Runoff losses from irrigated dairy pastures treated with phosphorus fertilisers of differing solubility in south-eastern Australia

摘要

In response to increasing concern about environmental quality, water authorities in many countries are imposing legislation limiting phosphorus (P) concentrations in water, which is having an impact on farming practice. This experiment investigated the agronomic effects and runoff losses associated with different forms of P fertiliser applied to an irrigated dairy pasture (soils were Vertic Calcic Red Chromosols; average Olsen P, 50 mg P/kg) in north-central Victoria, Australia. Single superphosphate(SSP), a sulfurised diammonium phosphate, or partially acidulated phosphate rock was surface-applied at 50kg P/ha in March 2005 to a border-check, flood-irrigated dairy pasture (ryegrass-white clover) ten days before a scheduled irrigation. Dissolved reactive P (DRP) and total P (TP) were measured in runoff from whole bays on one replicate and from microplots on all three replicates for a period of 9 weeks. In all runoff events and all treatments, concentrations of DRP and TP in runoff greatly exceededwater quality guidelines for acceptable limits (0.045 mg P/L). The SSP resulted in significantly higher concentrations of P in runoff than the less water-soluble fertilisers. Even after the fifth irrigation, runoff from all fertilisers still exceeded the control. These results suggest that: (i) P fertilisers should not be applied in high-risk situations as insurance against yield loss; (if) the current recommendation of withholding irrigation for 3 days after fertiliser application is insufficient to prevent potentially significant losses occurring; and (iii) runoff losses were dependent on the type of fertiliser applied, with a smaller proportion of P applied as sulfurised DAP lost in runoff.