采用人工暴雨试验发现：相同土壤含水量条件下，10 °,15 °,20 °,25 °紫色土小区在 130 mm/h 雨强降雨下细沟发生的临界坡长平均值分别为 6.13, 4.12, 2.72, 1.55 m ，细沟发生的临界坡长与坡度呈二次抛物线关系；土壤含水量变幅为 16 ％～ 26 ％条件下细沟发生临界坡长先增长后变短。据此总结了采用地埂防治坡耕地细沟侵蚀的治理模式，针对不同坡度地块细沟发生的临界坡长，采用地埂或者分割地块，并在地埂上种植经济效益高的植物篱，既控制了细沟的发生，又弥补了地埂占地导致的农业减产；同时在旱季和雨季分别调整边沟的尺寸，调整地块土壤含水量从而控制细沟因含水量变化导致的细沟发生临界坡长缩短。

Rill erosion is one of the main form of slope erosion, which is between sheet erosion and gully erosion. Once rill erosion takes place, the rate of soil erosion will be double increased. It is important, through Investigating the critical slope length of rills occurred in different slope cultivated lands under torrential rain, to direct the prevention of rill, reduce sediment and preserve the water and soil. Utilizing artificial rainfall tests showed that, under the same soil moisture content and in a 130mm /h torrential rain, the mean critical slope length on purple cultivated land of slope angle 10 °， 15 °， 20 °， 25 ° were 6.13 m ， 4.12 m ， 2.72 m ， 1.55 m ， respectively. A quatratic parabola relationship between critical slope length of rill ( L_R) and slope grade (J) was given. When the water content of soil varied from 16% to 26%, the critical length increased firstly and then decreased. For the sake of avoiding rill erosion occurrence, we designed a new cultivated mode, named “ ridge & plant hedge ”， which was to cut the slope length by ridges and hedgerows,on one hand to decrease sediment, on the other hand to regulate water content of soil.