Impact of Long-Term Application of Cadmium In Phosphate Fertilizer On Extractable Cadmium As Affected by Soil Characteristics.

Cadmium (Cd) can accumulate in soils from long-term application of phosphate fertilizer but the availability of the Cd added in P fertilizers will be affected by soil characteristics.  Field studies were established in 2002 at 7 sites across the Canadian prairies to evaluate the impact of repeated applications of 0, 20, 40 and 80 kg P ha^-1 of monoammonium phosphate (MAP) fertilizer containing 0.38, 70 or 210 mg kg^-1 of Cd.  The sites were planted each year, following a durum wheat-flax cropping sequence. In 2008, after 7 annual fertilizer applications, the accumulation of DTPA-extractable soil Cd was measured in the 0 to 7.5 and 7.5 to 15 cm soil depths of the control and the 80 kg P ha^-1 rate of each phosphate source. The DTPA extractable soil Cd in the surface 7.5 cm depth increased with application of MAP containing moderate or high concentrations of Cd, but concentration in the 7.5 to 15 cm depth only increased with the high-Cd MAP. Cadmium concentration in both durum wheat and flax increased with increasing input of Cd, but the magnitude of the effect varied with soil characteristics  and was not consistently related to DTPA-extractable soil Cd.  As the effect of Cd applied in MAP fertilizer on both DTPA-extractable Cd and grain Cd concentration is affected by soil characteristics, it is important to consider soil characteristics when assessing risk from Cd inputs into soils.