The Effect of Soil Degradation on Agricultural Productivity in Ethiopia: a Non-Parametric Regression Analysis

The paper estimates the effect of soil degradation on crop yields for dominant cereals in Ethiopia at a nation-wide level and analyses its relation with population density and fertiliser use. A soil degradation index is derived from an ordered qualitative classification on the degree of soil degradation and the area extension. Biophysical variability is incorporated by using, as dependent variable,the yield ratio (actual/potential yield) to correct for agro-climatic and crop genetic differences,and by including soil fertility as explanatory variable. The data set is cross sectional and obtained from gridded overlays on soil degradation,climate,soil,land form,population (and cattle) density. The relationships are estimated via non parametric (kernel density) regression and the estimation results are depicted in 3-D graphs. It appears that the relationship between yield ratio,land degradation and soil fertility is not very strong. Yet, three stylised facts can be identified. First,land degradation has its major impact on soils of lower fertility, where population levels are low. Secondly,on fertile soils,land degradation is largely compensated by fertiliser application. Finally,most people can be found on the slope facing a deep and dangerous precipice. A spatial representation of the elasticity of crop productivity with respect to soil degradation indicates that most vulnerable areas are located in the northern part of the country.