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Soil phosphorus buffering measures should not be adjusted for current phosphorus fertility


Burkitt, LL and Sale, PWG and Gourley, CJP, Soil phosphorus buffering measures should not be adjusted for current phosphorus fertility, Australian Journal of Soil Research, 46, (8) pp. 676-685. ISSN 0004-9573 (2008) [Refereed Article]

DOI: doi:10.1071/SR06126


Soil phosphorus (P) sorption is an important and relatively stable soil property which dictates the equilibrium between sorbed and solution P. Soil P sorption measures are commonly adjusted for the effect of current P fertility on the amount of P a soil sorbs. In the case of highly fertilised agricultural soils, however, this adjustment is likely to be inappropriate as it may mask changes in a soil's capacity to sorb P, which could affect future P fertiliser applications. A study was undertaken to compare adjusted or unadjusted methods of measuring P sorption using 9 pasture soils sampled from southern Victoria which had previously received P fertiliser and lime. The P sorption assessment methods included: P sorption isotherms, P-buffering capacity (PBC) measures (slope between equilibrium P concentration of 0.25 and 0.35mgP/L), and single-point P-buffering indices (PBI), with methods either adjusted or unadjusted for current P fertility. A single application of 280kgP/ha, 6 months before sampling, resulted in a general negative displacement of unadjusted P sorption isotherm curves, indicating reduced P sorption on 8 of the 9 soils. Adding the Colwell extractable P concentration to the amount of P sorbed before calculating the slope (PBC+ColP), tended to negate this fertiliser effect and, in 2 of the 9 soils, resulted in a significant increase in PBC +ColP values. Increasing rates of P fertiliser application (up to 280kgP/ha) resulted in a consistent trend to decreasing PBI values (unadjusted for Colwell P), which was significant at 4 of the 9 sites after 6 months. However, only minimal changes in PBI values were determined when PBI was adjusted for current P fertility (PBI+ColP). Phosphorus sorption properties appeared reasonably stable over time, although 2 soils, both Ferrosols, indicated significant linear increases in PBI values when these sites remained unfertilised for 30 months. Lime significantly increased both PBI and PBI+ColP values at all sites 6 months after application, but the effect generally diminished after 30 months, suggesting PBI measurements should not be taken immediately after liming. These results demonstrate that unadjusted measures of P sorption are more likely to accurately reflect changes in soil P sorption capacity following P fertiliser applications and suggest that the unadjusted PBI be used in commercial soil testing rather that the currently adjusted PBI+ColP. © CSIRO 2008.

Item Details

Item Type:Refereed Article
Research Division:Agricultural, Veterinary and Food Sciences
Research Group:Other agricultural, veterinary and food sciences
Research Field:Other agricultural, veterinary and food sciences not elsewhere classified
Objective Division:Plant Production and Plant Primary Products
Objective Group:Other plant production and plant primary products
Objective Field:Other plant production and plant primary products not elsewhere classified
UTAS Author:Burkitt, LL (Dr Lucy Burkitt)
ID Code:53417
Year Published:2008
Web of Science® Times Cited:31
Deposited By:Agricultural Science
Deposited On:2008-12-08
Last Modified:2009-04-06

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