Compatibility of four forage legumes with guinea grass (Panicum maximum Jacq.)

Livestock production in the tropics is constrained by decline in quantity and quality of the predominant tropical grasses during the growing season. Incorporation of forage legumes into grassland agriculture has been used as a panacea to mitigate the problem. However, in tropical regions, not much of success has been achieved due to strong competitive ability of the grass which reduces the content of the companion legume. It is with this background that four experiments were conducted to evaluate the compatibility of grass-legume mixtures and their suitability for plantation livestock integration. An investigation into the nature of competition between Panicum maximum (guinea grass) and each of the following legumes of contrasting growth habits; Stylosanthes guianensis (stylo), Centrosema pubescens (centro) Macroptilium bracteatum (burgundy) and Arachis pintoi (arachis) showed that dry matter yield in guinea-centro mixtures (2:2 and 3:1) species combination tended to be higher than the corresponding grass monoculture (differences were not significant). Mean relative yield total values were higher in guinea-stylo (1.41) and guinea-centro (1.4) the values seemed to be higher at 2:2 species combination except in the case of guinea-burgundy. The climbing/trailing legume (centro) appeared to be more compatible with guinea grass especially at 2:2 species combination compared to the erect (stylo), erect/climbing (burgundy) and prostrate (arachis) legumes. Compatibility of forage mixtures evaluated at 50:50 species combination in relation to dry matter yield and chemical composition indicates that guinea-arachis produced significantly greater (P<0.01) cumulative total dry matter yield compared to other mixtures. However, the yield was not significantly different from that of guinea monoculture. The erect legume (stylo) produced significantly higher (P<0.01) cumulative total dry matter yield than arachis in mixture with guinea. Similarly, relative yield of stylo tended to be higher than those of arachis and burgundy. Thus as a compromise between dry matter yield and pasture quality, grass-stylo mixture was recommended. The productivity of four mixtures guinea-arachis, guinea-burgundy, guinea-centro and guinea-stylo evaluated under 3 shade levels 0 (1701.9μmol m-2 s-1), 50 (583.3 μmol m-2 s-1) and 70% (520.2 μmol m-2 s-1) indicates that guinea-centro tended to produce higher yield among mixtures though differences were not significant. Centro in mixture with guinea recorded significantly higher yield (P<0.05) than arachis and burgundy. Interaction between legume species and shade levels on dry matter yield showed that the dry matter yields of centro and stylo were significantly greater than those of arachis and burgundy under 0% shade, however, centro recorded significantly higher yield than all legumes at 50% shade, a similar trend was observed at 70% shade but the difference was only significant when centro was compared with arachis. The dry matter yields of grass and legumes decreased with increasing shade level. Guinea-centro mixture was recommended based on higher dry matter yield of centro compared to other legumes especially at 50% shade. Allelopathy study conducted using laboratory bioassay and pot trial to test whether guinea grass had allelopathic effect on companion legumes indicates that shoot length in stylo was significantly (P<0.05) reduced at 1% leaf extract concentration. Dry matter yield and root length in burgundy were significantly decreased by root powder while the yields of centro and stylo were enhanced by leaf powder. In conclusion, the climbing/trailing legume (centro) was observed to be the most compatible with guinea. This is based on the facts that in study 1, guinea-centro mixture showed tendency towards higher dry matter yield than the corresponding monoculture of grass (guinea). I study 2, however, the guinea-centro mixture was not part of the treatments owing to lack of germination of the centro seeds. In study 3, centro produced significantly higher dry matter yield than arachis and burgundy and surpassed other legumes at 50 % shade. Centro was also not negatively affected by the allelopathic effect of guinea grass as observed in study 4.

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