DOWNWARD MOVEMENT OF CADMIUM AND PHOSPHORUS FROM PHOSPHATIC FERTILIZERS IN A PASTURE SOIL IN NEW-ZEALAND

Total cadmium (Cd) and phosphorus (P) concentrations in a pastoral soi l, amended annually for 10 years with four forms of P fertilisers, dec reased 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 phosph ate (DAP-10 mg kg(-1)), Jordan phosphate rock (JPR-5 mg kg(-1)) and co ntrol treatments to a depth of 120 mm. Total soil P in SSP treated plo ts 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 C d moved below 120 mm depth. Approximately 90% of the applied Cd was re covered in the soil of which 93% remained within the top 120 mm. Plant recovery of applied Cd was 1.5-4.5%. Plant available P (Olsen P) also decreased with depth. Plant available Cd (0.01 M CaCl2 extractable Cd ) was higher in the 30-75 and 75-120 mm soil depths compared to 0-30 m m soil depth. This may be due to strong adsorption of Cd by the surfac e soils which have a higher organic matter content and higher pH; fact ors which are known to increase Cd adsorption in soils. (C) 1997 Elsev ier Science Ltd.