Nitrogen, Volume 6, Issue 3 (September 2025) – 39 articles

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. Full article

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. Full article

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 NO_x) 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 NO_x 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 NO_x variability at the site. The analysis showed peaks in early morning NO_x 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. Full article

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. Full article

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 (CL_{Red_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. Full article

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 (NR_max) (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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

Efficient use of nitrogen and phosphorus is crucial for achieving sustainable wheat production. Slow-release nano-fertilizers offer a targeted strategy to minimize nutrient losses, reduce excessive fertilizer application, and improve crop yield. This study introduces urea–hydroxyapatite (n-UHA) nanohybrid as a slow-release fertilizer synthesized to enhance nitrogen (N) and phosphorus (P) delivery efficiency in wheat (Triticum aestivum L.). Physical characterization techniques, including Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Zetasizer, and Fourier Transform Infrared Spectroscopy (FTIR), confirmed the formation of spherical n-UHA with a particle size of 106 nm. FTIR results indicated the formation of physically bound urea as a coating layer on the particle surface. Foliar application of n-UHA at 2500 and 5000 ppm N significantly increased tiller intensity and grain yield compared to conventional urea. The highest biological yield, approximately 16 t ha⁻¹, was achieved with 5000 ppm n-UHA plus supplemental soil phosphorus (P), representing a 4-fold increase over the control. Conventional urea treatments, in comparison, only doubled yield. Notably, increasing conventional urea concentration from 2500 to 5000 ppm N did not significantly increase the yield even with additional P-soil supplement, while applying 5000 ppm N from n-UHA with supplemental P provided an approximate 25% yield increase compared to 2500 ppm n-UHA without P. The n-UHA’s slow-release mechanism supported prolonged tiller intensity, enhanced protein content, and higher biomass yield and chlorophyll content. This study showed that the slow-release mechanism of urea in the monohybrid due to hydrolysis resulted in localized acidity from carbonic acid production on the leaf surface area and contributed to dissociating phosphate ions from hydroxyapatite, making phosphorous more accessible. The enhanced performance of n-UHA is due to its controlled nutrient release, enabled by the physical binding of urea with hydroxyapatite nanoparticles. This binding ensures a synchronized supply of nitrogen and phosphorus aligned with plant demand. The nano-hydroxyapatite composite (N/Ca 6:1) supplies balanced nutrients via efficient stomatal absorption and gradual release. As an eco-friendly alternative to conventional fertilizers, n-UHA improves nitrogen delivery efficiency and reduces N-evaporation, supporting sustainable agriculture. Full article

As interest in biochar as a soil amendment increases, the co-application of biochar and fertilizer warrants investigation. Biochar may improve soil properties, affect crop yields, and mitigate environmental impacts, but more work is needed to determine its effect on nitrogen (N) cycling from commercially available organic fertilizers. A 102 d laboratory incubation was conducted to better understand the effect of three rates of biochar (0%, 5%, and 10%) on net N mineralized from (1) mineral soil (Cecil sandy loam), (2) organic peat-based potting media, and (3) two commercial organic fertilizers (feather meal and meal-based pellet mix) applied to the mineral soil or the potting media. After 102 d, the biochar treatments did not affect net N mineralized from the mineral soil but decreased (from 190 to −286.9 mg N kg⁻¹) the net N mineralized from the potting media, likely due to N immobilization. Biochar applied at 5 or 10% did not affect the amount of organic N mineralized from the organic fertilizers applied to potting media (average 58.9%), but biochar at 5% decreased from 46.5 to 28.1% of organic N mineralized from the organic fertilizers applied to mineral soil. Full article

Accurate nitrogen (N) content estimation in grassland vegetation is essential for ecosystem health and optimizing pasture quality, as N supports plant photosynthesis and water uptake. Traditional lab methods are slow and unsuitable for large-scale monitoring, while remote sensing models often face accuracy challenges due to hyperspectral data complexity. This study improves N content estimation in the typical steppe of Inner Mongolia by integrating hyperspectral remote sensing with advanced machine learning. Hyperspectral reflectance from Leymus chinensis and Cleistogenes squarrosa was measured using an ASD FieldSpec-4 spectrometer, and leaf N content was measured with an elemental analyzer. To address high-dimensional data, four spectral transformations—band combination, first-order derivative transformation (FDT), continuous wavelet transformation (CWT), and continuum removal transformation (CRT)—were applied, with Least Absolute Shrinkage and Selection Operator (LASSO) used for feature selection. Four machine learning models—Extreme Gradient Boosting (XGBoost), Support Vector Machine (SVM), Artificial Neural Network (ANN), and K-Nearest Neighbors (KNN)—were evaluated via five-fold cross-validation. Wavelet transformation provided the most informative parameters. The SVM model achieved the highest accuracy for L. chinensis (R² = 0.92), and the ANN model performed best for C. squarrosa (R² = 0.72). This study demonstrates that integrating wavelet transform with machine learning offers a reliable, scalable approach for grassland N monitoring and management. Full article

The nitrogen (N) requirement of sugarcane (Saccharum spp.) is very high due to the extensive growth of biomass. N fertilisers are applied excessively to ensure the optimum growth of the sugarcane crop. Improper N management causes a decrease in nitrogen utilisation efficiency (NUE) and contributes to N losses via leaching and gaseous emissions in the form of ammonia (NH₃) and nitrous oxide (N₂O), leading to unintended negative consequences. Asynchronous timing between the sugarcane N demand and supply by the N sources exacerbates these losses. Therefore, proper N management strategies need to be implemented to mitigate losses and enhance NUE. This review provides an overview of global sugarcane cultivation and discusses the N requirements for sugarcane crops. Additionally, it summarises the various strategies utilised in N management for sugarcane cultivation and evaluates their effectiveness. Furthermore, it identifies research gaps and outlines future research directions. Full article

This study presents a four-year evaluation (2020–2024) of an integrated climate mitigation project on a pig farm in Ávila, Spain, at an elevation of over 1100 m above sea level with continental climate conditions. The project aimed to reduce greenhouse gas emissions (GHG) and nitrogen pollution by implementing solid–liquid filtration followed by biological treatment in a 625 m³ Sequencing Batch Reactor (SBR) operating under a nitrification–denitrification (N-DN) regime. The SBR carried out four daily cycles, alternating aerobic and anoxic phases, with 5 and 8 m³ inlets. Aeration intensity and redox potential were continuously monitored to optimize bacterial activity. Analytical parameters (pH, electrical conductivity, solids content, nitrogen, phosphorus, and potassium) were measured using ISO methods and tracked frequently. Annual emission reductions were 75% for N₂O, up to 97% for NH₃, and 80% for N₂. In the summer months, we observed higher efficiency reduction for N₂, NH₃, and NO₂. Additionally, there was a 75% average reduction for COD and up to 92% for total GHG emissions. This real-world case study highlights the effectiveness of SBR-based N-DN systems for nutrient removal and emission reduction in high-altitude, climate-sensitive regions, contributing to EU nitrate directive compliance and circular economy practices. Full article

An attempt was made to understand the interactive consequences of subjecting a rhizospheric microbial community of xTriticocereale (Triticale) to higher CO₂ levels and soil nitrogen addition in the short term in a tropical agro-ecosystem. Open-top chambers (OTCs) were used to grow the test crops for a single season under ambient CO₂ (AC) and elevated CO₂ (EC) along with two variable N dosages: recommended (N₀: 0.053 g N/kg of soil) and high (N₂: 0.107 g of N/kg of soil) levels. Variations in the composition of microbial communities and abundances were investigated using phospholipid fatty acid analysis (PLFA). A significantly (p < 0.001) increased microbial biomass content (MB) was observed under EC compared to AC, while the addition of N had a minor effect. A decreased fungi/bacteria (F/B) ratio (~38%) was observed with high N application in the CO₂ enrichment treatment. Bacteria were more abundant, while fungal abundance decreased under N₂ and EC. Gram (+ve) bacteria used these conditions to thrive under N₂ and EC, while Gram (−ve) bacteria declined. No significant effects on actinomycetes were noticed in any of the treatments. However, eukaryotes acquired more benefits and flourished in response to EC. Varied responses were noted for the Shannon diversity index (H’) under EC. Overall, (i) bacteria (Gram-positive) and eukaryotes dominated under EC and high N addition, while fungi decreased, and (ii) EC and high levels of N addition did not affect actinomycetes. Short-term exposure under the given conditions was found to alter the rhizospheric microbial community. However, multiple season studies are needed to elucidate whether these short-term responses are transient or continuous. Full article

Salinity is a major abiotic stress limiting black gram (Vigna mungo) productivity, particularly in arid and semi-arid regions. Saline soils negatively impact plant growth, nodulation, nitrogen fixation, and yield. This study evaluated the efficacy of co-inoculating salt-tolerant plant growth-promoting bacteria Paenibacillus sp. SPR11 and Bradyrhizobium yuanmingense PR3 on black gram performance under saline field conditions (EC: 8.87 dS m⁻¹; pH: 8.37) with low organic carbon (0.6%) and nutrient deficiencies. In vitro assays demonstrated the biocontrol potential of SPR11, inhibiting Fusarium oxysporum and Macrophomina phaseolina by 76% and 62%, respectively. Germination assays and net house experiments under 300 mM NaCl stress showed that co-inoculation significantly improved physiological traits, including germination rate, root length (61.39%), shoot biomass (59.95%), and nitrogen fixation (52.4%) in nitrogen-free media. Field trials further revealed enhanced stress tolerance markers: chlorophyll content increased by 54.74%, proline by 50.89%, and antioxidant enzyme activities (SOD, CAT, PAL) were significantly upregulated. Electrolyte leakage was reduced by 55.77%, indicating improved membrane stability. Agronomic performance also improved, with co-inoculated plants showing increased root length (7.19%), grain yield (15.55 q ha⁻¹; 77.04% over control), total biomass (26.73 q ha⁻¹; 57.06%), and straw yield (8.18 q ha⁻¹). Pod number, seed count, and seed weight were also enhanced. Nutrient analysis showed elevated uptake of nitrogen, phosphorus, potassium, and key micronutrients (Zn, Fe) in both grain and straw. To the best of our knowledge, this is the very first field-based report demonstrating the synergistic benefits of co-inoculating Paenibacillus sp. SPR11 and Bradyrhizobium yuanmingense PR3 in black gram under saline, nutrient-poor conditions without external nitrogen inputs. The results highlight a sustainable strategy to enhance legume productivity and resilience in salt-affected soils. Full article

Legumes are among the most important crops globally, serving as a major food source for protein and oil. In tropical regions, the cultivation of legumes has expanded significantly due to the increasing demand for food, plant-based products, and sustainable agriculture practices. However, tropical environments pose unique challenges, including high temperatures, erratic rainfall, soil infertility, and a high incidence of pests and diseases. Indeed, legumes are vulnerable to infections caused by bacteria, fungi, oomycetes, viruses, and nematodes. This review highlights the importance of legumes in tropical farming and discusses major diseases affecting productivity and their impact on the economy, environment, and lives of smallholder legume farmers. We emphasize the use of legume genetic resources and breeding, and biotechnology innovations to foster resistance and address the challenges posed by pathogens in legumes. However, an integrated approach that includes other cultivation techniques (e.g., crop rotation, rational fertilization, deep plowing) remains important for the prevention and control of diseases in legume crops. Finally, we highlight the contributions of plant genetic resources to smallholder resilience and food security. Full article

Fertilization is a critical measure for vegetation restoration and ecological reconstruction in degraded grasslands. However, little is known about the long-term effects of different combinations of nitrogen (N), phosphorus (P), potassium (K) on plant and microbial communities in degraded grasslands. This study conducted a four-year (2017–2020) N, P, K addition experiment in the Khorchin Grassland, a degraded typical grassland located in Zhalute Banner, Tongliao City, Inner Mongolia, to investigate the effects of fertilization treatment on plant functional groups and microbial communities after grazing exclusion. Our results showed that the addition of P, NP, and NPK compound fertilizers significantly increased aboveground biomass of the plant community, which is mainly related to the improvement of nutrient availability to promote the growth of specific plant functional groups, especially annual and biennial plants and perennial bunchgrasses. However, the addition of N, P, and NP fertilizers significantly reduced the species diversity of the plant community. At the same time, the addition of N, P, and NP fertilizers and the application of N and NP significantly reduced fungal species diversity but had no significant effect on soil bacteria. Our study provides new insights into the relationships between different types of fertilization and plant community productivity and biodiversity in degraded grasslands over four years of fertilization, which is critical for evaluating the effect of fertilization on the restoration of degraded grassland. Full article

Intensive vegetable farming emits high nitrous oxide (N₂O) due to traffic-induced compaction, highlighting the need for preventing nitrogen (N) losses through better traffic management. This study examined the effects of Controlled Traffic Farming (CTF) and Random Traffic Farming (RTF) on N₂O emissions using intact soil cores (diameter: 18.7 cm; depth: 25 cm) collected from a vegetable production system in Pukekohe, New Zealand. Soil cores from CTF beds, CTF tramlines, and RTF plots were analysed under fertilised (140 kg N/ha) and unfertilised conditions. N₂O fluxes were monitored over 58 days using gas chambers. The fertilised RTF system significantly (p < 0.05) increased N₂O emissions (5.4 kg N₂O–N/ha) compared to the unfertilised RTF system (1.53 kg N₂O–N/ha). The emission from fertilised RTF was 46% higher than the maximum N₂O emissions (3.7 kg N₂O–N/ha) reported under New Zealand pasture conditions. The fertilised CTF system showed a 31.6% reduction in N₂O emissions compared to fertilised RTF and did not differ significantly from unfertilised CTF. In general, CTF has demonstrated some resilience against fertiliser-induced N₂O emissions, indicating the need for further investigation into its role as a greenhouse gas mitigation strategy. Full article

This study assesses sediment toxicity in the historically contaminated Orbetello Lagoon (southern Tuscany) using Paracentrotus lividus embryo development bioassays. Elutriates from 15 sites were analysed for trace metals, organic matter, and ammonium. Despite elevated mercury concentrations, toxicity did not consistently correlate with metal levels. Instead, Principal Component Analysis (PCA) identified ammonium as a key driver of developmental toxicity, suggesting that it significantly influences both biological effects and metal bioavailability. These results demonstrate that ammonium, often overlooked, can confound sediment toxicity assessments and should be integrated into risk evaluation frameworks for coastal systems affected by legacy pollution. Full article

The low nitrogen-use efficiency (NUE) in sandy soils, due to high porosity and poor nutrient retention, necessitates proper management in fertilization. This study aims to evaluate the effect of biochar-coated urea (BCU) with different coating thicknesses and nitrogen doses on soil nitrogen content, nitrogen uptake, NUE, growth, and yield of sweet corn in sandy soil. The experiment used a factorial randomized block design with two factors, including biochar coating thicknesses (i.e., 14% and 29%) and fertilization doses (i.e., 50%, 100%, 150%, 200%, and 250%). The results showed that the 29% biochar coating thickness led to 9.9–21.3% higher plant height, N uptake, and N-use efficiency, but it led to 22.8% lower yield, as compared to the 14% biochar coating thickness. Additionally, the application of BCU doses of 100% and 150% (~161 and 241.5 kg N/ha) led to 9.2–97.3% higher maize growth, yield, N uptake, and NEU as compared to the other doses (i.e., 50%, 100%, 250%). This study confirmed that the combination of a 29% biochar coating thickness with 150% of the recommended BCU dose (~241.5 kg N/ha) was the best combination, resulting in the highest N uptake, growth, and yield of maize. Full article

Nitrogen (N) availability often limits primary productivity in terrestrial ecosystems, and arbuscular mycorrhizal fungi (AMF) can enhance plant N acquisition. This study investigated the interactive effects of N fertilization and AMF inoculation on N uptake, plant performance and phenolic acid content in Hyssopus officinalis L., with the aim of promoting sustainable N management in H. officinalis cultivation. A factorial randomized complete block design was employed to evaluate four AMF inoculation strategies (no inoculation, root inoculation, soil inoculation and combined root–soil inoculation) across three N application rates (0, 0.5 and 1,1 g N pot⁻¹ (7 L)) in a controlled greenhouse environment. Combined root and soil AMF inoculation alongside moderate N fertilization (0.5 mg N pot⁻¹) optimized N use efficiency, maximizing plant biomass and bioactive compound production. Compared to non-inoculated controls, this treatment combination increased N uptake by 30%, phosphorus uptake by 24% and potassium uptake by 22%. AMF colonization increased chlorophyll content and total phenolic compounds under moderate N supply. However, excessive N application (1 g N pot⁻¹) reduced AMF effectiveness and secondary metabolite accumulation. Notably, AMF inoculation without N fertilization yielded the highest levels of anthocyanin and salicylic acid, indicating differential N-dependent regulation of specific biosynthetic pathways. The interaction between AMF and N demonstrated that moderate N fertilization (0.5 g N pot⁻¹) combined with dual inoculation strategies can reduce total N input requirements by 50%, while maintaining optimal plant performance. These findings provide practical insights for developing N-efficient cultivation protocols in medicinal plant production systems, contributing to sustainable agricultural practices that minimize environmental N losses. Full article

The agronomic effectiveness of biofertilizers is influenced by strain origin, genetic identity, crop genotype, soil type, and environmental conditions. For best results, both the plant and rhizobia strain must be adapted to the common harsh soil conditions in the tropics. While plant varieties have changed over the years, complementary research on new strains effectiveness under varying soil fertility conditions has lagged in southern Africa. Seven field experiments were established in the main soybean-producing areas of Zimbabwe in the north, central, and north–east regions to evaluate agronomic benefits of new rhizobia strains against the current exotic commercial strain (MAR1491). One site was irrigated (site 3), and the other six sites were rainfed (sites 1, 2, 4, 5, 6, and 7). While trends in inoculation response varied from site to site due to site conditions, inoculation with the strains NAZ15, NAZ25, and NAK128 consistently yielded high grain yields, which were similar to the current commercial strain MAR1491 and to application of mineral fertilizer (51.75 and 100 kg N ha⁻¹). Grain yield levels were generally below 2 t ha⁻¹ for sites 2, 3, and 5 and above 2 t ha⁻¹ for sites 1, 4, and 6, while for the irrigated site 3, they ranged upwards of 3 t ha⁻¹. When irrigated, all strains except NAK9 performed similarly in terms of grain yields and aboveground N uptake. Further testing on the inclusion of the indigenous strains NAZ15, NAZ25, and NAK128 in multi-strain commercial inoculant production targeting application in regions and soils where they excel beyond the current exotic strain MAR1491 is recommended. Full article

The growing negative environmental effects associated with chemical fertilizers have led to the promotion of organic fertilizers in agriculture. The purpose of this study was to evaluate the impacts of organic fertilization on nitrogen and phosphorus content, uptake and use efficiency in Origanum dictamnus (Dittany) cultivation. With this aim, a randomized complete blocks field experiment was carried out in Istron Kalou Xoriou (Agios Nikolaos—Crete). The study included three fertilization treatments (N0: 0 kg/ha⁻¹, N1: 1250 kg/ha⁻¹ and N2: 2500 kg/ha⁻¹). Throughout the growing period, measurements were taken for the plant’s content, uptake and efficiency indices of total nitrogen (TN) and phosphorus (P). The findings indicated that the fertilization doses affect nutrient uptake and efficiency. The highest values of TN and P were recorded 60 days after transplants. N1 treatment showed the greatest improvement in nitrogen use efficiency, while phosphorus use efficiency reached its maximum level under N2 treatment. That research can contribute to achieving an in-depth insight of organic fertilization practices for aromatic and medicinal plants such as Dittany, promoting a sustainable agricultural strategy and enhancing product quality. Full article

The substrate-induced respiration-inhibition (SIRIN) method has been used to estimate fungi-derived N₂O emissions, but its contribution to soil N₂O emissions remains unclear. There is a need to quantify the fungal fraction of N₂O production more precisely. Here, using isotopocule analysis, we assessed the relative contribution of fungi to soil N₂O production potential under denitrifying conditions, where key limiting factors of denitrification (soil moisture, soil NO₃⁻, and electron donor) were removed. The result showed that the ratio of fungi-derived N₂O emissions (R_F) was 0.83~4.28% in paddy soils, 13.80~23.21% in vineyard soils, and 15.34~65.94% in vegetable field soils, respectively. This indicated that the bacteria were the dominator of soil N₂O production potential in most cases, but fungal pathways could be significant in vegetable field soils. The experiment with bactericide addition showed that inhibitors could affect non-target microorganisms in the SIRIN method. Our further analyses suggest that it is worth to explore the effect of soil organic carbon and microbial synergies on fungi-derived N₂O emissions. Full article