Comparative evaluation of commercial rhizobial inoculants of soybean

Abstract

Inoculation of soybean seeds with root-nodule bacteria results in a significant increase in nodulation and yield. Two commercial rhizobial inoculants available on the South African market were tested for their efficacy under standardised conditions in a short-term greenhouse experiment. The rhizobial inoculants used were: (1) Plant Health Products mix (PHP), a wet formulation containing Trichoderma harzianum Eco-T^® [strain KD] and Bradyrhizobium japonicum [strain WB74] and (2) ‘Product X’, a commercial dry tri-formulation containing Trichoderma spp. and three Bradyrhizobium strains. Seeds treated with the PHP mix yielded plants with significantly greater chlorophyll content (P < 0.01), percent nitrogen (P = 0.001), and nodule occupancy (P < 0.01) when compared with plants that had been treated with Product X. Correlation analysis indicated that 99% of the variation in nitrogen content levels was predicted by chlorophyll content meter readings. The use of the registered PHP product was shown to be the more efficient and reliable rhizobial inoculant for the improved growth and development of soybean.

Keywords: Bradyrhizobium, soybean inoculant, Trichoderma