Research Paper: SWdSoil and Water Effect of soil type, peat and farmyard manure addition, slope and their interactions on wash erosion by overland flow of some Trinidadian soils E.I. Ekwue*, C. Bharat, K. Samaroo Faculty of Engineering, Mechanical and Manufacturing Engineering, The University of the West Indies, St. Augustine, Trinidad and Tobago article info Article history: Received 24 April 2008 Received in revised form 24 October 2008 Accepted 15 November 2008 Available online 27 December 2008 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. ª 2008 IAgrE. Published by Elsevier Ltd. All rights reserved. 1. Introduction Soil loss, and its associated impacts, is one of the most important and probably the least well known of today’s environmental problems. The estimated resulting costs of this phenomenon can be large; in the United States about US$44 billion annually (Pimental et al., 1995), the United Kingdom, £90 million (Envi- ronment Agency, 2002) and in Indonesia, US$400 million in Java alone (Magrath and Arens, 1989). These costs originate from both on-site and off-site effects of erosion (Morgan, 2005). On-site effects are particularly important on agricultural lands. They include the loss of soil, a breakdown in soil structure, a reduction * Corresponding author. E-mail address: edwin.ekwue@sta.uwi.edu (E.I. Ekwue). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/issn/15375110 1537-5110/$ – see front matter ª 2008 IAgrE. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biosystemseng.2008.11.012 biosystems engineering 102 (2009) 236–243