Effect of continuous straw-Chinese milk vetch synergistic return to the fieldon yield, nutrient accumulation and soil fertility of double cropping rice

Objectives Rice straw and Chinese milk vetch are important in-situ organic fertilizer resources in the paddy cultivated system. The trend of rice yield increase, nutrient accumulation and soil fertility change characteristics after continuous straw-Chinese milk vetch synergistic return to the field were analyzed to make comprehensive utilization of straws and green fertilizer resources.

Methods The field experiment was conducted from 2016 to 2018 under double-cropping rice system, covering 6 seasons. Three treatments included: neither rice straw returning nor Chinese milk vetch planting in winter (CK); whole rice straws returning but no Chinese milk vetch planting (T1); whole rice straws returning and Chinese milk vetch planting (T2). The chemical fertilizer was applied in the same way and rate for all the three treatments. The rice yield, nutrient absorption and soil fertility were analyzed.

Results Compared with the CK, the annual rice yields in T1 and T2 were increased over the experimental years, and in range of 1.93%–9.15% and 1.34%–12.48%, respectively. According to the analysis on rice yield variation coefficient and sustainability index, both the T1 and T2 treatments were in favor of keeping sustainable and high annual yields of rice, and T2 performed better than T1 did. The contribution rates of straw returning in T1 and T2 were 6.92% and 11.10%, respectively, with that of T2 higher than T1. The T2 treatment significantly increased the accumulation of N, P and K in early rice, and also in late rice due to the aftereffect. After the late rice harvest in 2018, the soil organic matter, total N, available P and K contents were reduced by 9.03%, 11.11%, 3.87% and 10.57% in T1 compared with those in the begin of experiment, while they were increased by 20.51%, 25.00%, 24.16% and 20.37% in T2 compared with CK, and organic carbon, total nitrogen and availabl phosphorus contents in T2 were increased by 2.73%, 7.14% and 14.19% compared to those in T1.

Conclusions In the double-season rice rotation system, the co-returning of rice straw and Chinese milk vetch is more effective than sole straw returning in stimulating the NPK accumulation in rice, maintaining the high and stable yields of both early and late rice, and at the same time improving soil fertility.