Runoff and Soil Loss of Vegetative Fallow and Farmland of South-Eastern Nigeria

Abstract

The effects of two different land uses—namely, 10 year-old vegetation fallow land and farmland—on soil erosion and soil loss were investigated in a part of the rainforest zone of Nigeria. Measurements of 61 sites where rainfall had produced runoff and 54 sites where rainfall had generated soil erosion were carried out from March to November in the 2012 rainy season. The average runoff amounts for the 10 yr-old and farmland plots were 0.11 mm and 0.41 mm, respectively. The average soil loss for the 10 yr-old vegetation fallow land and farmland plots was 12.43 kg.ha-1 and 127.68 kg.ha-1, respectively. The differences in runoff and soil loss between the treatments were highly signifi cant (P < 0.001). The study showed that soil erosion had occurred on the 10 yr-old vegetation fallow plot even with greater aerial coverage conditions resulting in the loss of nutrient-rich topsoil, though the plot had signifi cantly reduced runoff and soil loss compared with the farmland plot. The signifi cant reduction in soil loss with increasing rainfall events on the 10 yr-old plot was indicative of the importance of vegetation in promoting good hydrological functioning in the area. The fi nding from the statistical analyses identifi ed rainfall as the principal cause of losses on the 10 yr-old fallow plot, while on the farmland, rainfall and tree girth were the main causes of soil erosion. The continuous loss of nutrient-rich topsoil, if not checked, may affect the ability of the degraded soil to replenish lost nutrient for subsequent farming. However, to reduce the rate of losses of both runoff and soil on cultivated farmlands, all trees should not be cut down during farming operations as is practiced in this part of the world.