This study has been extracted from the "Bulletin du réseau érosion no 20 (2000)" published by IRD and GTZ.

Introduction

The term “soil conservation” is frequently used to mean a variety of activities by humans to control the rate of degradation, loss of soil, and yield of sediment from the landscape by wind, water and gravity (FAO, 1985). Except under forest conditions, surface horizons of most tropical soils having clay and organic matter contents are generally not well aggregated under cultivation. The soil aggregates are weakly developed and unstable to raindrop impact. On quick wetting during rain, these aggregates slake easily to form a surface seal or crust. Such formations occur when the surface ground is bare or incompletely covered by the vegetative canopy or surface mulch. In addition to sealing and crusting, migration of fine soil particles into underlying layers is often observed especially when the soil surface is disturbed by tillage and/or continuous cropping. The loss of pore continuity at the soil surface by sealing and crusting or at the adjacent soil layers by eluviation of fine topsoil particles causes the reduction of water infiltration. As a result, runoff and soil loss can significantly increase especially on sloppy grounds. Soil erosion is one of the major constraints of agricultural development of the highlands in the tropics. More than 80% of cultivated lands in these regions are prone to severe erosion as a result of improper agricultural practices. Previous workers (Alegre et a!., 1986; Lal, 1989; Hulugalle et aL, 1990; Babalola et al., 1993) reported the decreases in infiltration due to the loss of pore continuity during cultivation. The poor performance of crop on the surface ground contributes to its effectiveness in soil conservation.(E1-Swaity et al., 1988). High runoff and soil loss were also reported in marginally cultivated and bare fallow lands and infiltration invariably decreased as sealing and crusting developed with time (Sabel, 1988). The erodibility factor K of the USLE remains the conventional index to identify lands prone to erosion. However, the long-term knowledge of water infiltration and other soil parameters such as bulk density and pore continuity may be useful to easily estimate susceptibility of soils different management practices to runoff and soil loss. Such a simple approach is needed especially when expertise and equipment for soil erosion studies are the limiting factors. This paper intends to report the importance of water infiltration in characterizing runoff and soil loss in most tropical soils.

The complete version of the document is available in PDF format (9 pp; 161 Kb) at the following address:

ftp://ftp.fao.org/docrep/nonfao/lead/x6128e/x6128e00.pdf