Cadmium uptake by cucumber from soil amended with phosphorus fertilizers

Cadmium (Cd) concentrations in some phosphorus (P) fertilizers may be high enough to cause significant Cd accumulation in plants. A 2-year field experiment was conducted on a Sultan silt loam (Aquandic Xerochrept) to determine how the availability to cucumber (Cucumis sativus L.) of Cd from a triple superphosphate (TSP) and a western phosphate rock (PR) was affected by rate of Cd input and liming. A water-soluble Cd salt, CdCl2, was included for comparison. Cucumber vine growth increased with increasing TSP application rates but was unaffected by the application of PR or CdCl2. Cucumber fruit yield, however, was unaffected by the application of either P fertilizer or CdCl2. Concentrations of Cd in cucumber vine or fruit responded to increased Cd inputs from PR, TSP, or CdCl2, and the vine was the primary sink for Cd that accumulated in the plant. Both vine and fruit Cd correlated better with soil total Cd than with labile Cd extractable by 0.05 M CaCl2 or DTPA (diethylenetriaminepentaacetic acid). A unique characteristic of cucumber vine- or fruit-Cd is that it was unaffected (P > 0.05) by lime rate and Cd source and not closely related to labile or exchangeable Cd as measured by 0.05 M CaCl2, in contrast to previous findings for other vegetable or grain crops. Root exudates could have controlled the solubility of Cd in the soil. The low availability of Cd from these sources to the plant was evidenced by the low uptake coefficient of Cd (0.461 to 1.059) from the soil to the cucumber fruit and low Cd recovery (0.43%) in both vine and fruit of Cd added.