Growth and Yield Response of Cowpea (Vigna unguiculata L. Walp) to Different Row Spacings and Frequency of Weeding in Nyakomba, Nyanga North

Abstract

Cowpea (Vigna unguiculata (L) Walp) is an important legume grown in the semi-arid areas of sub-Saharan Africa. It is a deep rooted hardy crop with good drought tolerance and fixes atmospheric nitrogen through symbiosis with nodule bacteria thereby improving soil fertility. In Zimbabwe, cowpea it is the most commonly grown pulse in communal areas. The major problem encountered by farmers in Zimbabwe is the interference of weeds within the crop, due to the fact that planting is done in wide spacing and cowpea has an initial slow growth. During the rainy season weeds come in two to three flushes and compete with cowpeas for nutrients, space, and light. There is inadequate information on the critical time of weed removal in cowpeas hence the need to address this problem in Nyanga north. The major objective of the research was to evaluate the effects of row spacing and frequency of weeding on cowpeas growth and yields under rain fed conditions at Nyakomba in Nyanga. The specific objectives were to; (i) determine the effects of weeds on growth of cowpea as influenced by row spacing, and (ii) determine the effects of weeds on yield of cowpea as influenced by frequency of weeding and spacing. Two experiments were conducted at Nyakomba Irrigation scheme. Both experiments were laid in a Randomized Complete Block Design (RCBD). Some 200kg/ha compound D basal fertiliser was applied at planting. The semi-determinate Cowpea variety CBC 2 was used at a seed rate of 30kg/ha. Experiment one comprised of 9 treatments with three spacings used namely; 75cm*15cm, 60cm*15cm and 45cm*15cm. Experiment 2 comprised of 8 treatments namely; one hand weeding and hoeing at 2WAE, one hand weeding and hoeing at 3WAE, One hand weeding and hoeing at 4WAE, two hand weeding and hoeing at 2 and 5WAE, weed-free check and weedy check. The insecticide Acetamiprid was used to control aphids. Data collected included plant height, number of leaves per plant, number of branches per plant, days to 50% flowering, days to 90% maturity, number of pods per plant, number of seeds per pod, 100 seed weight, aboveground dry biomass yield, harvest index, grain yield for both experiments. From experiment one it was concluded that row spacing of 45cm*15cm had greater mean number of leaves (81.067), mean aboveground dry biomass yield (6785.2 kg/ha) and mean grain weight (2.8000t/ha). From Experiment two, it was concluded that two hand weedings and hoeing at 2 and 5 WAE had a great mean aboveground biomass yield (6440.0 kg/ha) mean yield (2.440 t/ha) and yield loss of 12.920%. It can be recommended that spacing of 45cm *15cm and weeding at 2 and 5 WAE should be adopted by farmers in Nyanga north.