Yield components of nodulated cowpea (Vigna unguiculata) and maize (Zea mays) plants grown with exogenous phosphorus in different cropping systems

A 2-factorial experiment, involving three levels of phosphorus (0, 40, and 80 kg/ha) and four cropping systems (mono crop, maize–cowpea inter-row, maize–cowpea intra-row, and maize–cowpea intra-hole cropping) was conducted in the field for two consecutive years in 2003 and 2004 at Nietvoorbij (33°54′S, 18°14′E), Stellenbosch, South Africa. Plant density (number of plants per hectare) was 166 666 for sole cowpea, 111 111 for maize–cowpea inter-row, 55 555 for maize–cowpea intra-row and 55 555 for maize–cowpea intra-hole cropping. Applying 40 or 80 kg phosphorus (P)/ha significantly increased cowpea grain yields by 59–65% in 2003 and 44–55% in 2004. With maize, the increases in grain yield were 20–37% in 2003 and 48–55% in 2004 relative to the zero-P control. In both cropping seasons, the number of pod-bearing peduncles per plant, the number of pods per plant, the number of seeds per pod, and grain yield per cowpea plant were significantly increased with the application of exogenous P. In contrast, the number of pod-bearing peduncles per plant, the number of pods per plant, the number of seeds per pod, and the grain yield per plant were all significantly depressed by mixed culture relative to mono crop cowpea. There was also a significant interactive effect of P and cropping system on cowpea, such that, all cowpea yield components were generally lower in intercrop relative to mono crop. In all instances, the yield component of mono crop cowpea and, to some extent, inter-row cowpea, were markedly increased by the provision of 40 or 80 kg P/ha relative to the zero-P control. Intercropping maize with cowpea produced higher total yields per unit land area than the mono crop counterpart.