Comparative evaluation of commercial rhizobial inoculants of soybean

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 eff...