Effect of land use on soil properties in river valleys of eastern Tibet

The Qinghai-Tibet Plateau is the most ecologically critical region as it is the source area of some large rivers,such as Yangtze,Huanghe,Lancang,and Yarlung Tsangbo rivers.Based on the field investigation and laboratory analysis of soil samples,this paper discussed the soil physical and chemical properties under different types of land use in main river valley areas in eastern Tibet.The results suggested that distinct differences of soil physical properties among soils under various types of land use were found,cropland and bare land had the higher content of sand compared with other types of land uses,while all the soils in this region tended to be desertified in texture;Due to the accumulation of organic matter,the soil in north-facing slopes contained higher nitrogen;While cropland soil contained higher P and K contents after the agricultural practices mainly owing to fertilization;Among all the types of land use,the bare land soil had the lowest nutrient contents,which were significantly lower than woodland soils despite of its relatively high silt content.The soil organic matter content influenced all the other N,P,K nutrients,which was positively correlated with total N,available N total P,available P and available K(R0.527,N=97).The correlation between soil nutrients and silt content also disclosed the susceptibility of nutrient losses of disturbed soil by tillage,especially on steep hillslopes during rainfall events.Above all,organic matter management,in terms of land use scenario,is crucial for the significant protection of the regional ecology.