The Combined Effects of Land Usage and Topography on Soil Moisture Change in a Loess Area

【Background and objective】 Soil water is the main water resource for plants grown in the semi-arid loess plateau in northwestern China. Understanding its dynamics in response to environment and management changes is important to improve its use efficiency. The aim of this paper is to investigate the combined effect of land usage and topography on soil moisture. 【Method】 The experiment was conducted at a loess area in Ningwu county, Shanxi province. We measured soil water content in the depth of 0~200 cm under different conditions from July to September in 2020. The effect of land usage including artificial forest, natural grassland and cultivated land, on soil moisture at different locations in slopes and slope direction was analyzed and discussed. 【Result】 ①Temporal variation in soil moisture and precipitation was consistently correlated. With the increase in soil depth, soil moisture content decreased first followed by stabilization or increase at both the up-slope and the down-slope. In contrast, the change in soil moistures along the soil profiles in the gully bed was variable and did show any identifiable trend. ②Soil moisture content varied with land usage due to the difference in water consumption between the plants, with the soil moisture in the uphill varying with land usage in the order of natural grassland > cultivated land > artificial forest. In contrast, the soil moisture content at the gully bed varied with land usage in the order of forest land > cultivated land > natural grassland due to the low elevation of the artificial forest and its closeness to a river. ③On average, soil moisture content increased from the uphill to the gully bed, and the soil moisture in the shady slopes was greater than in the sunny slopes. 【Conclusion】 Our results show that to maintain soil moisture at ecologically functional levels, the best solution is to plant artificial forest with high water consumption at the downhill, gully bed and the shady slope, while letting the plants to grow naturally is suitable for the uphill and sunny slopes.