Kolawole G.O. and Oyeyiola Y.B.
Organic residues had been identified has having the potential to replace mineral fertilizers as cheap source of nutrients for cultivated crops. Pot experiment was conducted at the Department of Agronomy, Ladoke Akintola University of Technology, Ogbomoso, Nigeria to determine the comparative
response of cowpea to different levels of mineral P fertilizer and organic residues. The experiment which was laid out as completely randomized design replicated four times had Pueraria, Mucuna, Tithonia compost, cow dung, goat and poultry manures as the organic residues each applied at
5tDM/ha. Single super phosphate was applied at 15, 30, 45, and 60 kg P2O5/ha. Pots without mineral fertilizer and residues were included for comparison.
Poultry manure, Tithonia compost and Mucuna residues produced cowpea grain weights that were comparable to those observed for the mineral P fertilizer treatments but significantly higher than what was obtained for cow dung and Pueraria residues. Similarly, shoot weight obtained for pots that
received mineral P fertilizer was not significantly (P?0.05) different from that recorded for pots that had poultry manure and Tithonia compost treatments. Generally, pots that received organic residues amendments had higher shoot P content than those that received mineral P fertilizer. Shoot P content
was significantly highest in cow dung treatment (2.57%) and lowest in pot without any amendment (0.78%). Grain P was significantly higher in pots that had poultry manure treatment (7.51%) than other treatments. Cow dung (3.33%) and Goat manure (3.77%) had significantly lowest grain P content.
Shoot P uptake did not differ among the treatments whereas; grain P uptake was significantly highest in poultry manure treatment (21.53 mgP/pot) while goat manure had the least value (6.73 mgP/pot). Total P uptake was significantly higher in poultry manure (27.20 mgP/pot) and Tithonia compost (19.82
mgP/pot) treatments compared with any of the mineral P fertilizer treatments and the other organic residues amendments. From the results presented, poultry manure and Tithonia compost can serve as alternative source of P for cowpea production.