The economical substitution of nitrogenous fertilizer by biological fixation by a leguminous covering under rotation systems with corn (Zea mays L.), is one of the agricultural research themeswith highest potential for developing technologies aimed to achieve a sustainable corn production in the tropics. An experiment was conducted during twoconsecutive corn cycles at Cuyuta-Guatemala, in order to quantify the equivalence of urea dos es and the N supplied by two legumes (Canavalia ensiformis L. and Mucuna deeringianum Bort). During the first cycle, the corn yield showed a significant response to the N-urea as well as to the incorporation of green manure. During the second cycle, the residual effect of the legumes on the corn yield was markedly lower and the differences among rotation systems depended on the N level and plant population. The rotation effect with green manure and its relation with the doses of urea approved the substitution of N-fertilizer by green manure. The main factors affecting the yield response under the different rotation systems were: doses of N-fertilizer, amount of N in the superficial biomass of the legume and the final plant population.