Temporal-spatial Distribution Of Soil Water Resources And Their Relationship With Land Use,Landform And Annual Precipitation In Wangdonggou Watershed

Soil water is an important part of regional water resources in the Loess Plateau.The deep soil and its parent material of loess can be regarded as a huge soil reservoir,and its water storage function can effectively alleviate the drought caused by uneven precipitation and ensure the normal growth of plants.Therefore,understanding the temporal and spatial distribution characteristics of soil water resource and its influencing factors is of great significance for the rational and sustainable use of water resources,which will promote regional food production as well as forest and grass construction.Taking the Wangdonggou small watershed in Changwu County,Shaanxi Province as an example,this paper integrated existing literature data,measured the soil water content of different landform and land use patterns at a depth of 0-6 m before and after the dry season of 2019-2020.The temporal and spatial distribution characteristics of soil water resource,the soil water balance characteristics and their relationship with land use and landform during the dry season were analyzed,the main conclusions are as follows:(1).The shallow soil water content of farmland and wasteland showed great differences before and after the rainy season,which was obviously affected by the rainfall during the rainy season.The soil water content of apple orchard was affected by annual precipitation and tree age,but the influence of tree age on soil water content was mainly reflected in the soil layer below 2 m.Within a certain age range,the deep soil water content decreased with the increase of tree age.(2).Land use and landform have different effects on soil water resources at the end of the rainy season,the soil water storage of 0-6 m soil layer of the wheat field,26 a apple orchard,and Robinia pseudoacacia forest on the tableland were 1550 mm,1385 mm,and1335 mm,respectively.The soil water storage of 0-6 m soil layer of the wasteland,wheat field,26 a apple orchard and Robinia pseudoacacia forest at the ridgetop were 1604 mm,1551 mm,1180 mm and 958 mm,respectively.The soil water storage of 0-6 m soil layer located in the upslope wasteland,wheat field,26 a apple orchard,and Robinia pseudoacacia forest were 1634 mm,1659 mm,1089 mm and 979 mm.The soil water storage of 0-6 m in the downslope wheat field,26 a apple orchard and Robinia pseudoacacia forest were 1728 mm,1210 mm,and 1036 mm,respectively.In general,the soil water resources of farmland and wasteland at the end of the rainy season were better than those of apple orchard and Robinia pseudoacacia forest,and the soil water resources of the downslope were better than those of the upslope and the ridgetop.(3).The impact of land use and landform on soil water resource at the end of the dry season(the beginning of the rainy season).The 0-6 m soil water storage of the wheat field,waste apple orchard,26 a apple orchard and Robinia pseudoacacia forest on the tableland were 1341 mm,1306 mm,1266 mm and 949 mm,respectively.The 0-6 m soil water storage of the wasteland,wheat field,26 a apple orchard and Robinia pseudoacacia forest at the ridgetop were 1452 mm,1295 mm,1127 mm and 767 mm,respectively.The 0-6 m soil water storage of wheat field,wasteland,26 a apple orchard and Robinia pseudoacacia forest on the upslope were 1439 mm,1320 mm,1011 mm and 854 mm,respectively.The soil water storage of 0-6 m in the downslope wheat field,26 a apple orchard,wasteland and Robinia pseudoacacia forest were 1309 mm,1130 mm,892 mm and 857 mm,respectively.The distribution of soil water resources in the small watershed at the end of the dry season was basically the same as that at the beginning of the dry season.The soil water storage in farmland and wasteland were larger than those in the forest,and the downslope soil water storage were larger than the upslope and the ridgetop.(4).Analysis of soil water balance in dry season showed that the water consumption of apple orchards of different tree ages in the dry season were similar.The soil water consumption of waste apple orchard,26 a apple orchard and winter wheat field on the tableland were 132 mm,239 mm,and 329 mm,respectively.The soil water consumption of the wheat fields at the tableland,ridgetop,upslope,and downslope were 329 mm,483 mm,339 mm,and 538 mm,respectively.The soil water consumption of Robinia pseudoacacia forest on the upslope,downslope,and ridgetop were 244 mm,298 mm and 332 mm,respectively.The soil water consumption of the wasteland at the ridgetop,upslope and the downslope were 301 mm,433 mm,and 437 mm,respectively.It can be seen that in the dry season of winter and spring,the soil water consumption of wheat fields and wastelands were greater than that of forest land.There might be other reasons for the higher water consumption of sloping land under different utilization conditions.