Estimating and modelling the risk of redox-sensitive phosphorus loss from saturated soils using different soil tests

Phosphorus (P) loss from agricultural soils can negatively affect water quality. Models and management to decrease losses increasingly focus on P that is available and transported from areas in the landscape that are regularly saturated – and periodically anaerobic. Current models use soil tests conducted in oxic conditions, which do not represent anaerobic conditions. This could lead to inaccurate P loss predictions in wetter areas, where runoff and P loss would be generated. In the present study, anoxic water extractable P test (anoxic WEP) and sodium bicarbonate-dithionite extractable P (Dithionite-P) tests were first developed using samples from New Zealand and Ireland, and were used to predict P that is available under anoxic conditions in the short- and long-term. Using archived soils from New Zealand and Ireland, it was confirmed that present testing was under-predicting losses, which could have implications for modelling and correlations with agriculture and water quality.