Abstract: Nitrogen limitation is an important factor for the improvement of crop water production potential in rain-fed areas of the Loess Plateau. The reasonable deep application of nitrogen fertilizer is a promising method to increase yield of rain-fed crop. Based on APSIM model, this study simulated spring wheat yield under different nitrogen application rates and depths, by using meteorological observation data from 1990 to 2020 in the semiarid areas of central Gansu Province, aiming to provide theoretical reference for optimizing wheat fertilization strategy. The results showed that the determination coefficient of simulated spring wheat yield, biomass and soil water content in 0-200 cm soil profile was greater than 0.80, the normalized root mean square error was less than 0.2, and the model validity index was greater than 0.5. These results indicated that the model had good fitting and adaptability in the test area. Across all the levels within the experimental design, increasing nitrogen application rates could significantly increase the yield of spring wheat in different precipitation years, and increasing nitrogen application depth could significantly increase spring wheat yield in wet and normal years, but had no effect in dry years. The rate and depth of nitrogen application had significant interaction effects on spring wheat yield in wet and normal years, but not in dry years. According to the binary quadratic regression fitting equation, when the potential maximum yield reached 2749 kg·hm^-2 in wet year, nitrogen application depth was 22.7 cm, and nitrogen application rate was 245 kg·hm^-2. When the maximum potential yield reached 2596 kg·hm^-2 in normal year, nitrogen application depth was 20.6 cm, and nitrogen application rate was 235 kg·hm^-2. Integrating the effects of nitrogen application rate and depth on yield, biomass and agronomic efficiency of nitrogen fertilizer, and farmer's fertilizer application habits, the recommended nitrogen application depth was 20-23 cm, and nitrogen application amount was 120-150 kg·hm^-2, which could further improve water productivity and nitrogen use efficiency of spring wheat in arid areas of central Gansu Province.

Key words: APSIM, spring wheat, nitrogen application rate, nitrogen application depth, yield, nitrogen use efficiency