Effect of leaf bud removal and partial leaf harvesting on growth, development and yield of cowpeas (Vigna unguiculata [L.] Walp.)

Abstract

Cowpea (Vigna unguiculta [L.] Walp.) originates in tropical Africa. Most producers engage in “dual purpose” cowpea production, where sequential harvests of leaves arc made, followed by seed harvest at the end of the season. Despite its importance ns a leafy vegetable in Botswana, few studies have been conducted to evaluate the effects of leaf harvesting on grain yield and Nj fixation in cowpea. The use of cowpea leaves for human consumption involves defoliation, particularly at the early stages of plant growth. The objective of the first study was to determine the effects of cowpea leaf bud removal and leaf harvesting on growth, development, grain yield and quality as well as nodulation of Tswana variety (cream colour-TSWANA) and the landrace (speckled brawn-LEELATSILWANE). In a second experiment the effects of frequency of cowpea leaf bud removal and leaf harvesting (frequency of organ removal) was determined on growth, development, grain yield and quality as well as nodulation of TSWANA variety. The treatments were randomized within the experimental blocks. A plot size of 3.5 x 2.4 m having 6 rows was used. Spacing was 75 cm intra- and 20 cm inter-row respectively. Five seeds were planted per hill and thinned to one seedling seven days after emergence. Each treatment was replicated four times. The trials were from August 2013 to December 2014. The data collected was subjected to analysis of variance (ANOVA) using Statistical Analysis System (SAS, 2011) programme. Where a significant F- test was observed, treatment means separated using the Least Significant Difference (LSD) at P=0.05. The first main objective of this study was to determine the effects of cowpea leaf bud removal and leaf harvesting (organ removal) on growth, development, grain quality as well as nodulation of two locally cultivated TSWANA variety (cream colour) and the landrace (speckled brown- LEELATS1LWANE). As hypothesized, organ removal had a significant effect on the growth, development, yield and nodulation of the two genotypes with the exception of branching. Correlation analysis reveal a negative correlation between leaf accumulation to nodule size, nodule numbers, and fat content and a significantly positive correlation discovered between leaf accumulation and the number of branches, number of seeds per pod and biomass. The second objective of this study was to determine the effects of frequency of cowpea leaf bud removal and leaf harvesting (frequency of organ removal) on growth, development, grain quality as well as nodulation of TSWANA variety. The TSWANA variety’s growth, development, grain yield and nodulation does not respond to more frequent organ removal. The variety performs better if the leaf bud is removed once in its life time. The study suggests that producers should not engage in “dual purpose” cowpea production for all cowpea varieties and landraces, as not all respond to leaf harvesting production. This is because the two genotypes responded differently to the treatment.