黄土丘陵区枣林地土壤水分时空变化研究

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

为探索枣树种植对黄土丘陵沟壑区土壤水分的影响,在陕西省米脂县,以5 a和15 a枣林地及14 a更新枣林地（与15 a枣林同年栽植,14 a时截枝截干更新）为研究对象,对枣林地土壤水分进行长期定位观测,分别研究了不同树龄枣林地的土壤水分差异、土壤水分与土壤质地关系、枣树耗水深度以及土壤干燥化问题。结果表明：1）不同树龄枣林地土壤水分存在显著差异,随树龄增加,枣树年耗水量增大,枣树耗水深度增加。2）枣林地枣树根系吸水影响范围内的土壤水分与粉粒含量呈显著正相关关系。3）不同树龄枣林地的耗水深度分别为5 a枣林地440 cm、14 a更新枣林地800 cm、15 a枣林地840 cm。4）5 a枣林地在根系吸水影响范围内出现了100 cm深的重度干燥化土层（土层深度为400-500 cm）,14 a更新枣林地在根系吸水影响范围内出现了300 cm深的重度干燥化土层（土层深度为300-600 cm）,15 a枣林地在根系吸水影响范围内分别出现了100 cm深的重度干燥化土层（土层深度为200-300 cm）和300 cm深的极度干燥化土层（土层深度为300-600 cm）。枣林地土壤水分状况与树龄、土壤质地相关,截干更新具有减少耗水的作用。研究结果可为今后半干旱山地枣林可持续经营及防治林地土壤干层研究提供一定理论依据。

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 14 th 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 400-500 cm depth soil layer with 100 cm thick dried soil layer, severe desicca-tion in the 300-600 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 200-300 cm depth soil layer with 100 cm thick dried soil layer and extreme desiccation in the 300-600 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.