EFFECT OF LEVEL AND SOURCE OF SHADE ON THE BIOMASS OF SPEARGRASS IN NIGERIA

Field studies were conducted in Oyo, Nigeria, to determine the effect of level and source of shade (polyethylene plastic fabric and vclvctbean canopy) on the dry matter of speargrass (Imperata cylinchica (L.) Raeuschel). Shade levels provided by the plastic fabric were 0 (full solar radiation), 50,75, and 88% of the incident solar radiation. Velvctbean shade levels of 40.5 to 97% were provided by densities of 4, 8, and 16 plants m^-1. In 1999, the vcl vetbean canopy intercepted 40.5% of solar radiation at 3 weeks after treatment (WAT) and 82% between 5 and 11 WAT. At 11 WAT, vclvctbean shading reduced the speargrass biomass by 48% and shade from plastic fabric by 41 %. In 2000, radiation interception by the vel vetbean canopy was 86.7 - 91.2% between 3 and 11 WAT. Shade from the vel vetbean canopy reduced speargrass biomass by 90%) and shade from plastic fabric by 44% at 11 WAT. Velvetbean biomas and LAI were negatively correlated with speargrass biomass (r = -0.85 to -0.91 , P 0.05) and incident solar radiation (r =-0.88 to -0.89, P 0.05). Solar radiation was positively correlated with speargrass biomass (r = 0.46 to 0.79, P = 0.05). The similarity of the effects on speargrass biomass of shading by plastic fabric and velvetbean indicated that shading was the principal mechanism by which velvetbean suppresses speargrass.