Estimating soil water storage recovery under former planted forest on steep slopes in the semiarid area of the Loess Plateau

Deep-rooted vegetation systems in the semiarid area of the Loess Plateau in China may result in deeper soil layers becoming depleted to unsustainable soil moisture levels. The main purpose of this study was to estimate water recovery in the 2-10 m soil layer once the initial deep-rooted vegetation was converted from forest to annual cropland and natural grassland under current climate conditions. Soil moisture at the 0-10 m depth of continuous crop and natural grass lands, crop and natural grass lands of former forest, and planted mature growing forest was measured repeatedly. The soil water storage of mature growing forest was set as the water recovery initial baseline, and that of continuous crop and grass lands were set as the upper limits for water storage recovery of crop and grass lands of former forest. The water recovery rate of annual crop land of former forest was 14.9 mm.yr^-1, the total time needed for water to recover to present continuous cropland was 41.2 years. Results showed very little water recovery under natural grasses of former forest with the estimated water recovery rate being 0-2 mm yr^-1. At such a minimal rate, the time necessary for the soil water levels to recover to present continuous natural grassland conditions would be 719.3 years. The results of this study indicate that a considerable period of time is necessary for soil water levels to recover in the Loess Plateau region once the soil has been depleted to a certain level. These types of condition may have long term environmental impacts which require further investigation to efficiently manage the water resources of this area.