Laboratory incubation studies were conducted to evaluate the effects of fertilizer P and poultry manure applied either separately, or in combination, on the changes in Olsen extractable P in twelve neutral to alkaline calcareous, non-calcareous and acidic soils treated with four levels of fertilizer P (0, 6, 12 and 18 mg kg(-1) with or without the addition of 2 x 10(3) mg kg(-1) (4.5 Mg ha(-1)) of poultry manure. The calculated effect of combined application of P and poultry manure revealed a higher increase in Olsen extractable P compared to the summed values of Olsen extractable P due to fertilizer P and poultry manure applied separately. The increase in Olsen P due to poultry manure ranged from 6-24 mg kg(-1) at 6 mg kg(-1) of applied fertilizer P. The effect of poultry manure in increasing the Olsen extractable P decreased with successive increments in fertilizer dose. The effect of ageing indicated that P application alone decreased the Olsen extractable P up to certain incubation periods for different soils, and thereafter showed an increasing trend. The combined addition of poultry manure and fertilizer P, however, caused a continuous increase in Olsen extractable P. The results have a practical implication for increasing the efficiency of fertilizer P applied in combination with poultry manure and keeping the P in the available form for a longer period.