Rational utilization of Chinese milk vetch improves soil fertility, rice production, and fertilizer use efficiency in double-rice cropping system in East China

This study aimed to explore the effect of Chinese milk vetch (CMV) on soil fertility and rice production in double rice cropping systems. A field experiment was conducted including the following six treatments: Ck (no NPK mineral fertilizer and no CMV), CMV0 (NPK mineral fertilizer and no CMV), and CMV1-4 (NPK mineral fertilizer and 7500 kg ha(-1) CMV, 15,000 kg ha(-1) CMV, 22,500 kg ha(-1) CMV, 30,000 kg ha(-1) CMV) from 2008 to 2018. The results showed that the application of CMV enhanced the organic matter, the total nitrogen, the available phosphorus, pH, and enzyme activities (except for the cellulase) in paddy soils. The organic matter and total nitrogen of CMV3 were increased by 15.99% and 8.07% compared with CMV0 and the increase rate of the organic matter and total nitrogen was by an average of 0.413 and 0.029 g kg(-1) per year compared with the initial soil, respectively. The CMV return also improved the enzyme activities (except for the cellulase). Meanwhile, the CMV returned to soil increased dramatically the yields of early rice, late rice, and double rice by 13.46%-26.23%, 13.63%-20.84%, and 13.55%-25.76% compared with CMV0, respectively. The yields of early rice, late rice, and double rice of the CMV3 were highest among all the treatments. The application of CMV improved the agronomic efficiency (AE) and the partial factor productivity (PFP), especially for CMV3. The AE and PFP values of double rice for CMV3 increased by 64.54% and 25.76%, respectively. The application of CMV also increased the sustainability index and reduced the coefficient of variation of the rice yields. In addition, there was negative linear relationship between the amount of CMV needed to generate higher yields of double rice and the years of CMV application. In conclusion, CMV addition at 15,000-22,500 kg ha(-1) combined with mineral fertilizer had beneficial effects on the productivity, the stability of rice yield as well as the fertilizer efficiency in double rice cropping system.