EFFECTS OF REMOVAL OF ORGANIC MATTER AND SESQUIOXIDES ON SURFACE SOIL STRUCTURE OF SOME SELECTED NIGERIAN SOILS

Abstract

Changes in water-stable aggregation depicting those associated with bringing soils under bush fallow to continuous cultivation were determined for six soils from Nigeria as related to artificial removal of organic matter and/or sesquioxides from the soils. Wet sieving, and mechanical analysis methods of aggregate analysis were used. Water-stable aggregation was appreciable under fallow with mean weight diameter of the aggregates ranging from 2.1 to 4.3 mm. More than 75% of the water-stable aggregates of the soils was due to individual or combined effect of organic matter and sesquioxides. Organic matter binding was prominent In all the soils, virtually responsible for aggregation in the Alagba and Iwo soils (Alfisols) and Ngala (Vertisol) and produced equivalent enhancement of water-stable aggregation as sesquioxides in the more acid Itagunmodi and lkom soils (Ultisols). Aggregation In the plinthic Gambari soils was attributed mainly to sesquioxides of the selected soils. Results indicate greater vulnerability of the Alfisols compared to Ultisols reflecting differences in the sources of aggregate stabilisation.