Simulation of soil water dynamics and water productivity of apple trees in different areas of Shaanxi Province, China

Abstract

Using WinEPIC and partial least squares regression model, we compared the driving factors of water productivity and soil moisture dynamics of several mature apple plantations in Shaanxi from 1981 to 2016. For the hilly and gully region of northern Shaanxi, the residual loess platform region in Weibei, and Guanzhong Plain, the average annual yield of mature apple forests was 16.94, 22.62 and 25.70 t·hm-2, the annual average evapotranspiration was 511.2, 614.9 and 889.88 mm, and the water productivity was 3.81, 3.82 and 3.24 kg·m-3, respectively. In northern Shaanxi and Weibei regions, water stress was the most serious, with the average annual stress days being 54.89 and 28.38 d, respectively. The N-level stress in Guanzhong region was severe, with an average annual stress day of 25.87 d. The largest factor affecting the yield of apple plantations in the northern Shaanxi and northern Weibei regions was the precipitation. The standardized regression coefficients were 0.274 and 0.235, respectively, the amount of N applied had a significant impact on the yield, with regression coefficients of 0.224 and 0.232, respectively. The maximum impact factor in Guanzhong region was the amount of N applied, with a regression coefficient of 0.335, followed by the amount of water supplied and the amount of applied P. The regression coefficients were 0.154 and 0.147, respectively. The dominant factor affecting the water productivity of apple plantations in northern Shaanxi and Weibei was precipitation, and the standardized regression coefficients were 0.238 and 0.194, respectively. The most important impact factors in Guanzhong region were the amount of N applied and the amount of water supplied, and the regression coefficients were 0.182 and 0.178, respectively. During the simulation period, the total water consumption of apple plantations in the northern Shaanxi, Weibei and Guanzhong regions was 1152.17, 1342.95 and 1372.42 mm, respectively. The effective water content decline rates of 2-15 m soil layers were 63.44, 57.08 and 51.41 mm·a-1, respectively. The dry layer of deep soil appeared after 8, 13 and 17 years, and the dry layer was stable to 11 m deep for 18, 21 and 26 years, respectively, suggesting the drying status was severe. The management focus of apple plantations in different regions should be determined by the dominant factors of water productivity.