Abstract: In the hilly-gully regions of Loess Plateau,the erosion-incision induced by long-term water and soil loss resulted in the disappearance of topsoil and the bareness of three types of soil(loess parent material,red-clay,and mantle rocky soil),which increased the difficulty of afforestation.In this paper,the afforestation principle "selecting suitable tree species for suitable soils" and the drought-resistance planting technique of "cave padded plastic film" were put forward,which could broaden the soil types to suit for planting trees.This planting technique was examined at the Xiaobangou basin of Yan'an city from 1997 to 2001,and the results showed that this technique could promote root growth in topsoil layer,keep soil water for 4 months,and significantly improve the survival rate and growth volume of all types of trees.The afforestation effects were better on the three types of soil in Loess Plateau,if the new planting technique was adopted.The red clay and mantle rock soil distributed on the both sides of gully with rich ground water were better for shallow-root trees to grow,and could obtain better effects if planting in scientific mixed planting.

Key words: assimilation carbon, mineralization, transformation, soil ¹⁴C labeling.