A comparison of some surface soil phosphorus tests that could be used to assess P export potential
David Nash A D , Murray Hannah A , Kirsten Barlow B , Fiona Robertson C , Nicole Mathers A , Craig Butler A and Jessie Horton AA Department of Primary Industries, Ellinbank Centre, 1301 Hazeldean Rd, Ellinbank, Victoria 3821, Australia.
B Department of Primary Industries, Rutherglen Centre, RMB 1145, Chiltern Valley Road, Rutherglen, Victoria 3685, Australia.
C Department of Primary Industries, Hamilton Centre, Private Bag 105, Hamilton, Victoria 3300, Australia.
D Corresponding author. Email: David.Nash@dpi.vic.gov.au
Australian Journal of Soil Research 45(5) 397-400 https://doi.org/10.1071/SR06142
Submitted: 10 October 2006 Accepted: 17 July 2007 Published: 16 August 2007
Abstract
Phosphorus (P) exports from agricultural land are a problem world-wide and soil tests are often used to identify high risk areas. A recent study investigated changes in soil (0–20 mm), soil water and overland flow in 4 recently laser-graded (<1 year) and 4 established (laser-graded >10 years) irrigated pastures in south-eastern Australia before and after 3 years of irrigated dairy production. We use the results from that study to briefly examine the relationships between a series of ‘agronomic’ (Olsen P, Colwell P), environmental (water-extractable P, calcium chloride extractable P, P sorption saturation, and P sorption), and other (total P, organic P) soil P tests.
Of the 2 ‘agronomic’ soil P tests, Colwell P explained 91% of the variation in Olsen P, and Colwell P was better correlated with the other soil tests. With the exception of P sorption, all soil P tests explained 57% or more of the total variation in Colwell P, while they explained 61% or less of Olsen P possibly due to the importance of organic P in this soil. Variations in total P were best explained by the organic P (85%), Calcium chloride extractable P (83%), water-extractable P (78%), and P sorption saturation (76%). None of the tests adequately predicted the variation in P sorption at 5 mg P/L equilibrating solution concentration.
The results of this limited study highlight the variability between soil P tests that may be used to estimate P loss potential. Moreover, these results suggest that empirical relationships between specific soil P tests and P export potential will have limited resolution where different soil tests are used, as the errors in the relationship between soil test P and P loss potential are compounded by between test variation. We conclude that broader study is needed to determine the relationships between soil P tests for Australian soils, and based on that study a standard protocol for assessing the potential for P loss should be developed.
Additional keywords: cultivation, soil P test, laser graded, phosphorus, surface soil.
Acknowledgments
The authors would like to acknowledge the Victorian Department of Primary Industries, GippsDairy and Dairy Australia who funded this project. The authors also acknowledge the Macalister Research Farm Co-operative Ltd on whose farm the trials were undertaken and Prof. Aldo Bagnara and Dr Roger Armstrong for their comments on the manuscript.
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