Tropical soils under moderate to high rainfall are known to be deficient in nutrients, mostly phosphorus and nitrogen. In many cases forage yields from improved grasses are low because of poor soil fertility and repeated harvesting which depletes the soil of nutrients, which are then not replenished. In order to successfully establish and maintain pastures on tropical soils, substantial application of fertilizers are necessary (Onayinka and Akinyemi, 1976).
Farmers should, therefore, be educated on the value of fertilizer application for increasing forage production and be advised to practice it either using chemical fertilizers, or more appropriately, manure which would also improve the texture of the soil. Most grasses require application of nitrogen and phosphorus fertilizers at establishment. Inorganic fertilizers are generally unavailable and expensive for smallholder farmers (Nyathi and Gambiza, 1994).
Experiments to determine the appropriate levels of fertilizer and manure that are required to sustain herbage production of Napier grass and hybrid Pennisetum have indicated that manure could be used in place of inorganic fertilizers. In order to obtain maximum benefit from manure/fertilizer application to forages, priority should be placed on selecting species with high residual fertility utilization capacity.