Determination of input threshold of nitrogen fertilizer based on environment-friendly agriculture and maize yield

Abstract: The purpose of this study was to get a win-win input threshold value of nitrogenous fertilizer. The three-year fertilization experiment was carried out in Wuyuan County, Hetao irrigated area, Inner Mongolia to study the effect of different nitrogen usage rate on maize yield, soil nitrogen residues and nitrogen balance. The experiment was conducted on the anthropogenic-alluvial soil with pH value of 8.5, organic matter content of 16. 17 g/kg, 18.76 mg/kg Olsen phosphorus (P) content, 149 mg/kg available potassium (K) content, 6.95 mg/kg ammonium nitrogen (NH4+-N) content, 16.20 mg/kg nitrate nitrogen (NO3--N) content, and soil bulk density of 1.49 g/cm3. The supplied variety of maize was Haodan 168. Six N treatments (0, 135, 180, 225, 270 and 360 N kg/hm2 in 2011; 0, 180, 240, 300, 360 and 480 N kg/hm2 in 2012 and 2013) were randomly placed in 18 plots with 3 repetitions. Forty percentage of N fertilizer was incorporated into 0-20 cm surface soil before sowing. Meanwhile, concentrated superphosphate (150 P2O5 kg/hm2) and potassium chloride (75 K2O kg/hm2) as P and K fertilizer were applied to soil before sowing. Sixty percentage of N fertilizer was applied to soil at the huge bellbottom period. After harvest, soil N (NH4+-N and NO3--N) was monitored, grain yield and straw yield were calculated according to the weighed results from sampling small plot (30 m2). N recovery was calculated by the method of difference. N balance between N input and N output was calculated during the whole growth stage of maize. Results showed that the grain yield increased first and then decreased with the increase of N application rate. Moreover, the N storage in 2 m soil showed an exponentially increasing trend with the increase of N application rate. In addition, the soil profile N had an increasing trend with the increase of N application rate and year. However, the N content of soil layer showed a decreasing trend in 0-80 cm with the increase of soil depth. The N application rate, the grain yield, the mineral N in 2 m soil, the N recovery rate of soil, the N recovery rate of plant, and the N recovery rate of soil-maize system were 237 kg/hm2, 13.7 t/hm2, 478 kg/hm2, 24%, 41%, and 65%, respectively, and with these the N surplus was 0. The value between 95% of the highest yield and the highest yield was 13.2-13.9 t/hm2, whose N application rate, the mineral N in 2 m soil, the N surplus, the N recovery rate of soil, the N recovery rate of plant, and the N recovery rate of soil-maize system were 193-291 kg/hm2, 419-563 kg/hm2, -19%-23%, 21%-26%, 41%, and 62%-67%, respectively. As a result, the reasonable N input threshold of maize is 193-291 kg/hm2 in Hetao irrigated area, which can ensure the crop yield and low N surplus, and high N recovery rate in soil-maize system. This research can provide scientific basis for N application for maize production in Hetao irrigated area.