Selection of local soybean rhizobia as biofertilizer from acidic soil of East Wollega, Ethiopia

Abstract

Soybean [Glycine max (L.)] is a leguminous crop that harbors root nodule bacteria that fix atmospheric nitrogen. However, the dinitrogen-fixing potential of the isolates varies due to different factors that necessitate the selection of the most efficient ones from local soils. In this study, 70 soybean root nodule bacteria isolates were extracted from the acidic soil of East Wollega Zone, Ethiopia. Colony characteristics and physiological and agronomic properties of the isolates were determined. Sixty-six isolates were confirmed as slow-growing soybean rhizobia based on renodulation, cultural characteristics, and cluster analysis with reference strains. About 5.5%, 35%, and 45% of the isolates were tolerant of 8% salt and 45°C temperature and pH 3 of incubation conditions, respectively. The highest nodule number, nodule wet weight, nodule dry weight, shoot height, shoot dry weight, shoot wet weight, and shoot length recorded were 38 ± 1 (SRU66), 1.71 ± 0.1 g/plant (SRU66), 0.63 ± 0.49 g/plant (SRU19), 36.7 ± 1 cm/plant (SRU36), 1.41 g/plant (SRU25), 10.8 ± 1 g/plant (SRU1), and 72.0 ± 1 cm/plant (SRU1), respectively. In general, soybean rhizobial isolates in this study were diverse in their morphology, ecophysiology, substrate utilization, and symbiotic effectiveness. Seven isolates, SRU11 (82.2%), SRU25 (141.7%), SRU26 (96.5%), SRU27 (187.4%), SRU31 (1013%), SRU36 (116.1%), and SRU70 (96.5%), were strong in their relative symbiotic effectiveness and are recommended as bioinoculants to boost the productivity of the soybean after a test under field environment.