Cadmium Availability to Plants as Affected by Repeated Applications of Phosphorus Fertilizers

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Abstract
Effects of repeated applications of different P fertilizers on Cd availability to plants were studied. A sandy and a loam soil were treated with lime to achieve three pH levels. Oat (Avena sativa L.), ryegrass (Lolium multiflorum L.), carrot (Daucus carota L.) and spinach (Spinacia oleracea L.) were grown as test crops in the greenhouse. Application of Cd-containing NPK fertilizers, ranging from 2.7 to 12.52 mg kg−1 Cd, increased the Cd concentrations in plant species as well as the DTPA- and NH4NO3-extractable Cd in the soils. Use of phosphate rock increased neither the extractable soil Cd nor the Cd concentration in plants. The low recovery of Cd from phosphate rock might be due both to low solubility of the phosphate, but also to a generally lower recovery of Cd when the added amount increases. The DTPA- and NH4NO3-extractable soil Cd were significantly increased by repeated applications of high-Cd NPK fertilizer, but the increases in plant Cd concentration over the years were not consistent. Cadmium concentration in plants generally decreased with increasing soil pH.