Soil productivity and erosion: biophysical and farmer perspective assessment for hill slopes
A priority for research is the quantification of the productive capability of soils on hillslopes. Data on soil biophysical changes and their impact on erosion are limited, especially on aspects which represent the farmers' perspective. The terms soil quality and soil productivity are defined and presented conceptually in models to identify information needs and to examine the biophysical and farming system components that are important to smallholders. Of the principal processes in declining soil productivity, reduction in soil depth and increasing difficulty of gaining production are most often identified by farmers. Using examples from Sri Lanka, field techniques of biophysical assessment of erosion, conservation, and their impacts are presented, with a focus on Gliricidia contour hedgerows. Techniques, such as measuring the armor layer of small stones, soil pedestals, and sedimentation in drains, are useful to assess erosion rates. Impacts can be identified by soil depth as a measure of historical erosion, differential growth of crops, and farmers' assessments of yields. Farmers' observations on the practices that they employ are essential in making realistic assessments of conservation measures for promotion. Field-based techniques are easy to use, rapid to undertake, and best represent the farmer-perspective.