Charactoristics Of Soil Moisture And Runoff On Abandoned Slopeland In The Hill And Gully Loess Plateau Region

In order to prevent the widely severe soil and water loss,national departments had implemented a project to return farmland to forests(grass)in the Loess Plateau since the 1990 s.Along with the vegetation recovery,the area of vegetation with higher coverage was increasing,and the area of vegetation with lower coverage was decreasing,which greatly improved the local ecological environment.However,the restoration of vegetation drastically consumed the soil moisture,causing a huge soil moisture crisis,which severely limited the further vegetation restoration and its sustanibility in the Loess Plateau region,and because of different patterns of recovery,the degrees of water consumption were different.Therefore,after years of vegetation recovery,what was the level of the available water among different vegetation types? As rainfall was the only source of soil moisture,what was the state of its recharging to soil moisture? Was it still severe that rainfall produced surface runoff? It was very urgent to figure outthose questions.In this study,different abandoned slope cropland,with two bare lands as controll,in Fangta watershed of Ansai County were selected as the research objects.Based on field investigation and monitoring of vegetation,rainfall,soil moisture and surface runoff during 2015-2017,the above issues were analyzed and studied.The main results were as follows:(1)Variations of monthly rainfall and rainfall among different grade both were various.Along with increasing of maximum rainfall of 30 minutes,the number of corresponding rainfall events decreased.The rainfall with maximum rainfall of 30 minutes less than 5 mm was the main form of rainfall in the experimental area,accounting for 84%.(2)With the continuous restoration of vegetation,except for Sophoradavidii connmunity and Robinia pseudoacacia forest,the number of families,genera,and species of other vegetation communities increased.With the vegetation recovery,establishment species of the 8-year Artemisia scoparia community and 13-year Stipabungeana community had changed.The order of vegetation and litter coverage among different plant communities was Robinia pseudoacacia forest and shrub communities>Artemisia community>herbaceous communities and the crust coverage showed the opposite order.(3)The order of water supply(absorption)capacity and water holding capacity of different vegetation communities showed that Bothriochloa ischaemum community>shrub community>Artemisia community>herbaceous communities>Robinia pseudoacacia forest.Soil moisture in the 0-20 cm soil layer in different vegetation types was ineffective to plant even after some rainfall events,Soil moisture in 20-100 cm soil layer was unavailable to plant in Robinia pseudoacacia forest,but it was available to plants in other vegetation types after different rainfall events in 2015-2017.(4)The order of soil moisture content among different vegetationin different year was Robinia pseudoacacia forest < shrub communities <Artemisia species < herbaceous communities < bare land.But soil moisture distribution in the soil profile basically remained unchanged in the different years.The coefficient of variation of surface soil moisture was greater than that of deep soil moisture among different vegetation,and the order about coefficient of variation of soil moisture among different vegetation types was Robinia pseudoacacia forest>shrub communities >Artemisia species > herbaceous communities > bare land.(5)With the increasing of rainfall amount,the depth of soil water recharge among different vegetation types increased.The depth of soil water recharge in bare land and Artemisia communities increased as the increasing of rainfall intensity,and there was no significantly correlation between the depth of soil moisture recharge and rain intensity in Robinia pseudoacacia forest and shrub communities.The depth of soil moisture recharge decreased with the increasing of coverage of vegetation and litter,although it was not significantly.(6)The average runoff yields among different vegetation types under the rainfall conditions of small rain,moderate rain,and big and heavy rain were 0.0028~0.4262 mm,0.0148~1.6257 mm,and 0.1341~3.9476 mm,respectively.The order of runoff yield among different vegetation types under different rainfall grades was Robinia pseudoacacia forest and shrub communities<Artemisia communities and herbaceous communities<bare land,and the stability of the runoff showed the opposite trend among different communities.There were significantly positive correlations between runoff and rainfall amount,runoff and rainfall intensity,respetively.Under the same rainfall conditions,there was a negative correlation between runoff yield and depth of soil moisture recharge among different vegetation types.