Abstract: 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 annualNO₃^--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 N_3. 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 theNO₃^--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.

Key words: nitrate leaching, in-situ determination, wheat-maize rotation, Iris hexagona, salicylic acid, cadmium, growth.