Cadmium in soils and potato tubers under grower management in two contrasting soil types of Hokkaido, Japan

In Japan, little has been reported on cadmium (Cd) concentration in upland soils, and its relation to Cd concentration in crops and vegetables other than rice. Cd concentration in the surface soils and potato tubers of growers' fields in two main potato production areas in Japan with contrasting soil types (Andisols and Inceptisols) was investigated. Soil and tuber samples were obtained from 90 growers' fields with variable management histories. Total and Mehlich-3 soil Cd concentration were determined, and Cd concentration in the peeled potato tubers was also measured. A significant positive correlation was found between total Cd and phosphorous concentration in the soils reflecting the historical heavy application of phosphate fertilizer in both soil types. Although the total Cd concentration was much higher in Andisols, the Mehlich-3 Cd as well as tuber Cd concentration was lower in Andisols than in the Inceptisols, suggesting that Cd in Andisols may be specifically adsorbed by humic substances and amorphous clay minerals. The Cd concentration of the peeled potatoes in all samples was less than 100 mu g kg(-1) fresh weight below the threshold set by the Codex Alimentarius guidelines. The Cd concentration in the tubers tended to be higher when the soil phosphate retention index and base saturation were lower, and this tendency was stronger when both conditions are satisfied. Differences in soil properties and not the total soil Cd concentration were the dominant factor affecting potato tuber Cd accumulation. It is quite possible to reduce the amount of phosphate fertilizer appropriately to minimize the accumulation of Cd in both soil types as well as by increasing the soil base saturation to suppress the transfer of Cd from the soils to the potato tubers is especially important in the Inceptisols.