Soil erosion and pollution loading from agricultural land in Bukoora sub-catchment

Abstract

High enrichment of eroded material in terms of fine particles and nutrients content is a result of the selective character of the erosion processes. The consequences are both on-site and off site and the concentration of fine particles and organic matter of eroded materials in w ater bodies leads to considerable pollution loads. The correlation between soil and nutrient exports agricultural land and suspended solid and nutrient loads in rivers of Bukoora sub-catchment in the Lake Victoria basin was determined. Soil and nutrient losses were measured from instrumented runoff plots. Thirteen instrumented runoff plots were established on banana, coffee, rangelands and annual crops. The distribution of different land-use types was mapped using 1: 120000 map and field transects. The coverage of the different land-use types was 10.5% (annuals); 17.1% (banana); 7.6% (coffee); 16%(banana-coffee); 11.8% (banana-annuals); 24%(rangelands), 1.9% (fallow); 3.2% (coffee-annuals); 7.5% (forest); and 0.4 % (bare land). Seasonal sediment, total available P, and total nitrogen export from agricultural land showed a very strong to moderate linear relationship with the corresponding parameter load at three hydrological stations. A similar pattern was observed between sediment export and total P and total N load. Generally, loadings from all the two micro-catchments were not highly correlated to the corresponding export parameters and sediment export from agricultural land compared to loads within the two micro-catchments. The pattern of correlation coefficient indicate that a lumped seasonal precipitation is not enough to model the export of sediment and associated loads in the two micro-catchments. Excessive nutrient losses by water erosion is a major soil degradation driving force leading to decreased production per unit area and hence increasing poverty.