Nutrient balances and expected effects of alternative practices in farming systems of Uganda

Nutrient balances were estimated for small-scale farming systems at four sub-humid, medium altitude locations in eastern and central Uganda. Data from several sources were used to estimate nutrient fluxes, including farmer interviews, observations of the fanning systems, soil analyses, and the output of simulation models. Results from the three locations were combined because of similarity of farming systems, with the Palissa location treated separately. Nutrient balances were determined to be negative for all crops except for N and P in the banana-based land use type (LUT) which benefited from the transfer of nutrients from other land use types in organic materials. The annual crops-LUT occupied more land than other LUTs and accounted for more nutrient loss than all other LUTs combined. Crop harvest and soil erosion were the major causes of nutrient losses at the crop and LUT levels. N and K balances were positive and negative, respectively, for the fallow and pasture LUTs. Harvests and livestock dung and urine were brought to the household LUT, and the losses in this relatively small LUT appeared to be high from burning, volatilization and erosion. No farmer used fertilizer and nutrients in any form were applied to banana, only. Marketing and purchasing of commodities resulted in farm-level nutrient deficits for Palissa but had little effect on the balances at other locations. The cumulative effect of several low-input management practices was estimated to give nutrient balances of near zero for N and P, but K losses at the held-level continued to be high. (C) 1998 Elsevier Science B.V. All rights reserved.