The study was conducted in a greenhouse at the Institute of Agricultural Research and Training (IAR&T) Ibadan, Nigeria to evaluate the influence of P source, rate and frequency on dry matter yield of maize and cowpea grown sequentially in three soil types. Three sources of P: Ogun phosphate rock (OPR:20.2% P2O5); Crystallizer super (CS: 31.4% P2O5) and Single super phosphate (SSP: 18.0% P2O5); Four rates (0, 20, 40 and 60 kg/ha P2O5) and Two frequencies (regular and alternate application) were studied on three soil types (Ilora-Udipsamment; Ibadan- Arenic Haplustalf and Epe - Aquic Arenic Haplustalf
soils). The experiment was laid out in a split-split plot arrangement, using completely randomized design. Phosphate application significantly enhanced dry matter yields of maize and cowpea. Single super phosphate (SSP) gave a higher total biomass than the phosphate rocks (PR). On Ilora soil with the regular application frequency in the first cropping, maize total biomass was increased by SSP from 4.23 g/plant to 8.20, 9.25 and 9.72 with 20, 40 and 60 kgP/ha while it was increased to 6.78, 6.26 and 6.34g with OPR but to 6.88, 7.60 and 7.15 g with CS. Cowpea yields were increased from 2.12 g/plant to 3.28,4.04 and 3.36 g with SSP; to 3.34, 3.27 and 2.61 with CS and to 2.59, 2.78 and 2.39 g with OPR. On
Ibadan soil, maize biomass yield ranged between 6.13 and 6.37 g with OPR; between 7.22 and 7.56 with
CS and between 6.80 and 10.45 g with SSP. Cowpea yields were between 6.54 and 7.81 with OPR;
between 5.70 and 6.80 with CS and were between 6.59 and 8.94 with SSP. Both Ogun and crystallizer super PRs gave comparable dry matter yields of maize and cowpea as single super phosphate. Best growth performance was observed with application of 60 kg/ha in all the soils. Significant treatment effects in shoot, root and total dry matter yields of maize and cowpea were obtained with 60 kg P/ha. Alternating maize with cowpea gave a higher total plant biomass than continuous maize. Regular
frequency of application was superior to alternate frequency of application. Cumulative apparent P recovery of maize and cowpea at the end of final cropping was maximal with 20 kgP/ ha SSP in the three soils. It had 75, 80 and 70% recoveries for Ilora, Ibadan and Epe soils respectively
