Solubility and phytoavailability of cadmium in soils treated with nitrogen fertilizers

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Mitchell, Leslie Grant
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Studies were conducted to examine the effects of some commonly-used fertilizers on cadmium extractability, concentration of Cd in the soil solution, and concentration of Cd in plants grown on nitrogen-fertilized soils. Soil extractions were performed on a clay loam soil using different concentrations of fertilizer solutions, and the extracts were analyzed for Cd. Only solutions of ammonium sulfate solubilized a significant amount of Cd, with the increase in extracted Cd being unrelated to pH. The same clay loam soil was incubated at field capacity with various fertilizers and extracted with water and diethylenetriaminepentaacetic acid (DTPA) after 1-28 days to see if time had any effect on Cd solubilization. Time did not significantly affect cadmium extractability. Ammonium sulfate and urea were the only fertilizer salts to increase the amount of extractable Cd, and the increase in cadmium solubility was not related to pH. In a third study, wheat plants were grown in pots containing a fine sandy loam soil with diff rent rates of urea fertilizer. At different stages of plant growth, plant material was analyzed and the soil solution was removed using water displacement. Cadmium concentration in the soil solution and in the plant tissue increased significantly with nitrogen rate. Many of the plant nutrients showed similar increases in the soil solution and in the plant with increasing nitrogen rate. These increases were related to increasing ionic strength of the soil solution and a general reduction in soil pH. Plant growth and transpiration also increased with increasing nitrogen rate, allowing plants to take up increased amounts of Cd by mass flow. The increase in Cd phytoavailability with increasing nitrogen rate may be caused by the combined effect of increasing ionic strength, decreasing pH, and increasing plant growth.