Abstract

Jude J. O. Odhiambo

Much of the smallholder farming sector in Limpopo province of South Africa is located on infertile degraded soils, with nitrogen being one of the predominantly deficient nutrient. The use of green manure legume cover crops in combination with Nitrogen (N) fertilizers is one option for improving N inputs into such farming systems. The objectives of this study were to (1) screen a number of green manure legume cover crop species, mucuna (Mucuna pruriens); sunhemp (Crotalaria juncea), lab- lab (Lablab purpureus); cowpea (Vigna unguiculata) and butterfly pea (Clitoria ternatea) in order to determine their suitability for the region and (2) to determine the effect of the green manure and nitrogen fertilizer on maize yield. The legumes were screened during the winter seasons of 2005 and 2006 and the summer seasons of 2005 - 2006 and 2006 - 2007. The bestbet legumes (mucuna, sunhemp and lab-lab) were then evaluated to determine their effect on maize grain yield with or without nitrogen fertilizer. The treatments imposed were mucuna, sunhemp, lab-lab, and a control with (75 kg N ha-1 ) or without (0 kg N ha-1 ) N fertilizer. Maize was harvested at maturity to determine the grain yield. In the screening trials, legume biomass yield ranged between 41 to 1,672 kg ha-1 , while the N content ranged between 2 to 58 kg N ha-1 in the winter trials. In the summer trials, biomass yield ranged from 899 to 13,586 kg ha-1 , while the N content ranged between 27 to 302 kg N ha-1 . Maize yield ranged between 4.0 to 6.4 tons ha-1 in the 2006 - 2007 seasons and between 5.8 to 8.4 tons ha-1 in the 2007- 2008 season. Control (-N) treatment had the lowest yield in both seasons. Overall, legume treatments, with or without N fertilizers produced between 19 to 58% more grain yield than control (-N). Of the green manure legumes screened, mucuna, lablab and sunhemp seem to be the most suitable green manure legume cover crops for this area and should be planted in the early summer season to maximize biomass production and N accumulation. Use of green manure legumes has the potential to increase maize yield in smallholder farms in Limpopo province.