Abstract:Field experiments (2013 and 2014) were carried out to improve nitrogen use efficiency and decrease nitrate nitrogen leaching for summer maize. Two nitrogen fertilizers, including urea (with nitrogen application rates of 0, 80, 160 and 240kg/hm2, 40% of nitrogen fertilizer was applied as basic and 60% of it was top dressed at bell stage; namely N0, N80, N160 and N240) and controlled-release fertilizer (with nitrogen application rates of 0, 60, 120, 180 and 240kg/hm2, all applied as basic fertilization; namely K0, K60, K120, K180 and K240) were chosen to investigate the effects of different nitrogen application rates on root growth, yield, nitrogen absorption and nitrogen use efficiency of summer maize and nitrate nitrogen distribution in soil. The results showed that characteristic parameters of summer maize root at filling stage presented a trend of increase and then decreased along with the improvement of nitrogen application rate for both of the two nitrogen fertilizers. The characteristic parameters of summer maize root were higher in N160 of the urea treatments and higher in K120 of the controlled-release fertilizer treatments than those of the other treatments. In addition, compared with root surface area, total root length and yield had higher correlation. This meant that root length of summer maize played an important role in yield improvement under different nitrogen application rates. Furthermore, the nitrate nitrogen accumulation of the controlled-release fertilizer treatments agreed much better with the plant requirement for nitrogen than that of the urea treatments. In contrast to urea treatments, nitrate nitrogen content of the controlledrelease fertilizer treatments had less variation and the maximum nitrate nitrogen content was shallower in 0~200cm soil layer at harvest. Among the two nitrogen fertilizers treatments, N160 and K120 had greater yield, nitrogen harvest index and nitrogen use efficiency than other treatments. And K120 was potential in saving fertilizer and increasing efficiency, which could averagely increase nitrogen harvest index by 5.38% and improve nitrogen use efficiency by 4.96% compared with N160 in two years. In conclusion, the nitrogen application rate of treatment K120 was appropriate for summer maize cultivation in Guanzhong Region, Shaanxi Province.
