AVAILABILITY OF CADMIUM IN SOME PHOSPHORUS FERTILIZERS TO FIELD-GROWN LETTUCE

摘要

Although evaluations of the availability of cadmium (Cd) contaminants in phosphate fertilizers have been made, few have examined the transfer efficiency of Cd from fertilizers to plants, especially under field conditions. This 2-year field study determined the transfer of added Cd to lettuce (Lactuca sativa L.) (Royal Green) from a western phosphate rock (PR) and a triple superphosphate (TSP) as affected by liming and rate of fertilizer (or Cd) input. A readily soluble Cd salt, CdCl_2, was included in the study for comparison. The cumulative amounts of Cd added from the fertilizers and CdCl_2 over the 2-year period ranged from 0 to 1440 g ha~(-1). Lettuce yield increased with increasing TSP rates, but was unaffected by PR. Significant (P < 0.01) effects of Cd source and rate, lime, and year were found on Cd accumulation by lettuce. The transfer of the added Cd was consistently higher for CdCl_2 than for the fertilizers regardless of lime rate. A contrasting year effect was also found between the two P fertilizers. In the second year of application, the Cd transfer efficiency increased in the soil treated with the PR, but decreased in the soil treated with the TSP. The Cd transfer efficiency for the plant was better measured with DTPA-Cd (r~2 = 0.78 - 0.80) or CaCl_2-Cd (r~2 = 0.57 - 0.76) than with soil total Cd (r~2 = 0.39 to 0.54) across all Cd sources and lime rates. This is because DTPA-Cd or CaCl_2-Cd reflected the influences of the amount of Cd added, Cd source, and lime rate on Cd accumulation by the plant better than did the soil total Cd. Of the amount of Cd added from the fertilizers an average of 1.0% or less was accumulated in the harvested lettuce tissue. Applications of the fertilizers at high rates could result in increased Cd accumulation in the soil over time.