Temporal and spatial variations in soil moisture under jujube forests in the Loess Hilly Region

To study the impact of jujube forest on soil moisture in the loess hilly and gully region, a long-term observation of soil moisture in Mizhi County, Shaanxi Province was conducted. Short-term soil moisture with measured soil physical properties, and soil moisture in four types of jujube forests were investigated. The jujube forest types were 5 years and 15 years jujube forests, and 14 years regenerated jujube forest (planted at the same time with the 15 years jujube forest and regenerated in the 14th year). Then the differences in soil moisture in relation to soil texture in different jujube forests were analyzed. The depths of water consumption by jujube trees and the soil desiccation in jujube forests were also studied. The results showed significant difference in soil moisture among different jujube forests. The quantity and depth of water consumption increased with increasing age of jujube tree. This suggested larger water consumption of soil of older jujube trees. Along the soil profile, average soil moistures of 5 years jujube forest and 14 years regenerated jujube forest was not significantly different, but they all significantly different from that of 15 years jujube forest. This suggested that an effective measure of water saving was to timely update jujube forests. Soil moisture was significantly positively related with soil silt particle content, which influenced water uptake by jujube tree roots. The depth of water consumption of jujube forests was 440 cm in 5 years jujube forest, 800 cm in 15 years jujube forest and 840 cm in 14 years regenerated jujube forest. There was apparently severe desiccation in the 400500 cm depth soil layer with 100 cm thick dried soil layer, severe desiccation in the 300600 cm depth soil layer with 300 cm thick dried soil layer in the influence range of jujube tree root water uptake, respectively under 5 years jujube forest and 14 years regenerated jujube forest. Then there were two desiccation layers in the influence sphere of 15 years jujube forest root water uptake, which were severe desiccation in the 200300 cm depth soil layer with 100 cm thick dried soil layer and extreme desiccation in the 300600 cm depth soil layer with 300 cm thick dried soil layer. Compared with other studies, this research increased the depth of soil under jujube forests. Based on earlier research results, we proposed a new method with the soil moisture of wild grassland as reference, to creatively evaluate soil desiccation of jujube forest by using soil relative aridity. Soil moisture condition in jujube forest was related to the age of jujube and soil texture. Regenerated trees following cutting trunks consumed less water. The results provided theoretical basis for sustainable development of jujube forests, soil moisture regulation and dry soil layer control in jujube forestlands in semi-arid mountainous regions. To some extent, this promoted restoration of vegetation in these areas.