Study on Gradient Variation of Physical Parameters of Soil along the Drought Valley of Heishui River

The drought valley of Jinsha River in Hengduan Mountains is characterized with both dry season and monsoon,where the development of local agriculture is restricted by soil degradation and desertification.This paper studies on gradient variation of physical parameters of undisturbed soil along the whole drought valley of Heishui River,one of the branches of Jinsha River.The results showed that the physical properties of the soil have different variation style along the river.Gravel content of the soil is higher at middle reach and debouchure.While the content of aggregate with size of 5mm or more is lower at middle reach and debouchure,and the content of aggregate with size less than 1 mm is higher at debouchure and headstream.The bulk density of the soil gets higher along the stream and the headstream soil has the lowest unsaturated hydraulic conductivity.The study shows that nonuniformity,different hydrothermal condition and their combination play a vital role in the degradation process.Therefore,different measures should be taken for ecological restoration according to factual conditions in different degradation of soil and vegetation.