| It is of great significance to study the law of soil moisture dynamics under different vegetation in karst area after conservation to farmland.Three different vegetation types and farmland in karst area of Chenqi small watershed in Puding county,GuiZhou province were taken as research objects.Soil moisture distribution was measured using TDR probes,soil moisture characteristics curves were determined with the pressure membrane meter method.Combined with field monitoring and laboratory test results,we analyzed the influence of different vegetation types on the spatio-temporal dynamics of soil moisture and soil moisture characteristics curve.The study of these problems can provide important theoretical guidance for the selection of low-efficiency forest and vegetation restoration in the process of returning farmland to forest and grassland.The main research results are as follows:(1)The soil moisture in order from large to small of different vegetation types were: shrubland,shrubgrass,secondary forest,and farmland with the mean value of 18 cm,14cm,13 cm and 9cm,respectively,indicates that after returning farmland soil moisture content of three different vegetation types was obviously higher than that of farmland and have better water conservation function.The change of soil moisture across soil profile were relatively small for shrubland,shrubgrass and secondary forest with the increase of soil depth,while the soil moisture increased apparently at 30 cm depth in farmland.The shrubland had the greatest water conservation function.The response of profile soil moisture dynamics to rainfall was significantly affected by vegetation type.This may be due to the deep roots,stable soil structure,high water holding capacity and good soil and water conservation effect of growing shrubs.(2)The soil moisture characteristic curves were measured by pressure membrane meter for comparative analysis.At low suctions,the soil moisture decreased rapidly,while soil moisture decreased gradually at high suctions.The shrubland has the highest soil water content,followed by shrubgrass and secondary forest,and the farmland has the lowest soil water content.That indicated that the soil water content of the three different vegetation types was higher than that of the farmland.This may be ascribed to the relatively low land cover and organic carbon content as well as simple vegetation type.Thus,the soil water holding capacity and the ability to prevent evapotranspiration are relatively weak.The VG model was used for parameter solution and curve fitting,VG model parameters associated with soil texture,the saturated water content and air entry value increased with the increase of clay content,three different vegetation types because of its farmland soil clay content is greater than the farmland.Therefore,the saturated water content in three differentvegetation types were higher than that of farmland,the air entry value in shrubland was the highest due to its largest clay content.At the same time,the soil moisture characteristic curve of the farmland and three different vegetation types can be well fit using VG model,with relatively small sum of squared residuals.(3)According to the field measurement,the averaged soil available water capacity showed:shrubland>secondary forest>shrubgrass>farmland.Moreover,soil available water content is affected by soil texture.The shrubland has the highest available water content,while the farmland has the lowest soil available water content.Through soil equivalent pore diameter analysis,from 0-10 cm to 20-30 cm depth,the large pore content decreased by 11.4%,11.8%,6.5%,and 11.4%,the tiny pore decreased by5.0%,6.9%,3.8%,and 5.0%,and the effective porosity content increased by 6.3%,4.9%,2.7%,and 6.3%,respectively.The soil water holding capacity and effective water content increased with the increase of micro pore content. |
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