Pedology and its relationship to cropping decisions in Kamuli District, Uganda

Abstract

Kamuli District offers an opportunity to understand pedology and cropping decisions in an area that has been underdocumented. Broad, flat summits and narrow convex shoulders are composed of residuum formed from Precambrian granite. Valleys mirror the summits, that is, broad flats composed of alluvium that are rimmed by narrow concave toeslopes. The alluvial landscape is a mix of Holocene terraces and modern floodplains. Gentle, linear backslopes gently merge into footslopes connecting the summits and valleys. These positions are composed of residuum-derived colluvium. These geologic and geomorphic differences create a systematic soil landscape pattern with Oxisols predominating on summits and shoulders, Ultisols predominating on the backslopes and footslopes, and Alfisols predominating across the valleys. The backslopes are more intensively cultivated compared to the summits and valleys. A comparison between cultivated and uncultivated areas revealed a dynamic relationship dependent on landscape position and human impacts. Critical human impacts include upland erosion, declining soil organic matter content, available phosphorus, total nitrogen, and exchangeable bases. Each of these appears to be gradually diminishing soil function, which has dire implications for future food security in Kamuli District.