黄土高原地区土壤可蚀性及其应用研究

Evaluation of soil erodibility on the Loess Plateau

通过回顾已有的成果 ,分析评价了我国土壤可蚀性研究的进展及存在的问题 ,提出我国土壤可蚀性研究中的标准小区定义。运用野外观测资料 ,研究计算了黄土高原地区土壤可蚀性指标值。结果表明 ,陕北和晋西北一带黄土可蚀性 K值变化于 0 .3～ 0 .7之间 ,并且有以陕西子洲、绥德一带为最大 ,以此为中心 ,向南、向北和向东都减少的变化趋势。

Soil erosion is now universally reckoned as an ecological environment problem,which results in land degradation and a band of ecological problems such as water pollution and flood disaster,Especially in the vast northwest region of China,a key to restore ecological environment is to control soil erosion.Besides vegetation disruption,rainfall concentration,and steep farmland ect,the susceptibilities of loess to erosion substantially conduce to severe soil erosion on the loess plateau.Soil erodibility being an important index to evaluate the soil sensitivity to erosion,how to precisely study and evaluate soil erodibility is of great importance to understand soil erosion regularity,predict soil loss,and evaluate land productivity. Since the study on the effect of soil properties on erosion began in 50s in China,an abundance of achievements about soil erodibility have been scored.But as a result of diverse perspectives and methods, a number of problems still exist.the first problem is that divers indices to evaluate soil erodibility are present.The second is that the definitions of unit plot are not uniform.The third is that algorithms used to calculate soil erodibility factor K are inconsistent.The fourth is that lacking observed data leads to little reliability of calculated results when formulae are used to predict K values.All these problems not only adversely affect the progress of the soil loss prediction research in China,but also interfere with exchange and comparison with international achievements .On the base of data from field plots.the selection of soil erodibility index and its determination method were discussed in this paper.Meanwhile,values of eodibility factor K for the soils on the loess plateau were determined and analyzed. To date,there are mainly three different types of methods applied in soil erodibility study.The first one is based on measurement of physical and chemical properties of soil.But in can't be used to predict soil loss because how to quantitatively relate soil erodibility to soil loss was not established.The second one is based on the results from water flow experiments,which determines soil erodibility directly by measuring soil loss scoured by water.In 40s,however,Gussak noted that when this method was applied to measure the erodibility of two different soils,opposite orders appeared when inflow rates were different.So it is impossible for this method to exactly characterize the effect of soil properties on erosion.The third is field measurement from unit plots.Though soil erodibility factor can be directly calculated through observation data from field plots,soil erodibility was found to alter with slope gradient and even was regarded as a dynamic index being a function of natural properties,topography,precipitation,and soil conservation because improper indices were adopted in previous studies on loess erodibility in China.It is obvious that erodibility of different soils is impossible to be compared because this type of indices fails to directly reflect the influence of soil properties.We recommend that a good index used to describe soil erodibility should follow the principles of uniqueness and practicality.So-called uniqueness denotes that a type of soil corresponds to a certain eodibility value to reflect impact of soil property on erosion.Even though soil erodibility may interact with some factors such as slope,rainfall,and land use etc in measurement,it is sure that soil erodibility should not vary with these factors.Otherwise,the erodibility of soil would have myriad values and lost its meaning in soil loss prediction because the change in rainfall,landuse and topography is uncertain.So-called practicality denotes that soil erodibility must be a quantitative numeric index and be easy to be measured. In 1963,Olson and Wischmeier proposed the practical index of soil erodibility as soil loss per rainfall erosivity index unit as measured on a unit plot,which has definite physical meaning and is convenient to measure.When measured on unit plots its values can be determined by