**2.8 Fertilizer requirement**

Prior to the introduction of inorganic compounds, soil fertility has been improved through the breakdown of raw natural materials in the environment. This provided the soil with the needed nutrients for crop growth from only organic matter and this was enough in sustaining life [54]. Rob [54] noted that synthetic fertilizers do not add to the humus content of soil nor substitute it. Growth and dry matter yield of *Amaranthus cruentus* as affected by organic manure investigated by Daramola *et al* [55] showed that soil amendment using organic nitrogen sources produced the tallest plants, greater number of leaves, more branches and dry matter yield in comparison with the control. Olajide [23] conducted a study on influence of four poultry manure rates (0, 10, 20 and 30 t ha−1) on early growth of African walnut and reported that morphological traits were positively affected with the application of PM at 10 t ha−1, increase in PM beyond this rate resulted to a decline in growth of African walnut. The decline in growth at 20 t ha−1 and 30 t ha−1 of PM indicated that adequate amount of nutrients were released by the 10 t ha−1 of PM to complement the inherent nutrient in the soil. Sufficient nutrient supply produced high quality and better nutritious plants [56, 57]. As reported by Adebayo *et al*. [58], when manure is supplied at the required quantity, plants tend to grow at their optimal potential.
