Abstract
Purpose
Chinese milk vetch (MV) is widely used in rice yield enhancement because of the huge nitrogen (N) substitution potential. However, the proper substitution rate of MV for N fertilizer and its effect on carbon sequestration and nutrient retention in soil aggregates remains unknown.
Method
A 10-year field experiment was conducted to investigate the effects of different MV substitution rates on soil aggregate stability, nutrient retention, and soil quality in a double rice cropping system. The treatments included no fertilizer (CK), 100% NPK fertilizer (N100), recommended N supply by different proportions of MV (N80G20, N60G40, N40G60, N20G80)
Result
Compared with the N100 treatment, the N80G20 and the N60G40 treatment increased the mean weight diameter (MWD) by 4.2% and 5.3%, and the geometric mean diameter (GMD) by 7.7% and 12.1%, respectively. The N60G40 treatment significantly increased the labile organic carbon content and carbon pool management index by 24.7% and 45.0%, respectively. N80G20 and N60G40 treatments directly increased total nitrogen (TN) and total phosphorus (TP) in macro-aggregates (> 0.25mm), and improved the contribution of total nutrients in > 2mm aggregate. Compared with the N100 treatment, the N60G40 treatment improved TN, TP and TK by 6.0%, 9.3% and 5.6%. Incorporating MV improved the soil quality index (SQI), with N60G40 treatment improved the most by 34.1%. And the grain yield increased significantly with the increasing SQI. Substituting 20–60% of N by MV can sustain grain yield. However, a higher substitution rate significantly reduced grain yield, particularly in the early rice.
Conclusions
Consequently, Incorporating MV to substitute 20–40% N fertilizer can enhance soil structure by improving the proportion of macro-aggregates, thereby improving nutrient retention and soil quality. This study provides a sustainable and eco-friendly approach in the double rice cropping systems.