SOIL PHYSICAL CHANGES AND CROP ROOT GROWTH FOLLOWING DIFFERENT METHODS OF LAND CLEARING IN WESTERN NIGERIA

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Abstract
The effects of 4 different methods of land clearing in western Nigeria on soil physical properties of an Alfisol and on the root growth of the following crop were studied. The methods used were manual clearing and clearing with a shearblade, a treepusher and a treepusher/root rake. Soil physical properties measured were bulk density, saturated hydraulic conductivity, infiltration rate and cumulative infiltration, total porosity, pore size distribution, and soil water retention. Mechanical clearing increased bulk density and proportion of medium-sized pores (2-14.3 .mu.m radius) and decreased infiltration rate, cumulative infiltration, saturated hydraulic conductivity, total porosity, and proportion of macropores (> 14.3 .mu.m radius). Soil water content at a potential of 0 kPa [kilopascal] was significantly reduced, whereas that at potentials of -10 and -33 kPa was increased. In comparison with the forested control, the magnitude of changes in soil physical properties was in the order of manual clearing < treepusher < shearblade < treepusher/root rake. Although the differential effects of land clearing methods on the soil were reflected only in the initial pattern of maize root growth during the seedling stage, it was sufficient to affect grain yield. Root growth of mucuna and cowpea were not affected by the changes in soil physical properties.