Effects of film mulching on nitrogen use efficiency of spring maize and soil available nitrogen variations in the middle reaches of Yangtze River

【Objectives】The mechanism of film mulching on spring maize grain yield, N accumulation, N use efficiency and soil available nitrogen spatial and temporal variations was studied under different N application rates, to provide theoretical basis for the practical use of the film mulching technology on spring maize in the middle reach of Yangtze River. 【Methods】 A split-block field experiment was conducted with film mulching(F)or no film mulching(NF)as main factor and N application rates as the deputy factor: N0, N135, N202.5, N270 and N337.5. Plant samples were collected at jointing, silking and maturity stage of maize, the N contents were determined and the nitrogen accumulation amount(TNAA)and agronomy nitrogen use efficiency(ANUE)and nitrogen recovery efficiency(NRE)were calculated; at the same stage, soil samples of 0-20, 20-40 and 40-60 cm in depth were collected, and the NO-3-N and NH+4-N contents were analyzed. The yield and yield components were investigated after harvest. 【Results】There were significant differences of film mulching and N application on grain yield, ear number, ear kernels number and 100-kernel weight. Compared with NF, film mulching significantly increased grain yield by 23.0%-45.9%(P0.01), the main reason was that the ear kernels number were increased by 7.6%-37.0%(P0.05)and 100-kernel weight increased by 0.5-2.1 g(P0.05). N application significantly increased grain yield of spring maize by 102.2%-168.6%(P0.01), the main reason was the increase of ear kernels number(60.2%-125.0%,P0.01), instead of the ear number and 100-kernel weight. Spring maize TNAA was increased significantly by film mulching and N application in the tested growth stages, but the interaction of the two experimental factors was only showed at silking stage. Compared to NF, film mulching increased the ANUE by 45.32%-164.23% with different N application rates, but not significant on the NRE(2.34%-17.64%). The ANUE and NRE were respectively increased by 26.21%-43.71% and 26.75%-47.20% with N application. There were still no significantly interact effects of film mulching and N application on ANUE and NRE. Film mulching increased fertilizer nitrogen releasing rate by increased soil temperature and reduced precipitation in the same stage, so the soil available N contents were significantly increased in the 0-20 cm depth under N 135-270 kg/hm2 levels and 20-40 cm depth under N 202.5 and 270 kg/hm2 levels, and in the 40-60 cm depth soil at V6 stage. 【Conclusions】 The significant interaction of film mulching and N application on the N accumulation at silking stage was beneficial to the increase of ear kernel number, and the N accumulation during kernels filling stage, which promotes the kernel filling and the final 100-kernel weight. Under the experimental conditions, with flim mulching, the N application should be controlled in range of 202.5-270 kg/hm2 in spring maize in the middle reaches of Yangtze River for high grain yield and high nitrogen use efficiency.