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Intensive dairy operations in Australia regularly apply P fertiliser to maintain productive pasture species. However, extractable soil test P (STP) concentrations in this industry commonly exceed those required to maximise pasture production, a situation which can increase the risk of P loss to surrounding waterways. The current study examined relationships between STP (Olsen P and CaCl2 P) and surface runoff P concentrations from a red silty loam (Ferrosol), commonly used for pasture production in south-eastern Australia. Soil was mixed and re-packed into soil trays and a rainfall simulator was used to generate surface runoff. A wide range of soil Olsen P concentrations (0–20 mm, 15–724 mg/kg; 0–100 mm, 9–166 mg/kg) was created by surface-applying a range of P fertiliser rates 8 months before the rainfall simulations. A comparison of the 2 STP methods suggests that Australian soils have higher labile P concentrations for given Olsen P concentrations compared with those measured internationally, suggesting a greater likelihood of P loss in runoff. Furthermore, significant curvilinear relationships between STP and dissolved reactive P (DRP <0.45 µm) in surface runoff for both Olsen P depths (0–20 mm, r2 = 0.94; 0–100 mm, r2 = 0.91; P < 0.01) were determined, as well as significant linear relationships between DRP and both CaCl2 depths (0–20 mm, r2 = 0.83; 0–100 mm, r2 = 0.92; P < 0.01). This confirmed that the concentrations of P in surface runoff increased with increasing STP, providing further evidence of an urgent need to reduce excessive STP concentrations, to reduce the risk of P loss to the environment.

Item Type:	Refereed Article
Research Division:	Environmental Sciences
Research Group:	Soil sciences
Research Field:	Soil chemistry and soil carbon sequestration (excl. carbon sequestration science)
Objective Division:	Environmental Management
Objective Group:	Terrestrial systems and management
Objective Field:	Terrestrial systems and management not elsewhere classified
UTAS Author:	Burkitt, LL (Dr Lucy Burkitt)
UTAS Author:	Carlson, SM (Mr Scott Carlson)
UTAS Author:	Donaghy, DJ (Associate Professor Danny Donaghy)
ID Code:	53969
Year Published:	2010
Funding Support:	Australian Research Council (LP0455221)
Web of Science® Times Cited:	16
Deposited By:	Agricultural Science
Deposited On:	2009-02-03
Last Modified:	2011-04-13
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