Effects of Plant Density on the Performance of Cowpea in Nigerian Savannas

Abstract

SUMMARYGrain yields of cowpea [Vigna unguiculata (L.) Walp.] in the Nigerian savannas are low even with the cultivation of improved varieties. The recommended spacing for cowpea is 75 × 20 cm with two seeds planted per stand. This corresponds to plant population of 133 333 plants ha −1 , which may not be sufficient for optimal cowpea yield. Field experiments were conducted to determine plant density effects on cowpea performance in the Northern Guinea and the Sudan savannas of Nigeria and also to determine if genotypes varied in their response to plant density. Four cowpea varieties with contrasting maturity duration were planted in single, double and triple rows on ridges spaced 75 cm apart to achieve corresponding densities of 133 333, 266 666 and 400 000 plants ha −1 , respectively. Plant densities of 266 666 and 400 000 plants ha −1 gave higher crop performance in terms of light interception, biomass production, yield and yield components for all cowpea varieties. Yield increases were related largely to increased pod and seed production but the effect of seed size on yield was relatively minor. Our results provide evidence that the current density of 133 333 plants ha −1 used by farmers is not optimum for cowpea production. Smallholder farmers can increase cowpea grain and fodder yields if they use a density of 266 666 plants ha −1 in cowpea cultivation. Further yield increases when cowpea is planted at 400 000 plants ha −1 may not be sufficient to offset the cost of seed.

Does Nitrogen Matter for Legumes? Starter Nitrogen Effects on Biological and Economic Benefits of Cowpea (Vigna unguiculata L.) in Guinea and Sudan Savanna of West Africa

“…The difference in the performance of cowpea in both zones and seasons might be due to the difference in amount of rainfall received during the cropping seasons (Figure 1). The range of cowpea grain and fodder yields obtained agreed with yields of cowpea reported in earlier studies [7,21]. The effect of variety on grain yield in both zones could be partly attributed to the difference in SW and fodder yield.…”

“…The Padi-Tuya variety matured later than the Apagbaala variety which gave the latter variety more growth period to accumulate enough dry matter to be partitioned into grain size, grain, and fodder yields. Kamara et al [21] also reported that differences in 100 SW of cowpea varieties contributed to the difference in grain yield among cowpea varieties. The significant effect of N fertilizer seen on grain and fodder yields and NUE in both zones could be due to the efficient use of N fertilizer for maximum economic yield.…”

Improving cultivation of cowpea in West Africa

“…The use of ridges spaced 75 cm apart with the recommended plant spacing of 20 cm corresponds to plant population of 133 333 plants ha −1 , which may not be sufficient for optimal cowpea yield. The low plant density resulting from wide row spacing usually leads to low yields in some grain legume crops, such as cowpea (Kamara et al, 2016). Grain yields of the widely available stress-tolerant cowpea cultivars hardly go above 1.7 t ha −1 on farmers' fields, despite the enormous gain in genetic improvement over the past three decades .…”

“…These varieties are usually spaced 30 cm apart to avoid overcrowding stress, while the erect types are spaced 20 cm apart to compensate for lower branching habit. To ensure that the optimum population is achieved on the widely spaced ridges, Kamara et al (2016) recommended planting two rows of cowpeas placed equidistant on the ridges. In an experiment in northern Nigeria, they planted four cowpea varieties with contrasting maturity duration in single, double and triple rows on ridges spaced 75 cm apart to achieve corresponding densities of 133 333, 266 666 and 400 000 plants ha −1 , respectively.…”

“…These varieties should, therefore, be planted in mid-July to mid-August. However, planting these varieties later than mid-August in the dry savannahs will risk crop failure because of early cessation of rain in October (Kamara et al, 2016). On the other hand, the erect, early and medium maturing varieties that are photoperiod-insensitive can be planted anytime in the year provided there is sufficient rainfall or irrigation facilities.…”