Effect of long-term fertilization on winter wheat water utilization in rain-fed farmland of the Loess Tableland

The water utilization of winter wheat in dryland farming was studied according to the data measured at the long-term fertilization experiment, which has been established for 22 years on the Loess Plateau. The results indicated that soil water consumption depth was affected by the infiltration depth during raining season before seeding, and it was as deep as 200 cm in the soil profile in the study year. As for ASWS(available soil water storage) at seeding stage after long-term fertilization, single phosphorus application treatment was similar to the controlled treatment, while single nitrogen application or mixed nitrogen-phosphorous application or mixed nitrogen-phosphorous-potassium application was less than the control treatment. For the mixed nitrogen with 90kg/ha phosphorus or mixed phosphorus with 90kg/ha nitrogen treatment, ASWS at seeding stage took a descendant trend as the nitrogen rates or the phosphorus rates increased from 0 to 180kg/ha, while for this experiment year, soil water consumption by crop was decreased by the former treatments contrary to the latter. For phosphorus application of 90 kg/ha, both available soil water content and soil water consumption of winter wheat in the study year were significantly decreased by increasing nitrogen application. For nitrogen application of 90 kg/ha, available soil water content was decreased with increased phosphorus application, while soil water consumption of winter wheat was increased. Compared with the control treatment, single phosphorus application, mixed nitrogen-phosphorous application, and mixed nitrogen-phosphorous-potassium application increased utilization rate of available soil water content. Mixed nitrogen-phosphorus application increased utilization rate of available soil water content in comparison with the single applications of the two fertilizers, but compared with single phosphorus application, mixed nitrogen-phosphorus application decreased the proportion of soil water consumption to crop water consumption and increased the dependency of crop yield on precipitation during the growing season. Harvest index, grain yield, and water use efficiency for mixed nitrogen-phosphorus application and mixed nitrogen-phosphorus-potassium application were all increased in comparison with single nitrogen application or single phosphorus application treatments. When phosphorus was applied at 90 kg/ha, the difference in harvest index for various nitrogen application rates was not significant, while grain yield and water use efficiency were higher than those in the case of single phosphorus application. When nitrogen was applied at 90 kg/ha, harvest index, grain yield, and water use efficiency at different phosphorus application rates were all increased in comparison with single nitrogen application.