GROWTH, SYMBIOTIC AND YIELD RESPONSES OF SOYBEAN (Glycine max L.) VARIETIES TO BRADYRHIZOBIUM INOCULATION AND PHOSPHORUS APPLICATION AT ALAGE, CENTRAL RIFT VALLEY OF ETHIOPIA

Abstract

Soybean (Glycine max L.) is one of the most important food legumes of great nutritional value that has the highest protein content (40%) of all food crops and is equivalent to the protein of animal product. However, in Ethiopia its productivity is constrained mainly by low soil fertility and lack of improved varieties. A field experiment was conducted during 2020 belg cropping season at Alage Central Rift Valley of Ethiopia with the objective of evaluating the effects of Bradyrhizobium japonicum strain inoculation and P fertilizer rates on growth, symbiotic and yield response of soybean varieties. The treatments studied includes four P levels (0, 10, 20 and 30 kg P ha-1 ), two inoculation levels (un-inoculated and inoculated with Bradyrhizobium strain; TAL-379) and two soybean varieties (Afgat and Nova) in randomized complete block design with factorial arrangement with three replications. The results revealed that the main effect of varieties were significantly (P≤ 0.01) influenced most of measured parameters. The results also revealed that inoculation of soybean varieties with Bradyrhizobium strain TAL-379 significantly (P≤ 0.01) influenced days to maturity, nodule number, nodule dry weight, shoot dry weight, root dry weight, pod number plant-1 , hundred seed weight, grain yield, above ground biological yield and harvest index. Conversely, days to emergence, days to flowering, plant height and seed number pod-1 was not statistically affected by inoculation of strain TAL-379. The effect of P fertilizer was also significant for most of studied parameters except branch number and harvest index. The interaction effect of varieties x strain, strain x P, and varieties x P caused significant variation on days to maturity, number of nodule, nodule dry weight, shoot dry weight, root dry weight, pod plant-1 , hundred seed weight, grain yield and above ground biological yield. Hence, the use of Afgat variety with Bradyrhizobium strain TAL-379 inoculation significantly gave the highest grain yield (2.99 t ha-1 ) followed by the interaction of Afgat variety with the supply of 20 kg P ha-1 (2.89 t ha-1 ). Grain yield was positively and significantly correlated with most of studied parameters. From the economic point of view the partial budget analysis of the study treatments revealed that the highest net return (63750 ETB ha-1 ) was gained from Bradyrhizobium strain TAL-379 inoculation followed by application of 20 kg P ha-1 and Afgat variety. Thus, it could be recommended that the use of Afgat variety, Bradyrhizobium strain TAL-379 and application of 20 kg P ha-1 to get higher yield and profit of this crop at Alage Central Rift Valley of Ethiopia. However, verification of the result on farmers’ fields across season and areas could be required before wide use of this study to put the recommendation in firm ground