Cadmium Uptake by Soybean From Phosphorus Fertilizer.

Some phosphorus (P) fertilizers are contaminated with Cd. As part of a larger experiment, we studied whether soybeans [Glycine max (L.) Merr.] grown with and without P fertilizer accumulated different amounts of  Cd. We grew two cultivars of soybean, one a traditional Thai variety (Chiangmai 60 or CM 60) and one an improved cultivar developed at Khon Kaen University in Thailand (KKU 74) for 101 days under greenhouse conditions in soil (Morrill loam) that was unfertilized (7.44 ppm P via soil test) or was fertilized with triple superphosphate (40 ppm P added to the soil). At harvest, root and shoot dry weights were determined, and roots and shoots were analyzed for Cd.  Seeds were not analyzed because they were immature at termination of the experiment. The dry weights of KKU 74 roots without and with P fertilizer were 4.44±0.44 and 5.93±0.68 g/plant (mean ± SE), respectively. The dry weights of CM 60 roots without and with P fertilizer were 3.31±0.38 and 5.70±0.73 g/plant. Dry weights of KKU 74 shoots without and with P fertilizer were 20.96±2.44 and 39.61±5.56 g/plant. Dry weights of CM 60 shoots without and with P fertilizer were 16.29±1.24 and 33.40±4.84 g/plant. Roots of KKU 74 without and with P fertilizer had 5.74±0.23 and 9.89±0.66 ppm Cd, respectively. Roots of CM 60 without and with P fertilizer had 8.92±0.83 and 9.73±0.98 ppm Cd. Shoots of KKU 74 without and with P fertilizer had 0.89±0.06 and 1.38±0.12 ppm Cd. Shoots of CM 60 without and with P fertilizer had 1.11±0.06 and 1.50±0.09 ppm Cd. All concentrations of Cd were above 0.20 ppm Cd, the maximum concentration of Cd that should occur in plants based on analyses of plants growing on non-contaminated soil. Phosphorus fertilizer approximately doubled the Cd in roots of KKU 74, but had little effect on the Cd concentration in the roots of CM 60. Phosphorus fertilization increased the Cd in the shoots of both cultivars. Because the P-fertilized shoots had more Cd, it needs to be considered as a contaminant in soybean leaves when used as forage.