Effect of cadmium on soybean (Glycine max L) growth and nitrogen fixation
To study the effect of cadmium (Cd) on soybean growth and nitrogen (N2) fixation, an experiment was performed in sand culture using Hoagland nutrient solution. At the time of sowing, different cadmium level that is 0, 4, 8 and 16 mg kg-1 sand was created using Cd (NO3)2. Soybean shoots and root lengths shoot and root biomass, nodule density and Cd uptake was recorded on 2, 4, 6, 8, 10, and 12 weeks after the emergence. To calculate the relative abundance of ureide and % Pfix (proportion of plant N derived from N2-fixation), xylem sap was collected and analyzed for ureide, nitrate and amino-N at pod fill stage. The application of Cd adversely affected soybean growth, nodulation and N2 fixation as a function of time and increase in Cd concentration. Maximum reduction in the root and shoot length was found with higher Cd level that is 16 mg kg-1 sand after 10 weeks of the growth. Similarly, nodulation and the proportion of plant N (% Pfix) derived from N2 fixation decreased sharply as Cd concentrations increased during the whole growth stages and the maximum reduction was observed in the Cd level of 16 mg kg-1 sand followed by 8 and 4 mg kg-1 sand, respectively. Cadmium uptake increased with the highest Cd application after each bi-weekly harvest of growth.
Keywords: Cd, growth, nodulation, N2 fixation, soybean.