Modeling global oceanic nitrogen deposition from food systems and its mitigation potential by reducing overuse of fertilizers.

Growing population and consumption pose unprecedented demands on food production. However, ammonia emissions mainly from food systems increase oceanic nitrogen deposition contributing to eutrophication. Here, we developed a long-term oceanic nitrogen deposition dataset (1970 to 2018) with updated ammonia emissions from food systems, evaluated the impact of ammonia emissions on oceanic nitrogen deposition patterns, and discussed the potential impact of nitrogen fertilizer overuse. Based on the chemical transport modeling approach, oceanic ammonia-related nitrogen deposition increased by 89% globally between 1970 and 2018, and now, it exceeds oxidized nitrogen deposition by over 20% in coastal regions including China Sea, India Coastal, and Northeastern Atlantic Shelves. Approximately 38% of agricultural nitrogen fertilizer was excessive, which corresponds to 15% of global oceanic ammonia-related nitrogen deposition. Policymakers and water quality managers need to pay increasingly more attention to ammonia associated with food production if the goal of reducing coastal nitrogen pollution is to be achieved for Sustainable Development Goals.

Optimized nitrogen application ameliorates the photosynthetic performance and yield potential in peanuts as revealed by OJIP chlorophyll fluorescence kinetics.

BACKGROUND: Nitrogen (N) is a crucial element for increasing photosynthesis and crop yields. The study aims to evaluate the photosynthetic regulation and yield formation mechanisms of different nodulating peanut varieties with N fertilizer application. METHOD: The present work explored the effect of N fertilizer application rates (N0, N45, N105, and N165) on the photosynthetic characteristics, chlorophyll fluorescence characteristics, dry matter, N accumulation, and yield of four peanut varieties. RESULTS: The results showed that N application increased the photosynthetic capacity, dry matter, N accumulation, and yield of peanuts. The measurement of chlorophyll a fluorescence revealed that the K-phase, J-phase, and I-phase from the OJIP curve decreased under N105 treatment compared with N0, and WOI, ET0/CSM, RE0/CSM, ET0/RC, RE0/RC, φPo, φEo, φRo, and Ψ0 increased, whereas VJ, VI, WK, ABS/RC, TR0/RC, DI0/RC, and φDo decreased. Meanwhile, the photosystem activity and electron transfer efficiency of nodulating peanut varieties decreased with an increase in N (N165). However, the photosynthetic capacity and yield of the non-nodulating peanut variety, which highly depended on N fertilizer, increased with an increase in N. CONCLUSION: Optimized N application (N105) increased the activity of the photosystem II (PSII) reaction center, improved the electron and energy transfer performance in the photosynthetic electron transport chain, and reduced the energy dissipation of leaves in nodulating peanut varieties, which is conducive to improving the yield. Nevertheless, high N (N165) had a positive effect on the photosystem and yield of non-nodulating peanut. The results provide highly valuable guidance for optimizing peanut N management and cultivation measures.

Soil N2 O emissions from specialty crop systems: A global estimation and meta-analysis.

Nitrous oxide (N2 O) exacerbates the greenhouse effect and thus global warming. Agricultural management practices, especially the use of nitrogen (N) fertilizers and irrigation, increase soil N2 O emissions. As a vital sector of global agriculture, specialty crop systems usually require intensive input and management. However, soil N2 O emissions from global specialty crop systems have not been comprehensively evaluated. Here, we synthesized 1137 observations from 114 published studies, conducted a meta-analysis to evaluate the effects of agricultural management and environmental factors on soil N2 O emissions, and estimated global soil N2 O emissions from specialty crop systems. The estimated global N2 O emission from specialty crop soils was 1.5 Tg N2 O-N year-1 , ranging from 0.5 to 4.5 Tg N2 O-N year-1 . Globally, soil N2 O emissions exponentially increased with N fertilizer rates. The effect size of N fertilizer on soil N2 O emissions generally increased with mean annual temperature, mean annual precipitation, and soil organic carbon concentration but decreased with soil pH. Global climate change will further intensify the effect of N fertilizer on soil N2 O emissions. Drip irrigation, fertigation, and reduced tillage can be used as essential strategies to reduce soil N2 O emissions and increase crop yields. Deficit irrigation and non-legume cover crop can reduce soil N2 O emissions but may also lower crop yields. Biochar may have a relatively limited effect on reducing soil N2 O emissions but be effective in increasing crop yields. Our study points toward effective management strategies that have substantial potential for reducing N2 O emissions from global agricultural soils.

Reducing Soil-Emitted Nitrous Acid as a Feasible Strategy for Tackling Ozone Pollution.

Severe ozone (O3) pollution has been a major air quality issue and affects environmental sustainability in China. Conventional mitigation strategies focusing on reducing volatile organic compounds and nitrogen oxides (NOx) remain complex and challenging. Here, through field flux measurements and laboratory simulations, we observe substantial nitrous acid (HONO) emissions (FHONO) enhanced by nitrogen fertilizer application at an agricultural site. The observed FHONO significantly improves model performance in predicting atmospheric HONO and leads to regional O3 increases by 37%. We also demonstrate the significant potential of nitrification inhibitors in reducing emissions of reactive nitrogen, including HONO and NOx, by as much as 90%, as well as greenhouse gases like nitrous oxide by up to 60%. Our findings introduce a feasible concept for mitigating O3 pollution: reducing soil HONO emissions. Hence, this study has important implications for policy decisions related to the control of O3 pollution and climate change.

Tracking Carbon and Ammonia Emission Flows of China's Nitrogen Fertilizer System: Implications for Domestic and International Trade.

China is the world's largest producer, consumer, and exporter of synthetic nitrogen (N) fertilizer. To assess the impact of domestic demand and international exports, we quantified the life-cycle CO2eq and ammonia (NH3) emissions by tracking carbon (C) and nitrogen (N) flows from coal/gas mining through ammonia production to N fertilizer production, application, and export. In 2020, China's N fertilizer system emitted 496.04 Tg of CO2eq and 3.74 Tg of NH3, with ammonia production and N fertilizer application processes contributing 36 and 85% of the life-cycle CO2eq and NH3 emissions, respectively. As the largest importers of N fertilizer, India, Myanmar, South Korea, Malaysia, and the Philippines collectively shifted 112.41 Tg of CO2eq. For every ton of N fertilizer produced and used in China, 16 t of CO2eq and 0.18 t of NH3 were emitted, compared to 9.7 t of CO2eq and 0.13 t of NH3 in Europe. By adopting currently available technologies, improving N fertilizer utilization efficiency and employing nitrification inhibitors could synergistically reduce CO2eq emissions by 20% and NH3 emissions by 75%, while energy transformation efforts would primarily reduce CO2eq emissions by 59%. The production of ammonia using green electricity or green hydrogen could significantly enhance the decarbonization of China's N fertilizer system.

Effect of composite organic amendment on Cd(II) ions stabilization and microbial activity under various ammonium sulfate levels.

To attenuate the risk of Cadmium(Cd) contamination and the deterioration of soil quality caused by excessive nitrogen fertilizer application in greenhouse, a composite organic amendment (spend mushroom substrate and its biochar) was prepared to remedy Cd(II) ions contaminated soil (0.6 mg/kg) under different N fertilizer levels. The results showed that in the absence of a composite organic amendment, the soil pH decreased by 0.15 when the N level increased from 0.1 to 0.8 g N⋅kg-1. However, the pH increased by 0.86-0.91, the exchangeable Cd(II) ions content decreased by 26.0%-26.7%, the microbial biomass increased by 34.34%-164.46%, and the number of copies of the AOB gene increased by 13-20 times with the application of composite organic amendment and the increase of N level. Both Pearson correlation analysis and Mantel test demonstrated the reduction in Cd(II) ions availability, the restoration of soil properties and the increase in microbial biomass all contributed to the composite organic amendment, which is of importance for soil remediation under excessive N fertilizer.

Regulating Leaf Photosynthesis and Soil Microorganisms through Controlled-Release Nitrogen Fertilizer Can Effectively Alleviate the Stress of Elevated Ambient Ozone on Winter Wheat.

The mitigation mechanisms of a kind of controlled-release nitrogen fertilizer (sulfur-coated controlled-release nitrogen fertilizer, SCNF) in response to O3 stress on a winter wheat (Triticum aestivum L.) variety (Nongmai-88) were studied in crop physiology and soil biology through the ozone-free-air controlled enrichment (O3-FACE) simulation platform and soil microbial metagenomics. The results showed that SCNF could not delay the O3-induced leaf senescence of winter wheat but could enhance the leaf size and photosynthetic function of flag leaves, increase the accumulation of nutrient elements, and lay the foundation for yield by regulating the release rate of nitrogen (N). By regulating the soil environment, SCNF could maintain the diversity and stability of soil bacterial and archaeal communities, but there was no obvious interaction with the soil fungal community. By alleviating the inhibition effects of O3 on N-cycling-related genes (ko00910) of soil microorganisms, SCNF improved the activities of related enzymes and might have great potential in improving soil N retention. The results demonstrated the ability of SCNF to improve leaf photosynthetic function and increase crop yield under O3-polluted conditions in the farmland ecosystem, which may become an effective nitrogen fertilizer management measure to cope with the elevated ambient O3 and achieve sustainable production.

Effects of straw returning combined with blended controlled-release urea fertilizer on crop yields, greenhouse gas emissions, and net ecosystem economic benefits: A nine-year field trial.

Although straw returning combined with blended controlled-release urea fertilizer (BUFS) has been shown to improve wheat-maize rotation system productivity, their effects on greenhouse gas (GHG) emissions, carbon footprints (CF), and net ecosystem economic benefits (NEEB) are still unknown. Life cycle assessment was used to investigate a long-term (2013-2022) wheat-maize rotation experiment that included straw combined with two N fertilizer types [BUFS and (conventional urea fertilizer) CUFS] and straw-free treatments (BUF and CUF). The results showed that BUFS and CUFS treatments increased the annual yield by 13.8% and 11.5%, respectively, compared to BUF and CUF treatments. The BUFS treatment increased the yearly yield by 13.8% compared to the CUFS treatment. Since BUFS and CUFS treatments increased soil organic carbon (SOC) sink sequestration by 25.0% and 27.0% compared to BUF and CUF treatments, they reduced annual GHG emissions by 7.1% and 4.7% and CF per unit of yield (CFY) by 13.7% and 9.6%, respectively. BUFS treatment also increased SOC sink sequestration by 20.3%, reduced GHG emissions by 10.7% and CFY by 23.0% compared to CUFS treatment. It is worth noting that the BUFS and CUFS treatments increased the annual ecological costs by 41.6%, 26.9%, and health costs by 70.1% and 46.7% compared to the BUF and CUF treatments, but also increased the net yield benefits by 9.8%, 6.8%, and the soil nutrient cycling values by 29.2%, 27.3%, and finally improved the NEEB by 10.1%, 7.3%, respectively. Similar results were obtained for the BUFS treatment compared to the CUFS treatment, ultimately improving the NEEB by 23.1%. Based on assessing yield, GHG emissions, CF, and NEEB indicators, the BUFS treatment is recommended as an ideal agricultural fertilization model to promote sustainable and clean production in the wheat-maize rotation system and to protect the agroecological environment.

Optimizing fertilizer usage for source reduction of salt and fluoride ion runoff discharge from a soda saline-alkali paddy field.

Planting rice is a beneficial strategy for improving soda saline-alkali soil, but it comes with the challenge of increased runoff discharge of salt and fluoride (F-) ions. The use of different nitrogen (N) fertilizers can impact this ion discharge, yet the specific characteristics of ion runoff under different N-fertilizer applications remain unclear. A field experiment was conducted in this study, applying five commonly used N-fertilizer types to monitor the ion runoff throughout an entire rice growing season. Salt ions and F- runoff discharge was significantly affected by N-fertilizer type, runoff event, and their interaction (p < 0.001). Regardless of N-fertilizer types, sodium (Na+) and bicarbonate (HCO3-) ions were consistently discharged from runoff in soda saline-alkali fields, constituting 20.55-25.06 % and 47.57-50.49 % of total ion discharges, respectively. Compared to no N-fertilizer (CK) and other N-fertilizer treatments, the organic-inorganic compound fertilizer (OCF) application significantly reduced Na+ and HCO3- runoff discharge, causing a decrease in the competitive adsorption capacity between HCO3- and F- (p < 0.05). The use of OCF and inorganic compound fertilizer (ICF) lowered pH in runoff water, resulting in reduced dissolution capacity of calcium fluoride in the soil and thereby decreasing total F- runoff discharge. In conclusion, OCF proves to be an effective N-fertilizer in mitigating salt ions and F- runoff discharge in soda saline-alkali paddy fields. Additionally, ICF demonstrates the ability to control F- runoff discharge.

Effect of nitrogen fertilizer on the quality traits of Indica rice with different amylose contents.

BACKGROUND: Nitrogen is a key factor affecting the quality of rice. Studying the impact of nitrogen fertilizer on the taste, physicochemical properties, and starch structure of Indica rice with different amylose contents is of great significance for scientifically fertilizing and cultivating high-quality rice varieties for consumption. RESULTS: The results indicate that increasing nitrogen fertilizer application reduces the amylose content and increases the protein content, resulting in a decrease in taste quality. Simultaneously, it reduces the intergranular porosity of starch particles, improving the appearance and milling quality of rice. Compared to the N1 treatment (nitrogen fertilizer application rate of 90 kg ha-1), the taste of low-amylose rice (Yixiangyou 2115) and high-amylose rice (Byou 268) decreased by 14.24% and 19.79%, respectively, under N4 treatment (nitrogen fertilizer application rate of 270 kg ha-1). The effect of nitrogen fertilizer on low-amylose rice is mainly reflected in increased rice hardness, enthalpy value, and setback viscosity, resulting in a decline in taste. The effect of nitrogen fertilizer on high-amylose rice is mainly reflected in a decrease in peak viscosity, an increase in gelatinization temperature, and crystallinity under high nitrogen levels. CONCLUSION: Increasing nitrogen fertilizer application can improve the appearance and milling quality of rice, but it also leads to an increase in protein content, hardness, gelatinization enthalpy, decrease in breakdown value, and a decline in palatability. In practical production, different production measures should be taken according to different production goals. © 2024 Society of Chemical Industry.

Changes in the lodging resistance of winter wheat from 1950s to the 2020s in Henan Province of China.

BACKGROUND: Lodging is a major factor contributing to yield loss and constraining the mechanical harvesting of wheat crops. Genetic improvement through breeding effectively reduced the lodging and improved the grain yield, however, the physiological mechanisms involved in providing resistance to lodging are different in the breeding stage and are not clearly understood. The purpose of this study was to compare the differences in the lodging resistance (LR) of the wheat varieties released during the different decades and to explore the effect of the application of nitrogen (N) fertilizer on the plasticity of LR. RESULTS: A field study was conducted during the cultivation seasons of 2019-2020 and 2020-2021, in soil supplemented with three N levels: N0 (0 kg ha-1), N180 (200 kg ha-1), and N360 (360 kg ha-1) using eight varieties of wheat released for commercial cultivation from 1950 to date. The results obtained showed that genetic improvement had significantly enhanced the LR and grain yield in wheat. In the first breeding stage (from 1950 to 1980s) the lodging resistant index increased by 15.0%, which was primarily attributed to a reduced plant height and increased contents of cellulose, Si, and Zn. In the second breeding stage (the 1990s-2020s) it increased by 172.8%, which was mainly attributed to an increase in the stem diameter, wall thickness, and the contents of K, Ca, Fe, Mn, and Cu. The application of N fertilizer improved the grain yield but reduced the LR in wheat. This was mainly due to an increase in plant height resulting in an elevation of the plant center of gravity, a decrease in the contents of cellulose, and a reduction in the area of large-sized vascular bundles in the stems, even if N supplementation increased the concentrations of K, Ca, and Si. CONCLUSION: Although breeding strategies improved the stem strength, the trade-off between the grain yield and LR was more significantly influenced by the addition of N. Overcoming this peculiar situation will serve as a breakthrough in improving the seed yield in wheat crops in the future.

Molecular Mechanism and Agricultural Application of the NifA-NifL System for Nitrogen Fixation.

Nitrogen-fixing bacteria execute biological nitrogen fixation through nitrogenase, converting inert dinitrogen (N2) in the atmosphere into bioavailable nitrogen. Elaborating the molecular mechanisms of orderly and efficient biological nitrogen fixation and applying them to agricultural production can alleviate the "nitrogen problem". Azotobacter vinelandii is a well-established model bacterium for studying nitrogen fixation, utilizing nitrogenase encoded by the nif gene cluster to fix nitrogen. In Azotobacter vinelandii, the NifA-NifL system fine-tunes the nif gene cluster transcription by sensing the redox signals and energy status, then modulating nitrogen fixation. In this manuscript, we investigate the transcriptional regulation mechanism of the nif gene in autogenous nitrogen-fixing bacteria. We discuss how autogenous nitrogen fixation can better be integrated into agriculture, providing preliminary comprehensive data for the study of autogenous nitrogen-fixing regulation.

Biochar combined with different nitrogen fertilization rates increased crop yield and greenhouse gas emissions in a rapeseed-soybean rotation system.

Biochar as agricultural soil amendment has been extensively investigated for its potential to sequester carbon, to mitigate greenhouse gases (GHGs) emissions, to enhance soil fertility and enhance crop yields. In this study, we investigated the impact of varying N fertilization rates in conjunction with biochar on soil properties, crop yield, and GHGs emissions in a rapeseed (Brassica napus L.)-soybean (Glycine max (L.) Merrill) rotation system for one year. Biochar and N fertilizer were applied following a factorial combination design of three biochar (B0: 0 t hm-2, B1: 15 t hm-2, and B2: 60 t hm-2) and three N fertilizer application rates (H: 100%, M: 75%, and L: 50% of the conventional application rates). In general, there was no significant effect of N fertilizer and its interaction with biochar application on soil water content, pH, and total carbon content, but the addition of biochar significantly increased these parameters (P < 0.05). The yield of both crops were significantly augmented by biochar up to 75% compared to using N fertilization alone, potentially due to enhanced N use efficiency. However, biochar significantly increased the cumulative N2O and CH4 emissions by as much as 2.2 times and 19 times, respectively, during the rapeseed season, thereby elevating the global warming potential (GWP) and the yield-scaled GWP. Nevertheless, the significantly increased soil carbon content following biochar addition might boost soil carbon sequestration, which could counterbalance the escalating GWP induced by GHGs. Therefore, we recommend a comprehensive and long-term evaluation of biochar's impact by considering crop yield, GHGs emissions, and carbon sequestration in agricultural systems to ensure sustainable agricultural management.

Effect of co-application of straw and various nitrogen fertilizers on N2O emission in acid soil.

In order to explore the alteration of N transformation and N2O emissions in acid soil with the co-application of straw and different types of nitrogen (N) fertilizers, an incubation experiment was carried out for 40 days. There are totally five treatments in the study: (a) without straw and N fertilizer (N0), (b) straw alone application (SN0), (c) straw with NH4Cl (SN1), (d) straw with NaNO3 (SN2), and (e) straw with NH4NO3 (SN3). N2O emissions, soil physicochemical properties, and abundance/activity of ammonia-oxidizing archaea (AOA) were measured. The results showed that the combined application of straw and N enhanced N2O emissions, particularly, SN2 and SN3 treatments. Moreover, the soil pH was lower in co-application treatments and the average decreasing rate was 9.69%. Specially, the pH was lowest in the SN1 treatment. The results of correlation analysis indicated a markedly negative relationship between pH and N2O, as well as a negative relationship between pH and net mineralization rate. These findings suggest that pH alteration can affect the N transformation process in soil and thus influence N2O emissions. In addition, the dominant AOA at the genus level in the SN2 treatment was Nitrosopumilus, and Candidatus nitrosocosmicus in the SN3 treatment. The reshaped AOA structure can serve as additional evidence of the changes in the N transformation process. In conclusion, as the return of straw, the cumulation of N2O from arable acid soil depends on the form of N fertilizer. It is also important to consider how N fertilizer is applied to reduce the possibility of N being lost in the soil as gas.

Insight into mechanisms of biochar-fertilizer induced of microbial community and microbiology of nitrogen cycle in acidic soil.

Biochar has been shown to affect the nitrogen (N) cycle in soil, however, it is unknown how this occurs. Therefore, we used metabolomics, high-throughput sequencing, and quantitative PCR to explore biochar and nitrogen fertilizer effects on the mitigation mechanisms of adverse environments in acidic soil. In the current research, we used acidic soil and maize straw biochar (pyrolyzed at 400 °C with limited oxygen). Three maize straw biochar levels (B1; 0t ha-1, B2; 45 t ha-1, and B3; 90 t ha-1) along with three N fertilizer (urea) levels (N1; 0 kg ha-1, N2; 225 kg ha-1 mg kg-1, and N3; 450 kg ha-1 mg kg-1) were employed in a sixty-day pot experiment. We found that the formation of NH+ 4-N was faster at 0-10 days, while the formation of NO- 3-N occurred at 20-35 days. Furthermore, the combined application of biochar and N fertilizer most effectively boosted soil inorganic N contents compared to biochar and N fertilizer treatments alone. The B3 treatment increased the total N and total inorganic N by 0.2-24.2% and 55.2-91.7%, respectively. Soil microorganism, N fixation, and nitrification capabilities increased with biochar and N fertilizer addition in terms of N-cycling-functional genes. Biochar-N fertilizer had a greater impact on the soil bacterial community and their diversity and richness. Metabolomics revealed 756 distinct metabolites, including 8 substantially upregulated metabolites and 21 significantly downregulated metabolites. A significant amount of lipids and organic acids were formed by biochar-N fertilizer treatments. Thus, biochar and N fertilizer triggered soil metabolism by affecting bacterial community structure, and N-cycling of the soil micro-ecological environment.

Study on N application and N reduction potential of farmland in China.

The frequent occurrence of extreme weather in recent years poses a significant threat to food production. Ensuring food production and rationalizing the use of agricultural resources require addressing the problem of the improper application of chemical fertilizers. Several effective measures have been implemented in China to reduce agricultural non-point source pollution. Among them, the reduction of excessive nitrogen fertilizer application proves to be the most effective approach in controlling surface pollution from cultivation. Currently, it is crucial to clarify and quantify crop nutrient fertilizer requirements while evaluating the potential for reducing nitrogen fertilizer usage in China. Nitrogen requirements for major crops grown in China were assessed based on the theory of crop nutrient balance, assuming constant grain production as a guarantee. In this paper, we analyze the potential for nitrogen reduction through short-term, medium-term, and long-term scenario predictions. The results show that in the next 3 years, China has a reduction potential of 34.98%, but this potential is not sustainable. Over the next 10 years, there is a reduction potential of 15.04%, with most provinces experiencing a balanced state of soil nitrogen cycling. Hainan, Beijing, Shaanxi, and Fujian have higher reduction potential, with possible reductions of 69.95%, 64.14%, 60.72%, and 54.10%, respectively. However, there are still provinces in China where nitrogen fertilizer is insufficient, leading to soil nitrogen consumption. Specifically, Heilongjiang, Jiangxi, and Shandong Provinces need to increase their nitrogen fertilizer applications by 87.00%, 35.97%, and 8.31%, respectively. The long-term scenario analysis over the next 30 years shows a reduction potential of 40.96%. Among the regions analyzed, Hainan, Beijing, Shaanxi, Fujian, and Ningxia have higher nitrogen fertilizer reduction potentials, with values of 78.97%, 78.48%, 74.25%, 67.87%, and 67.72%, respectively. However, Heilongjiang Province still needs to increase nitrogen fertilizer application by 44.20% to address soil nitrogen depletion. Conversely, Tibet and Qinghai, with high organic fertilizer yields, lower chemical fertilizer usage, and low nitrogen loss coefficients, are well-suited for organic agriculture development. For areas with high organic fertilizers usage and a risk of fertilizer loss, we recommend implementing the organic-inorganic mixed fertilization planting mode.

Arbuscular Mycorrhizae Shift Community Composition of N-Cycling Microbes and Suppress Soil N2O Emission.

Mycorrhizae are ubiquitous symbiotic associations between arbuscular mycorrhizal fungi (AMF) and terrestrial plants, in which AMF receive photosynthates from and acquire soil nutrients for their host plants. Plant uptake of soil nitrogen (N) reduces N substrate for microbial processes that generate nitrous oxide (N2O), a potent greenhouse gas. However, the underlying microbial mechanisms remain poorly understood, particularly in agroecosystems with high reactive N inputs. We examined how plant roots and AMF affect N2O emissions, N2O-producing (nirK and nirS) and N2O-consuming (nosZ) microbes under normal and high N inputs in conventional (CONV) and organically managed (OM) soils. Here, we show that high N input increased soil N2O emissions and the ratio of nirK to nirS microbes. Roots and AMF did not affect the (nirK + nirS)/nosZ ratio but significantly reduced N2O emissions and the nirK/nirS ratio. They reduced the nirK/nirS ratio by reducing nirK-Rhodobacterales but increasing nirS-Rhodocyclales in the CONV soil while decreasing nirK-Burkholderiales but increasing nirS-Rhizobiales in the OM soil. Our results indicate that plant roots and AMF reduced N2O emission directly by reducing soil N and indirectly through shifting the community composition of N2O-producing microbes in N-enriched agroecosystems, suggesting that harnessing the rhizosphere microbiome through agricultural management might offer additional potential for N2O emission mitigation.

Effects of nitrogen reduction combined with organic fertilizer on growth and nitrogen fate in banana at seedling stage.

Nitrogen reduction combined with organic fertilizer is of considerable significance for the sustainable development of agriculture. A pot experiment using nitrogen reduction combined with organic fertilizer was conducted to explore the effects of different treatments on matter accumulation, physiological resistance, and fertilizer nitrogen fate in banana seedlings. Compared with conventional fertilization, a 20% reduction of nitrogen did not affect the dry weight, chlorophyll content, physiological resistance, and fertilizer utilization rate of banana seedlings, but significantly reduced the nitrogen leaching loss and increased the nitrogen soil residue. Compared with conventional fertilization, organic nitrogen substituting 20% or 30% of the nitrogen reduced by 20% significantly promoted dry matter accumulation and physiological resistance. Organic nitrogen substituting 30% of the 20% reduction of nitrogen increased the dry matter of the whole plant by 24.94%, the nitrogen uptake in the root by 30.87%, the chlorophyll content by 6.05%, the soluble sugar content by 16.88%, Peroxidase (POD) activity by 26.35%, Catalase (CAT) activity by 27.48%, and Super Oxide Dismutase (SOD) activity by 22.97%. Compared with conventional fertilization, all organic substitution treatments significantly reduced fertilizer nitrogen leaching loss, apparent loss, and increased nitrogen soil residue. Compared with the 20% reduction of nitrogen, organic nitrogen substituting 30% of the 20% reduction of nitrogen significantly increased nitrogen utilization by 16.34% and soil residue rate by 13.26%, and reduced nitrogen leaching loss by 35.46%. The results of the present study revealed that a 20% reduction of nitrogen fertilizer with a 30% organic substitution application promoted matter accumulation, enhanced the physiological resistance of banana seedlings, increased the utilization and residue of nitrogen fertilizer, and reduced nitrogen pollution.

Effects of Nitrogen Fertilizer on Quality Characteristics of Wheat with the Absence of Different Individual High-Molecular-Weight Glutenin Subunits (HMW-GSs).

High-molecular-weight glutenin subunits (HMW-GSs) are important components of gluten, which determine the grain quality of wheat. In this study, we investigated the effects of nitrogen (N) fertilizer application on the synthesis and accumulation of grain protein and gluten quality in wheat lines with different HMW-GSs absent. The results showed that the absence of the HMW-GS in the wheat variety Ningmai 9 significantly decreased the contents of gluten, glutenin macropolymer (GMP), protein compositions, HMW-GS and HMW-GS/LMW-GS. The reduction in glutenins was compensated to some extent by an increase of gliadins. The absence of x-type HMW-GSs (1, 7 and 2 subunits) had a greater effect on gluten and GMP properties than y-type HMW-GSs (8 and 12 subunits). The content of protein compositions, gluten and GMP increased with an increase of N level; however, the increment in wheat lines with the absence of HMW-GS, especially in Ax1a, Bx7a and Dx2a, was lower than that in the wild type under various N levels. The expression level of genes encoding HMW-GSs, and activities of nitrate reductase (NR) and glutamine synthetase (GS), differed significantly among the investigated wheat lines. The reduction in gene expression and activities in Ax1a and Dx2a may account for the reductions in gluten, GMP, protein compositions, HMW-GS and HMW-GS/LMW-GS.

Reduced nitrogen fertilization under flooded conditions cut down soil N2O and CO2 efflux: An incubation experiment.

Unreasonable water (W) and inorganic nitrogen (N) fertilization cause an intensification of soil greenhouse gas (GHGs) emissions. W-N interactions (W × N) patterns can maximise the regulation of soil GHGs efflux through the rational matching of W and N fertilization factors. However, the effects of W × N patterns on soil GHGs efflux and the underlying mechanism remain unclear. In this study, urea fertilizers were applied to paddy soils in a gradient of 100 (N100), 80 (N80), and 60 mg kg-1 (N60) concentrations. Flooding (W1) and 60% field holding capacity (W2) was set for each N fertilizer application to observe the effects of W × N patterns on soil properties and GHGs efflux through incubation experiments. The results showed that W significantly affected soil electrical conductivity and different N forms (i.e., alkali hydrolyzed N, ammonium N, nitrate N and microbial biomass N) contents. Soil organic carbon (C) content was reduced by 14.40% in W1N60 relative to W1N100, whereas microbial biomass C content was increased by 26.87%. Moreover, soil methane (CH4) fluxes were low in all treatments, with a range of 1.60-1.65 µg CH4 kg-1. Soil nitrous oxide (N2O) and carbon dioxide (CO2) fluxes were significantly influenced by W, N and W × N. Global warming potential was maintained at the lowest level in W1N60 treatment at 0.67 g CO2-eq kg-1, suggesting W1N60 as the preferred W × N pattern with high environmental impact. Our findings demonstrate that reduced N fertilization contributes to the effective mitigation of soil N2O and CO2 efflux by lowering the soil total N and organic C contents and regulating soil microbial biomass C and N.