Runoff, Soil and Nutrient Losses from Major Agricultural Land-use Practices in the Lake Victoria Basin, Uganda
Soil degradation by water erosion is recognized to be a major agTicultural and environmental probkm in the Lake Victoria basin. The objective of this study was to quantifY runoff, soil and nutrient losses from major agricultural land-use types (Annual crops, banana, coffee and degraded rangelands) and assess the efficiency of contour bunds ·in reducing these losses in two selected micro-catchments of the Lake Victoria Basin. The experiment was conducted on 13 runoiT plots or 15 by 10 m. Each land-usc type was replicated three times, except banana. Contour bunds were hand constructed I wo years after establishment of runoff plots, at 20-m spacing interval. Before the establishment of contour bunds, the average annual runoff ranged between 3 I 5. 47 and 2438.92 m3 ha' 1/yr, with relatively higher amount of rainfall water loss on rangelands compared to banana and colfee (p=0.022). The avarage annual soil loss ranged from 27.7 to 86.7 t/ha/yr, with higher soil loss on annuals compared to banana and coffee (p=0.038). Seasonal soil losses contributed for more than 75% of the annual losses for all agriculrural land-use. while seasonal runoff contributed the same proportion only for banana and rangelands (p<0.05). Eroded sediments had relatively high nutrient concentrations than the remaining soils, and varied with land-use and /or seasons (p<0.05). The amount ofN, P, K and organic matter (OM) lost through erosion was relatively high, and varied with seasons (p<0.05). The establishment of contour bunds increased OM, Ca and Na content in eroded sediments. while it decreased total OM, TN losses for all land-use types except on rangelands where they increased one year afler. These exports from agricultural land play a major role in the nutrient enrichment of rivers and open bodies. •
Key words: Pollution, Sustainability, Farming system, Land-use, Soil nutrient losses.