Tillage Practices Regulate Soil Physicochemical Traits and Microbial Characteristics of Winter Rapeseed (Brassica napus L.) in Rice–Rapeseed Rotation Systems with Rice Straw Incorporation

Abstract

Straw incorporation generally improves soil nutrient availability, aggregate stability, microbial activity, as well as carbon dioxide (CO2) emissions. However, the regulatory effects of tillage regimes on soil physicochemical properties, microbial community structure, and CO2 emission rates (CER) remain largely unexplored in rice–rapeseed rotation systems incorporating straw residue in the upper Yangtze River basin. A two-year field experiment in Sichuan’s Xindu District adopted three tillage practices: rotary tillage combined with whole rice straw incorporation (RT), deep plowing combined with whole rice straw incorporation (DP), and no-tillage with whole rice straw mulching (NT). Compared with NT, both RT and DP significantly lowered soil bulk density (BD) and macroaggregate stability, and elevated soil available nitrogen (AN), available phosphorus (AP), and available potassium (AK). On average, the AN, AP, and AK were significantly increased by 7.4%, 9.0%, and 80.3% in RT and by 4.1%, 43.9%, and 42.2% in DP relative to NT, respectively. Compared with the NT, the CER was significantly decreased by 37.1% in RT and by 12.9% in DP. Notably, RT effectively mitigated CER. Microbial α-diversity was significantly higher in the NT relative to other tillage treatments. Proteobacteria dominated the bacterial community, and Ascomycota dominated the fungal community. RT and DP increased the relative abundance of Proteobacteria and suppressed Ascomycota simultaneously. Redundancy analysis revealed positive associations between Proteobacteria and both AN and AK, whereas Ascomycota positively correlated with BD, MWD, and CER. Mantel test confirmed significant correlation between soil microbial community compositions and the soil properties, including BD, AN, AK, and CER. Relative to the other tillage practices, RT is conducive to soil quality improvement and CER reduction, and can be recommended for sustainable rice-rapeseed production locally.