Effect of long-term fertilization on wheat yield under different precipitation patterns.

Rational application of nitrogen and phosphorus is one of the main pathways to enhance wheat yield. The optimum dosage of nitrogen and phosphorus used in different precipitation patterns was studied using the binary quadratic regression equation, which could provide a basis for fertilization of wheat in Loess Plateau. The results showed that the amount of nitrogen and phosphorus ferti-lizer required for the maximum yield was dependent on precipitation patterns. The maximum wheat yield in normal years was 4229 kg·hm-2 , with the dosage of nitrogen and phosphorus applied being 172 and 164 kg·hm-2 , respectively. The maximum wheat yield in wet years was 4896 kg·hm-2 , with the dosage of nitrogen fertilizer being 2% more than that in normal years, 175 kg·hm-2 , and the dosage of phosphorus was about 1% less than that in normal years, 162 kg·hm-2 . The application of nitrogen and phosphorus in dry years was about 16% and 5% less than that in normal years. When the dosage was more than that, wheat yield began to decline. The economic optimum fertilization differed in different precipitation patterns. The economic optimum nitrogen and phosphorus fertilization in normal years was 161 and 151 kg·hm-2 , while in dry years it was 135, 143 kg·hm-2 , respectively. The economic optimum fertilization in wet years was about 3% and 1% more than that in normal years, 167 and 153 kg·hm-2 . The economic optimum fertilization was 6%-8% lower than optimum amount of fertilization. In actual production, it was recommended to reduce the amount of nitrogen and phosphorus by 10% in order to improve the utilization rate of fertilizer and get the maximum benefit.