Factors affecting the change in extractable phosphorus following the application of phosphatic fertiliser on pasture soils in southern Victoria
Burkitt, LL and Gourley, CJP and Sale, PWG and Uren, NC and Hannah, MC, Factors affecting the change in extractable phosphorus following the application of phosphatic fertiliser on pasture soils in southern Victoria, Australian Journal of Soil Research, 39 pp. 759-771. ISSN 0004-9573 (2001) [Refereed Article]
Nine pasture soils from high rainfall zones of southern Victoria were analysed for a range of chemical and physical properties before receiving a single application of P fertiliser in the form of triple superphosphate (TSP), single superphosphate (SSP), or TSP and lime (5 t/ha) at amounts ranging from 0 to 280 kg P/ha. Soils were analysed for bicarbonate-extractable P concentration, using both the Olsen P and Colwell P methods, 6 and 12 months after fertiliser application. A strong positive linear relationship existed at all sites between the amount of P applied and both the Olsen P and Colwell P concentrations. The slopes of these relationships measured the change in extractable P concentration (Î"EP) per unit of P applied, whilst the inverse of the Î"EP value indicated the amount of P fertiliser required above maintenance to increase the extractable P concentration by 1 mg/kg. These values ranged from 5 to 15 kg P/ha, depending on soil type. The Î"EP measured by the Olsen (Î"EPOlsen) method was closely related to selected soil properties and P sorption measures, whilst the Î"EPColwell values were also closely related to selected soil properties and P sorption measures, but only when one particular site, an acidic sand, with a high organic carbon content was excluded from the analysis. In general, simple, direct measures of soil P sorption could allow the estimation of Î"EP values on different soil types. The application of P in the form of SSP resulted in a trend for higher Î"EP values than occurred with TSP. This difference was significant on 3 sites (P < 0.05), but depended on the method of extraction and the time after fertiliser application. The application of lime significantly (P < 0.001) increased soil pH (H2O and CaCl2) and decreased the concentration of exchangeable Al, 6 months after treatments were applied, but generally had little impact on Î"EP values.