Food quantity and quality of cassava affected by leguminous residues and inorganic nitrogen application in a soil of low natural fertility of the humid tropics

The aim of this study was to test the hypothesis that the quality and quantity of biofortified cassava root in a humid tropical environment can be modified with the application of a combination of low- and high-quality residues of leguminous tree species. The experiment was designed as a 6 x 2 factorial (a combination of 4 legume species versus 2 levels of nitrogen) with 4 replications in a randomized block design and the following treatments: Gliricidia + Acacia, Gliricidia + Leucaena, Gliricidia + Clitoria, Leucaena + Acacia, Leucaena + Clitoria, and a control without legumes. We analyzed the shoot weight, number of roots/plant, root weight, root production, proximate composition, as well as the mineral, carotenoid, and pro-vitamin A contents. Root production increased with the application of high-quality residues. The protein level influenced the carotenoid content. The allelopathic effect of exotic genera - Leucaena and Acacia -, especially when combined, can decrease the mineral content such as potassium and, therefore, reduce the accumulation of starch.