Effect of phosphorus fertilizer application on the performance of maize/soybean intercrop in the southern Guinea savanna of Nigeria

Field experiments were conducted at the Teaching and Research Farm, Ladoke Akintola University of Technology, Ogbomoso, Nigeria in 2007 and 2008 to determine the effects of phosphorus fertilizer application on performance of intercropped maize and soybean. The experiments, arranged as a split plot in a randomized complete block design, replicated four times. A cropping system with sole maize, sole soybean and maize/soybean intercrop formed the main plot treatments while P rates with 0, 15 and 30 kg P₂O₅ ha^?1 were the subplot treatments. For both years, neither P fertilizer application nor cropping systems had a significant effect on maize grain yield. However, soybean grain yield was significantly higher (92.3% in 2007 and 44.5% in 2008) under sole cropping than under maize/soybean intercropping. On average, N fixed by soybean increased with the increase in P rate (from 51.8% without P to 60.5% with 30 P), but there was no significant difference in N fixed by sole soybean and soybean/maize intercrop. However, the interaction effect on N fixed between cropping systems and P rates was significant (P ≤ 0.05). N, P and K contents in maize grain were significantly higher (>100%) in intercropped maize than in sole maize. The cropping systems had no significant effect on post-harvest soil chemical characteristics. The land equivalent ratio was 1.52 in 2007 and 1.78 in 2008. The result shows that in utilizing legumes for N enrichment, the alleviation of P deficiency can enhance N₂-fixation by legumes. Furthermore, P replenishment in a maize/soybean intercrop may improve maize grain quality even though yield is not increased.