Nitrogen

The increased frequency of extreme heat stress events due to climate change is adversely impacting rice yield. Nitrogen (N) is an essential element in the synthesis of chlorophyll in rice, contributing substantially to the achievement of spikelet fertility and addressing the high yields. Two experiments were conducted in Japan and Afghanistan in 2020 and 2022, respectively, utilizing IR64 and Nipponbare (NPB) varieties to elucidate the efficacy of N top-dressing on spikelet fertility and yield of rice under heat stress conditions. In experiment I, the treatments involved were based on N application before panicle emergence in pots, including (1) control (fertilized at the tillering stage), (2) control + N topdressing, (3) heat stress (fertilized at the tillering stage), and (4) heat stress + N topdressing. Experiment II consisted of (1) control (basal dressing at the tillering stage) and (2) control + N topdressing, which was conducted under field conditions. Results showed that N application significantly (p < 0.05) increased SPAD values and spikelet fertility rates in both experiments. A positive correlation (range; r = 0.83–0.98) was observed between enhanced SPAD values and spikelet fertility rates in IR64 and NPB rice varieties under both ambient and heat stress conditions. Moreover, there were notable increases in photosynthetic rate (7.4% to 52.6%) and leaf transpiration. N top dressing significantly (p < 0.05) increased the panicle length, panicle weight, number of secondary branches/panicle, filled grain/panicle, total spikelets/panicle, and yield/plant. However, there was no significant difference in the number of primary branches per panicle and 1000-grain weight. In addition, the number of unfilled grains/panicle decreased from 5.5 to 49.7% with N top dressing in both experiments. Applying N as a top dressing improved the spikelet fertility percentage and other yield components, resulting in a high yield/plant. Full article

The key objectives of contemporary agriculture are restoring biodiversity, preserving ecosystem health, reducing the effects of climate change, and producing safe and healthy foods. Maintaining high soil fertility while reducing greenhouse gas emissions requires a precise assessment of how fertilization and crop rotation affect carbon and nutrient cycles in agroecosystems. Fertilization affects soil conditions, which alters the environment for soil microbial development and influences the number and composition of soil microbial communities, leading to changes in nutrient and carbon cycling. There is a lack of long-term experimental data on the impact of fertilizer treatments on soil CO₂ emissions, soil microbial communities, and their interactions. The novelty of this study is that it identified the fertilization effects on soil carbon sequestration, soil properties, and microbial communities in the context of a long-term fertilizer experiment in Luvic Chernozem. The fertilization treatments that were continuously pplied for 64 years under a four-crop (wheat, barley, corn, and bean) rotation were nitrogen (N), phosphorus (P), potassium (K), NP, NK, PK, NPK, and control. The chemical and microbiological soil properties and soil CO₂ emissions were monitored. The highest organic carbon content was observed under the NPK (1.42%) and NP (1.43%) treatments. N fertilizer application most significantly affected soil properties, including pH, electrical conductivity, and soil organic carbon content, altering the environment for soil microbial development and influencing the number and composition of soil microbial communities. On average, the field-measured soil C-CO₂ emissions were the most intensive under NP (2.76 kg ha⁻¹ h⁻¹), NPK (2.83 kg ha⁻¹ h⁻¹), and PK (2.51 kg ha⁻¹ day⁻¹) treatments. Full article

Soybean, an important leguminous crop valued for its high protein and oil content, obtains most of its nitrogen through symbiotic fixation processes. The symbiosis between soybeans and rhizobium can provide sufficient nitrogen for soybean growth. However, the signaling pathways underlying the establishment of the symbiosis are not so clear, especially the rhizobial type III effector-induced host response. In this study, we found that the single mutant HH103 nopAA::kan significantly affected the nodule number in soybeans. To further demonstrate the NopAA-triggered response in soybeans. Initial quantitative real-time PCR (qRT-PCR) tests showed that NopAA affects the expression of the soybean gene GmERF5, which was significantly upregulated upon inoculation with HH103 nopAA::kan, acting as a positive regulator of nodulation. The direct interaction between NopAA and GmERF5 was confirmed through yeast-two hybrid analysis. Furthermore, overexpression of GmERF5 in hairy roots indicated that GmERF5 may underlie the nodule phenotype of soybeans in response to NopAA. These findings provide new insights into the mechanisms by which soybean genes respond to rhizobial type III effectors to regulate symbiosis. Full article

Water scarcity is a global crisis and of particular concern in arid regions like Morocco. One creative solution is mining unusual water sources, such as landfill leachate. The presence of nitrogen in the sediment was studied as part of the use of sugar lime sludge in treating landfill leachate for irrigation purposes. A volume of 40 L of landfill leachate was treated with three different concentrations of sugar lime sludge (25%, 35%, and 50%). After homogenization and agitation of the mixture for 24 to 36 h, it was permitted to settle through the concrete decantate and supernatant. Nitrogen was efficiently decanted into the sediment during the composting process with green waste, enhancing the quality of the finished compost. The supernatants underwent physicochemical and microbiological analyses to ascertain their suitability for irrigation. The findings showed that the number of fecal streptococci was decreased by 99.13% at a 25% concentration of sugar lime sludge. The percentage of organic matter in the sediment rose from 10% to 40%, suggesting that the leachate had partially depolluted. The pH and electrical conductivity of the supernatants were within irrigation guidelines. The safety of diluted supernatants for plant germination was verified by phytotoxicity experiments conducted on maize seeds. The compost made from the decantate and green waste showed acceptable physical and chemical properties. Statistical analysis was conducted using JAMOVI software version 2.6.26. One-way ANOVA was used to assess the significance of treatment effects on microbiological and physicochemical parameters. The results confirmed statistically significant differences (p < 0.05) between the sludge concentrations, supporting the effectiveness of the treatment process. This study demonstrates how sugar lime sludge can be used to turn landfill leachate into a sustainable and safe irrigation water source, resolving environmental issues and promoting creative water management techniques. Full article

Nitrogen fertilization plays a critical role in promoting plant growth, improving physiological and biochemical traits, and enhancing wheat productivity. This study aimed to evaluate the effects of seven nitrogen (N) doses—0, 45, 90, 135, 180, 225, and 270 kg N ha⁻¹—on wheat performance under semi-arid subtropical conditions over three consecutive growing seasons (2015–2018). A randomized complete block design (RCBD) was used to assess a comprehensive set of agronomic, physiological, biochemical, and nutritional parameters. Key factors examined included grain yield, above-ground biomass, nitrogen harvest index, total nitrogen content in grains and straw, and physiological traits such as photosynthetic rate, stomatal conductance, transpiration rate, and the accumulation of soluble proteins, sugars, and amino acids. The study also incorporated multivariate statistical techniques, such as multi-trait genotype–ideotype distance index (MGIDI), principal component analysis (PCA), and descriptive statistics to identify the most effective nitrogen dose. Results indicated that 180 kg N ha⁻¹ (T₄) was the most effective treatment for improving wheat growth, physiological efficiency, and grain yield, with 135 kg N ha⁻¹ (T₃) also showing favorable outcomes. In contrast, higher doses (225 and 270 kg N ha⁻¹) led to diminished performance, suggesting a threshold beyond which nitrogen becomes counterproductive. These findings support 180 kg N ha⁻¹ as the optimal dose for maximizing yield and biochemical quality while contributing to more sustainable and profitable wheat production. Full article

Despite extensive research on how climate and environmental factors influence leaf stoichiometry at national and global scales, experimental evidence on their effects at the community level remains limited, particularly in extremely arid regions. Herein, we investigated the leaf stoichiometry including carbon (C), nitrogen (N), and phosphorus (P) along a fine-scale riparian gradient (50–1250 m from the riverbank) in an extremely arid Populus euphratica forest in northwest China. Our results show that the community-averaged leaf total carbon (TC), total nitrogen (TN), and total phosphorus (TP) contents were 442.58 mg/g, 21.69 mg/g, and 1.18 mg/g, respectively. The community-averaged C:N, C:P, and N:P ratios were 20.74, 379.97, and 18.43, respectively. Compared to findings from other studies, the P. euphratica community exhibited lower leaf TC and TP contents but higher TN content and N:P ratios. A high N:P ratio (mean = 18.43, N:P > 16) suggests that the P. euphratica community is more susceptible to phosphorus limitation. Along the riparian gradient, community-averaged leaf TC, C:N, and C:P increased significantly, reaching their maximum (479.49 mg/g, 27.12, and 478.06, respectively) at 1250 m from the riverbank. Conversely, leaf TN and TP contents, as well as N:P, decreased significantly with increasing distance from the river, reaching their minimum values (17.49 mg/g, 0.99 mg/g, and 17.17, respectively) at 1100–1250 m. Soil available phosphorus, soil water content, soil bulk density, and soil electrical conductivity significantly influenced the leaf stoichiometry of the P. euphratica community, collectively explaining 61.78% of the total variation. Among these factors, soil water content had the most pronounced effect, surpassing soil available phosphorus, bulk density, and electrical conductivity in shaping leaf stoichiometric characteristics. Our findings indicate that at fine spatial scales, the distribution of leaf nutrients and stoichiometry seem to be predominantly influenced by local-scale factors such as soil water content, soil nutrient levels, and salt stress; P. euphratica forests would be experiencing more negative impacts in leaf nutrients and stoichiometry due to increased droughts or salt stress. Full article

Rice is a major crop for half of the world’s population, and nitrogen (N) fertilizers play a crucial role in its production. However, imbalanced N fertilizer uses and traditional fertilization practices have led to low nitrogen use efficiency (NUE), increased N footprints, and reduced rice yields and farmers’ income. There are limited studies where the integration of both agronomic and molecular advancements to enhance NUE is discussed, particularly in developing countries. This review highlights novel agronomic and molecular strategies to enhance NUE, rice yields, and profitability, while minimizing environmental impact. The agronomic strategies include the 4R Nutrient Stewardship framework, enhanced efficiency nitrogen fertilizers (EENFs), nano-fertilizers, biochar-based fertilizers, biological N fixation, and sensor-based fertilizer management in major rice-growing countries. The molecular mechanisms focus on N uptake, assimilation, and utilization, highlighting the role of hormones, key genes, transcription factors (TFs), and regulatory pathways. Moreover, we examine promising rice genotypes and cultivars with improved NUE and grain yield. Additionally, this paper offers deep insights into recent advancements in molecular genetics, such as multi-omics approaches (transcriptomics, metabolomics, and metagenomics), the Genome-Wide Association Study (GWAS), Quantitative Traits Loci mapping (QTLs), Single Nucleotide Polymorphisms (SNPs) analysis, and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR-Cas9)-mediated genome editing, which serve as valuable tools for developing rice cultivars with enhanced NUE and grain yield. Full article

Rosemary (Salvia rosmarinus L.) is a versatile and resilient plant with significant culinary, medicinal, and ecological value. This study evaluates the impact of four nitrogen (N) fertilization levels (0, 50, 100, and 150 kg N ha⁻¹) on the morphological, physiological, and agronomic traits, as well as vegetative indices, of rosemary over two growing seasons (2022 and 2023). The results indicate that plant height and leaf area index (LAI) increased with N application. Additionally, physiological characteristics such as chlorophyll content, photosynthetic efficiency, and assimilation rates (A) increased by an average of 32%, 17%, and 55%, respectively, compared to the control. Biomass production also improved with N fertilization, with yields rising by 32% in 2022 and 58% in 2023. Furthermore, both essential oil concentration and essential oil yield were enhanced by N application. Radiation use efficiency (RUE), water use efficiency (WUE), agronomic efficiency (AE), and partial factor productivity (PFP) also increased, indicating more efficient utilization of environmental resources. Moreover, higher N rates consistently enhanced vegetation indices, reflecting improved plant health, greenness, biomass, photosynthetic activity, and energy utilization. Therefore, this study highlights that the optimal N range appears to balance biomass yield and essential oil yield while maximizing the efficiency of environmental resource use. Full article

In Spain, several major cities face high rates of avoidable deaths due to NO₂ exposure. Understanding NO₂ atmospheric dynamics is essential to support public health efforts and policymaking. Recent satellite products have proven useful in characterizing urban atmospheric composition in various regions. This study compares NO₂ concentration data from in situ air quality monitoring networks and the Sentinel-5P TROPOMI satellite in Spain’s three largest cities (Madrid, Barcelona, and Valencia), alongside O₃ levels —due to its close photochemical relationship with NO_x—wind speed and direction, temperature, relative humidity, and solar radiation. Data from 2022 were analyzed using Pearson correlation coefficients and Principal Component Analysis (PCA) to identify key relationships and patterns. Results showed a consistent negative correlation between NO₂ and O₃, wind speed, temperature, and solar radiation. Differences between in situ and satellite data were more pronounced in coastal cities, influenced by wind patterns and urban morphology (Madrid: r = 0.86, v = 1.34 m/s; Valencia: r = 0.68, v = 2.97 m/s; Barcelona: r = 0.65, v = 8.04 m/s). These insights enhance the understanding of NO₂ behavior in urban environments and support the use of remote sensing to estimate surface-level pollution in areas lacking ground-based monitoring infrastructure. This is the first study in Spain to jointly evaluate NO₂ from satellite and in situ data across multiple cities, linking pollutant concentrations with meteorological and chemical drivers to improve surface-level estimation strategies and support air quality assessment in under-monitored areas. Full article

Although intensive farming practices have greatly increased food production, they have undermined the soil ecosystem services on which agriculture depends. Biochar application in soils is increasingly gaining worldwide acceptance as a means of addressing these environmental challenges while enhancing agricultural productivity. Biochar offers dual benefits that support food security and ecological well-being through enhanced soil fertility and plant nutrition. These benefits include water retention, promotion of soil microbial functioning, carbon sequestration, and nutrient absorption, among others. In spite of these known benefits, many studies continue to emphasize the roles biochar plays in enhancing soil health and crop yields but often neglect the influence of biochar characteristics, which are key in optimizing these soil ecosystem services. Thus, it is important to understand how biochar characteristics influence soil in supporting, regulating, and provisioning ecosystem services. This review offers a comprehensive and integrative assessment on how biochar’s characteristics influence key soil ecosystem services rather than examining each service individually. The focus is on how biochar feedstock material and pyrolysis temperature determine the characteristics of generated biochar and how these characteristics influence biochar’s efficacy in supplying soil ecosystem services and nutrient dynamics for enhanced crop yields. Full article

Wheat requires a high quantity of nitrogen to grow efficiently and produce a high number of nutritious grains (=high yield). The consequences of fertilizer use in uncontrolled conditions are well known, e.g., nitrogen leakage leading to impacts on ecosystems. One solution to reduce these impacts could be activated carbon, which is already used to treat wastewater. In this study, we assessed the efficiency of four activated carbon formulations applied to two agricultural soils in a column leaching test, a greenhouse pot experiment, and a field experiment. In the latter two experiments, wheat was grown with one dose of one selected activated carbon and several nitrogen fertilization conditions. The goal was to find an activated carbon that could stabilize nitrate while improving soil health and thus increase wheat yields. We showed that nitrogen leaching reduction (between 59% and 79% when significant in the column test) was dependent on the raw material used and the activation process. The controlled pot experiment demonstrated that wheat growth was dependent on nitrogen application (60 to 80% increase) and that the activated carbon addition did not enhance yields. Finally, field trials showed that the addition of 1% activated carbon did not result in higher wheat yields compared to those in the non-amended plots in both the absence and presence of nitrogen. In conclusion, although the activated carbon chosen is a strong nitrate-retaining agent, it does not deliver the expected yield gains, probably due to excessive retention, which prevents increased plant growth. More research is needed to improve activated carbon as a fertilizer. Full article

This study introduces a novel methodology for predicting cotton yield by integrating machine learning (ML) with mechanistic soil modeling. This hybrid approach enhances yield prediction by combining data-driven ML techniques with soil process modeling. Using the developed yield model, yield curves for various nitrogen (N) levels can be constructed to identify the optimal N dose that maximizes yield. Estimating cotton N requirements is crucial, as growers often apply excessive N, exceeding the amount needed for maximum yield. By comparing the Mean Absolute Error (MAE) between predicted and observed cotton yield values across three ML algorithms, i.e., Random Forest (RF), XGBoost, and LightGBM, the RF model achieved the lowest error (422.6 kg/ha), outperforming XGBoost (446 kg/ha) and LightGBM (449 kg/ha). Additionally, the RF model exhibited high sensitivity to N fertilization, ranking N as the most influential variable in feature importance analysis. Furthermore, phosphorus (P) availability in the soil model was found to be a significant factor influencing the RF yield model, highlighting P’s crucial role in cotton growth and productivity. Full article

Beef-cattle manure (BCM) can be an effective source of nitrogen (N) for crop production. However, N availability from manure can be difficult to quantify across varying environments. The Magruder Plots are a continuous winter wheat (Triticum aestivum L.) fertility study established in 1892 in Stillwater, OK, USA. In the study, wheat grain yield responses to BCM that is applied every four years are compared to those following annual applications of inorganic nitrogen (N), phosphorus (P), and potassium (K) fertilizers. This long-term, comprehensive dataset facilitates the evaluation of manure N availability and uptake across a wide range of growing environments; thus, the objective of this paper was to use 56 years of data from the Magruder Plots to benchmark current N-based manure application guidelines for Oklahoma. The results from this analysis revealed some discrepancies compared to regionally accepted guidelines for manure N availability. Existing guidelines for Oklahoma suggest that 50 to 70% of total N in BCM will become plant-available in the first year after application; however, the Magruder Plots have only averaged 23% total N availability in year one. The three seasons after manure application averaged total N availability of 20, 16, and 14%, respectively, which much more closely align with the existing estimates for Oklahoma of 10 to 20% N availability after year one. This study suggests that N availability of BCM in the first year after application in Oklahoma has a more accurate estimate of 10 to 30% of total N. Full article

Increasing soil salinity is threatening agricultural productivity which implies the development of new sustainable strategies to deal with this challenge. The main objective here is to assess the potential for improving the tolerance of alfalfa to salinity by combining inoculations with rhizobia and AMF. However, the distinguishing feature of this study is the comparison of two alfalfa varieties’ microbial response to salinity. The greenhouse trial was conducted on an Australian variety Siriver and an indigenous Demnate population, which were inoculated with Rhizoglomus irregulare and/or native AMF, and/or a RhOL1 rhizobial strain. The RhOL1 strain was selected from nine rhizobia tested for their plant growth promoting rhizobacteria (PGPR) activities. In addition to its ability to tolerate high salinity levels (769 mM) and solubilize insoluble phosphate as well as potassium, it can also synthesize auxins such as IAA. The application of these biofertilizers was carried out in the absence and the presence of the saline stress (0 and 120 mM NaCl). The double inoculations of native AMF and RhOL1 significantly improve the shoot and root dry biomass, plant elongation, number of formed leaves, and mineral nutrition, as well as the number of nodules and the rate of mycorrhizal root colonization. The synergistic effects between the native AMF and RhOL1 strain have been demonstrated in this study. However, the behavior of alfalfa genotypes towards microbial inoculation was significantly different. The ability to react to the double indigenous RhOL1 + AMF inoculation is more important in the Siriver than in the Demnate population. Thus, the possibility of formulating biofertilizers is based on the AMF–rhizobia–hote tripartite combination for alfalfa production in saline areas. Full article

This study investigated the effects of Bradyrhizobium elkanii inoculation and nitrogen (N) fertilization on the growth of Pseudalbizzia niopoides seedlings in a nursery and their subsequent performance in soil. P. niopoides is a legume tree native to Latin American tropical forests, known to nodulate but with no previously identified rhizobial partner. Seedlings were grown in a nursery under varying N fertilization rates (0, 250, 500, 1000, and 2000 mg L⁻¹) with and without B. elkanii inoculation. Morphological traits, nodulation, and post-planting growth were assessed. Both inoculation and N fertilization significantly enhanced seedling growth in the nursery. However, high N rates suppressed nodulation and caused root toxicity. Inoculated seedlings exhibited improved growth after planting, particularly at lower N rates. Notably, inoculated seedlings without added N demonstrated vigorous new root proliferation after three months, highlighting the beneficial effects of the symbiosis. In terms of nitrogen fertilization in nurseries, a N rate up to 500 mg L⁻¹ produced satisfactory plant growth and no prejudicial effects on the symbiosis establishment. However, it is possible to raise seedlings even in the 0 mg L⁻¹ N rate, with a vigorous root emission during the post-planting growth. This study provides valuable insights into the interaction between a specific rhizobia strain and P. niopoides, with implications for nursery practices and sustainable agroforestry systems. Full article

Alley cropping, an agroforestry system that integrates trees and arable crops, holds the potential to improve both crop yields and soil health. It has been found to be effective for upland crops in many countries of the world. However, the utilization of alley cropping to improve soil health in the terrace ecosystem of Bangladesh is poorly understood. Therefore, this study was undertaken to assess the changes in soil biochemical properties and quantify the cabbage yield under three alley widths of Leucaena leucocephala (3.0, 4.5, and 6.0 m size) and five nitrogen (N) levels [0, 40, 80, 120, and 160 kg N ha⁻¹ (0, 25, 50, 75, and 100% of recommended N rates, respectively) with the addition of pruned materials of L. leucocephala (Ipil-ipil)]. The field experiment was conducted following a split-plot design, where alley width was considered as the main-plot factor and N rate as the sub-plot factor. Within each main plot, the five N rates were replicated thrice. Control plots with similar N doses were applied accordingly without addition of pruned materials to compare the results with alley cropping. Data were collected on the biochemical properties of the soil [soil pH, organic carbon (C), total N, available phosphorus (P), exchangeable potassium (K), microbial biomass C, and biomass N] and the yield of cabbage quantified [edible head weight (kg plant⁻¹) and head yield (t ha⁻¹)] under different alley widths and control. Findings revealed that organic C, total N, available P, exchangeable K, microbial biomass C, and biomass N in the topsoil exhibited maximum values in the L. leucocephala-based alley plot, which is proved to be a possible solution of restoration of degradable land. Additionally, L. leucocephala-based alley cropping improved the soil pH, indicating a potential avenue for more-sustainable land management practices. Results also showed that alley widths and N rates have significant effects on cabbage (Brassica oleracea L. var. capitata) yield. Alley width of 6.0 m along with 100% N provided the highest cabbage yield followed by 75% N in 6.0 m alley, and the control with 100%. The wider alley minimizes tree–crop competition, allowing for optimal cabbage production. These aforementioned results suggest that alley cropping with L. leucocephala is a promising approach to enhance soil fertility and crop productivity in the terrace ecosystem of Bangladesh. Full article

This study explores the economic benefits and challenges associated with biodegradable waste composting, highlighting its role in promoting sustainability through a circular economy framework. We reviewed the relevant literature and found 160 articles for this study, including the keywords “Biodegradable waste”, “Compost production”, and “Economic Potential”. Considering quality studies, we employed the PRISMA technique to conduct a comprehensive data synthesis and evaluate 89 articles for the final review. Our findings highlight that composting offers significant advantages, including waste reduction, cost savings in waste management, carbon credit, a source of nitrogen, job creation, and reduced reliance on synthetic fertilizers. Further, it supports environmental sustainability by improving soil health, mitigating greenhouse gas emissions, and reducing landfill use. However, challenges such as high upfront costs, quality control, and market competition with chemical fertilizers remain barriers to widespread adoption. The study extends the literature by emphasizing that the integration of composting into a circular economy can foster innovation, enhance local economies, and contribute to climate change mitigation. Furthermore, it offers a promising pathway for advancing sustainability. Future research should focus on improving composting technologies, optimizing their applications, and developing stronger policy frameworks to ensure the successful implementation of biodegradable waste composting practices. Full article

Soil nitrogen (N) is a crucial nutrient for agricultural productivity and ecosystem health. The accurate and timely assessment of total soil N is essential for evaluating soil health. This study aimed to determine the impact of bootstrapping techniques on improving the predictive accuracy of indirect total soil N in conventional wheat fields in Al-Muthanna, Iraq. We integrated a novel methodological framework that integrated bootstrapped and non-bootstrapped total soil N data from 110 soil samples along with Landsat 9 imagery on the Google Earth Engine (GEE) platform. The performance of the proposed bootstrapping-enhanced random forest (RF) model was compared to standard RF models for soil N prediction, and outlier samples were analyzed to assess the impact of soil conditions on model performance. Principal components analysis (PCA) identified the key spectral reflectance properties that contribute to the variation in soil N. The PCA results highlighted NIR (band 5) and SWIR2 (band 7) as the primary contributors, explaining over 91.3% of the variation in soil N within the study area. Among the developed models, the log (B5/B7) model performed best in capturing soil N (R² = 0.773), followed by the ratio (B5/B7) model (R² = 0.489), while the inverse log transformation (1/log (B5/B7), R² = 0.191) exhibited the lowest performance. Bootstrapped RF models surpassed non-bootstrapped random forest models, demonstrating enhanced predictive capability for soil N. This study established an efficient framework for improving predictive capacity in areas characterized by limited, low-quality, and incomplete spatial data, offering valuable insights for sustainable nitrogen management in arid regions dominated by monoculture systems. Full article

Nitrate pollution in aquatic environments poses significant environmental and public health issues, mostly due to industrial activities and agricultural runoff. Biological denitrification, the favored method for removing nitrates, typically needs an external carbon source to support microbial processes. Traditional electron donors like methanol, ethanol, and acetate are effective but introduce economic, environmental, and operational challenges such as cost variability, flammability hazards, and excessive residual organic material. Recently, solid-phase carbon sources—like biodegradable polymers and organic agricultural waste—have shown promise as alternatives because they allow for controlled carbon release, improved safety, and enhanced long-term sustainability. This review systematically examines the performance of solid-phase carbon in wastewater denitrification by analyzing peer-reviewed studies and experimental data. The findings suggest that solid-phase carbon sources, including polycaprolactone (PCL) and polyhydroxyalkanoates (PHA), offer stable and extended carbon release, ensuring consistent denitrification effectiveness. Nonetheless, challenges remain, including optimizing biofilm development, balancing carbon availability, and reducing operational costs. Furthermore, the review emphasizes the potential for integrating machine learning in process optimization and highlights the need for more research to enhance the economic viability of these materials. The findings confirm the practicality of solid-phase carbon sources for extensive wastewater treatment and their capability to sustainably address nitrate contamination. Full article