Forty percent revenue increase by combining organic and mineral nutrient amendments in Ugandan smallholder market vegetable production

Linkages between poverty and soil fertility decline in sub-Saharan Africa indicate the need for effective strategies to restore soils, while improving smallholder incomes. Combining organic and inorganic nutrient resources offers a promising means to address this issue, via improvements to nutrient cycling and key soil properties. Yet few studies have examined this practice from an economic perspective and none have explored its potential in intensively managed, market vegetable crops. We address this issue through a demonstrative, on-farm research trial examining the agronomic and economic benefits of mixing manure and inorganic fertilizer for smallholder cabbage production in rural Uganda. Cabbage was grown on eight replicate farms in close association with a farmer field school on vegetable production. Inorganic fertilizer, urea and NPK, and cattle manure were applied alone and in combination, based on equivalent monetary inputs, yielding six treatments: (1) 100 % fertilizer, (2) 75 % fertilizer and 25 % manure, (3) 50 % fertilizer and 50 % manure, (4) 25 % fertilizer and 75 % manure, (5) 100 % manure, and (6) a control without nutrient inputs. Initial soil fertility was evaluated prior to planting and cabbage biomass, nutrient content, and market value were assessed at harvest. Our findings demonstrate that combining manure and inorganic fertilizers produced up to 26 % higher biomass and 40 % higher market value on average than fertilizer or manure alone treatments. Incomes could be increased by 114.68 USD per growing season based on the current area of land that farmers dedicate to cabbage production, compared to using manure or inorganic fertilizer alone. Furthermore, the input ratio of manure to fertilizer appears to be flexible and thus easily adjusted to price fluctuations. This research provides a clear means for smallholder farmers to better allocate soil fertility investments and enhance incomes from market vegetable production. This research also highlights the importance of involving farmers in agricultural research for efficient evaluation of new technologies, building local capacity and yielding rapid impacts.