Int. Conference Soil Science Sociey of East Africa, Busitema University edition:26 location:Uganda date:21-24 November 2011
Soil loss due to crop harvesting (SLCH) has been established as an important soil erosion process that has significantly contributed to soil degradation in highly mechanised agriculture. Preliminary investigations into soil loss due to cassava roots and sweet potato as a case study from low input traditional agriculture in Uganda has shown that soil loss was negligible for sweet potato but considerable for cassava (3.4 t ha −1 yr). With this
study we aim to come to a more comprehensive understanding of SLCH in Uganda. This study was conducted in Eastern Uganda with the following objectives: (1) To assess the
magnitude of SLCH for cassava and sweet potato under low input agriculture and the amount of nutrients lost due to SLCH, (2) to investigate the factors that determine the
magnitude of SLCH, by doing further research under a broader variation of soil texture types and soil moisture conditions and investigate other possible factors as well, (3) to look at possible differences in SLCH between small-scale farmers and commercial farmers, and (4) to investigate if the soil lost along the road or at markets contributes to the eutrophication and siltation of Lake Victoria. As commercial farmers transport sweet potatoes and cassava from the field to the market, possible losses along the route were distinguished. During heavy rain storms, the soil lost along the road and in markets is
washed away down the road into the swamp that finally drains into Lake Victoria. Samples were taken at markets and in fields. Soil sticking to the roots was washed and the soil suspension was oven dried to estimate the amount of soil lost after harvesting.Mean annual soil loss was negligible for sweet potato (0.8 t hayr) but considerable for cassava (3.4 t hayr). Clay content and gravimetric soil moisture content (GMC) appeared to be the most important factor controlling SLCHspec (the soil loss value per unit of crop mass) in this study. SLCHspec was larger for commercial farms than for small-scale farms.
This could possibly be due to a lower sand content for the samples taken at commercial farms.Soil lost along the road was 2.5 t ha yr for cassava and 0.8 t ha yr for sweet potato.
The estimated amount of nutrients gathering the lake through SLCH loss along the road ranges from 1.1 to 3.5 kg N ha yr and 0.02 to 0.06 kg P ha yr. From this study we can
conclude that SLCH has only a minor contribution to the siltation of Lake Victoria and does not contribute to the eutrophication of Lake Victoria.