Effect of NPK fertilizer on nodulation at flowering / podding and at harvesting, was investigated in two early maturing cowpea varieties (Asontem and Asetenapa) in the major cropping seasons (March to August) of 2009 and 2013. In Trial 1 (2009), three levels of NPK fertilizer, comprising (i) no fertilizer, (ii) starter fertilizer only, using 23-10-05 at 125 kg/ha applied 9 days after sowing, and (iii) starter fertilizer plus a top-dress of 50 kg/ha sulphate of ammonia 21 days after sowing were tested in . 2 x 3 factorial in a randomized complete block design with four replications. In Trial 2, a blanket dressing of 40 kg/ha triple super phosphate was combined with four rates of 23-10-05 NPK at 0, 30, 60 and 120 kg/ha, in a 2x4 factorial randomized complete block design with eight replications. In Trial 1, total nodule count per plant was higher than active nodules (p<0.05) at early flowering (12.66 & 2.24, respectively) and at harvest (10.49 & 0.23, respectively) in both varieties. However, in Trial 2, total and active nodules were not significantly different at the same stage of development: 6.1 & 5.9, respectively, at podding and 2.3 & 1.9, respectively, at harvest. In the two trials, variety and fertilizer significantly affected nodulation but the trends were not consistent. In Trial 1, neither fertilizer nor variety was significant in total or active nodule count at early flowering or at harvest (p>0.05). On the other hand, in Trial 2, Asontem bore significantly more nodules at podding (8.4 per plant) than Asetenapa (3.7 per plant), though fertilizer was not significant. By harvesting time, the total number of nodules per plant had reduced to a mean of 2.2. In this, Asontem had 2.5 at harvesting, while Asetenapa had 1.9 nodules per plant. Keywords: cowpea, nodulation, NPK, Asontem, Asetenapa Acknowledgement: The authors are grateful to Prof. F. K. Fianu for his mentorship and guidance in the statistical analysis and for proof-reading the write-up
