Groundnut Residue Management and Soil Fertility in Western Uganda.

Crop residues are an important contributor to soil organic matter and to nutrient cycles, especially within low-input, intensive agricultural systems in sub-Saharan Africa. Within these systems, legumes often are the main source of added nitrogen and thus management of legume residues can have a large impact on potential crop yields, soil nutrient cycles and overall soil health. Soil and agronomic analyses of diverse groundnut fields in western Uganda in conjunction with an associated farmer survey revealed current agricultural management practices, particularly in regards to residues. In half (n=56) of the surveyed fields, groundnut residues were burned, piled, or removed, and in half (n=53) residues were surface spread or incorporated. Relative to uncultivated reference soils from Kibale National Park, the agricultural soils contained 11% less carbon (C), 28% less nitrogen (N), and had a 26% higher C:N ratio. As only 12% of farmers reported adding any type of organic or inorganic fertilizer into the surveyed fields, the nitrogen input from groundnut residues could make a critical difference in subsequent crop yields and for soil health over the long-term. Mean field size for surveyed groundnut fields was 0.085 ha. In 88% of fields, groundnut was planted with at least one intercrop, most often maize and/or cassava. While the majority of households identified maize as the most profitable crop, groundnuts were a close second, and 76% of households categorized themselves as “very much” dependent on crop sale profits. Household consumption accounted for half of the groundnut harvest. This study underscores the need not only for legume intercrops and rotation, but for effective legume residue management in order to realize the full potential of residue benefits. Promotion of best legume residue management practices could halt or slow soil degradation, particularly N depletion, in western Uganda.