Nitrogen Loss Research Articles

Potential Growth of Anammox Bacteria under Aerobic Conditions.

Anammox bacteria are obligate anaerobic bacteria that exist widely in nature with sufficient amounts of dissolved oxygen. However, whether anammox bacteria can grow under aerobic conditions remains unclear. In this study, we found that the production of nitrate in the anammox system under aerobic conditions was significantly higher than that under anaerobic conditions without total nitrogen loss. Anammox bacteria can grow by oxidizing nitrite and dehydrogenating hydrazine to produce electrons for carbon fixation. The hydrazine dehydrogenase in anammox bacteria was inhibited under aerobic conditions, and the nitrite oxidoreductase transcription expression of anammox bacteria increased by 2.7 times compared to that under anaerobic conditions, which was the main way for anammox bacteria perform carbon fixation. DNA-stable isotope probing with 13C bicarbonate found the existence of anammox bacteria with 13C isotopes in aerobic cultivation, further proving that anammox bacteria can grow under aerobic condition. More than half of the pathways in glycolysis, the Wood-Ljungdahl pathway, and the tricarboxylic acid cycle were upregulated in anammox bacteria in aerobic condition. Large amounts of bacterioferritins are the important antioxidative enzymes in anammox bacteria in the aerobic environment, which contributes to their stronger oxygen adaptation than other anaerobes. This study expands our understanding of the growth mechanism of anammox bacteria as well as the oxygen adaptation strategies of obligate anaerobic bacteria.

Partial replacement of inorganic fertilizer with organic inputs for enhanced nitrogen use efficiency, grain yield, and decreased nitrogen losses under rice-based systems of mid-latitudes

In the rice-based system of mid-latitudes, mineral nitrogen (N) fertilizer serves as the largest source of the N cycle due to an insufficient supply of N from organic sources causing higher N losses due to varying soil and environmental factors. However, aiming to improve soil organic matter (OM) and nutrients availability using the best environmentally, socially, and economically sustainable cultural and agronomic management practices are necessary. This study aimed to enhance nitrogen use efficiency (NUE) and grain yield in rice-based systems of mid-latitudes by partially replacing inorganic N fertilizer with organic inputs. A randomized complete block design (RCBD) was employed to evaluate the effects of sole mineral N fertilizer (urea) and its combinations with organic sources—farmyard manure (FYM) and poultry compost—on different elite green super rice (GSR) genotypes and were named as NUYT-1, NUYT-2, NUYT-3, NUYT-4, NUYT-5, and NUYT-6. The study was conducted during the 2022 and 2023 rice growing seasons at the Rice Research Program, Crop Sciences Institute (CSI), National Agricultural Research Centre (NARC), Islamabad, one of the mid-latitudes of Pakistan. The key objective was to determine the most effective N management strategy for optimizing plant growth, N content in soil and plants, and overall crop productivity. The results revealed that the combined application of poultry compost and mineral urea significantly enhanced soil and leaf N content (1.36 g kg− 1 and 3.06 mg cm− 2, respectively) and plant morphophysiological traits compared to sole urea application. Maximum shoot dry weight (SDW) and root dry weight (RDW) were observed in compost-applied treatment with the values of 77.62 g hill− 1 and 8.36 g hill− 1, respectively. The two-year mean data indicated that applying 150 kg N ha⁻1, with half provided by organic sources (10 tons ha⁻1 FYM or poultry compost) and the remainder by mineral urea, resulted in the highest N uptake, utilization, and plant productivity. Thus, integrated management of organic carbon sources and inorganic fertilizers may sustain the productivity of rice-based systems more eco-efficiently. Further research is recommended to explore root and shoot morphophysiological, molecular, and biochemical responses under varying N regimes, aiming to develop N-efficient rice varieties through advanced breeding programs.

Spatial-temporal patterns of foliar and bulk soil 15N isotopic signatures across a heterogeneous landscape: Linkages to soil N status, nitrate leaching, and N2O fluxes

The natural abundance of plant and bulk soil 15N isotopic signatures provides valuable insights into the magnitude of nitrogen cycling and loss processes within terrestrial ecosystems. However, 15N isotopic signatures are highly variable in space due to natural and anthropogenic factors affecting N cycling processes and losses. To date, most studies on foliar and bulk soil 15N isotopic signatures have focused on N-limited forest ecosystems at relatively large spatial scales, while similar studies in N-enriched ecosystems at finer spatial scales are lacking. To address this gap and evaluate links between soil 15N isotopic signatures and ecosystem N cycling and loss processes (plant N uptake, N leaching, and gaseous loss), this study quantified foliar and bulk soil 15N isotopic signatures, soil physicochemical parameters, gaseous (N2O), and hydrological (NO3) N losses at 80 sites distributed across a heterogeneous landscape (∼5.8 km2). To account for the spatial-temporal heterogeneity, the measurements were performed in four campaigns (March, June, September 2022, and March 2023) at sites that considered different land uses, soil types, and topography. Results indicated that foliar and bulk soil 15N isotopic signatures were significantly (P < 0.05) more enriched in arable and grassland ecosystems than forests, suggesting a more open N cycle with significant N cycling and losses due to higher N inputs from fertilizers. Similar to soil inorganic N, N2O fluxes, and NO3 leaching rates, landscape-scale foliar and soil 15N isotopic signatures varied widely spatially, particularly at grassland and arable land (−3 to 9.0‰), with bivariate and multivariate analyses also showing significant relationships between landscape-scale soil 15N isotopic signatures and the aforementioned parameters (r2: 0.29 to 0.82). Based on these relationships, our findings suggested that foliar and bulk 15N isotopic signatures may capture fine-scale areas with persistently high and low environmental N losses (N2O fluxes and NO3 leaching) within a heterogeneous landscape.

How to effectively reduce sloping farmland nutrient loss and soil erosions in the Three Gorges Reservoir area

Fertilization and soil conservation measures play crucial roles in influencing nutrient loss and soil erosion on sloping farmlands. However, the long-term effects of these measures and the characterization of nutrient loss and sediment yield under different rainfall types and crop growth stages were not well studied. Therefore, we designed six treatments for sloping farmlands in the Three Gorges Reservoir Area with a field experiment. A field experiment included downslope cultivation with chemical fertilizer (DF), downslope cultivation with chemical fertilizer plus manure (DFM), cross-slope cultivation with chemical fertilizer plus manure (CFM), no-till straw cover with chemical fertilizer plus manure (NSFM), ridge plant hedges with chemical fertilizer plus manure (RFM), and biochar interception ditches with chemical fertilizer plus manure (BFM). The results indicated that soil and water conservation measures in association with manure substitution significantly reduced runoff depth (14.3–22.5 %), sediment yield (10.3–46.5 %), and total nitrogen (TN) loss (13.5–36.5 %) compared to DF. NSFM significantly reduced total phosphorus (TP) loss by 17.4 % and the TP loss from the other treatments did not show significant differences compared to DF. Rainfall intensity and runoff depth were identified as critical factors influencing nutrient loss and soil erosion. NSFM showed maximal nutrient reduction performance under different rainfall intensities, while DFM was not significantly effective. NO3--N and particulate P dominated the loss of TN and TP. The first 30 minutes of runoff generation and the seedling stage were identified as risk periods for N and P loss. The study suggests that the NSFM treatment was the appropriate method to prevent soil and water nutrient loss. This provides important insights for the precise control of nutrient loss and soil erosion on sloping farmlands.

Integrated modelling of fertilizer and climate change scenario impacts on agricultural production and nitrogen losses in Austria

The European Commission's Farm to Fork strategy aims at reducing nutrient losses and fertilizer use, but has been criticized for its expected negative impacts on European economy, agriculture, and food supply. We apply an integrated modelling framework to analyze potential effects of fertilizer reductions on land use, nitrogen losses, and agricultural output of two fertilizer and four climate change scenarios. The fertilizer scenarios comprise a uniform 20 % reduction of mineral N fertilizer (f20) and a combination of several fertilizer restrictions (fcm). The model results indicate that the restrictions in fertilization lead to decreases in crop production of 6 to 9 %, whereas intensive and extensive grassland production increases. N losses to air, water, and soil are substantially reduced by 9 % (f20) and 20 % (fcm), yet fall short of the intended 50 % reduction. The regional heterogeneity of the model results shows that tailored measures need to be elaborated by taking climate change developments, the regional heterogeneity of prevalent farming systems, and bio-physical conditions into account. Uniform measures applied to the national policy context fall short to attain policy targets cost-effectively. N emission capping, taxes or managerial measures such as crop rotational N balancing are options to be explored in future research.

Nitrogen use efficiencies, flows, and losses of typical dairy farming systems in Inner Mongolia

Dairy farming is a notable source of nitrogen (N) emissions, impacting both atmospheric and aquatic ecosystems, thus necessitating a detailed analysis of nutrient dynamics to curtail nutrient wastage. However, N flow variability and its environmental ramifications differ markedly among dairy farms, and a holistic understanding of these differences is lacking in Inner Mongolia, the biggest dairy production province in China. Utilizing data from 187 dairy farms and employing the NUFER-farm model, this study assessed N flows, N use efficiency (NUE), and N losses across four predominant dairy farming systems in Inner Mongolia. These systems include traditional pastoral dairy farms (PF), smallholder dairy farms with croplands (SF), industrial landless farms (IDF), and coupled dairy cattle and cropland-intensive farms (CDF). Our findings indicate considerable differences in N flows, NUE, and losses among the systems. On average, N deposition and N fertilizer were the primary N sources for PF and SF, respectively, whereas IDF and CDF derived over 90% of their N inputs from purchased feeds. PF and SF recycled all available manure N on-farm, whereas IDF and CDF recycled only approximately 36% of the total available manure N. N losses constituted 39–72% of total N outputs, with ammonia emissions accounting for 68–73% of total N losses across all farm types. In particular, PF had a higher N loss per kilogram of dairy product than other systems. Farm-level NUE ranged from 17 to 35%, with manure management practices showing significant variability, underscoring the potential for enhanced strategies to reduce N losses through improved manure treatment.

Combined effects of soil colloid and soil extracellular enzymes on nitrogen loss from sloping farmland

The extracellular enzyme plays a crucial role in nitrogen (N) conversion. Soil colloid serves as an important transporter of N transport in hydrological processes. This study investigated soil colloid-mediated N loss co-transporting with soil extracellular enzymes. Five simulated rainfall experiments were conducted under four tillage treatments in a purple sloping farmland in Sichuan, China. The N concentrations, soil mineral colloids, and four carbon (C), N and phosphorus (P) acquisition extracellular enzymes (βG, AP, NAG, and LAP) in surface runoff and interflow were measured. The results showed that cross-slope tillage with straw returning practices significantly reduced the concentrations of TN, PN, NH4+, and DON in surface runoff. The activities of N and P acquisition enzymes in interflow were higher than in surface runoff, while C acquisition enzymes showed the opposite trend. The BG and AP enzymes dominated in surface runoff, while AP and NAG dominated in interflow. The concentrations of fine soil mineral colloids (SMC, φ<1 μm) and coarse mineral colloids (CMC, φ＞1 μm) in interflow were higher than that in surface runoff. The extracellular enzymes were found to co-transport with soil colloid migration during the hydrologic process. The involvement of colloid in extracellular enzyme migration in surface runoff was primarily due to SMC, while in interflow, it was the joint action of SMC and CMC. Surface runoff is always in N and P limits, while interflow is only in the P limits. With a SEM combined model quantitatively analysis, we found the synergistic transport of soil colloid and extracellular enzymes significantly impacted TN loss, explaining 95 % and 55 % of the differences between surface runoff and interflow N loss pathways. This emphasizes the importance of understanding the co-transport mechanism between soil colloid and extracellular enzymes in N loss processes.

Evaluating the impact of weather forecasts on productivity and environmental footprint of irrigated maize production systems

Integrating weather forecasts into decision support systems empowers farmers to optimise irrigation schedules, thereby boosting crop yields and conserving water. However, inaccurate forecasts can jeopardise productivity and irrigation efficiency. This study combines a crop model with a stochastic pseudo-weather forecast algorithm to: (1) determine the reliability needed in a weather forecast algorithm for effective irrigation management; and (2) assess the impact of weather forecast reliability on the productivity and environmental footprint of various maize cropping systems across diverse climates. It employs the Next Generation of Agricultural Production Systems sIMulator (APSIM NextGen) to simulate maize growth at eleven locations representing diverse climates globally. Various planting schedules, soil types, irrigation systems, and nitrogen availability levels were considered to examine the effects of perfect and imperfect weather forecasts. The findings underscore the potential of integrating weather forecasts into irrigation management for enhanced productivity and sustainability. High-confidence forecasts and longer lead times increase yields (up to 11 %) and improve sustainability outcomes, particularly in wetter climates and for conditions with low nitrogen availability. Conversely, when the accuracy of forecasts is low, forecast-driven irrigation management may lead to yield reductions compared to a baseline system, especially in drier climates (up to 26 % reduction), necessitating tailored management strategies. Soil type and farmer's risk tolerance further influence the effectiveness of forecast-driven irrigation management, emphasising the need for context-specific approaches. By understanding and leveraging the interconnected impacts of weather forecasts on yield, water use efficiency, nitrogen loss, and greenhouse gas emissions, farmers can optimise productivity while minimising environmental impacts.

Pilot scale on-site demonstration and seasonality assessment of nitrogen recovery and water reclamation from pig's slurry liquid fraction

Livestock slurry has gathered significant interest as a secondary raw material for fertilisers industry due to its content on macronutrients -nitrogen, phosphorous, and potassium- and organic carbon. In this study, the performance of an on-site pilot plant composed by microfiltration, membrane-assisted stripping, and reverse osmosis for selective recovery of nitrogen as fertiliser and water reclamation was demonstrated for 2 years in a pig farm, referenced to 8 batches for seasonal assessment. Microfiltration mitigated the seasonal variation in the composition of pig slurry leading to stable process efficiency in the following steps. Membrane-assisted stripping resulted in the recovery of up to 56% of nitrogen as high-purity ammonium sulphate, and up to 42% of reclaimed water as reverse osmosis permeate. The proposed train of technologies reported proper performance and robustness during the whole demonstration period as it resulted in the production of reclaimed water and ammonium sulphate with no significant quality variations. The energy cost for both products obtained in this study was found in the average of the previous works reviewed with 12.49 kWh kg−1 NH3 produced, and 0.37 kWh m−3 of reclaimed water. The environmental assessment showed that nitrogen losses could be reduced by up to 90 kg N ha−1 d−1 by replacing manure spreading with precise fertilisation techniques, enabled by the selective recovery of nitrogen from SLF. Finally, the financial study showed that the scaling up of the proposed train of technologies would result in benefits for farms with more than 1600 pig heads.

Combining abilities and quantitative inheritance of sorgoleone exudation in Sorghum bicolor

AbstractSorghum (Sorghum bicolor) has the ability to inhibit the conversion of ammonium to nitrate (biological nitrification inhibition [BNI]) in the rhizosphere, which in turn prevents the loss of bioavailable nitrogen. Sorgoleone is a lipidic compound secreted by sorghum root hairs and is responsible for roughly 60% of BNI activity in sorghum. Previous studies revealed variation in sorgoleone secretion among different accessions and cultivars. However, little information is available regarding the genetic inheritance of sorgoleone secretion in sorghum. To increase sorgoleone through breeding, an understanding of the inheritance of this trait is required. In this study, 21 seed parents and 21 pollinator parents from the Texas AgriLife Research sorghum breeding program were crossed in an incomplete factorial design to generate 158 hybrids, and sorgoleone secretion from both hybrids and inbreds was quantified. There was significant variation in sorgoleone secretion across hybrids and inbred lines, and small but significant mid‐parent heterosis was observed in the hybrids. A linear mixed model analysis to calculate general and specific combining abilities for inbred parents and hybrids detected significant genetic effects for the male, the female, and male × female interactions (p &lt; 0.001). Broad‐sense heritability was high ( = 0.87), while narrow‐sense heritability for the seed parents and pollinator parents was moderate (= 0.35 and = 0.39, respectively). These results indicate that sorgoleone exudation is primarily driven by additive genetic effects, but dominance effects are important for optimum production. These findings indicate that selection for increased sorgoleone root exudation among elite, adapted grain sorghum hybrids and inbred should be effective.

Innovative approach for assessing nitrogen loss risk to surface waters from crop production in a watershed scale through nitrogen surplus index method

Although various measures are applied to control farmland nitrogen loss at the field scale, effective control strategies at the watershed scale are still lacking due to poor understanding of nitrogen loss risks across different scales. Therefore, an innovative approach to assess the risk of nitrogen loss to surface waters from crop production at the watershed scale was established, with nitrogen surplus, a more accurate indicator, as a major source factor introduced to the traditional index method. Furthermore, this approach was applied in the Baiyangdian Lake Watershed, a typically agricultural-dominated watershed in China, and the control strategies for farmland nitrogen loss reduction were investigated with scenario analysis. The major results included: (1) Areas with high (2–4 for risk to river, 1.6–3.2 for risk to lake) and very high (>4 for risk to river, >3.2 for risk to lake) risks of nitrogen loss in crop production were relatively small. For example, in the wheat-maize rotation system, these areas accounted for only 2.1–3.5 % and 0.9–1.8% of the total study area, respectively. Additionally, the critical source areas of nitrogen loss were concentrated around the receiving water bodies. (2) The nitrogen surplus in wheat season increased the nitrogen loss to surface waters. Compared to the maize season, the area with high and very high risk for nitrogen loss to the nearby river in wheat-maize rotation system increased by 58.3% and 141.4%. Furthermore, the areas with high and very high risk for nitrogen loss to the lake in wheat-maize rotation system were 129.6% and 220.6% more than that during maize season. (3) Nitrogen loss risk to the nearby rivers was correlated with nitrogen surplus, but nitrogen loss risk to the lake was related to the transport coefficient. (4) The optimized scenario for nitrogen loss reduction in crop production was the combination of nitrogen surplus being less than 20 kg/ha and 500 m banning area around the river with no fertilizer application, which reduced the nitrogen loss risk to the nearby river and to the lake by 94–95% and 89–95%. The results of this study provide a scientific basis for nutrient resource management and non-point source pollution control.

Nitrogen reduction enhances crop productivity, decreases soil nitrogen loss and optimize its balance in wheat-maize cropping area of the Loess Plateau, China

In winter wheat-summer maize double cropping, fertilization changes the nitrogen (N) balance in the soil N pool, grain N uptake, N loss, and nitrogen use efficiency (NUE), ultimately impacting crop productivity and environmental health. For agricultural systems to maintain yields at lower environmental costs, N budgets must be balanced. Still, there is a deficiency in the reporting of N budgets of farming systems that incorporate all N flows. We evaluated the effects of various N fertilizer application rates on soil N balance and crop productivity in the 2017–2021 winter wheat-summer maize growing seasons. These rates included non-N fertilization (N0), 75 kg·N·ha−1 (N75), 150 kg·N·ha−1 (N150), 225 kg·N·ha−1 (N225), and conventional N fertilizer application rate, 300 kg·N·ha−1 (N300). Our analysis was based on a long-term field fertilization experiment and in-situ observation (established in 2010). The results show that fertilization significantly increased crop yields (wheat: 29.2 %–97.6 %; maize:25.4 %–98.1 %; annal: 27.0 %–96.7 %), among which N225 showed the highest increase value, compared with N0. Moreover, the N225 maximized grain N uptake by 201.0 %, reducing N losses and increasing N sequestration compared to the conventional N application rate of N300. N balance changes from negative to positive as the N application rate increases (wheat: −63.78–85.24 kg·ha−1; maize: −55.77–82.25 kg·ha−1; annal: −119.58–167.46 kg·ha−1·yr−1). Combining years of N inputs and outputs, the N225 is more balanced. Therefore, our study shows that an appropriate reduction of N fertilizer (N225) can help maintain agricultural productivity and promote N sequestration in farmland by reducing environmental N loss. Maintaining the virtuous cycle of N in the farmland ecosystem is beneficial and essential for the efficient utilization, high yield, and sustainable development of farmland resources.

Reducing soil nitrogen losses from fertilizer use in global maize and wheat production

Reducing soil nitrogen losses from fertilizer use in global maize and wheat production

Modified Slow-Release Urea Fertilizers on Yield and Nitrogen Use Efficiency of Wheat Crop (Triticum aestivum L) for Safe and Sustainable Agricultural System

ABSTRACT Safeguarding the agricultural environment from pollution is one of the most critical challenges facing the world in the context of climate change. The loss of nitrogen fertilizers through agricultural runoff or volatilization in the form of nitrate or ammonia emissions is a significant contributor to pollution. This loss also represents an economic waste that may lead to increased prices of agricultural products. Therefore, finding a solution to this problem has become imperative. An experiment was conducted on wheat plants using various rates of urea coated with slow-release materials. The study aimed to assess the impact of these fertilizers on wheat growth and yield, nutrient uptake, and nitrogen utilization efficiency (NUtE). Results demonstrated that urea fertilizers coated with slow-release materials outperformed conventional fertilizers in terms of wheat growth and yield, uptake of nitrogen, phosphorus, and potassium, as well as NUtE. The most favorable outcomes were achieved using urea-formaldehyde, urea-humic, and urea-biochar fertilizers at 100% of the recommended nitrogen application rate. This resulted in economically viable grain production with high fertilizer efficiency. Based on these findings, we recommend applying either urea-formaldehyde or urea-humic at a rate of 107 kg N ha−1 to produce wheat grain and straw with enhanced NUtE. This approach can help reduce environmental pollution caused by nitrogen losses.

Hydrochloric acid-modified biochar enhances nitrogen retention and microbial diversity in mollisols

The annual decline in the quality of China's mollisols and associated nitrogen loss necessitates effective interventions. This study investigates the effects of hydrochloric acid-modified biochar (BC-H700), derived from corn straw, on nitrogen retention and microbial diversity in mollisols through pot experiments. Through 100 days of continuous study found the application of 6 % BC-H700 significantly improved soil properties, increasing pH by 18.60 %, organic matter by 1.6 %, ammonium nitrogen by 26.96 %, and nitrate nitrogen by 23.04 %. By inquiring impact of BC-H700 on microbial enzyme activities in 60-day revealing BC-H700 also enhanced the activities of key nitrogen-transforming enzymes (AMO, NOR, NOS) and functional genes (nirK, norB, nosZ) while reducing narG gene abundance and NR enzyme activity. These changes indicate that BC-H700 promotes nitrification, inhibits denitrification, enhances nitrogen retention, and reduces N2O emissions. Furthermore, BC-H700 improved microbial diversity, increasing the abundance of beneficial bacteria such as Actinobacteria, Proteobacteria, Nitrospirae, and Gemmatimonadetes. The main environmental factors affecting soil bacterial community structure were identified as organic matter, NO3-, NO2-, AMO, NOR, and NOS. Overall, BC-H700 facilitates nitrogen transformation and retention through complex interactions with soil properties and microbes. This study contributes to understanding biochar's role in soil nitrogen management and offers practical insights for improving mollisol health.

Synergistic effects of biochar and laccase on nitrogen conversation and degradations of two artificial sweeteners during the sewage sludge composting

This study investigates the effects of biochar, laccase, and their combined application on nitrogen transformation, the degradation of sucralose (SUC) and acesulfame (ACE), and the dynamics of bacterial communities during sewage sludge composting. The results indicated that NH3 emissions were reduced by 41.2 %, 17.5%, and 40.8 % in the biochar, laccase, and biochar-laccase treatments, respectively, compared to the control. Meanwhile, N2O emissions decreased significantly by 26.8 % and 16.0 % for the biochar and biochar-laccase treatments, respectively, but increased by 8.1 % for the laccase treatment. Additionally, the biochar, laccase, and biochar-laccase treatments enhanced the degradation of SUC and ACE by 36.6–68.3 % and 49.2–69.8 %, relative to the control, respectively. Network analysis showed that the additive-treatment enhanced the cooperation within bacterial communities, and solidified artificial sweeteners degradation, especially under biochar-laccase application. Phylogenetic investigation of communities by reconstruction of unobserved states further indicated that biochar, laccase, biochar-laccase treatment increased enzymes associated with the degradations of organic matter and artificial sweeteners. In conclusion, it suggested that a combined addition of biochar and laccase was an effectively way to reduce nitrogen loss and promote artificial sweeteners degradations during sewage sludge composting.

Effects of biochar on the transformation and utilization of nitrogen fertilizer in the black soil region of Northeast China

Nitrogen (N) fertilizer is often used in production practice to effectively maintain crop productivity; however, low nitrogen use efficiency (Nue) has always been a problem. Specifically, the transformation and utilization of nitrogen fertilizer by biochar and the driving mechanisms remain unclear. We used four biochar application rates (0, 3750, 7500, and 11,250 kg·ha−1) and analyzed the effects of biochar on nitrogen fertilizer utilization, residue, and loss over three years using 15N isotope tracer technology. The results showed that (1) biochar improved the nitrogen use efficiency of maize plants, reduced total nitrogen loss, and increased the maize yield. Compared to the control treatment in the same year, the application of 7500 kg·ha−1 biochar increased the nitrogen use efficiency by 24.27 %, 27.77 %, and 35.82 %, and the yield increased by 21.1 %, 26.7 %, and 24.5 %, respectively. (2) Biochar increased the proportion of mineral nitrogen supplied by fertilizer in the mineral nitrogen pool. The application of 7500 kg·ha−1 biochar increased mineral nitrogen by 3.05 %, 3.22 %, and 3.8 %, respectively, compared to the control treatments in the same year. Biochar promoted the transformation of nitrogen in the 0–40 cm soil layer to three different soil nitrogen pools, especially the organic nitrogen pool. (3) Biochar significantly improved the soil bacterial community and increased the abundances of N transformation functional genes. The redundancy analysis (RDA) showed that the gdhA mineralization gene was the driving factor of nitrogen fertilizer transformation, contributing 43.6 % of the variance. In summary, the application of 7500 kg·ha−1 of biochar for two consecutive years was conducive to maintaining farmland soil fertility, while its use would not be recommended for more than three consecutive years.

Mitigating soil nitrification and greenhouse gas emissions in non-paddy cropping systems by micro-molar hydrogen peroxide

Non-paddy cropping systems play a significant role in food production. However, excessive nitrogen loss from non-paddy soils through nitrate leaching and ammonia volatilization poses a significant challenge to environmental sustainability. In this study, microcosm and field-scale experiments were conducted to explore the potential for using hydrogen peroxide (H2O2) to mitigate nitrogen loss and greenhouse gas emissions, aiming at filling gaps in knowledge regarding the underlying biochemical mechanisms. The results show that input of micromolar H2O2 from either artificial addition or natural rainwater into soils in the presence of magnetite (Fe3O4) could trigger Fenton-like reaction, which inhibited microbially mediated nitrification of soil-borne ammonium but did not affect the growth of the test crop plant (water spinach). In the absence of Fe3O4, input of rainwater-borne H2O2 into non-paddy soils caused reduction in the emissions of nitrous oxide (N2O) and carbon dioxide (CO2). There was a trend showing that the degree of reduction in N2O and CO2 fluxes increased with increasing concentration of rainwater-borne H2O2. It was likely that microbially mediated reduction of iron oxides took place during rainfall events, providing Fe(II) that is needed for reaction with rainwater-borne H2O2, triggering Fenton-like reaction to inhibit the soil microbes that mediate production of N2O and CO2 in the soils. The findings obtained from this study have implications for developing strategies to manage soil‑nitrogen to minimize its environmental impacts.

Uncovering the spatial characteristics of global net anthropogenic nitrogen input at high resolution and across 1.42 million lake basins

Global Net Anthropogenic Nitrogen Input (NANI) at high resolution is crucial for assessing the impact of human activities on aquatic environments. Insufficient global high-resolution data sources and methods have hindered the effective examination of the global characteristics and driving forces of NANI. This study presents a general framework for calculating global NANI, providing estimates at a 5-arc-minute resolution and over 1.42 million lake basins in 2015. The results highlight the region near the Tropic of Cancer as a concentration area for high NANI and an inflection point for latitude-based accumulation variation. It also emphasizes the uneven distribution of NANI among continents, with Asia and Africa having the highest proportions, yet their high and low values are notably lower than those of Europe and South America. A similar pattern is observed in global lakes, where Asia has the smallest quantity and volume, but the highest NANI intensity. In contrast, North America and Europe have larger quantities and volumes but the lowest NANI intensity. The global distribution characteristics reveal a clustering pattern in high and low values, with 1.25 % of the area having a sum of NANI exceeding 20 %. The uncertainty analysis regarding model parameters indicates that continents with the highest NANI do not always exhibit the highest uncertainty. These results bridge the gap between global nitrogen sustainable management and anthropogenic nitrogen input. They support research on spatiotemporal changes and controlling factors of global river nutrient loads, as well as the impact of climatic factors on basin nitrogen loss and its variability.

Effects of Different Straw Return Modes on Soil Carbon, Nitrogen, and Greenhouse Gas Emissions in the Semiarid Maize Field.

Returning straw to the field is a crucial practice for enhancing soil quality and increasing efficient use of secondary crop products. However, maize straw has a higher carbon-to-nitrogen ratio compared to other crops. This can result in crop nitrogen loss when the straw is returned to the field. Therefore, it is crucial to explore how different methods of straw return affect maize (Zea mays L.) farmland. In this study, a field experiment was performed with three treatments (I, no straw returned, CK; II, direct straw return, SR; and III, straw returned in deep furrows, ISR) to explore the effects of the different straw return modes on soil carbon and nitrogen content and greenhouse gas emissions. The results indicated that the SR and ISR treatments increased the dissolved organic carbon (DOC) content in the topsoil (0-15 cm). Additionally, the ISR treatment boosted the contents of total nitrogen (TN), nitrate nitrogen (NO3--N), ammonium nitrogen (NH4+-N), dissolved organic nitrogen (DON), and DOC in the subsurface soil (15-30 cm) compared with CK. When it comes to greenhouse gas emissions, the ISR treatment led to an increase in CO2 emissions. However, SR and ISR reduced N2O emissions, with ISR showing a more pronounced reduction. The ISR treatment significantly increased leaf and grain biomass compared to CK and SR. The correlation analyses showed that the yield was positively correlated with soil DOC, and soil greenhouse gas emission was correlated with soil NO3--N. The ISR technology has great potential in sequestering soil organic matter, improving soil fertility, and realizing sustainable agricultural development.