Nutrient absorption, translocation in rice and soil nitrogen
equilibrium under different nitrogen application doses

【Objectives】A systematic analysis on the rice yield, component factors, nutrient absorption, translocation, nitrogen use efficiency and nitrogen balance in soil under different nitrogen levels was performed to provide theoretical basis for rational amount of applied nitrogen in rice field in northeast China, and the interactions relationship between nitrogen, phosphorus and potassium in soil as well as relationships between nutrient and yield were discussed.【Methods】 The field experiment was carried out by using local major rice varieties (Fuyou 135 and Jijing 511) at Hongguang State Farm of Qianguo County in Songyuan City of Jilin province from 2012 to 2013, and the experiment includes five treatments with different nitrogen levels (0, 60, 120, 180 and 240 kg/hm2). As plant samples, stem-sheath, leaf and grain parts at returning green stage, mid-tillering stage, heading stage, filling stage and maturity stage were collected to measure the contents of nitrogen, phosphorus and potassium, respectively. Based on these data, the nutrient absorption, translocation, nitrogen use characteristics parameters, and the relationships between nutrient absorption, translocation and yields of the plant at the main growth stages of rice were calculated or evaluated. The soil samples from 0-100 cm soil depth (each layer 20 cm) were respectively collected before transplanting and after harvest of rice to measure the contents of ammonium and nitrate nitrogen. Depending on the soil bulk density of each layer, the amount of inorganic nitrogen accumulation in 0-100 cm soil layer was calculated to profile soil nitrogen balance.【Results】 Data showed that when the amounts of applied N were ranged from 60 kg/hm2 to 180 kg/hm2, the rice yield increased with increasing amounts of nitrogen fertilizer, and decreased when the amount of applied N was over N 180 kg/hm2. Based on the prices factors of rice and fertilizers in the past years, N rates for obtaining maximum yield were 212.8 kg/hm2 and 220.6 kg/hm2 respectively, and the range of nitrogen application was ranged from 202.2 kg/hm2 to 231.6 kg/hm2. N rates for getting the optimum yield were 203.0 kg/hm2 and 209.1 kg/hm2, and the range of nitrogen application was determine to be between 192.9 kg/hm2 and 219.6 kg/hm2 by simulating between rice yield (y) and nitrogen fertilizer application (x), respectively. Nitrogen fertilizer application could significantly improve the accumulation of nitrogen, phosphorus and potassium at main growing stages, and increased the translocation of nitrogen, phosphorus and potassium to grains at heading stage. The accumulation amount of nutrients at heading stage is proportional to the amount of translocation to grain under N 180 kg/hm2. Nitrogen fertilizer rates over 180 kg/hm2 had negative effects on the translocation of nitrogen, phosphorus and potassium to grain. Nitrogen agronomic efficiency and partial factor productivity were significantly decreased because of increasing nitrogen fertilizer application. The highest nitrogen recovery efficiency in current season was in the treatment of N 180 kg/hm2. Correlation analysis showed that the yield had significantly or extremely significantly positive correlations with absorption and translocation of nitrogen, phosphorus and potassium at the main growth periods of rice, and the highest correlation coefficient was exhibited at the filling stage. Nitrogen fertilizer application could significantly improve residual Nmin at 0-100 cm soil after harvesting, and increase in nitrogen fertilizer application apparently enhanced the losses of N.【Conclusions】Optimum nitrogen fertilizer application could significantly improve rice yield, the total nutrient accumulation at different growing stages, the translocation amount of nitrogen, phosphorus and potassium from straw to grain during the late growth period of rice, and apparently reduce losses of soil N. Comprehensively, considering on the rice yield, benefit, nitrogen recovery efficiency in season and nitrogen balance in soil, the optimum nitrogen application rate was determined to be ranged from 192.9 kg/hm2 to 219.6 kg/hm2 in this experiment.