Effect Of Pisha Sandstone Addition On Water Movement And Alfalfa Growth In Sandy Soil

Surface coal mining in the Jin-Shaan-Meng contiguous area,which locates in the arid and semi-arid ecologically fragile areas,has produced large areas of waste dump.The re-vegetation on the waste dumps is very difficult due to drought,lack of water,and the rough,thin,poor structure topsoil and its poor capacity to retain water.How to efficiently and cost-effectively improve the topsoil and increase its capacity of water retention and drought resistance using the local materials has become an important issue for land reclamation and ecological restoration in this region.In our research,the widely distributed Pisha sandstone is selected as a sandy soil conditioner.The laboratory and pot experiment tests are carried out to study the soil hydraulic parameters,infiltration,evaporation and the suitability of alfalfa growth on different restructured topsoil.And the process of soil water movement and the distribution of soil profile water are simulated by Hrdrus-1D model.Then the suitable restructured soils are proposed for plant growth in this mining area.The main research conclusions are listed as follows:(1)With the increase of the proportion of Pisha sandstone in sandy soil,the soil water holding capacity and saturated water content increased,the saturated hydraulic conductivity and infiltration rate decreased gradually,and the soil water content increased under the same matrix suction.Which shows that the Pisha sandstone has the function of hindering water movement,and it could be used as a modifier to improve the water absorption and holding capacity of the sandy soil.Comparing with the soil hydraulic parameters of loessial soil,the 40% of the Pisha sandstone added to the sandy soil(S4)are the closest to the loessial soil,which can be selected as the most appropriated proportion to improve sandy soil in the study area.(2)Under the same soil material,the water retention capacity of the layered soil is higher than that of the homogeneous mixed soil.The water retention capacity enhancement of layered soil(the upper coarse with lower fine and the upper fine with lower coarse)is similar.And the water retention capacity enhancement of the fine embed into coarse treatment is the highest;The van Genuchten model of homogeneous soil water characteristic curve is used to simulate the soil water content at different soil matric potential.The residual water content and saturated water content of the layered soil are higher than that of homogeneous soil under the same soil material,and the shape parameter ? value decreased compared with the homogeneous soil.This study can provide theoretical basis and technical support for studying the water retention and water availability of layered soil,and the reconstruction of topsoil in the mining area.(3)The infiltration capacity of homogeneous soil is in order from large to small as sandy soil,the mixture,Pisha sandstone.For the layered soil,the upper the Pisha sandstone interlayer is,the larger the thickness is,the more obvious hindrance to the water infiltration.For the multiple interlayers and the same position of the upper layer,the number of Pisha sandstone interlayer has no significant effect on infiltration.The cumulative evaporation of the soil in which the Pisha sandstone is embed into the sandy soil does not change significantly,but the water storage capacity of the layered soil increases significantly.From the point of view of water holding capacity,the layered soil could be used as a suitable model for the topsoil reconstruction in the mining area.(4)Inverse modeling by Hydrus-1D software has several advantages in estimating soil hydraulic parameters.Which can well simulate the water movement under one-dimensional water infiltration.In the reconstruction soil by Pisha sandstone and sandy soil,we can use the readily available soil water data with the time to reverse the soil hydraulic parameters,which greatly reduces the difficulty of obtaining these parameters.(5)Mixing the Pisha sandstone with the sandy soil or the layered soil with Pisha sandstone and sandy soil all can promote alfalfa growth.The higher biomass and more uniform root distribution in the layered soil indicated that the layered structure soil with Pisha sandstone interlayer in sandy soil is suitable for plant growth.The distribution of soil water is controlled by the Pisha sandstone layer,which affects the growth of alfalfa.The layered soil with 20 cm Pisha sandstone at 20-40 cm in the sandy soil is recommended for the topsoil reconstruction,considering the plant biomass,root system,operability and economic input.