Effects of nitrogen application rate on nitrogen absorption and utilization in summer maize and soil NO₃^--N content under drip fertigation

Inappropriate management of fertilizers is common in high-yield summer maize cultivation regions in the piedmont plain of Taihang Mountain, Hebei Province. Fertilizers overuse results not only in serious waste, but also in agricultural non-point source pollution. This study focused on appropriate nitrogen application to support high yield of summer maize under water-fertilizer integration condition. Using 'Zhengdan-958' as the test maize cultivar, four nitrogen rates (N0:no fertilizer; N1:120 kg·hm^-2; N2:240 kg·hm^-2; N3:360 kg·hm^-2 of nitrogen) were set up in 2014-2015 summer maize cultivation seasons under drip fertigation condition. The effects of different nitrogen application rates on the uptake and utilization of nitrogen in summer maize and on nitrate nitrogen content in soil were determined. The results showed that while dry matter weight and yield of maize under N0 treatment significantly decreased, there were no significant differences among N1, N2 and N3 treatments. Nitrogen content and accumulation in maize under N1 treatment significantly increased compared with that under N0 treatment. In the range of N1-N3, nitrogen content and accumulation differed among different years, which increased with increasing nitrogen application rate. However, nitrogen accumulation rate decreased gradually with increasing in nitrogen application rate. Nitrogen harvest index was the highest under N2 treatment among all treatments. Nitrogen recovery efficiency, nitrogen agronomic efficiency, nitrogen productive efficiency and nitrogen use efficiency decreased significantly with increasing nitrogen application rate. In 2014, nitrate nitrogen content under all nitrogen treatments decreased gradually in the 0-100 cm soil layer. In 2015, nitrate nitrogen content in N2 and N3 treatments reached cumulative peak in the 80-100 cm soil layers. This was related to increasing nitrate nitrogen leaching in the soil, which reach down to the 100 cm soil layer when nitrogen rate exceeded 240 kg·hm^-2 during the two years of maize cultivation. Based on the relation between N application rate and yield fitted by one variable quadratic equation, the highest maize yield needed nitrogen application rate in the range of 199-209 kg·hm^-2 and economic nitrogen application rate in the range of 174-187 kg·hm^-2. Considering the ecological environment and economic benefits, the economic nitrogen application rate was the optimal mode for summer maize under drip irrigation condition.