The effect of different treatments on nodulation and plant growth. Nodule number per plant at 3 weeks (a) and 4 weeks (b); nodule dry weight at 3 weeks (c) and 4 weeks (d); shoot dry weight per plant at 3 weeks (e) and 4 weeks (f); and root dry weight of soybean (per plant) at 3 weeks (g) and 4 weeks (h) after inoculation. The data are expressed as means and SD of three replications. B: B&D nutrient solution; H: modified Herridge nutrient solution; 7: pH 7.0; 4: pH 4.0. In each graph, values followed by different letters are significantly (P < 0.05) different.