Soil Water Deficit And Replenishment Potential Of Different Land Use Types On The Loess Plateau

As a key variable in the soil-plant-atmosphere continuum,soil moisture plays a decisive role in the ecological effects of vegetation construction.At present,water shortage has become serious with climate warming and the increasing of vegetation cover.Water stress is one of the most important factors causing vegetation degradation and even death.The degradation of vegetation will inevitably lead to soil degradation.How to maintain the sustainability of soil water is the key of ecological environment sustainable development.Therefore,to clarify the interaction between land use types and soil,explore the consumption and replenishment process of soil water,which is of great significance in rational utilizing limited water resources and improving soil water environment.In this study,a large-scale land use survey,soil sample collection and soil moisture measurement were carried out on 180 sample sites in the Loess Plateau,with forestland,shrub and grassland as the research objects and cultivated land as the control.According to the zonal distribution of precipitation and soil types in the study area,it can be divided into three precipitation zones: 300-400 mm,400-550 mm and 550-700 mm,and three soil types: aeolian soil,loess soil and dark loessial soil.This study based on different precipitation zones and soil types,quantitatively analyzed the effects of land use types on soil structure and soil organic matters.Exploring the changing and relative deficit of soil water under different land use types.Revealing the potential of soil water compensation by quantifying the water recharge during infiltration process.Moreover,combined with the soil properties,to explore the main factors affecting soil water and infiltration process.The main conclusions are as follows:(1)The effects of land use types on soil structure and organic carbon storage were different under different precipitation zones in Loess Plateau.In the 300-400 mm precipitation zone,forestland construction significantly reduced soil clay content,mainly in the aeolian soil area.In addition,vegetation construction reduced soil carbon storage,forestland with the largest negative effect and the lowest in grassland.The non-capillary porosity of shrubland and grassland was significantly increased in aeolian sandy soil.In the 400-550 mm and 550-700 mm precipitation zones,the stability of soil aggregates was significantly higher in shrubland than that of forestland and grassland in loessal soil,while it was higher in forestland and shrubland than grassland in dark loessial soil.(2)Compared with farmland,soil water deficit degree of forestland,shrubland and grassland were different.In the 300-400 mm precipitation zones,soil water consumption was mainly in the 0-200 cm soil layer in aeolian sandy soil.Soil water deficit in shrubland was about 28% higher than that in forestland and twice as high as that in grassland in 300-500 cm soil layer.In the 400-550 mm precipitation zones,soil water deficit in 100-300 cm soil layer was higher than that in other soil layers.However,the soil water deficit under the gradient of precipitation mainly occurred in loessal soil.In the aeolian sand soil,the soil water deficit was positive below the soil layer of 200 cm.In the 550-700 mm precipitation zones,the soil water deficit in loessal soil was higher than that in dark loessial soil.On the whole,the soil water deficit in shrubland was significantly higher than that in forestland.Moreover,it was approximately 20% and 57% higher in shrubland than forestland and grassland in loessal soil,respectively.Precipitation,soil types and land use types had significant effects on soil water content.The main factors affecting soil water content under different precipitation gradients were clay,silt content,total porosity,capillary porosity,aggregate stability and 0.5-5 mm water-stable macro-aggregate.Under same soil types,precipitation,temperature and potential evapotranspiration have significant effects on soil water storage.(3)Soil infiltration rate was positively correlated with cumulative replenishment.In the300-400 mm precipitation zones,the infiltrability in aeolian sand soil was forestland >shrubland > grassland.The cumulative replenishment of forestland and shrubland were about34% and 18% higher than that of grassland,respectively.In the 400-550 mm precipitation zones,the infiltrability in loessal soil was shrubland > grassland > forestland.The cumulative replenishment of shrubland were about 30% higher than that of forestland and grassland.In the 550-700 mm precipitation zones,the infiltrability in dark loessial soil was grassland >forestland > shrubland.The cumulative replenishment of grassland was about 39% and 48%higher than forestland and shrubland,respectively.With the increase of precipitation and the transition of soil types from aeolian sand soilloessal soil-dark loessial soil,soil infiltration rate showed a decreased trend,and the factors affecting infiltration rates were increased.Soil aggregate and organic matter were significantly correlated with infiltration rate in 400-550 mm precipitation zones and loessal soil area.Particle composition,pore structure and water-stable aggregate were significantly correlated with infiltration rate in 550-700 mm precipitation zones and dark loessial soil.The comprehensive analysis showed that the infiltration rate was significantly correlated with clay,silt content and 0.25-3 mm water stable aggregate.With the prolongation of infiltration process,the effects of total porosity on infiltration rate were increased.Capillary porosity was significant negative correlated with infiltration rate,while non-capillary porosity was positive correlated with infiltration rate.(4)In the 300-400 mm precipitation zones,part of shrub density was maintained at the cost of soil water consumption,indicated that the planting density was higher.In the 400-550 mm precipitation zones,the maintenance of the current planting density of forest and shrub was also at the cost of soil water consumption,and the planting density of forest and shrub in this area was generally high.The comprehensive income analysis also indicated that the various income of shrubland was relatively low.Thus,the suitability of shrubland should be considered when establishing shrub in this area.In the 550-700 mm precipitation zones,part of the forest density was maintained at the cost of soil water consumption.Therefore,the relationship between vegetation density and soil water should be considered in vegetation construction in order to maintain sustainable of soil water environment.This study showed that in the area with precipitation less than 400 mm,soil silt content and organic carbon storage in forestland were less than that of farmland,shrub land and grassland.Climatic conditions,soil structure characteristics and soil types has the significant effects on the spatial distribution of soil water.The soil water deficit degree of forestland,shrubland and grassland was different,and the deficit was higher in forestland and shrubland than that of grassland.The potential infiltration recharge of different land use types was different under different rainfall areas and soil types.Soil water consumption and water compensation potential of different land use types should be considered comprehensively according to regional precipitation,so as to realize the sustainable of regional ecological environment.