Researchers seek to fine-tune analysis

New research could lead to more accurate interpretation of phosphorus soil tests from WA cropping paddocks, and may save growers money through the recommendation of lower phosphorus fertiliser rates.

The study was conducted by the Department of Agriculture and Food WA (DAFWA) and Murdoch University researchers under the Grains Research and Development Corporation (GRDC) project, 'Better fertiliser decisions for cropping systems in Western Australia'.

DAFWA researcher Geoff Anderson told the 2012 Crop Updates in Perth this week that results generated by the Colwell-P test - commonly used to analyse soil samples - were analysed using the Mitscherlich equation, which tended to over-estimate the critical phosphorus levels needed to achieve maximum crop yields.

Critical soil test levels are the minimum level of a particular nutrient necessary to achieve potential crop yields.

"Our research has identified an alternative equation - the Beta sigmoid equation - that we believe will overcome this problem and result in a more profitable and environmentally sustainable production system for wheat, lupin and canola production in WA," Dr Anderson said.

"The Beta sigmoid equation was developed in 2003 by international researchers to help predict plant growth, and has not previously been applied to soil data.

"The use of the new equation in soil data analysis is yet to be peer reviewed by experienced soil scientists."

Dr Anderson said the research into the accuracy of the Colwell-P test and Mitscherlich equation was conducted by analysing fertiliser data from DAFWA experiments dating to 1990.

The aim of the GRDC project is to help growers and advisers maximise returns from their investment in fertiliser, and better define critical soil concentrations for nitrogen, phosphorus, potassium and sulphur, as well as minimise the loss of nutrients to the environment.