The inter-annual characteristics of nitrogen recovery efficiency of double cropping rice system on paddy soil under long-term fertilization

A 26 year different fertilization experiment was conducted to investigate rice yields and dynamics of nitrogen recovery efficiency (NRE) of double rice cropping system in red paddy soil at Jinxian,Jiangxi province. There were six treatments, unfertilized control (CK), inorganic fertilizer nitrogen (N), N and P (NP), N and K (NK), NPK, and NPK with manure (NPKM). The results show that there are significant differences of NREs in the six treatments, and the average values of NRE in 26 years are 9.4%-11.6%, 13.0%-18.5%, 19.8%-26.1% and 14.1%-22.9% for the N, NP, NPK and NPKM treatments, respectively. The NREs of double cropping rice are significantly improved under the application of PK combined fertilizer and manure, and the NRE of early rice is higher than that of late rice. The NREs of early rice under the NPK and NPKM treatments are 6.3 and 8.8 percentage point higher than those of late rice, respectively. The NREs of both early rice and late rice are significantly decreased at a rate of about 0.6 percentage point/a under the N and NK treatmentsover the 26 years. There are no significant changes in the NREs of rice under the NPK and NPKM treatments over the 26 years. Compared with the NPK fertilization, the NPKMfertilization resulted in 19.0% and 21.7% grain yield increases of early rice and late rice, respectively. We conclude that chemical fertilizer in combination with manure is amore effective fertilization to improve grain yield and maintain NRE for red paddy soil.