EFFECTS OF COARSE-FRAGMENT CONTENT AND SIZE ON SOIL-EROSION UNDER SIMULATED RAINFALL

Farmers have long considered coarse fragments a hindrance in potato pr oduction. Rock picking or crushing has become a routine operation. Usi ng simulated rainfall events and runoff-erosion plots (1 m X 1 m), the effects of coarse-fragment content (0, 7, 15 and 25% by volume) and s ize (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 objecti ves were to quantify the influence of coarse fragments on soil erosion and to convert these relationships into mathematical equations for us e with existing models to predict soil loss. Although there were only marginal increases in infiltration and reductions in runoff attributab le to increasing content and size of coarse fragments, the rate of soi l loss from the control was higher than that from all other treatments . In general, the rate of son loss decreased with increasing content a nd size of coarse fragments. The effects of content and size of coarse fragments on soil-loss reduction, either individually or in combinati on, were expressed mathematically with correlation coefficients greate r than 0.82. The study also revealed that for a given volumetric coars e-fragment content, the percentage surface cover increased with increa sing coarse-fragment size. This finding has important practical implic ations because most reporting of coarse fragments is done on the basis of volume rather than percentage surface cover.