Nutrient Content of Poultry Manures and the Optimum Rate for Eggplant Fruit Yield in a Weathered Tropical Ultisol

ABSTRACT

Three field experiments on West African eggplant {Solanum spp.) responses to rates of poultry manure conducted in a weathered tropical Ultisol between 1990 and 1991 are reported. The poultry manures collected from different locations differed markedly especially in their contents of the major fertilizer elements of N (16–36%), P (17–43%), K (6–56%) and Mg (13–51%). A manure rate of 15 t ha⁻¹ appeared satisfactory for eggplant production, although no quadratic response on eggplant fruit yield was observed at the highest rate of 20 t ha⁻¹. Yield responses to manure application were best predicted by a linear function within the range of 0 to 20 t ha⁻¹ manure. Fruit yield increases with increased manure application came essentially from more fruits harvested per plant and from higher average fruit weights. The leaf and fruit elemental concentrations were not increased in relation to increasing quantities of the elements supplied with increasing manure rates, in part due to possible dilution effects.