GROWTH, NODULATION AND YIELD RESPONSE OF COWPEA [Vigna unguiculata (L.) Walp.] VARIETIES TO BRADYRHIZOBIUM INOCULATION IN DALE AND HAWASSA, SIDAMA REGION, SOUTHERN ETHIOPIA

Abstract

Cowpea [Vigna unguiculata (L.) Walp] is an important legume crop grown widely in lowland areas of Ethiopia. However, its yield remains low due to the lack of improved varieties and soil fertility decline. Therefore, the current study was conducted to evaluate the growth, nodulation, and yield response of cowpea varieties to Bradyrhizobium inoculation in Dale and Hawassa, Sidama Region, Southern Ethiopia during the 2022 main cropping season. The treatment combination consisting of four cowpea varieties (Bole, TVU, White Wonder Trailing, and Keti), with two levels of Bradyrhizobium inoculation (non-inoculated and inoculated with the strain: MBI-cowpea) was laid out in Randomized Complete Block Design in a factorial arrangement with three replications. The size of each experimental plot was 2 m in length x 4. 2 m in width with inter and intrarow spacing of 0.6 and 0.2 m respectively, as well as 1 and 1.5 m between two adjacent plots and replications, respectively. The representative soil samples were randomly taken from the experimental sites from 20 different spots at a depth of 0–20 cm and analyzed the soil texture, soil pH, total N, organic carbon, available P, and cation exchange capacity at Hawassa university soil science laboratory. Phenology, growth, nodulation and yield related parameter data’s were collected and subjected to ANOVA using SAS software version 9.0. The economic analysis was carried out using partial budget procedure. The results revealed that the day to 50% flowering, day to 90% physiological maturity, nodule fresh and dry weight, plant height, number of primary branches, fresh and dry shoot weight, root fresh weight, number of pods plant-1 , number of seeds pod-1 , hundred seed weight, and grain yield were significantly influenced by the main effect of varieties and Bradyrhizobium inoculation. However, days to 50% emergence and harvest index were significantly affected only by varieties. The nodule number, effective nodule, leaf area, leaf area index, root dry weight, root length, above ground biomass, and straw yield were significantly influenced by the interaction effect of varieties and Bradyrhizobium inoculation. Grain yield was positively and strongly correlated with nodule number, nodule dry weight, plant height, leaf area, shoot and root dry weight, number of pods plant-1 , pod length, number of seeds pod-1 , above ground biomass, and straw yield. The results showed that the White Wonder Trailing variety with Bradyrhizobium strain MBI-cowpea produced the highest grain yield (3.5 t ha-1 ), with a net benefit of 67171.3 ETB ha-1 and a marginal rate of return of 1386.7%. Therefore, this combination could be recommended to increase the grain yield of cowpea and economic profit earned in the study areas, and areas having similar agroecologies. However, this experiment was conducted in a single season, a lower number of varieties and two levels of Bradyrhizobium strain, repeating over multiple seasons, using a large number of cowpea varieties, and more Bradyrhizobium strains will be demanding to come up with a plausible recommendation.