Effects of Green Manure, Straw Returning to Fields, and Regulatory Agents on Carbon and Nitrogen Pool Management Indices in Super Hybrid Rice

This study investigates the effects of green manure and straw incorporation, along with different regulators (goethite, ethephon, and sodium dichloroethyl sulfonate) on soil carbon and nitrogen pool management indices of the super hybrid high-yield rice variety “Jingliangyou Huazhan”. The findings hold significant implications for rational resource utilization, enhancing soil fertility, and expanding carbon and nitrogen pools.

A field experiment was conducted from 2022 to 2024 in Gaoqiao Town, Changsha County, Hunan Province. Six treatments were set up, including chemical fertilizer + rice straw returning (CK), chemical fertilizer + rice straw and green manure returning (M), 30% nitrogen reduction + rice straw and green manure returning (R), chemical fertilizer + rice straw and green manure returning + goethite (F), chemical fertilizer + rice straw and green manure returning + ethephon (E), and chemical fertilizer + rice straw and green manure returning + sodium dichloroethyl sulfonate (S). The soil carbon and nitrogen pool management indices were calculated, and their key influencing factors were analyzed.

1) carbon and nitrogen reservoir management indices (CPMI and NPMI) exhibited significant seasonal and interannual variations across treatments. CPMI showed pronounced fluctuations, while NPMI increased annually with the third-year NPMI exceeding the previous two years by 43.63% and 36.18%, respectively; 2) compared to the control (CK) treatment (straw return plus chemical fertilizer alone), all other treatments generally increased both CPMI and NPMI. Treatment M showed the most significant enhancement effects for CPMI and NPMI (199.08 ± 44.60 and 96.29 ± 9.19, respectively), while treatments with three regulators showed 4.24%‒15.27% lower CPMI and 6.20%‒14.08% lower NPMI than M. Notably, treatment S significantly reduced NPMI (p < 0.05); 3) random forest and structural equation modeling analyses indicated that DOC and TDN were primary factors influencing CPMI, while TDN was the main factor affecting NPMI.

The combined application of chemical fertilizer and rice straw green manure to fields is more effective in enhancing the soil carbon and nitrogen reservoir management index of super rice, representing the optimal choice for improving soil fertility and expanding soil carbon and nitrogen reservoirs.