Effect of soil type, peat, slope, compaction effort and their interactions on infiltration, runoff and raindrop erosion of some Trinidadian soils

This study follows an earlier one which showed that organic materials in form of peat and farmyard manure decreased wash erosion. A rainfall simulator was added to a soil test bed so that soil erosion by raindrops could be monitored. The design of the soil test bed allowed soil slope to be controlled. The apparatus was used to test the raindrop erosion of three Trinidadian soils (a sandy loam, a clay loam and another clay) with three levels of added peat (0%, 4% and 8% by mass), compacted at three levels (95 kPa, 137 kPa and 179 kPa) and exposed to a rainfall intensity of 90 mm h(-1) falling on soils on four slope gradients (9%, 15%, 21%, and 30%). The aim of the test was to investigate how peat reduces the soil erosion process and was carried out by making intermediary measurements of infiltration and runoff. Bulk density and penetration resistance of the soils were measured prior to the measurement of raindrop erosion. Both bulk density and penetration resistance decreased with increasing levels of peat in all the three soils. Mean cumulative infiltration decreased from 6.6 mm to 4.3 mm; mean cumulative runoff increased from 17.9 mm to 39.0 mm and soil erosion increased from 1.56 kg to 2.78 kg in each case when the soil slope increased from 9% to 30%. Peat incorporation increased infiltration, and decreased runoff and soil erosion in all soils at all combinations of slopes and compaction efforts. Soil erosion was greater in the sandy loam than in the clay and clay loam soils. Compaction of the soil was found to increase surface runoff and decrease infiltration and soil loss. Results from this study confirm that the major reason why peat reduces soil erosion by rainfall is its effect in decreasing bulk density, increasing infiltration, and reducing runoff, rather than stabilising the soil. Multiple linear regression equations were developed for predicting soil erosion from the experimental factors. The results of this study further emphasise that for soil conservation, apart from adopting land use zoning of soils based on slopes, the incorporation of organic materials in steep arable slopes will greatly reduce soil erosion by water. (C) 2009 IAgrE. Published by Elsevier Ltd. All rights reserved.