tested fertilization combinations, N₂P₂K₂, corresponding to 600 kg N ha⁻¹, 500 kg P₂O₅ ha⁻¹, and 400 kg K₂O ha⁻¹, showed the best overall performance for six-year-old S. mukorossi ‘Yuanhua’ plantations under the conditions of this study. These findings indicate that balanced NPK fertilization can improve vegetative growth, fruit yield, yield stability, and gross output value in S. mukorossi ‘Yuanhua’ plantations. Full article

Adequate fertilization is essential for optimizing soybean productivity and seed quality, while supplementary fertilization plays a key role in correcting nutrient deficiencies and supporting plant performance under varying environmental conditions. This study evaluated the effects of the foliar application of macro- and micronutrients enriched with free amino acids and Ascophyllum nodosum extract applied at two phenological stages—six fully developed trifoliate leaves (V6) and beginning flowering (R1)—on soybean grain yield, protein content and oil content. Experiments were conducted over two growing seasons at ARDS Turda, Romania, using a randomized complete block design with three replications to compare three fertilization treatments: basic mineral fertilization (control), mineral fertilization supplemented with foliar application at the V6 vegetative stage, and mineral fertilization supplemented with foliar application at the R1 reproductive stage. Basic fertilization was performed before sowing using granulated nitroclacium at a rate of 100 kg ha⁻¹. Foliar fertilization included Naturamin WSP applied at a rate of 0.5 kg ha⁻¹ and Pleniflor and Naturfruit at a rate of 2 L ha⁻¹. Foliar fertilization at the V6 stage significantly improved grain yield in most cultivars, with increases ranging from 1% to 18%, particularly in the 000 and 00 maturity groups (MGs). Across the maturity groups, the highest average yields were recorded in MG 0 cultivars (up to 2845 kg ha⁻¹). In contrast, foliar application at the R1 stage was more effective in increasing seed protein content, with improvements of up to 11% in early maturity cultivars. Oil content showed only minor and inconsistent responses, with maximum increases of 4% depending on genotype. Linear Discriminant Analysis (LDA) revealed that environmental conditions and genotype explained most of the observed variation (Axis 1 = 89.91%, Axis 2 = 7.79%), indicating that cultivar response to foliar fertilization was strongly influenced by genotype × environment interactions. The effectiveness of foliar fertilization depends on application timing, cultivar maturity group and environmental conditions. Full article

Global food demand is projected to rise by approximately 56 percent between 2010 and 2050, intensifying reliance on synthetic nitrogen fertilizer during a time when only about half of all applied nitrogen is recovered by crops, with the remainder split between genuine environmental loss and retention within soil and biomass pools. The fraction that is genuinely lost drives substantial economic costs and contributes disproportionately to global nitrous oxide emissions, a greenhouse gas with a warming potential far exceeding that of carbon dioxide. This review synthesizes recent literature across three interdependent domains including nitrogen use efficiency strategies spanning agronomic, genetic, and microbial approaches, decarbonization pathways for ammonia synthesis ranging from conventional to green production routes, and gas sensing technologies for monitoring ammonia and nitrous oxide emissions in agricultural settings. Rather than treating these domains separately, this review proposes that their effects on overall emissions are complementary and potentially compounding rather than strictly additive. Efficiency improvements reduce the total fertilizer volume subject to production emissions, while cleaner production cannot offset nitrogen loss in the field. The exact extent of any combined benefit depends on the relative proportion of field emissions and production emissions within each farming system. Another important finding is the pronounced asymmetry in monitoring readiness. Ammonia sensing has reached field-deployable maturity for detection and concentration monitoring. In contrast, nitrous oxide sensing remains constrained by unresolved challenges in sensitivity and long-term stability despite the gas’s significant contribution to climate change. This asymmetry limits the verification of mitigation outcomes at farm and regional scales. The review further identifies that intervention effectiveness depends on farm structure in the studied context, that global nitrogen policy remains weighted toward incentivizing use rather than reducing pollution, and that the evidence base surveyed here is geographically uneven. Together, these findings indicate that reconciling rising food production with greenhouse gas reduction targets requires integrated frameworks linking field nitrogen budgets, production emissions, and monitoring capability, alongside policy instruments designed around their interdependence. Full article

In animal production, gases such as ammonia and greenhouse gases (GHGs) originate from wastes in three main compartments: the animal house of an experimental facility in Northern Italy, storage sites and the slurry-spreading process on cultivated soils. Dietary composition can influence slurry characteristics and gaseous emissions from pig production systems. This exploratory study investigated relationships among slurry composition, volatile fatty acids (VFAs), and gaseous emissions in weaned pigs fed either a conventional diet or a reformulated diet. Faecal samples produced by piglets fed two different diets were collected at three time points: 14, 28 and 42 d of age. Piglets were housed in 32 pens (2 animals per pen, with 16 pens per treatment) on a slatted floor and assigned to either a control diet (C) or a reformulated diet (T) including single-cell protein (SCP). The piglets were administered a starter phase (0–14 days) and a grower phase (14–42 days). Slurry samples were analysed for physicochemical parameters, VFAs, NH₃, N₂O, and CO₂ emissions. The reformulated diet was associated with higher total Kjeldahl nitrogen and volatile solids, together with changes in VFA profiles characterised by lower acetic and propionic acids and relatively higher lactic and n-butyric acids. NH₃ and CO₂ emissions tended to be lower in the reformulated treatment, whereas N₂O showed variable responses across sampling times. These findings indicate that dietary reformulation with SCP inclusion may influence manure characteristics and fermentation processes, with potential consequences for ammonia emission mitigation. Given the exploratory nature of the study and the non-iso-nutritional formulation of the diets, the results should be interpreted as treatment-level associations rather than evidence of direct causal effects. Further studies under controlled nutritional conditions are required to clarify the mechanisms linking dietary composition, manure properties, and environmental emissions in pig production. Full article

Nitric oxide (NO) is a small, highly reactive gaseous signaling molecule that plays diverse and context-dependent roles in microbial physiology and host–microbe interactions. Over the past decade, increasing evidence has revealed the dual nature of NO as both an antimicrobial effector and a signaling mediator involved in microbial stress responses, metabolism, biofilm dynamics, quorum sensing, virulence regulation, and symbiotic interactions. In microbial systems, NO influences adaptation to environmental stress and contributes to mechanisms associated with persistence and antimicrobial resistance. In host organisms, NO functions as a key component of innate immunity while also participating in beneficial interactions involving rhizobia, mycorrhizal fungi, and probiotic microorganisms. Despite its biological significance, accurate detection and quantification of NO remain challenging because of its transient nature, high reactivity, low physiological concentrations, and interference from related reactive oxygen and nitrogen species. Recent advances in biosensing technologies have substantially improved NO detection capabilities through the development of electrochemical, optical, enzyme-based, microfluidic, wearable, and implantable sensing platforms. These innovations are complemented by analytical techniques including electron paramagnetic resonance spectroscopy, mass spectrometry, fluorescence-based imaging, and advanced microscopy, which enhance sensitivity, specificity, and spatiotemporal resolution in complex biological environments. Concurrently, statistical and computational approaches—including sensor calibration models, multivariate analyses, machine learning algorithms, and bioinformatics pipelines—have become increasingly important for extracting biologically meaningful information from NO-related datasets. Unlike previous reviews that primarily focus on either NO biology or sensing technologies, this review integrates current knowledge of NO-mediated microbial physiology and host–microbe interactions with recent developments in biosensor engineering, analytical methodologies, statistical frameworks, and emerging artificial intelligence (AI)-driven data interpretation. We further highlight applications of NO detection in infectious disease diagnostics, antimicrobial screening, probiotic and biofertilizer evaluation, environmental microbiome monitoring, and real-time studies of symbiosis and infection. Finally, future directions including miniaturized sensing platforms, multi-omics integration, AI-assisted analytics, and sensor standardization are discussed. By unifying molecular, analytical, and computational perspectives, this review provides a multidisciplinary framework and roadmap for advancing NO-based research and translational applications across microbial, environmental, and host-associated systems. Full article

This study investigates nitrogen-fixing rhizobia associated with Pisum sativum, a member of the tribe Vicieae (Fabaceae), whose species establish symbioses with bacteria belonging predominantly to the symbiovar viciae within the Rhizobium leguminosarum complex (Rlc). Based on a comprehensive taxonomic revision of the F-clade within this complex, we report the identification and characterization of a novel rhizobial subspecies, Rhizobium laguerreae subsp. mediterraneum subsp. nov., isolated from pea nodules in Tunisia. Phylogenetic analyses based on 16S rRNA and multilocus sequence analysis (recA, atpD, dnaK, and glnII) placed strains 25PS6 and 10PS4 within the Rlc, while whole-genome phylogenomics using 2960 single-copy orthologues supported their assignment to a distinct monophyletic clade (Q-II). Subspecies-level clustering consistency was maximized using an optimized ANIm criterion of 97.40%, corresponding to 76.65% dDDH. Both strains belong to symbiovar viciae and exhibited improved symbiotic performance on pea plants compared to the reference strain, indicating strong symbiotic performance and potential relevance for biological nitrogen fixation. Cluster-specific SNP analysis identified 63 exclusive non-synonymous mutations with putative functional effects predicted in silico. These results suggest that cluster-specific nsSNPs may contribute to genomic differentiation within the Q-II lineage. Phenotypic and chemotaxonomic analyses further distinguished the novel subspecies based on carbon utilization, enzymatic activity, antibiotic resistance, and fatty acid profiles. Together, these findings highlight the genomic diversity within nitrogen-fixing rhizobia associated with legumes and identify a novel subspecies with potential agronomic relevance for improving symbiotic nitrogen fixation in pea cultivation. The proposed subspecies, Rhizobium laguerreae subsp. mediterraneum, is represented by strains 10PS4 and 25PS6, with strain 25PS6^T (=DSM 116212^T = LMG 33205^T) designated as the type strain. Full article

Effective nitrogen (N) management is essential for ensuring food security, promoting agricultural sustainability, and addressing climate change due to the rise in fertilizer use since the 20th century. However, environmental improvements from N management are subject to uncertainties and time lags. In this study, we analyzed data from 113 countries, focusing on N use efficiency and greenhouse gas emissions as key indicators. Our results illuminated a notable lag effect between improvements in these two indicators at the global scale, posing formidable challenges in achieving timely environmental benefits through N management strategies. We categorized countries into four groups based on agricultural sustainability, offering insights into the environmental impacts of various N management practices. Nations prioritize N management differently, reflecting the intricate interplay between socio-economic determinants and environmental considerations. Adopting integrated N management practices, which balance agricultural productivity and environmental conservation, represents an indispensable imperative for the advancement of sustainable agriculture. Full article

Nitrogen fertilization plays a central role in the intensification and sustainability of tropical pasture systems by influencing forage production, animal performance, and greenhouse gas (GHG) emissions. Although the individual components of these systems have been extensively studied, studies that simultaneously integrate soil nitrogen processes, forage responses, animal performance, and environmental outcomes within a unified framework remain scarce in the literature. This structured narrative review aimed to synthesize current knowledge on the role of nitrogen in tropical pastures, addressing soil–plant–animal–environment interactions with a focus on nitrogen use efficiency, productivity, and GHG emissions. Studies were selected from Google Scholar using keywords related to nitrogen fertilization, tropical forages, GHG emissions, and animal performance, prioritizing research conducted with C4 forage species. The reviewed evidence demonstrates that nitrogen fertilization consistently increases forage accumulation, tillering, crude protein concentration, stocking rate, and animal productivity per unit area; however, nitrogen recovery efficiency decreases at high application rates. The timing of nitrogen application, dose splitting, and the choice of nitrogen source are key management strategies to reduce N losses through volatilization, leaching, and gaseous emissions, improving nitrogen use efficiency in tropical pasture systems. Future studies should focus on providing integrated answers that simultaneously consider soil, plant, animal, and environmental components, in order to support more efficient and sustainable nitrogen management in tropical livestock systems. Full article

Excess or deficiency of nitrogen affects wheat yield significantly. Several destructive and non-destructive methods are used for nitrogen diagnosis to support precision fertilizer management in wheat. Recently, UAV-based remote sensing combined with machine learning has emerged as a promising approach for wheat nitrogen assessment. A systematic review was conducted to identify strengths and gaps in the methodologically diverse literature. The PRISMA approach was used to identify relevant literature from Scopus and Web of Science databases. The extracted data were used for comparative quantitative analysis to evaluate whether studies targeted direct nitrogen variables or proxy traits, how validation rigor influenced reported performance, and which growth stages were most commonly associated with nitrogen diagnosis. Across studies with comparable reported performance, direct nitrogen studies showed a median selected R² of 0.855, while close-proxy and indirect-proxy studies showed median selected R² values of 0.868 and 0.841, respectively. Validation design also differed markedly across the literature. Most studies relied on internal-only validation, and these studies showed a higher median selected R² (0.860) than studies using independent-like validation (0.825), suggesting that reported performance may often be optimistic under less rigorous validation frameworks. Growth-stage analysis showed that nitrogen diagnosis was most commonly investigated from jointing to grain filling with most studies focusing on multiple growth stages rather than on a single stage. This indicates the use of a broader diagnostic window rather than identifying single stages of practical importance. In conclusion, the reviewed literature represents a mixture of direct nitrogen and proxy or indirect studies with stronger within-study predictive capacity than in providing robust and transferable performance for practical nitrogen management. Future research should focus on direct nitrogen diagnosis and adopt independent validation designs to link diagnosis outputs to actionable precision nutrient management. Full article

Soil salinity inhibits biological nitrogen fixation (BNF) in legumes, compromising nitrogen nutrition and crop productivity. This study evaluated whether two halotolerant Mesorhizobium ciceri strains (S1, S2) can sustain BNF and alleviate moderate salt stress (100 mM NaCl) in three Tunisian chickpea (Cicer arietinum L.) cultivars (Amdoun, Béja 1, and Nour). Inoculated and non-inoculated plants were grown under controlled conditions. Salinity reduced shoot dry weight by 37.5–42% and severely impaired nodulation (≈60% reduction) in non-inoculated plants. Bacterial inoculation significantly increased germination rate, shoot and root biomass, and nodule number compared to non-inoculated salt-stressed controls. Improved nodulation corresponded to better nitrogen nutrition, reflected by higher leaf chlorophyll content (a proxy for nitrogen status). However, direct measurements of nitrogenase activity (e.g., acetylene reduction assay) are needed to confirm enhanced BNF. Inoculated seedlings also exhibited lower oxidative stress markers (hydrogen peroxide and malondialdehyde) and enhanced antioxidant enzyme activities (superoxide dismutase and glutathione peroxidase), indicating reduced reactive oxygen species damage. Cultivar-specific responses were observed: Amdoun responded best to S1, Béja 1 to S2 for biomass recovery, while Nour showed strong antioxidant induction but limited growth gain. We conclude that halotolerant M. ciceri strains improve chickpea performance under salt stress primarily by sustaining BNF and nodulation, thereby maintaining nitrogen nutrition. Strain–cultivar compatibility is critical for optimizing this bio-inoculant strategy in saline agroecosystems. Our findings identify the combination of cultivar Béja 1 with strain S2 as the most promising for biomass recovery under moderate salinity, providing a practical, strain–cultivar matching framework that can guide the development of effective bio-inoculants for chickpea production in salt-affected areas of Tunisia and similar Mediterranean regions. Full article

Maize is one of the most important agricultural crops worldwide, due to its high production potential and the multiple uses of its products. In the context of the need to maintain high yields and preserve soil fertility, the use of green manures together with mineral fertilizers can represent a sustainable solution. For this purpose, during the period 2024–2025, at the Turda Agricultural Research and Development Station (Cluj, Romania), a field experiment was carried out to evaluate the effect of two cover crops used as green manures, white lupin (Lupinus albus) and phacelia (Phacelia sp.), on the Turda 344 maize hybrid. Within each agrofund (classical, after lupin, and after phacelia), five fertilization variants were tested, consisting of basic fertilization and the supplementary application of mineral fertilizers and biostimulants. The results highlighted the major influence of climatic conditions on yield and grain quality, with the experimental year having a significant effect on the main parameters analyzed. In 2024, under basic fertilization, lupin and phacelia increased grain yield by 8.0% and 1.4%, respectively, compared with the classic agrofund, while in 2025, phacelia maintained a yield advantage of 1.4%. The highest yields were obtained in 2025, when climatic conditions were more favorable, and additional fertilization with ammonium nitrate determined the highest values, reaching 9748 kg/ha in the phacelia agrofund (+6.3% compared with the basic fertilization), 9544 kg/ha in the lupine agrofund (+7.2%), and 9612 kg/ha in the classical agrofund (+6.3%). Additional nitrogen application also led to the highest values of thousand kernel weight, highlighting the essential role of nitrogen in the grain filling process. Grain quality analysis showed that variations in starch and protein content had an inverse evolution between the two experimental years, suggesting the influence of climatic conditions and nitrogen availability on grain composition. Full article