Effect of fertilization and irrigation on wheat-maize yield and soil nitrate nitrogen leaching in high agricultural yield region in North China Plain

Field experiment with several coupled fertilization and irrigation treatments was conducted in State Experimental Station of Agro-Ecosystem in Fengqiu. Effect of fertilization and irrigation on wheat-maize yield, distribution of nitrate nitrogen in soil profile and the risk of nitrate nitrogen leaching under wheat-maize rotation system was studied. The results indicated that reasonable combined application of nitrogen and phosphorus fertilizers was the key to improve crop yield under appropriate irrigation rate. The effect of combined nitrogen with potassium or combined phosphorus with potassium on increasing crop yield was not significant. The statistic results showed that the effect order of different factors on wheat yield was nitrogen ≥ phosphorus＞irrigation＞ potassium, meanwhile the order on maize was nitrogen＞phosphorus＞potassium＞irrigation. Only the effect of nitrogen and phosphorus on crop yield was statistically significant. Effect of fertilization and irrigation on the distribution of nitrate nitrogen in soil profile was great. With increased nitrogen rate and irrigation rate, the nitrate nitrogen content of accumulation peak in soil profile increased, the thickness of the peak widened and the peak occurred in deeper soil. The nitrate nitrogen content in deep soil increased due to high nitrogen rate input. Therefore the risk of nitrate nitrogen leaching increased. An appropriate rate of nitrogen fertilizer and irrigation, and combined application of nitrogen and phosphorus played important roles on decreasing nitrate nitrogen accumulation in deep soil profile and therefore mitigating nitrate nitrogen leaching risk. The result of this research indicated that the appropriate rate of nitrogen and phosphorus fertilizers were 400 kg(N)·hm^-2·a^-1 and 225 kg(P₂O₅)·hm^-2·a^-1 respectively. The appropriate irrigation rate was less than 280 mm in one year in this research region under wheat-maize rotation system.