Downward movement of cadmium and phosphorus from phosphatic fertilisers in a pasture soil in New Zealand Original Research Article

Total cadmium (Cd) and phosphorus (P) concentrations in a pastoral soil, amended annually for 10 years with four forms of P fertilisers, decreased with soil depth. Single superphosphate (SSP) and North Carolina phosphate rock (NCPR) which had higher Cd contents (32 and 41 mg kg−1, respectively) produced higher total soil Cd than diammonium phosphate (DAP—10 mg kg−1), Jordan phosphate rock (JPR—5 mg kg−1) and control treatments to a depth of 120 mm. Total soil P in SSP treated plots to a depth of 120 mm and NCPR treated plots to a depth of 75 mm was also higher than the control plots. No significant fertiliser P and Cd moved below 120 mm depth. Approximately 90% of the applied Cd was recovered in the soil of which 93% remained within the top 120 mm. Plant recovery of applied Cd was 1.5–4.5%. Plant avaialble P (Olsen P) also decreased with depth. Plant available Cd (0.01 CaCl2 extractable Cd) was higher in the 30–75 and 75–120 mm soil depths compared to 0–30 mm soil depth. This may be due to strong adsorption of Cd by the surface soils which have a higher organic matter content and higher pH; factors which are known to increase Cd adsorption in soils