Effects of organic fertilization and tillage method on soil aggregates and organic carbon fractions in a wheat-rice system

In order to clarify the effect of different exogenous organic materials and tillage methods on soil fertility, with the rice and wheat rotation system as the study object, a two-year field experiment was conducted to study the short-term effects of different exogenous organic materials, tillage methods, and their interactions on soil aggregate and organic carbon composition. The results revealed that straw returning with rotary tillage method could decrease soil bulk density and increase total porosity. Compared with non-straw-returning treatment (CKR), the >0.05-mm water-stable aggregate content with straw-returning treatment under rotary tillage (SR) significantly increased (7.2%) in the wheat growing season. In addition, exogenous organic matter and tillage methods had significant effects on soil active organic carbon. Among them, easily oxidized organic carbon (EOC) was significantly affected by the interaction of exogenous organic materials and tillage method, and the acid-hydrolyzed organic carbon (LPI_c and LPII_c) was significantly affected by the tillage method. Compared with CKR treatment, the concentration of EOC and LPI_c with straw-returning treatment under rotary tillage increased by 0.3-2.6 g·kg^-1. The content of particulate organic carbon (POC) was significantly affected by exogenous organic materials, and the average POC content with straw-returning treatments was higher than that with organic fertilizer application treatments (increased by 0.75 g·kg^-1). In the short term, exogenous organic materials, tillage methods, and their interactions had negligible effect on the stability of organic carbon (black carbon and mineral-bonded organic carbon). In conclusion, straw returning combined with rotary tillage could improve the content of soil water-stable aggregates and active organic carbon (EOC, LPI_c, and POC).