| The Shanxi,Shaanxi and Mongolia contiguous area,located in the north of the Loess Plateau,China,is characterized by low precipitation and fragile ecological environment.At the same time,this area is also an important energy base in China.Coal mining brings huge economic benefits,but also causes great damage to the local environment.Land reclamation is the main measures to improve the mining ecological environment.However,land reclamation in this area is restricted by soil water shortage.For better understanding the influence of land reclamation on soil water in mining area and the water movement law in reconstructed soil,in this study,undisturbed soil columns(with inner diameter: 23 cm,height: 100 cm)of the three main soils in the contiguous region were taken to measure the infiltration capacity,soil water content change and plant growth,which would provide essential data for selecting suitable soil types for soil reconstruction.Moreover,the sample plot was laid out in original landscape near the refuse dump,and the infiltration capacity of soil was measured by using double rings.The change of soil water in the profile of 2 m deep was monitored by neutron probe,and the change of vegetation(including vegetation coverage and community composition,etc.)was monitored for providing background data for vegetation restoration in mining areas.Furthermore,five main vegetation types in the refuse dump were selected to obtain the infiltration indexes such as soil infiltration stability rate by using double rings.Water content in the 0-300 cm soil profile was monitored using neutron probe,and the temporal stability of soil water was analyzed by using the relative difference method in order to screen the suitable vegetation restoration model and to provide data support for the soil reconstruction in the mining area.Additionally,plot(120 cm long,120 cm wide and 100 cm deep)experiment in the refuse dump was set up to conduct soil reconstruction with hard loess,wind-sand soil and montmorillonite-enriched siltstone(MS),and alfa is planted.The soil physical quality of the soil is measured,and the infiltration and soil water dynamic were observed,in order to screen the soil configuration that is suitable for the climatic conditions of the mine.Besides,soil column(23 cm inner diameter,height 100 cm)experimental study was carried out to research the water movement in soil-plant system,which was used to clarify the soil water movement process and characteristics and the influence mechanism of soil types on soil water movement and distribution in new constructed soil.The main conclusions are as follows:(1)The soil water infiltration and variation characteristics of the three main kinds of soil(sandy soil,loessal soil and hard loess)in contiguous area showed that soil mixture had obvious effect on the water infiltration,the steady infiltration rate of the three kinds of soil is quite different,the minimum steady infiltration rate was found in hard loess(0.014 cm/min),steady infiltration rate in sandy soil was nearly 10 times that in hard loess.Due to its strong water holding capacity,hard loess showed a higher water storage capacity,slow evapotranspiration and low coefficient of variation.During the overwintering period,the soil water content in the hard loess section decreased uniformly,while the water content in the bottom of sandy soil was higher than that in the upper layer.In years with good soil water conditions,soil types had no significant effect on biomass(P < 0.05).While in conditions of insufficient soil water or short growth time,soil types had a significant effect on biomass.(2)The vegetation coverage in the original landform is about 38%;total of 15 plant species were observed,among which the dominant species were the herbaceous plants including Lemus angustus,Elymus dahuricus Turcz.and Stipa capillata Linn.,the others were associated species.The soil in original landform is loessial soil,with high infiltration capacity,low content of soil organic matter,weak alkalinity,and weak capacity of water and fertilizer preservation.The four topsoil treatment methods(original vegetation,deep ploughing,alfalfa planting and bare land)had no significant effect on the soil moisture in the original landform in 3 years.The replenishment depth of soil water by rainfall is 30-90 cm generally,and the soil water content below 100 cm hardly changed significantly.(3)The vegetation of Astragalus adsurgens Pall.and Stipa bungeana Trin.(SC)in the refuse dump had a high infiltration capacity(stable infiltration rate of 0.196 cm /min),which was significantly higher than other vegetation types in the refuse dump,and close to the stable infiltration rate in the condition of original landform.Soil water content of wasteland in refuse dump was significantly higher than that of other four type,while the soil water content under Medicago sativa(M)and Astragalus adsurgens Pall.(S)were the lowest.The soil water consumption of M and S was concentrated in 60-220 cm and 120-260 cm,respectively,while the soil water consumption of sea-buckthorn(SJ)and SC were concentrated in the surface layer of 80 cm and 40 cm,respectively.The sequence of soil water consumption is M>S>SJ>SC>H.Additionally,the results of time stability analysis showed that the soil depth of 90,120,180,140 and 140 cm were recognized as the representative soil layer of M,S,SJ,SC and H,respectively.The vegetation of Stipa bungeana Trin or natural recovery is beneficial to the soil water conservation in the refuse dump,while alfalfa and Astragalus adsurgens Pall.would cause serious soil water deficiency.(4)The results of plot experiment on improved sandy soil and hard loess using MS indicated that adding a small amount of hard loess in MS can significantly improve the permeability of MS.In addition,after addition of MS,the soil physical quality(SPQ)of sandy soil is significantly improved,which is indicated by the increase of available water content and relative field water holding capacity,and the decrease of soil aeration capacity.Among the sandy soil treatments,the improvement effect of SPQ in F3P1 is the most obvious,which were close to the optimal range of SPQ indicators provided by other researchers.However,addition of MS has little effect on the SPQ of hard loess.The profile average water content in sandy soil was significantly increased by adding MS.With the increase of the amount of MS,the water distribution in the soil profile became more even,and the MTSD(most temporal stability depth)becomes shallower.The biomass of sandy soil(or MS)can be significantly increased by adding a small amount of MS in sandy soil(or by adding a small amount of sandy soil in MS).Additionally,alfalfa biomass of hard loess can be increased by adding a small amount of MS.(5)The soil column experiment showed that the addition of MS can significantly reduce the steady infiltration rate and improve the water retention of sandy soil.Addition of a small amount of hard loess in MS(i.e.,1:3 treatment of hard loess and MS)had significantly increased the stable infiltration rate of MS(by about 1 time,P < 0.05).Moreover,MS addition significantly changed the water retention curve and parameters of sandy soil,but has little influence on hard loess.The simulation results of Hyrus 1D model displayed that the addition of MS reduces the fitting efficiency of model simulation and increases the root mean square error of fitting.The analysis of water balance components showed that the MS addition can significantly reduce the evaporation of sandy soil and improve the absorption and utilization of soil water by roots.(6)Comparted to the result of plot experiment,the results of column experiment were similar for the treatment of sandy soil but were quite different for the treatment of hard loess.The main reasons for this difference may be related to the scale change from soil column to field and the control of experiment conditions.On the one hand,the influence of the sidewall effect may be larger because the inner diameter of the soil column is smaller than that of the plot.On the other hand,the sand at the bottom of the soil column created a zero potential surface,which to some extent prevented the further downward migration of soil water and plays a role in water conservation,consequently,soil water content at the bottom of the soil column was increased,and the influence of different soil treatments on biomass was weaken.In addition,compared with the natural rainfall in the plot experiment(the total amount is 50 mm,but falls in several times),artificially irrigated(50 mm each time)in soil column could keep more water in the soil and reduce the loss of soil water by evaporation.This study provides important reference for land reclamation and vegetation selection after coal mining in Shanxi,Shaanxi and Mongolia border areas.However,this paper mainly focused on the mixing treatment of soil.but did not involve the influence of the depth of soil mixing and the profile configuration on the movement and distribution of soil water.In future study,the influence of soil mixing depth and profile configuration on soil water movement and distribution and plant growth should be focused in order to determine the soil configuration model that is suitable for local soil and climatic conditions. |
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