Inhibition of Nodulation and Nitrogen Nutrition of Leguminous Crops by Selected Heavy Metals

This work studied the effects, under greenhouse conditions, of six heavy metals (Cd, Co, Cr, Cu, Ni, and Pb) on three leguminous crops representing food, feed, and forage crops commonly grown in Egypt. Metal concentrations ranged from 0 to as high as 4.8 mmol kg(-1) soil. Results showed that all three plant parameters measured (dry matter yield, nodulation, and N uptake) decreased significantly with increasing heavy-metal concentrations. Plots of the natural log of each parameter against metal concentration were linear within the ranges studies. From the slopes of these regression lines, the concentration of each heavy metal required to achieve 50% reduction (R-50) of each parameter was calculated. In general, the lowest metal concentrations for R-50 were for Cd2+ and Pb2+ and the highest were for Cr3+ and Cu2+. Heavy-metal additions to soils should be closely monitored because they can negatively affect nodulation and N nutrition of leguminous crops.