Effect of soil type, peat and farmyard manure addition, slope and their interactions on wash erosion by overland flow of some Trinidadian soils

A laboratory facility was built to quantify wash erosion by overland flow. The design allowed slope gradient and flow rate of water to be controlled. The apparatus was used to test the wash erosion from three Trinidadian soils (a sandy loam, a clay loam and another clay), four levels (0, 4%, 8%, and 12% by mass) each with peat and farmyard manure (FYM) and exposed to five slopes (9%, 15%, 21%, 25% and 30%). The aim of the test was to increase the general understanding of how peat and FYM affect the soil erosion process. The water content, bulk density and penetration resistance of the soils were measured prior to the measurement of wash erosion. As water content increased, bulk density decreased in all the three soils with increasing levels of peat and FYM. Although penetration resistance declined with increasing levels of added peat, it increased with increasing FYM content. Mean wash erosion increased from 0.99 kg for soils on a 9% slope to 1.88 kg for a 30% slope. Increasing levels of added peat and FYM decreased wash erosion at all combinations of parameters. Wash erosion was greater in the sandy loam and the clay loam than in the clay soil at the higher slopes (>15%). The opposite trend occurred at the lower slopes (9% and 15%), where soil loss was greater in the clay. Results from this study demonstrate that the effect of incorporation of peat and FYM on wash erosion depends on the type of soil, the soil slope, and the level of added organic material. Multiple linear regression equations were developed for predicting wash erosion from the experimental factors. The results of this study imply that for improved soil conservation, apart from adopting the land-use zoning of soils based on slopes, the incorporation of organic materials into steep arable slopes will greatly minimise soil erosion by water.