QIN Jiahai, ZHANG Yong, ZHAO Yunchen, WANG Zhijiang, LI Caixia, GAO Haining
In order to reveal the soil physical and chemical properties, as well as the variations of nutrients and enzyme activities, in the degrading grasslands in the upper reaches of the Heihe River, Qilian Mountains, by using field investigation and laboratory tests, four kinds of grass profile are studied. It is found that as compares with non-degraded grassland, the mild degraded grassland, moderate degraded grassland and severe degraded grassland, in the depth range of 0~60 cm, organic carbon content decreases 10%, 12% and 28%, respectively; organic carbon density decreases 11%, 21% and 31%, respectively; total porosity decreases 3%, 7%and 12%, respectively; aggregate decreases 19%, 28% and 39%, respectively; clay particle decreases 6%, 12% and 18%, respectively; saturated storage capacity decreases 3%, 7% and 12%, respectively; field capacity decreases 10%, 14% and 19%, respectively; CEC decreases 8%, 17% and 33%, respectively; alkali-hydrolyzable nitrogen decreases 10%, 22% and 36%, respectively; rapid available phosphorus decreases 15%, 25% and 46%, respectively; rapidly available potassium decreases 4%, 8% and 13%, respectively; urease decreases 5%, 19% and 34%, respectively; sucrose decreases 27%, 43% and 54%, respectively; phosphatase decreases 15%, 32% and 44%, respectively; polyphenol oxidase decreases 12%, 25% and 38%, respectively; catalase decreases 14%, 30% and 46%, respectively; bulk density increases 4.3%, 8.6% and 14.7%, respectively; sand increases 12.5%, 25% and 38.5%, respectively; gravel increases 18%, 39% and 63%, respectively; pH value increases 0.10, 0.21 and 0.28 units, respectively; CaCO3 increases 3.9%, 8% and 12.1%, respectively. In the depth range of 0~60 cm, soil porosity, aggregate, clay particle, saturated storage capacity, field capacity, available NPK, soil organic carbon and enzyme activities decrease as: non-degraded grassland>mild degraded grassland>moderate degraded grassland>severe degraded grassland; bulk density, sand, gravel, pH value and CaCO3 increase as: non-degraded grassland3 increase with depth.