Cadmium Levels in Soils and Plants From Some Long‐term Soil Fertility Experiments in the United States of America

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Abstract
Phosphate fertilizers contain varying amounts of Cd and other heavy metals as contaminants from phosphate rock (PR). To determine whether periodic applications of P fertilizers resulted in measurable accumulations of Cd in soils and in harvested crops, soil and plant tissue samples from nine long‐term (> 50 yr) soil fertility experiments in the USA were analyzed for Cd, as well as P and other elements. Annual Cd rates were estimated to range from 0.3 to 1.2 g ha−1 in these experiments. Plant tissues analyzed were corn (Zea mays L.), soybean (Glycine max L. Merr.), and wheat (Triticum aestivum L.) leaves or grain, and timothy (Phleum pratense L.) forage. Results from these long‐term experiments have shown that plant uptake of Cd contaminants in P fertilizers containing < 10 mg Cd kg−1 is negligible. While the Cd accumulations in soil in these experiments could not be calculated, they would approximate that accumulated in most agricultural soils in the USA at this time. About 70% of the P fertilizers is produced from Florida PR, which contains < 10 mg kg−1 of Cd, as compared with about 10% from the western USA, which contains higher Cd levels. Therefore, adding Cd to soils as a contaminant in P fertilizers at rates ranging from 0.3 to 1.2 g Cd ha−1 does not appear to result in increased Cd levels in plants as a result of long‐term P fertilization.