Winter fallow straw–nitrogen co-application enhances rice yield and stability by regulating soil organic matter physical fractions and chemical composition

Abstract

Double-cropping rice systems face increasing challenges from climate-driven yield variability and soil degradation under intensive cultivation. Winter fallow straw–N management has been proposed as a promising strategy to improve soil organic matter (SOM) and productivity. However, its long-term effects on yield and SOM dynamics remain uncertain. This 11-year field experiment assessed long-term effects of winter fallow straw–N co-application on SOM fractions and composition, and grain yield and stability. Treatments were bare plots (CK), straw incorporation alone (S), basal N alone (N); and straw incorporation with 0 %, 30 % or 60 % of basal N co-applied during winter fallow (SN₀, SN₃₀, SN₆₀). Results showed that straw–N co-application enhanced early- and late-season rice yields, but yield responses showed interannual variability and sensitivity to seasonal climate. SN₃₀ achieved the highest average yields and relatively high yield stability, and enhanced SOC and SON primarily via increases in aggregate-occluded (o-POM) and mineral-associated (c-MAOM) fractions, rather than free particulate organic matter (f-POM). NMR spectroscopy revealed elevated levels of O-alkyl C and NCH functional groups, indicating intensified microbial processing of straw-derived organic matter. Random forest and squares path modeling identified SOM physical fractions as key drivers of average yield, while SOM chemical composition was more strongly associated with interannual yield stability. These findings highlight that both SOM quantity and quality, particularly MAOM fractions and nitrogen-rich compounds, are critical for maintaining productivity and resilience in intensive rice systems. Winter fallow straw–N management provides an effective strategy to enhance soil health and support production under climate variability.