Abstract: Background and Objective: Tropical soil has been reported to be low in essential nutrients required by plants. Inorganic fertilizers are expensive and scarce and this has necessitated shifting to the use of organic fertilizers such as animal manure since they have the potential to supply required nutrients to plants and are readily available and cost-effective. Materials and Methods: An experiment was conducted to evaluate the influence of manure rates and age at harvest on the growth, dry matter yield and nutritive quality of Megathyrsus maximus. The study was laid out in a 4×2 factorial design with four manure rates (Control (0), 60, 120 and 240 kg N/ha) and 2 ages at harvest (6 and 8 weeks after planting) (WAP). Results: Significant increase was recorded in the height of the grass with an increase in manure rate application up to 120 kg N/ha as well as with the increase in the age of the grass except for grass with the application of 240 kg N/ha. The number of leaves of grass increased with increased manure rates and age of growth. Dry matter yield increased with advancing age as well as an increase in the rates of poultry manure applied. At both ages of harvest, fertilized grass had higher CP content than the unfertilized grass with an increase in the rate of manure. Conclusion: Megathyrsus maximus with an application rate of up to 240 kg N/ha poultry manure and at 8 WAP is, therefore, recommended to be used in place of expensive inorganic fertilizer by the resource-poor farmers in the humid zone of Nigeria.