Vertical distribution characteristics and temporal stability of soil water in deep profile on the Loess Tableland, Northwest China.

Abstract

Study of impacts of land uses on spatiotemporal dynamics of soil water content (SWC) is of great significance for understanding the performance characteristics of regional water cycling under changing environment. Based on long-term located field observations, this paper explored the temporal dynamics of soil water in 0-15 m soil profile under four land use types on the Loess Tableland from September 2012 to December 2015. Results showed that the annually averaged SWCs over the 0-15 m soil profile for alfalfa field, fallow field, fertilized cropland and unfertilized cropland were 15.1%, 22.0%, 19.6% and 21.1%, respectively. Soil water contents along the shallow soil profile exhibited seasonal and annual wetting and drying cycle from March to June and July to October, and the profile depths were 0-2, 0-4.6, 0-3 and 0-4.2 m, respectively. Soil water contents along the deep soil profiles had better temporal stability and were influenced by land-use types. Du-ring the observation years, the yield and water consumption in alfalfa field increased, which caused the increase of deep soil desiccation, the 2-10 m soil profile had become stable dry layer, blocking the way of precipitation recharge.As for the soil water balance in other three land use types, it was negative in cropland and fallow field during winter wheat growing season, however, during spring maize growing season, it was negative in fertilized cropland but positive in unfertilized cropland and fallow field. During the fallow period, it was positive in the three land use types. The crop water use efficiency in the fertilized cropland was increased by more than 3 times than the unfertilized cropland.