Straw returning into the soil is a crucial method for boosting soil carbon levels. To research the influence of straw return practices on soil aggregates and organic matter content within the farmlands of the Northeast Black Soil Region, the objective was to clarify the varying impacts of these practices on soil carbon enhancement. In this study, 89 pertinent papers were acquired through a rigorous literature compilation. Meta-analysis and the linear regression method were employed to analyze the influence of field return methods, their duration on soil water-stable aggregates, and their organic matter content. Furthermore, the study delved into the trends in the variation of aggregates and organic matter in relation to mean annual temperature and precipitation. Our results showed that the straw-returning method has been discovered to predominantly bolster soil organic matter by altering the proportions of macro-aggregate content. Specifically, straw incorporation has led to a notable enhancement in the content of macro-aggregates (57.14%) and micro-aggregates (20.29%), in addition to augmenting the content of macro-, small, and micro-aggregate organic matter by 13.22%, 16.43%, and 15.08%, respectively. The most significant increase in large agglomerates was witnessed in straw return over a period of more than 5 years (115.17%), as well as shallow mixing return (87.32%). Meanwhile, the highest increase in the organic matter content of large agglomerates was recorded in straw return over 5 years (12.60%) and deep mixing return (8.72%). In the field validation experiment, a period of seven years of straw return significantly boosted the macro-aggregate content across various soil layers, ranging from 11.78% to 116.21%. Furthermore, among the various climatic factors, the primary determinants of disparities in study outcomes were the average annual temperature and average annual precipitation. Specifically, lower precipitation and higher temperatures were conducive to the enhancement of macro-aggregate formation and organic matter content.

Semi-arid Chernozem farmland in Northeast China faces the dual challenges of water scarcity and excessive nitrogen (N) fertilisation, yet quantitative understanding of coupled water–N use efficiency and environmental trade-offs under climatic variability remains limited. Using the WHCNS (Water, Heat, Carbon and Nitrogen Simulator) model calibrated and validated against field data (2022–2023) from Qiqihar, we quantified crop yield, water use efficiency (WUE), System-Level Nitrogen Conversion Efficiency (SLNCE) and N losses under five management regimes encompassing conventional fertilisation, straw mulching and organic manure substitution. Long-term climate adaptability was evaluated using precipitation scenarios from 2001 to 2023. Straw mulching reduced evapotranspiration by 12.2% and increased WUE to 2.09 kg·m⁻³. Combined chemical and organic fertiliser application (T223) achieved the highest yield (9745.9 kg·ha⁻¹) and WUE (2.14 kg·m⁻³), whereas a 30% reduction in chemical fertiliser with straw return (T323) reduced yield and SLNCE, indicating insufficient N supply. Organic substitution achieved the highest SLNCE (35.9 kg·kg⁻¹), exceeding the straw-only treatment by 29.1%. Nitrate leaching below 1 m was negligible, whereas gaseous N losses were the dominant loss pathway and increased with rainfall. SLNCE responded nonlinearly to precipitation, peaking at 420–451 mm; extreme drought years constrained yield through nitrogen limitation, whereas wet years increased gaseous N losses while maintaining relatively high yields. These results show that organic substitution can simultaneously enhance WUE and SLNCE, providing a climate-adaptive strategy for sustainable water–N management in semi-arid Chernozem soils.