Effects of crop rotation on plant- and microbial-derived carbon within particulate and mineral fractions in paddy soils

Abstract

Paddy soil is an important soil organic carbon (SOC) sink, and particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) are distinct components of SOC concerning their formation and function. However, the contributions of plant- (lignin phenols) and microbial- (amino sugars) derived C within the POC and MAOC fractions of SOC under various paddy field rotation systems have not yet been documented. Thus, we conducted an 8-year field experiment encompassing four distinct crop rotation systems: wheat-rice (W-R), rapeseed-rice (R-R), Chinese milk vetch-rice (A-R), and A-R with a 20 % reduction in nitrogen fertilizer (A-R-N). From 2017–2023, crop rotation improved the concentration of amino sugars (AS) in POC and the lignin phenols (VSC) in MAOC. Compared to the beginning of the experiment, the W-R significantly improved the SOC stock at 0–20 cm by 84.1 % by promoting the formation of POC (69.5 %) and MAOC (101.5 %) in 2023. W-R increased the content and proportion of AS in POC, as well as the content of VSC compared with the other treatments. Nevertheless, rice yield does not increase synergistically with SOC. On average, W-R had the lowest rice yield and decreased rice yield by 9.2 %, 2.8 %, and 5.6 % compared to R-R, A-R, and A-R-N, respectively. However, the annual yield of W-R was 9.7 %, 62.6 %, and 57.9 % higher than that of R-R, A-R, and A-R-N, respectively. Our findings highlight that incorporating rapeseed and Chinese milk vetch can increase next-stubble rice yield slightly but is not conducive to carbon sequestration in rice fields, and wheat-rice is a promising cropping system for sustaining SOC sequestration and crop production.