Soil aggregation, a critical component of soil structure, is significantly influenced by soil moisture content, which can vary substantially across different field conditions. The objective of this study was to evaluate the impact of soil relative water content (SRWC) on the performance and sensitivity of soil aggregate size distribution (DOSA) assessments. We conducted a comprehensive analysis across a range of SRWC levels and observed a consistently high recovery rate of sieving (exceeding 99.22%), indicating a robust methodology. The relative standard deviation (RSD) of DOSA was minimal, highlighting the high precision of sieving outcomes, particularly up to an SRWC of 40%. Cluster analysis, based on soil properties, identified six distinct soil groups, each demonstrating a significant correlation between the characteristic values of DOSA and SRWC, with determination coefficients (R²) above 0.717. This finding underscores the sensitivity of aggregate distribution to variations in moisture levels. However, the fitting curves varied among clusters at the same site, with the exception of clusters 5 and 6 at the Jinliuhuan Agricultural Sci-Tech Park (JLH), reflecting the intricate nature of soil–moisture interactions. Our results emphasize the necessity of sieving soil aggregates under controlled field moisture conditions to ensure reliable DOSA measurements. This research provides valuable insights into the dynamics of soil aggregation and its response to different moisture regimes, offering practical implications for enhancing sustainable agricultural practices. This study provides a comprehensive analysis of the impact of soil relative water content (SRWC) on soil aggregate size distribution (DOSA), revealing the high recovery rate and precision of sieving under various moisture conditions. The significant correlation between DOSA and SRWC, along with the varied responses across soil clusters, highlights the complex interplay between soil moisture and aggregate stability. These findings are crucial for optimizing soil aggregate assessments and sustainable agricultural practices.

Recovery efficiency of nitrogen fertilizers has always been an important issue, especially for N fertilizer recommendation rate in cropping systems. Based on the equilibrium of N in the soil–plant system, apparent accumulated N fertilizer recovery (NRE_ac) was determined for long-term (15-years) experiments in wheat (Triticum aestivum L.) and maize (Zea mays L.) rotations at five field sites with various soils and climate characteristics in China. The result showed that the frequency of cropping and the content of soil clay affected NRE_ac positively and negatively, respectively. In the absence of nutrient deficiencies and other soil constraints (from NPK (nitrogen, phosphorus and potassium) in S2-CP (site2-Changping) in Beijing, S3-ZZ (site3-Zhengzhou) in Henan province and S4-YL (site4-Yangling) in Shaanxi province), NRE_ac had a narrow range from 70% to 78% with the highest average of 75% in wheat and maize cropping system. Meanwhile, the value 75% of NER_ac is a rational value proved by 3414 experiments. Additionally, the nitrate-N approach suggested that nitrate-N could be utilized by subsequent crops, the amount of which is calculated by the equation −1.23 × [(NO₃⁻-N) − 87]. Furthermore, another simpler and feasible method was proposed to maintain basic soil fertility while achieving a rational grain yield and maintaining a safe environmental upper threshold of nitrate. The present study provided a suit of methods for N fertilizer recommendations for the optimization of N applications in wheat and maize cropping system in China.

In response to China’s drive to bring newly cultivated land into production, this study evaluated how combined organic fertilizer and microbial inoculants affect soil quality, bacterial community structure, and maize yield. Four treatments were evaluated: FC (chemical fertilizer only), T50 (50% organic fertilizer + 50% chemical fertilizer), T50M (T50 plus microbial inoculant), and CK (no fertilizer). T50M significantly increased yield compared to FC and CK (p < 0.05), achieving the highest yield of 6995.73 kg ha⁻¹. This was 20.09% greater than FC. Community composition analyses showed that soil in newly cultivated land was dominated by Blastocatellia, Vicinamibacteria, and Alphaproteobacteria, together accounting for over 35.7% of total bacterial abundance. Redundancy analysis at the class level explained 55.7% of variance; soil organic matter (SOM) and available potassium positively correlated with Alphaproteobacteria and Bacteroidia, while available phosphorus and nitrate nitrogen aligned with Actinobacteria and Bacilli. Path analysis indicated that SOM and total nitrogen were the strongest positive drivers of yield. Actinobacteria and Acidobacteriae also showed direct positive effects, whereas Verrucomicrobiae had a negative effect. These results demonstrate that integrated organic–microbial amendments can enhance soil fertility and alter microbial diversity toward taxa that can improve maize productivity.

In spite of the importance of N management in agricultural production, closing the full nitrogen balance remains a challenge, mainly due to the uncertainties in both fluxes of nitrogen input and output. We analyzed N deposition and its influence on crop productivity and field nitrogen balance based on data from three of 15 years (1990–2005) of experiments in North China. The results showed that the average annual nitrogen deposition was 76, 80, and 94 kg N/ha at Changping, Zhengzhou, and Yangling in a wheat-maize rotation system, respectively. The deposited N could support a corresponding total biomass production (wheat plus maize) of 9.6, 10.6, and 8.8 Mg/ha with a total grain yield of 3.8, 4.8, and 3.7 Mg/ha, however, that did not cause a further decline in soil organic matter. N fertilizer application could increase total biomass (grain) by 244% (259%) and 74% (119%) for wheat and maize, respectively. Under optimal N management, N deposition accounted for 17–21% of the total N inputs, which affected significantly the recovery efficiency of applied N. N deposition showed a significant spatial variation in terms of the fraction of dry and wet depositions. On an annual average, N deposition roughly balanced out N losses due to NH₃ volatilization and N₂O loss from nitrification and denitrification. NH₃ volatilization and NO₃⁻-N leaching each accounted for 16–20% of the total N outputs. A system modeling approach is recommended to investigate the spatial variation of N leaching as affected by climatic conditions, and to fully account for the nitrogen fluxes. The N deposition derived from this study can be used as the background N input into the wheat-maize double cropping system for N balance.

Introduction: Paddy soils represent key biogeochemical interfaces linking arsenic (As) transformation and carbon (C) cycling. Dimethylarsenate (DMAs), a widespread organoarsenic contaminant in rice paddies, can alter methane (CH ₄ ) dynamics, but the underlying mechanisms based on dissolved organic matter (DOM)-microbe interaction and the mitigation potential of biochar still remained insufficiently understood. Methods: Here, we investigated As biogeochemistry, CH ₄ emissions, DOM quantity and composition, microbial community assembly and functional gene variations through a 98-day microcosm incubation experiment using paddy soil amended with DMAs alone and DMAs combined with biochar. Results: We found that DMAs greatly promoted CH₄ emissions in a dose-dependent manner, with the DMAs120 treatment increasing cumulative CH₄ emissions by 60.4% relative to the control. DMAs underwent significant biotransformation, declining from 98.7% on the 7th day to 26.2% of the total As by day 98. Porewater DOC concentrations were significantly increased by up to 1.81-fold (DMAs120, day 28). PARAFAC analysis revealed that DMAs shifted DOM composition toward labile protein-like fractions, with tryptophan-like (C2) and tyrosine-like (C3) components increasing while microbial humic-like (C1) and terrestrial humic-like (C4) fractions decreased. Such labile DOM precisely matched substrate requirements of enriched anaerobic fermentative microbes, establishing synergistic metabolic networks to supply methanogenic precursors. DMAs markedly increased mcrA gene abundance by 4.2–7.6 times with negligible change in pmoA , confirming stimulated methanogenesis rather than suppressed oxidation. By contrast, biochar effectively decreased % DMAs in porewater, reducing CH ₄ emissions by 54.3% after 2% biochar amendment. Biochar also decreased DOC concentrations and protein-like DOM (C2, C3), reducing bioavailable substrates for methanogens. Furthermore, biochar suppressed mcrA gene abundances by 12.7–81.3%, while increased that of pmoA gene by 7.1–7.5 times, as well as increased porewater As(V) and enriched ammonia-oxidizing Candidatus_Nitrosopelagicus to potentially or indirectly stimulate anaerobic CH₄ oxidation. Discussion: These results establish mechanistic connections between DMAs biotransformation, DOM turnover and CH ₄ production in paddy soils, and verify that biochar restructures DOM-microbe interactions to mitigate DMAs-stimulated CH ₄ emissions. This study deepens insights into As-C biogeochemical coupling and offers practical support for simultaneous As remediation and greenhouse gas control in paddy ecosystems.