Straw Incorporation Thresholds for Soil Carbon and Nitrogen Stability in Maize Cropping and Fallow Systems

Straw incorporation (SI) increases soil organic carbon (SOC) and soil total nitrogen (STN). However, the differences in soil C and N fractions between the maize cropping and fallow systems under different SI rates in the black soil region of Northeast China remain unclear. In a 6‐year experiment, we examined these two systems by using circular frames with five annual SI rates (0, 9.2, 18.4, 27.6, and 36.8 Mg ha −1 ) to investigate their effects on soil C and N fractions and storage potential. SI significantly enhanced the SOC and STN concentrations in both systems. Compared to fallow, continuous maize cropping resulted in higher depletion of oxidizable organic C (EOC) and amino sugar N (ASN). However, it maintained greater light fraction organic C (LFOC), particulate organic C (POC), and hydrolyzable unknown N (HUN) concentrations in the 0–15 cm soil layer. Fallow increased the soil C:N ratio and exhibited higher average annual C and N sequestration rates (0.70 and 0.01 Mg ha −1 year −1 , respectively) compared to the maize cropping system. However, increasing SI rates did not significantly affect the transformation efficiency of straw‐derived nutrients. Conventional SI rates in continuous maize cultivation led to soil C and N losses, while higher SI rates and fallow management effectively retained nutrients. Thus, to prevent concurrent losses of soil C and N pools under continuous maize cropping in the 0–30 cm soil layer under current soil conditions, an annual input of at least 6.8 Mg C ha −1 year −1 and 0.2 Mg N ha −1 year −1 is recommended.