陕北丘陵区陡坡柠条林地与荒坡土壤水分变化研究

通过定点土壤水分测定与对比分析，研究了陕北丘陵区陡坡柠条林地与荒坡的土壤水分亏缺状况，年际年内动态变化规律，干燥化特征及其自然降水的补偿能力。结果表明，柠条林地与荒坡0-10m土层贮水量仅相当于田间持水量的26．2％～41．2％。荒坡地0-10m土层贮水量相当于田间持水量的39．8％～41．2％。土壤贮水量的分布是阳坡〈半阳坡〈阴坡，上坡位〈下坡位。年际间土壤水分的变异程度随土壤深度的增加而减弱，土壤贮水量的变化主要发生在2m以上土层内。土壤贮水量具有明显的季节变化特征，但滞后于降雨量变化。生长季内，柠条地与荒坡的土壤平均贮水量之间差异显著，土壤越深，其含水量变化程度越小。两种利用方式的土壤剖面都产生了不同程度的干化层。相比而言，柠条林地深层土壤干燥化强度明显大于荒坡地。丰水年柠条林雨水补偿深度仅为1．0m，荒坡也仅为1．2m。柠条林丰水年的雨水补偿深度比干旱年可增加60cm以上，5m土层贮水增量增加3倍以上。

Changes of Soil Moisture in Slope Caragana Land and Wasteland in the Hilly and Gullied Area of Northern Shaanxi

We investigated soil moisture deficit, inter-annual and inner-annual changes, dry layer features, and restored capability of natural precipitation in slope Caragana land and wasteland in the hilly and gullied area of Northern Shaanxi Province by positioned measurements and comparative analyses. Results showed that water storage in 0--10 m soil profile was only 26.2%-41.2% of its water-holding capacity in slope Caragana land, while it was 39.8%-41.2% in slope wasteland. Slope segments, in terms of spatial distribution of soil water storage, were in the ascendant order of south faced slope, semi-south faced slope, and north faced slope, as well as upper slope and lower slope. Inter-annual variation of soil moisture lowered with increased soil depth and the changes of soil water storage mainly took place in 0-2 m soil profile. Soil water storage was characterized by obvious seasonal changes but lagged behind rainfall. Within growing season, averaged soil water storages were of significant difference between slope Caragana land and wasteland and the variation of soil moisture content was alleviated with increased soil depth. There existed a dry soil layer in soil profile to different extent in both Caragana land and wasteland. Comparatively, in deep soil, the dried degree of the soil layer was greater in Caragana land than wasteland. In a bumper year of precipitation, the restored depth of soil moisture was down to 1.0 m of the soil profile in Caragana land and to 1.2 min wasteland. In Caragana land, the restored depth of soil moisture was 60 cm greater in a bumper year of precipitation than a lean year and soil water storage increased by 3 times in 0-5 m soil.