Rapid Techniques for Large-Area Detection of Soil Physical Degradation.
C. T. Omuto, Univ of Nairobi, Upper Kabete, Box 30197, Nairobi, Kenya and K. D. Shepherd, World Agroforestry Centre (ICRAF), ICRAF House, PO Box 30677-00100, Nairobi, Kenya.
Physical degradation undermines soils' ability to perform their many biophysical functions. Currently, there is lack of rapid methods to facilitate timely large-area assessment for effective control of the degradation. This study tested the combined applications of point-measurements of physical properties, soil spectral reflectance, and remote sensing for spatial prediction of the degradation in a large watershed. Infiltration and water retention measurements at selected sites were used to aid case-definition of the degradation. A tree classification was then developed with diffuse spectral reflectance to predict the degradation cases. 93 % accuracy with holdout cross-validation was achieved and the tree used to predict the degradation at multiple points in the study area. In addition, standardized deviations of Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) from long-term Landsat scenes were used to study the thermal and vegetation conditions at the sampled points. The deviations of LST and NDVI effectively predicted the degradation at other places with 80 % accuracy of ground reference data. This approach has the potential as a useful tool for guiding policy decision on sustainable land management.