Total soil cadmium concentrations in the Winchmore long-term phosphorus fertiliser trial are still increasing

Reliable data on the rate of cadmium (Cd) accumulation in soils that receive phosphorus (P) fertiliser is vital to help manage the impact of Cd in agricultural systems in New Zealand. Studies of the long-term P fertiliser trial at Winchmore, where soils have received 0, 17, or 34 kg P ha-1 yr-1 for > 60 years, have reported soil Cd concentrations over the last 15 years have either plateaued or are still increasing. To address this discrepancy, new soil Cd analysis was conducted on a wider set of archived soil samples from the Winchmore trial, along with some re-analysis of soil samples for Cd. When soil Cd data from previous studies were combined with the more recent set of Cd data, regression analysis indicated soil Cd concentrations in the 17, or 34 kg P ha-1 yr-1 fertiliser treatments are still increasing linearly over time. It is recommended soil samples from the long-term Winchmore trial continue to be analysed for Cd to confirm long-term trends, avoiding short-term perturbations. Such long-term trials are invaluable for providing robust information that will help in the ongoing management of Cd in New Zealand.