Effects of coarse-fragment content and size on soil erosion under simulated rainfall

Abstract

Farmers have long considered coarse fragments a hindrance in potato production. Rock picking or crushing has become a routine operation. Using simulated rainfall events and runoff-erosion plots (1 m × 1 m), the effects of coarse-fragment content (0, 7, 15 and 25% by volume) and size (1.0–1.9, 1.9–5.1 and 5.1–7.6-cm diam) on runoff, infiltration and soil loss were evaluated on an Orthic Dystric Brunisol. Study objectives were to quantify the influence of coarse fragments on soil erosion and to convert these relationships into mathematical equations for use with existing models to predict soil loss. Although there were only marginal increases in infiltration and reductions in runoff attributable to increasing content and size of coarse fragments, the rate of soil loss from the control was higher than that from all other treatments. In general, the rate of soil loss decreased with increasing content and size of coarse fragments. The effects of content and size of coarse fragments on soil-loss reduction, either individually or in combination, were expressed mathematically with correlation coefficients greater than 0.82. The study also revealed that for a given volumetric coarse-fragment content, the percentage surface cover increased with increasing coarse-fragment size. This finding has important practical implications because most reporting of coarse fragments is done on the basis of volume rather than percentage surface cover. Key words: Rock content, rock size, rainfall simulator, infiltration, soil loss