Contribution of Legume Rotations to the Nitrogen Requirements of a Subsequent Maize Crop on a Rhodic Ferralsol in Tanga, Tanzania

Abstract

Industrial fertilizers are expensive for small-scale farmers who, as  alternative, rely on legume crops for providing N for a subsequent maize crop. A legume-maize rotational experiment was carried out on a Rhodic
Ferralsol at Mlingano Agricultural Research Institute in Muheza, Tanga, Tanzania, to evaluate the effects of legumes rotation in meeting the N fertilizer requirements of maize. The experimental site was located at 39o 52’E, 5o 10’S and 183 metres above sea level (m.a.s.l.). The experiment was conducted for two rotation cycles whereby cowpea, pigeonpea or greengram were grown during the short rains followed by maize during the long rains. The maize rotations were imposed on plots on which legumes had been grown during the previous legume rotation. Monoculture maize was grown with treatments of 0, 25, 50 and 100 kg N ha-1 imposed for purposes of plotting N fertilizer response curves. Based on the response curve lines, the effects of the legume rotation on maize yields were  compared and translated as N fertilizer equivalency of the legumes in question. The grain and residue yields of the three legumes were  significantly different (P<0.01), a fact which was attributed to the genetic differences of the legume species. The maize yields following rotation with each of the three legumes were significantly higher (P<0.05) than those under continuous maize. The effects of the rotations on increasing the maize yields were equivalent to application of 25, 19 and 16 kg N ha-1 for the cowpea, pigeonpea and greengram rotations, respectively. It was, however, concluded that the contributions of N by the legumes in the legume-maize rotations were not enough to satisfy the maize N  requirements of 50 kg N/ha; hence supplementation with mineral N, in addition to the rotations, is necessary for increased yields.

Key words: Legume rotation, fertilizer equivalency, legume residues, maize, relative yield increase.