Effects of Leaf Harvesting Intensity and Frequency on Growth, Nodulation and Yield of Three Cowpea (Vigna Unguiculata L.) Varieties in Bor and Awerial County, South Sudan

Abstract

Cowpea (Vigna unguiculata L. Walp) is an important crop in South Sudan, however, its low production has been attributed to poor agronomic and leaf harvesting practices which cause a reduction in grain yield and quality because of interference of the source-sink relationship. The objectives of this study were to determine: (i) the effect of leaf harvesting intensity on growth, nodulation, and yield of selected cowpea varieties; and (ii) the effect of leaf harvesting interval on growth, nodulation, and yield of selected cowpea varieties. A randomized complete block design (RCBD) experiment in a 4×3×3 factorial arrangement (comprising intensity, frequency, and variety factors, respectively) was conducted in Bor and Awerial sites in South Sudan. The harvesting intensity treatments comprised control (no leaf harvesting), 20%, 40%, and 60% leaf harvesting, frequency treatments comprised 2, 3, and 4 weeks harvesting intervals while the cowpea varieties comprised improved variety M66 and landraces Lubia and Areng. Effects due to environment, variety, interval, and intensity were significant (p≤0.001) for days to flowering, maturity, number of nodules per plant, pod weight, grain yield, and shoot dry weight. An increase in leaf harvesting intensity (40 and 60% intensities) delayed flowering and maturity, and decreased shoot dry weight, 100-seed weight, grain yield, pod weight, and number of seeds per pod. Harvesting cowpea leaves at 20% intensity in both sites and 40% intensity at Bor resulted in increases in the number of leaves per plant and number of branches per plant compared to all the other treatments. Piece-meal harvesting delayed flowering and maturity, increased dry matter accumulation and reduce the number of nodules per plant. It also increased the number of leaves per plant, number of branches per plant, pod weight and number of pods per plant. Cowpea variety Areng and M66 had higher shoot dry weight, grain weight, grain yield, and the number of nodules, pods, and seeds per plant than variety Lubia. Among the three varieties evaluated for defoliation, variety Areng took a much longer time to flower compared to the other two varieties. A decrease in the dry matter at the flowering stage was

less pronounced on variety Areng. Variety M66 accumulated the least dry matter at different intensities and was less suitable for foliage harvesting after flowering. Cowpeas grown at Awerial produced a higher grain weight (0.93-1.04 t/ha) than those in Bor (0.78-0.94 t/ha). Both harvest interval and intensity had a significant effect on growth parameters, yield, and yield components of cowpea varieties. The sensitivity of the varieties to change in the Environment influences the production potential of cowpea varieties. Cowpea variety Areng and M66 are suitable for yield and foliage production with minimal environmental influence.