Assessment Of Soil Physical Degradation In Eastern Kenya By Use Of A Sequential Soil Testing Protocol. Agriculture, Ecosystems & Environment

Abstract

Soil physical degradation is a gradual process of many steps beginning from structural deterioration and ending in differential loss of finer particles through erosion. Control of the degradation remains a challenge to many scientists due to lack of proper assessment protocols. This study developed a sequential protocol with emphasis on definition of physical degradation and successive soil testing to determine the stages of degradation development. The protocol was tested in Cambisols, Arenosols, and Ferralsols in Eastern Kenya. Soil physical degradation due to 10 years land use change was defined as more than 25% drop in infiltration and water retention characteristics and aggregate stability and more than 30% increase in bulk density and silt content. Then a soil testing model was sequentially applied to identify physical degradation phases. Visual assessment of degradation symptoms, RUSLE model, and diffuse infrared spectral reflectance were used in the soil testing model as predictors of physical degradation. Visual assessment was found to be cheap and fast method for identifying final stages of physical degradation with 60% accuracy. Visual assessment combined with RUSLE model improved the assessment accuracy to 80%. Infrared spectral reflectance, which is sensitive to subtle changes in soil physical conditions, was also found as a potential surrogate predictor of early-warning signs of soil physical degradation. Inclusion of spectra into the assessment model improved the accuracy to 95%. This protocol is effective in identifying phases of soil physical degradation, which are useful for planning degradation control and monitoring schemes. Its further testing and worldwide application is recommended.