Response of a Promiscuous Soybean Cultivar to Rhizobial Inoculation and Phosphorus in Nigeria’s Southern Guinea Savanna Alfisol

An experiment was carried out at the Federal University of Technology (F. U. T.) Farm, Minna during the 2008 cropping season to investigate the number of nodules, dry shoot biomass, grain yield and, grain N and haulm N contents. An early maturing (75 days) promiscuous soybean cultivar (TGX 1485) was used. The experiment was laid out in a randomized complete block design with six N sources (Uninoculated, inoculated with four rhizobial types {R25B, IRj 2180A, IRc 461 and IRc 291} and 60 kg N ha-1 as urea) and three P – levels (0 kg P2O5 ha -1, 25 kg P2O5 ha -1 and 50 kg P2O5 ha -1) as treatments. These treatments were replicated four times. The four rhizobial inoculants were found to increase the parameters investigated over those of the control. Except for the nodule number that was significantly (P≤0.05) depressed by N fertilization among treatments, the IRj 2180A rhizobial strain produced yields that were comparable with those of the plots supplied with 60 kg N ha -1 . On the other hand, as P- rates increased the parameters investigated also increased. Key words: Rhizobial inoculation, phosphorus and promiscuous soybean cultivar