Effects Of Land Use On Soil Hydraulic Properties In The Loess Plateau,China

In order to evaluate the soil hydraulic parameters affected by the land use types in the Loess Plateau regions,the present study was carried out in 2015-2016.The loess soil area is very fragile in nature and in 1999 Chinese Government launched the special project titled as“Grain for Green”for the enhancement of soil dominance and a decrease of soil erosion in the Loess Plateau.On the other side due to extensive vegetation restoration on the Loess Plateau,The area?mainly the present study area?also facing some issue such as soil desiccation and river flow decrease which threaten the regional water recycling and drinking water safety.The research on macropores from root system is helpful to study the mechanism of groundwater recharge and improve the infiltration models of an inhomogeneous medium.Cropland,forestland,and grassland in different utilization years are the objects of this.The root characteristics of the soil core method and the root image scanning of the root analysis provide the relation between root development and the formation of macropores in the process of vegetation restoration.Additionally,indoor experiments of soil water characteristic curve also provide the base the link between pores characteristics.The results could be used to evaluate the influence on the soil recharge ability to groundwater,and it can help deeply understood of the regional hydrological response caused by Land Use and Land Cover Change and provide a national ecological construction with some reliable basis.Grassland has high value in soil organic matter 17.96±0.89 g kg^-1 at top soil layer,and the minimum was recorded in cropland maize 10.72±0.03 g kg^-1at sub-soil layer.The higher electrical conductivity was noted in common apple orchard followed by abandoned apple orchard,grassland,cropland wheat,cropland maize and shrub-grassland respectively.Conclusively,the results of soil basic properties demonstrate that grassland and shrub-grassland uses are the most efficient and suitable land use system to improve soil organic matter conservation compared to other land use.In order to protect soil quality and health to maintain the sustainable agricultural development,the conversion of farmland to grassland or other alternate suitable land use should be an ideal practice for soil organic matter and associated soil properties.Soil aggregate stability is akey indicator for controlling soil losses and to improve soil quality.Higher percentages of water stable aggregates were observed in the shrub grassland and grassland at 0-20 cm of soil layer 65%and 61%,respectively.Moreover,in comparison of croplands,cropland wheat has more percentage of dry stable aggregate and water stable aggregate 56%and 42%as compared to cropland maize 50 and 49%respectively.Whereas the abandoned apple orchard has 73%and 50%and common apple orchard have 55%and50%.Both mean weight diameters and geometric mean diameters of aggregate were recorded higher in grassland than the other land uses;the results are highly significant under different land use?p<0.05?.The formation of soil aggregates and their stability were positively correlated with soil organic carbon content and root biomass of different plant communities.Furthermore the correlation coefficient of mean weight diameter,geometric diameter,root biomass,and soil organic carbon content were also highly significant.Increased soil organic carbon concentrations were closely linked with the formation of macro-aggregates.Thus,converting farmland to forestland and grassland could improve water-stable aggregate and reduce soil disturbances in areas?like the Loess Plateau?with the highest erosion risk.The finding of this study shows that infiltration rate is enormously higher undergrassland10.58±0.02 cm min^-1,8.86±0.04 cm min^-1,5.39±0.06 cm min^-1,3.76±0.01 cm min^-1,1.36±0.03 cm min^-1,but falls considerably under shrub-grassland 9.03±0.01 cm min^-1,7.59±0.03 cm min^-1,4.11±0.01 cm min^-1,3.24±0.03 cm min^-1,0.66±0.01 cm min^-1 at different pressure heads 0 cm,-1 cm,-3 cm,-6 cm and-12 cm respectively.Whereas,the low infiltration rate was recorded in common apple orchard 6.02±0.04 cm min^-1,5.17±0.01 cm min^-1,3.76±0.02 cm min^-1,1.50±0.03 cm min^-1,0.59±0.02 cm min^-1 respectively.Furthermore,in comparison of croplands,cropland wheat has more than cropland maize i.e8.08±0.05 cm min^-1,6.20±0.06 cm min^-1,3.01±0.01 cm min^-1,1.64±0.02 cm min^-1,0.85±0.01cm min^-1 and 7.64±0.02 cm min^-1,7.59±0.05 cm min^-1,4.67±0.01 cm min^-1,2.21±0.03 cm min^-1,1.27±0.02 cm min^-1 at different pressure heads 0 cm,-1 cm,-3 cm,-6 cm and-12 cm respectively.Over the entire trend were noted as grassland,shrub-grassland,abandoned apple orchard,cropland wheat and cropland maize respectively.The results of soil pore contribution showed that grassland and shrub-grassland have a more number of pore?>1 mm?is88 pores m^-2 and 69 poresm^-2 compared to other land uses.Whereas,both cropland wheat and cropland maize contain 67 and 21 pores in m^-2.The decreasing trend was recorded as grassland and shrub-grassland,cropland wheat,abandoned apple orchard;common apple orchard;cropland maize respectively.On the other side,the effective porosity percentage was also observed in grassland compared to other land uses and the lowest were noted in common apple orchard.The result of soil water characteristic curve showed that grassland contain more saturated water content 44.89%compared to other study sites,and the minimum was noted in cropland maize 38.31%,however;more filed capacity was also recorded in grassland 28.93%compared to all other study sites,whereas the minimum was recorded in cropland maize 18.31%.Overall the decreasing trend of saturated water content was noted as grassland,abandoned apple orchard,shrub grassland,common apple orchard,cropland wheat,and cropland maize respectively.Furthermore at 0-10 cm of soil layer the maximum water content was also observed in grassland,followed by abandoned apple orchard,common apple orchard,shrub grassland,cropland wheat and cropland maize respectively.The analysis results of different root parameter showed that grassland contain more root biomass 95.75±1.16 g m^-2 than other study areas,while in comparison of croplands cropland wheat 51.46±1.27 g m^-2 has more root biomass than cropland maize 46.66±0.52 g m^-2.The notable reductions in soil root biomass were recorded in common apple orchard 10.81±0.18 g m^-2.Furthermore,the maximum root length density,root area index and root diameter were recorded in grassland i.e.26.72±0.63 cm cm^-2,5.95±0.32 cm² cm^-2,and 0.77±0.04 mm in comparison to other land use at 0-20 cm of the soil layer;while the minimum were noted in common apple orchard 2.53±0.13 cm cm^-2,1.86±0.08 cm² cm^-2,and 1.40±0.07mm.Overall,the study results show that soil physico-chemical properties,root characteristic and soil hydraulic properties can be improved with adoption of vegetation restoration.Vegetation restoration can also improve the accumulation of soil organic matter,root characteristic and both paly major role in the formation of soil aggregation and soil pores and improving soil infiltrationrate.