Soil water restoration of different land use after artificial forest in the semi-arid area of Loess Plateau

Planted forests can deplete deep soil water, forming an obstacle to sustainable land use in the semi-arid area of Loess Plateau. The purpose of this study was to examine effects of grazing and cropping on replenishment of deep soil water where forest plantations had depleted soil moisture at depths of 2～9.9 m. We compared soil moisture on plantation plots with that on plots where plantations were replaced by crops, grazed grassland, and ungrazed grassland seperately. Over a 20-year period there was no increase in soil water content in the grazed grassland at depths of 2～9.9 m. There was a small increase(0.5～3.7 mm/a) in soil water content in the protected grassland, however the slow rate of increase suggests that at least 150 years would be needed for ungrazed grassland soils to regain water content similar to that present prior to planting trees. Recharge of deep soil moisture was faster in cropland(15 mm/a), but at this rate it would still take about 40 years to restore cropland soil water content to pre-plantation conditions. The results of this study reveal long-term ecological effects of artificial forest in this water stressed area and give useful information to sustainable land use planning.