Find in Library

A long-term field experiment was carried out (since 2008) for evaluating the effects of different substitution rates of inorganic nitrogen (N) fertilizer by green manure (GM) on yield stability and N balance under double rice cropping system. Treatments included, (1) N₀ (no N fertilizer and no green manure); (2) N₁₀₀ (recommended rate of N fertilizer and no green manure); (3) N₁₀₀-M (recommended rate of N fertilizer and green manure); (4) N₈₀-M (80% of recommended N fertilizer and green manure); (5) N₆₀-M (60% of recommended N fertilizer and green manure); and (6) M (green manure without N fertilization). Results showed that, among all treatments, annual crop yield under N₈₀-M treatment was highest. Crop yield did not show significant differences between N₁₀₀-M and N₈₀-M treatments. Substitution of different N fertilizer rates by GM reduced the yield variability index. Compared to the N₀ treatment, yield variability index of early rice under N₁₀₀-M, N₈₀-M, and N₆₀-M treatments was decreased by 11%, 26%, and 36%, respectively. Compared to the N₀ treatment, yield variability index of late rice was decreased by 12%, 38%, 49%, 47%, and 24% under the N₁₀₀, N₁₀₀-M, N₈₀-M, N₆₀-M, and M treatments, respectively. During period of 2009−2013 and 2014−2018, nitrogen recovery efficiency (NRE) was highest under N₈₀-M treatment and N balance was highest under N₁₀₀ treatment. NRE of all treatments with GM was increased over the time from 2009−2013 to 2014−2018. All treatments with GM showed increasing trend of SOC over the years. Substitution of N fertilizer by GM also increased C inputs and soil C:N ratio compared to the N₁₀₀ and N₀ treatments. Boosted regression model indicated that C input, N uptake and AN were most influencing factors of crop yield. Thus, we concluded that N fertilization rates should be reduced by 20% under GM rotation to attain high yield stability of double rice cropping system through increasing NRE and C inputs.