Abstract

Oliver R. Khama, Kaiser Cedric and Lule E. Nelson

The use of green manure legumes (GLM) as cover crops in rotation with maize has the potential to enhance maize yields. The objectives of this study were to determine the effect of GML - maize rotation system on (i) maize growth and yield and, (ii) weed infestation levels. The two year (2007/8 and 2008/9 seasons) rotation system consisted of five GML cover crops, viz. mucuna, lablab, sunhemp, cowpea and butterfly pea followed by maize. GML biomass ranged between 0.8 and 13.6 Mg ha-1 , while nitrogen (N) content ranged between 10 and 279 kg N ha-1 . Maize grain yield following GML ranged between 2.6 and 10.59 Mg ha-1 . In 2007/8 season cowpea, mucuna, lablab and sunhemp plots had a lower weed dry matter (5.30, 11.97, 5.83 and 21.03 g m-2 , respectively) than the control (+N) (49.47 g m-2 ). In 2008/9 season, at 6 - 8 WAP, control (+N) had a higher weed dry matter than the other treatments, except of butterfly pea. The dominant weed species were Mexican ricardia (Ricardia brasiliensis), Yellow nutsedge (Cyperus esculentus), Guinea-fowl grass (Rottbollia cochinchinesis), Witch weed (Striga asiatica), Bermuda grass and Cynodon species. Green manure legume fallows can increase maize grain yield significantly and suppress the weed population as compared to natural fallow. However, maximizing biomass production and N accumulation is critical in order to reap the benefits of green manure. Hence, integrating GML into the existing cropping system will require that appropriate timing for planting GML be well established.