Phosphorus and selected metals mobilized from two commercial fertilizers into overland flow during border irrigation

Metals, present as impurities, may be used to trace phosphorus (P) derived directly from fertilizers in field studies. This paper reports a study that compared P to strontium, copper, zinc, cadmium, lead, chromium and nickel concentrations in overland flow from border irrigated fields, before and after fertilization with commercial diammonium phosphate (DAP), or single superphosphate (SSP) blends. The concentrations of P and various metal species in overland flow were within the guidelines for potable water. However, with the possible exception of chromium, all samples, including pre-fertilization samples, were outside the trigger values for Australian and New Zealand streams. Changes in the cadmium and strontium concentrations were related to changes in the total dissolved P (TDP) concentrations following fertilization. This suggests that these metals may be used for tracing P derived directly from fertilizers. However, the background concentrations of cadmium and strontium in overland flow varied between farms and the decay in P concentrations in the two irrigations following fertilizer application were not reflected in cadmium and strontium concentrations. These appear to be major limitations on the use of cadmium and strontium for tracing P derived directly from fertilizers.