Research of Erosion and Sediment Yield in Earth Road Drainages in Loess Gully Region PROGRESS OF NUCLIDE TRACING TECHNIQUE IN THE STUDY OF SOIL EROSION IN RECENT DECADE Study of Soil Erosion Using 137Cs Method in Rocky Desertification Region of Northern Guangdong Effect of non-tillage with straw mulch on wind erosion in irrigated oases of Hexi Corridor