| In order to study the changes of soil moisture under different land use modes,gully watershed runoff plots-chiu district stores to shrubs and weeds and natural slope-natural shrub land and artificial trees as the research object,analyzing the soil moisture under different site conditions of dynamic change characteristics and vertical distribution of time,to clarify once precipitation process characteristics of soil water supply,Using random forest model and RDA analysis to explore the effects of different influencing factors on soil moisture,the research has important practical significance for scientific understanding of water consumption law of different vegetation,as well as targeted ecological reconstruction and rational allocation of vegetation resources in the Loess Plateau.It provides a theoretical basis for rational allocation of water and soil resources,limited soil water resources management and soil erosion control.The main results are as follows:(1)Revealed the temporal dynamic change characteristics of soil moisture under different vegetation cover types.The average monthly soil moisture content of natural slopartificial tree plot was 6.77%,6.49%,6.23%,6.38%,11.21%,and 10.90%,respectively,and that of natural shrub plot was 5.92%,5.66%,5.23%,5.36%,10.64%,and 10.23%,respectively.The monthly average soil water content of runoff plot and shrub land was 5.9%,13.4%,8.8%,6.0%,8.0%,12.6%,respectively.The monthly average soil water content of barren land was 5.6%,14.8%,10.1%,6.6%,8.4%,13.6%,respectively.In general,the average soil water content of natural slop-plantation land was larger than that of natural shrub land,and that of runoff plot-barren land was larger than that of shrub land.The variation of soil water content was consistent with the seasonal variation of precipitation.(2)The vertical variation law of soil water was clarified.The vertical variation of soil moisture firstly increased and then decreased with the increase of soil depth.The surface soil moisture was affected by precipitation and evaporation,and the variability was high.The deep soil moisture was relatively stable.In the soil layer of 0-80 cm,80-100 cm was the active layer,100-160 cm was the secondary active layer,and 160-400 cm was the relatively stable layer.The range of the relative stable layer in the artificial tree land was larger than that in the natural shrub land.There were significant differences in soil moisture in different soil layers under different cover types(P < 0.05).Tree plots consume more deep soil water than shrub plots.(3)The variation law of soil moisture under secondary precipitation was clarified.The recharge characteristics of secondary rainfall are related to rainfall intensity.The higher the rainfall magnitude is,the greater the rainfall intensity is,the more significant the response of soil moisture is.Soil moisture on the response time of the precipitation increases with the increase of soil depth,weakened with the increase of soil depth,response time depth precipitation recharge is 100 cm,generally surface soil moisture and precipitation of correlation degree is high,while the deeper soil moisture is difficult to supply function by the time precipitation,precipitation and time correlation is low,The recharge rate of the natural shrub land on the natural slope was better than that of the artificial tree land,and the recharge characteristics of the secondary rainfall on the shrub land and the barren grass land were similar in the runoff plot due to the shallow observation depth.(4)The variation characteristics of soil physical properties under different vegetation cover types were elucidated.The contents of sand,silt and clay in each soil layer on natural slope,artificial arbor land and natural shrub land are as follows: 69.19%～73.99%,21.37%～27.59%,4.59%～6.89%,sand > silt > clay.The water retention of soil in artificial shrub land was better than that in natural shrub land,and the water permeability of soil in natural shrub land was slightly better than that in artificial tree land.(5)The influence degree of soil physical properties,precipitation and soil temperature on soil moisture was clarified.The random forest model was used to analyze the influence of soil physical properties on soil moisture change of natural slope vegetation.The RESULTS of MSE showed that the interpretation rates of soil porosity,soil bulk density,silt,sand and clay contents of natural slope vegetation on soil moisture were as follows: 19.4%,16.42%,11.54%,10.94% and 3.84%,and the explanatory rates of soil bulk density,porosity,silt,clay and sand contents in natural shrub land were as follows: 16.12%,13.08%,6.04%,5.79% and 1.59% of soil physical properties,indicating that soil bulk density and porosity are the main influencing factors of soil moisture.Redundancy analysis was used to rank the environmental factors affecting soil moisture.The results showed that the influence of precipitation on soil moisture was mainly concentrated in 0-100 cm soil layer,while the change of soil moisture in deep layer was greatly affected by other factors. |
PDF Full Text Request