Study On Spatial Variation Characteristics Of Soil Moisture Content In Small Watershed In Loess Hilly Region

Soil water is the main limiting factor for vegetation growth and ecological restoration in arid and semi-arid regions,and also the leading factor restricting sustainable land use.Soil water is often deficient in the loess plateau,In order to improve the ecological environment,a number of ecological restoration measures have been implemented.The study of soil moisture in the loess plateau can further understand the distribution of soil water resources,which is of great significance for water resources management,vegetation restoration and effective planning of agricultural production.In this study,the small watershed of Zhifang Gou as the research area,and the soil water of robinia pseudoacacia forest,caragana forest,grassland and agricultural land were taken as the research object.With the combination of different years of returning to farming,soil drilling method was used to sample at the sampling point.Determination of soil moisture content?mass moisture content?by drying method?105-108?,10h?;The low-temperature vacuum distillation method was used to extract soil water with LI-2000 plant water and soil water vacuum extraction system,and the liquid water isotope analyzer was used for soil water isotope analysis and determination.Studied the spatial distribution of soil water in small watershed,characteristics and influencing factors of soil water changes in different land use patterns,distribution characteristics of hydrogen and oxygen isotopes in soil water,the following main research results are obtained:?1?The small watershed of Zhifang Gou in the hilly area of the loess plateau has a large range of variation and an obvious spatial distribution pattern,which is mainly manifested as high in the south and low in the north.Land use type has a great influence on the vertical change of soil moisture in soil profile.The variation of korshinskii forest in the whole soil profile is characterized by decrease,then stabilization,then decrease and finally increasing.The root system of the grassland was shallower,and the utilization capacity of soil water was limited and the consumption was less.Agricultural land USES less soil water,and the effective use of layer in the surface layer,rainfall can supply deep soil water,and the winter water consumption is less,long-term accumulation,so the soil water content of agricultural land is higher.The sequence of soil average water content is:agricultural land?14.86%?>grassland?14.00%?>acacia?9.17%?>caragana?6.48%?.The distribution of soil water in each layer is basically the same.The soil water content in the whole depth of the soil layer is between 4.39-32.94%.The soil water content in the depth of soil layer 3-7m is not different,and this layer is the stable layer of soil water in this basin.?2?The spatial distribution of soil water in different land use patterns in small watershed in loess hilly region is obviously different,and the soil water content is generally lower.The average soil water content in each layer of korshinskii forest varied between 7.82%and 9.19%,the grass profile of each layer soil moisture content between9.28%-15.19%of the average,the average farmland the layers of soil water content is9.15%-15.03%range change,various land use type,soil moisture belong to medium variation,out of the grass,the other three types of land use data of soil water content affected by extreme value is small;Soil water was negatively correlated with the slope,slope direction?from the sunny slope to the negative slope?and the number of years of returning cultivation,and positively correlated with the land use mode?according to the order of robinia,caragana,grassland and farmland?.?3?Soil and water conservation measures should be taken to improve the effect of vegetation restoration.The influence of precipitation on soil water content was obvious,and the soil water content of the horizontal step converted grassland?13.38%?was>natural converted grassland?13.21%?.The variation trend of soil moisture content in the shallow layer of the horizontal and natural converted grassland is basically the same.In general,the level of the converted grassland below the depth of 200 cm was higher than that of the natural one.In different growth cycles,soil water content showed significant differences at different depths.Taking the growing period as an example,the average soil water content at 0-100 cm depth was in the natural converted grassland?12.46%?and>level stage converted grassland?11.58%?,while that at the 100 cm depth was in the natural converted grassland?14.02%?<the horizontal stage converted grassland?14.44%?.The influence of rainfall on soil moisture content at different depths was different,and the influence on surface soil moisture content was the greatest.?4?Soil water?¹⁸O and?D in the study area gradually enriched with the increase of soil depth.The variation characteristics of water,hydrogen and oxygen isotopes in different land use types are different.Soil water hydrogen oxygen isotope?¹⁸O grassland>agricultural land>robinia caragana,soil water hydrogen oxygen isotope?D farmland>grassland>robinia caragana.Due to rain in a short period of time after evaporation,fractionation process,such as water and soil is a new water and old times rainfall happened in time and space of a mixture of dilution water,so the different land use types of soil water of hydrogen and oxygen isotope fitting relationship and the relationship between the atmospheric precipitation line,are soil water hydrogen and oxygen isotope fitting line is located in the atmospheric precipitation line right;The variation characteristics of soil water?¹⁸O and?D of different land use types in the same soil layer are basically the same,and the variation varies in different soil layers.The replenishment effect of the rainfall is limited,and it can only replenish the surface soil water,but it is difficult to replenish the deep soil water.Therefore,the influence of the rainfall on soil water?¹⁸O and?D is also obvious.The minimum value and average value of soil water?¹⁸O are the same as that of>before and after rain.The maximum,minimum and average values of soil water are>before and after rain.Overall soil water?¹⁸O and?D before and after rain in the whole section.