Erodibility of Slash-and-Burn Soils along a Toposequence in Relation to Four Determinant Soil Characteristics

Abstract

Good crop yields are normally obtained in the first year after slash-and-burn farming system in south-eastern Nigeria, but decline rapidly thereafter. The suitability of land for slash-and-burn agriculture depends partly on its sensitivity to erosion. Erodibility of slash-and-burn soils, in relation to four determinant soil characteristics was studied to assess the effect of burning on some selected properties and erodibility of the soil. Soils from 0 to 0.15m and 0.15 to 0.30 m depths were collected before and after burning the plots, from three geomorphic surfaces of upper slope, middle slope, and valley bottom. Results obtained showed an increase in bulk density after burning and a corresponding decrease in total porosity. Soil pH and nutrient content increased significantly after burning, but soil organic carbon (SOC) and exchangeable acidity decreased with burning. Soil permeability was moderately slow in all the landscape positions. Erodibility increased significantly after burning by 20, 14 and 18 % in the upper slope (US), middle slope (MS), and valley bottom (VB) respectively. Soil pH was one of the soil characteristics that mostly determine soil erodibility (=-0.693*). We do not know the composition or the amount of ash added to the soil and so the changes in soil properties cannot be related quantitatively to ash input.

Keywords: erodibility, toposequence, slash and burn agriculture, susceptibility, permeability