Nitrate leaching characteristics of wheat-corn rotation farmland in Guanzhong area of Shaanxi

YIN Xiao-fang, TONG Yan-an, ZHANG Shu-lan, ZENG Yan-juan, GAO Peng-cheng, ZHOU Jun, YANG Xian-long (College of Resources and Environmental Sciences, Northwest A & F University, Yangling 712100, Shaanxi, China).

nitrate leaching; in-situ determination; wheat-maize rotation

By using in situ leaching device, a field experiment was conducted to study the effects of nitrogen fertilization rate and straw mulching on the nitrate leaching at 90 cm soil depth, nitrate accumulation in soil profile (0-100 cm), crop yield, and nitrogen balance of wheat-corn rotation farmland in Guanzhong area of Shaanxi. Six treatments were installed, i.e., no fertilization (N1, 0 kg·hm-2·a-1), conventional fertilization (N2, 471 kg·hm-2·a-1), recommended fertilization (N3, 330 kg·hm-2·a-1), reduced N application (N4, 165 kg·hm-2·a-1), increased N application (N5, 495 kg·hm-2·a-1), and recommended fertilization plus straw mulching (N3+S). The nitrate leaching loss was increased with increasing N fertilization rate. Excessive N fertilization and straw mulching could easily cause nitrate leaching. In treatment N3+S, the annual NO3--N loss at 90 cm soil depth was the greatest (22.32 kg N·hm-2), and the NO3--N loss from N fertilization was 16.44 kg N·hm-2·a-1, being 158.9% higher than that in treatment N3. Nitrate mainly accumulated in 20-60 cm soil layer. When the N application rate was 330 kg N·hm-2·a-1, straw mulching had less effect on the NO3--N distribution in soil profile. No significant difference was observed in the crop yield among the treatments, but reduced N application (N4) tended to decrease the yield. Under our experimental condition, a fertilization rate of 150 kg N·hm-2·a-1 for wheat and 180 kg N·hm-2·a-1 for maize could ensure the crop production and reduce the soil nitrate leaching and accumulation.