Responses of crop productivity and reactive nitrogen losses to the application of animal manure to China's main crops: A meta-analysis

Nitrous oxide (N2O) emission characteristics of farmland (rice, wheat, and maize) based on different fertilization strategies

Fertilizer application is the basis for ensuring high yield, high quality and high efficiency of farmland. In order to meet the demand for food with the increasing of population, the application of nitrogen fertilizer will be further increased, which will lead to problems such as N2O emission and nitrogen loss from farmland, it will easily deteriorate the soil and water environment of farmland, and will not conducive to the sustainable development of modern agriculture. However, optimizing fertilizer management is an important way to solve this problem. While, due to the differences in the study conditions (geographical location, environmental conditions, experimental design, etc.), leading to the results obtained in the literatures about the N2O emission with different nitrogen fertilizer application strategies have significant differences, which requiring further comprehensive quantitative analysis. Therefore, we analyzed the effects of nitrogen fertilizer application strategies (different fertilizer types and fertilizer application rates) on N2O emissions from the fields (rice, wheat and maize) based on the Meta-analysis using 67 published studies (including 1289 comparisons). For the three crops, inorganic fertilizer application significantly increased on-farm N2O emissions by 19.7-101.05% for all three; and organic fertilizer increased N2O emissions by 28.16% and 69.44% in wheat and maize fields, respectively, but the application of organic fertilizer in rice field significantly reduced N2O emissions by 58.1%. The results showed that overall, the application of inorganic fertilizers resulted in higher N2O emissions from farmland compared to the application of organic fertilizers. In addition, in this study, the average annual temperature, annual precipitation, soil type, pH, soil total nitrogen content, soil organic carbon content, and soil bulk weight were used as the main influencing factors of N2O emission under nitrogen fertilizer strategies, and the results of the study can provide a reference for the development of integrated management measures to control greenhouse gas emissions from agricultural soils.

Manure replacing synthetic fertilizer improves crop yield sustainability and reduces carbon footprint under winter wheat-summer maize cropping system

Manure replacing synthetic fertilizer is a viable practice to ensure crop yield and increase soil organic carbon (SOC), but its impact on greenhouse gas (GHG) emissions is inconsistent, thus remains its effect on CF unclear. In this study, a 7-year field experiment was conducted to assess the impact of replacing synthetic fertilizer with manure on crop productivity, SOC sequestration, GHG emissions and crop CF under winter wheat-summer maize cropping system. Five treatments were involved: synthetic nitrogen, phosphorus, and potassium fertilizer (NPK) and 25%, 50%, 75%, and 100% of manure replacing synthetic N (25%M, 50%M, 75%M, and 100%M). Compared with NPK treatment, 25%M and 50%M treatments maintained annual yield (winter wheat plus summer maize) and sustainable yield index (SYI), but 75%M and 100%M treatments significantly decreased annual yield, and 100%M treatment also significantly reduced annual SYI. The SOC content exhibited a significant increasing trend over years in all treatments. After 7 years, SOC storage in manure treatments increased by 3.06-11.82 Mg ha-1 relative to NPK treatment. Manure treatments reduced annual GHG emissions by 14%-60% over NPK treatment. The CF of the cropping system ranged from 0.16 to 0.39 kg CO2 eq kg-1 of grain without considering SOC sequestration, in which the CF of manure treatments lowered by 18%-58% relative to NPK treatment. When SOC sequestration was involved in, the CF varied from -0.39 to 0.37 kg CO2 eq kg-1 of grain, manure treatments significantly reduced the CF by 22%-208% over NPK treatment. It was concluded that replacing 50% of synthetic fertilizer with manure was a sound option for achieving high crop yield and SYI but low CF under the tested cropping system.

Effects of the three amendments on NH3 volatilization, N2O emissions, and nitrification at four salinity levels: An indoor experiment

The marked salinity and alkaline pH of coastal saline soil profoundly impact the nitrogen conversion process, leading to a significantly reduced nitrogen utilization efficiency and substantial gaseous nitrogen loss. The application of soil amendments (e.g. biochar, manure, and gypsum) was proved to be effective for the remediation of saline soils. However, the effects of the three amendments on soil nitrogen transformation in soils with various salinity levels, especially on NH3 volatilization and N2O emission, remain elusive. Here, we reported the effects of biochar, manure, and gypsum on NH3 volatilization and N2O emission under four natural salinity gradients in the Yellow River Delta. Also, high-throughput sequencing and qPCR analysis were performed to characterize the response of nitrification (amoA) and denitrification (nirS, nirK, and nosZ) functional genes to the three amendments. The results showed that the three amendments had little effect on NH3 volatilization in low- and moderate-salinity soils, while biochar stimulated NH3 volatilization in high-salinity soils and reduced NH3 volatilization in severe-salinity soils. Spearman correlation analysis demonstrated that AOA was significantly and positively correlated with the NO3--N content (r = 0.137, P < 0.05) and N2O emissions (r = 0.174, P < 0.01), which indicated that AOA dominated N2O emissions from nitrification in saline soils. Structural equation modeling indicated that biochar, manure, and gypsum affected N2O emission by influencing soil pH, conductivity, mineral nitrogen content, and functional genes (AOA-amoA and nosZ). Two-way ANOVA further showed that salinity and amendments (biochar, manure, and gypsum) had significant effects on N2O emissions. In summary, this study provides valuable insights to better understand the effects of gaseous N changes in saline soils, thereby improving the accuracy and validity of future GHG emission predictions and modeling.

Optimization of fertilization scheme based on sustainable wheat productivity and minor nitrate residue in organic dry farming: An empirical study

The substitution of chemical nitrogen fertilizer with manure holds the potential for a synergistic rise in wheat grain yield and protein concentration, while minimizing residual nitrate in soil. We conducted a 6-year field fertilization experiment including two manure treatments (with or without) and five nitrogen applications rates (0, 60, 120, 180 and 240 kg ha-1). The study investigated the impact of single chemical nitrogen (CN) and manure substitution for nitrogen fertilizer (MN) on the grain yield (GY), grain protein concentration (GPC), plant nitrogen uptake (PNupt) and plant nitrogen requirement (PNR) of wheat, and the dynamic change of soil nitrate-N. The findings revealed that: (1) the MN demonstrated a greater advantage over CN, as evidenced by a 13.4-16.0 % increase in GY, a 2.6-3.8 % increase in GPC, a 7.2-15.7 % increase in PNupt and a 1.5-4.7 % reduction in PNR. (2) Soil nitrate accumulation (SNA) significantly increased when fertilizer rates ≥180 kg ha-1 and the peak annually shifted to deeper layer. The MN increased the SNA0-100 by 20.9-21.8 %, but significantly reduced SNA0-200 by 11.8-13.5 % compared with the CN. Topsoil nitrate content (SNC0-20) can be adopted as a substitute for SNA0-100 to make the fertilization schedule convenient. (3) Regression analysis revealed (taking the MN for example) that the optimum N rates for the maximum GY (5417 kg ha-1) and GPC (15.3 %) were 164 and 211 kg N ha-1, respectively. The nitrate-N safety threshold was 62 kg ha-1 at the fertilizer rate of 89 kg N ha-1. Based on this, nitrogen fertilizer input reduced by 44.8-57.2 % and SNA0-200 by 17.9-33.6 %, with achieving 91.8-95.0 % of maximum GY and 89.7-92.9 % of maximum GPC. Substituting manure for nitrogen fertilizer achieved the potential of maintaining the grain yield and protein concentration while the minimization in soil nitrate residue. This study offers a feasible way for fertilization recommendation and nitrate residue controlling in dry farming.

Substitution of organic and bio-organic fertilizers for mineral fertilizers to suppress nitrous oxide emissions from intensive vegetable fields

To gain insight into the microbial mechanisms associated with the replacement of chemical fertilizers with organic or bio-organic fertilizers to mitigate soil nitrous oxide (N2O) emissions, we measured N2O emissions from greenhouse vegetable soils through field observations and pot experiments. Results showed that organic substitution suppressed N2O emissions by reducing soil mineral N content and stimulating the abundance of the nosZII gene. The trade-off effect of bio-organic substitution on N2O emissions may be due to the stimulated activity of the AOA-amoA gene, resulting in unfavorable conditions for N2O production and thus reduced N2O loss. We also linked the inhibitory effect of organic and bio-organic substitution on N2O emissions to the increased abundance of key species in bacterial co-occurrence networks represented by Patescibacteria as they were significantly and negatively correlated with N2O emissions. However, the mitigation effect of bio-organic substitution on N2O emissions was conteracted by an increase in Bacillus abundance due to the direct negative effect of Bacillus on the nosZII gene abundance. These findings suggest that conventional or bio-organic substitution is a promising strategy for alleviating the environmental costs of crop production.

Quantifying synergies and trade-offs in the food-energy-soil-environment nexus under organic fertilization

Recycling livestock manure in agroecosystems can maintain crop production, improve soil fertility, and reduce environmental losses. However, there has been no comprehensive assessment of synergies and trade-offs in the food-energy-soil-environment nexus under manure application. Here, we evaluate the sustainability of maize production under four fertilization regimes (mineral, mineral and manure mixed, manure, and no fertilization) from the aspect of food security, energy output, soil quality, and environmental impact based on a five-year field experiment. Manure and mineral mixed fertilization maintained grain and straw quantity and quality compared with mineral fertilization. Manure and mineral mixed fertilization increased stem/leaf ratio and field residue index by 9.1-28.9% and 4.5-17.9%, respectively. Manure also maintained the theoretical ethanol yield but reduced the straw biomass quality index by increasing ash. Further, manure application increased the soil quality index by 40.5% and reduced N2O emissions by 55.0% compared with mineral fertilization. Manure application showed the highest sustainability performance index of 19, followed by mineral (15), mixed (13), and without fertilization (8). In conclusion, manure application maintains food production and energy output, enhances soil quality, and reduces environmental impact, thereby improving the sustainability of maize production.

Integrative knowledge-based nitrogen management practices can provide positive effects on ecosystem nitrogen retention

Knowledge-based nitrogen (N) management provides better synchronization of crop N demand with N supply to enhance crop production while reducing N losses. Yet, how these N management practices contribute to reducing N losses globally is unclear. Here we compiled 5,448 paired observations from 336 publications representing 286 sites to assess the impacts of four common knowledge-based N management practices, including balanced fertilization, organic fertilization, co-application of synthetic and organic fertilizers, and nitrification inhibitors, on global ecosystem N cycling. We found that organic and balanced fertilization rather than N-only fertilization stimulated soil nitrate retention by enhancing microbial biomass, but also stimulated soil N leaching and emissions relative to no fertilizer addition. Nitrification inhibitors, however, stimulated soil ammonium retention and plant N uptake while reducing N leaching and emissions. Therefore, integrative application of knowledge-based N management practices is imperative to stimulate ecosystem N retention and minimize the risk of N loss globally.

Agricultural management strategies for balancing yield increase, carbon sequestration, and emission reduction after straw return for three major grain crops in China: A meta-analysis

Straw return can improve crop yield as well as soil organic carbon (SOC) but may raise the possibility of N₂O and CH₄ emissions. However, few studies have compared the effects of straw return on the yield, SOC, and N₂O emissions of various crops. Which management strategies are the best for balancing yield, SOC, and emission reduction for various crops needs to be clarified. A meta-analysis containing 2269 datasets collected from 369 studies was conducted to investigate the influence of agricultural management strategies on yield increase, soil carbon sequestration, and emission reduction in various crops after the straw return. Analytical results indicated that, on average, straw return increased the yield of rice, wheat, and maize by 5.04%, 8.09%, and 8.71%, respectively. Straw return increased maize N₂O emissions by 14.69% but did not significantly affect wheat N₂O emissions. Interestingly, straw return reduced the rice N₂O emissions by 11.43% but increased the CH₄ emissions by 72.01%. The recommended nitrogen application amounts for balancing yield, SOC, and emission reduction varied among the three crops, while the recommended straw return amounts were more than 9000 kg/ha. The optimal tillage and straw return strategies for rice, wheat, and maize were plow tillage combined with incorporation, rotary tillage combined with incorporation, and no-tillage combined with mulching, respectively. A straw return duration of 5-10 years for rice and maize and ≤5 years for wheat was recommended. These findings provide optimal agricultural management strategies after straw return to balance the crop yield, SOC, and emission reduction for China's three major grain crops.

Effect of replacing synthetic nitrogen fertilizer with animal manure on grain yield and nitrogen use efficiency in China: a meta-analysis

To reduce reliance on synthetic nitrogen (N) fertilizer and sustain food production, replacing synthetic N fertilizer with animal manure as an effective method is widely used. However, the effects of replacing synthetic N fertilizer with animal manure on crop yield and nitrogen use efficiency (NUE) remain uncertain under varying fertilization management practices, climate conditions, and soil properties. Here, we performed a meta-analysis of wheat (Triticum aestivum L.), maize (Zea mays L.), and rice (Oryza sativa L.) based on 118 published studies conducted in China. Overall, the results indicated that substituting synthetic N fertilizer with manure increased yield by 3.3%-3.9% for the three grain crops and increased NUE by 6.3%-10.0%. Crop yields and NUE did not significantly increase at a low N application rate (≤120 kg ha^-1) or high substitution rate (>60%). Yields and NUE values had higher increases for upland crops (wheat and maize) in temperate monsoon climate/temperate continental climate regions with less average annual rainfall (AAR) and lower mean annual temperature (MAT), while rice had higher increases in subtropical monsoon climate regions with more AAR and higher MAT. The effect of manure substitution was better in soil with low organic matter and available phosphorus. Our study shows that the optimal substitution rate was 44% and the total N fertilizer input cannot be less than 161 kg ha^-1 when substituting synthetic N fertilizer with manure. Moreover, site-specific conditions should also be considered.

Determining reclaimed water quality thresholds and farming practices to improve food crop yield: A meta-analysis combined with random forest model

Irrigated agricultural systems with reclaimed water (RW) play a crucial role in alleviating global water scarcity and increased food demand. However, appropriate reclaimed water quality thresholds and farming practices to improve food crop yield is virtually unclear. Therefore, for the first time, this study made a large compilation of previous studies using meta-analysis combined with a random forest (RF) model and analyzed the impact of RW versus freshwater (FW) on the yield of food crops (cereals, vegetables, and fruits). It was found that magnesium ion (Mg²⁺), calcium ion (Ca²⁺), electrical conductivity (EC), total nitrogen (TN), and potential of hydrogen (pH) were the most important factors for RW quality indicators. Based on the results, water managers should establish more conservative RW quality thresholds to promote food crop production, especially for salts and pollutants in RW. Compared to international water quality standards, it could be slightly relaxed the restrictions of TN in RW. The optimal farming practices obtained that irrigation amount of the mixed RW and FW (RW + FW) was from 1000 m³ ha^-1 to 5000 m³ ha^-1, and the cultivation period was no more than three years. Flood irrigation (FI) and drip irrigation (DI) for cereals were also recommended. Finally, a comparison of the determined results from this method with other scenarios published, finding a good agreement.