Soil Moisture Distribution And Dynamics Under Different Geomorphological Conditions In The Hilly And Gullied Area Of Northern Shaanxi Province

The hilly and gully region in northern Shaanxi is an arid and semi-arid region.Due to the shortage of soil water resources and serious soil erosion,the ecosystem in this region is very fragile.It is of great significance to explore the spatial and temporal distribution of soil water at different scales for regional water resources management,vegetation restoration and sustainable development.For this reason,this paper takes the slope-gully system in the fractured topographic area as an example,and carries out long-term continuous monitoring of soil moisture at 5 depths of 0~150 cm soil layer,so as to study the change characteristics of soil moisture at different topographic conditions and observation depths.The study on the occurrence characteristics of preferential flow in soil was carried out by dye tracer test.The main conclusions are as follows:(1)Soil moisture content has obvious seasonal and interannual variation characteristics,and the soil moisture content in time series was as follows: dam land > ditch slope > ditch edge > side.The coefficient of variation(CV)of soil moisture in each soil layer ranges from 63.1 % to 97.5 %.Soil moisture content was positively correlated with soil clay content,bulk density and total potassium content,but negatively correlated with silt content.Soil available water content also varied significantly under four topographic conditions: dam land > ditch edge > ditch slope > side.CV variation ranged from 50 % to 100 %,all of which were medium variation.There were significant differences in soil moisture content under four topographic conditions.With the increase of depth,the degree of soil desiccation decreased,and there was no desiccation in the 100~150 cm soil layer.The desiccant degree of soil in the 0~60 cm soil layer is seriously affected by seasonal factors,and the desiccant degree of soil can be alleviated or even disappear with the supplement of precipitation.The soil desiccant phenomenon of different degrees appeared in the groove edge,groove slope and west slope.(2)The dynamic changes of soil water storage in different soil layers over time are similar.The soil water storage in dam land was the highest,and the soil water storage at a depth of less than 60 cm is greatly affected by seasons.The depth of 60 cm can be regarded as the effect depth of topographic factors on soil moisture.When the depth of soil is more than 60 cm,the influence of topographic factors on soil water storage is more prominent.In the time series,the soil water storage in each soil layer has a strong correlation with the water storage in the upper soil layer.There was an autocorrelation relationship between the soil water storage volume and the soil water storage volume at depth of 0~150 cm under different terrains.However,the autocorrelation between the soil water storage volume at depth of 0~150 cm under different terrains is not significantly different.(3)The water movement pattern in sandy soil is complex and uneven.Water tends to migrate quickly to deeper soil layers through large pores,forming preferential flow and forming heterogeneous figure flow with obvious morphological characteristics in sandy soil with uniform structure.The characteristics of the soil itself affect the preferential flow characteristics.