GRDC - Crop Doctor - New soil test for calcareous zones [South, 1 August 2007]

Date: 01 Aug 2007


A new soil test for phosphorus is showing considerable potential for use in Australian calcareous soils, with the help of a PhD project supported by growers and the Australian Government through the Grains Research and Development Corporation (GRDC).

The test, diffusive gradients in thin films (DGT), was originally developed for testing metal contamination in the soils and waterways of the United Kingdom, but with some modifications it has been found to correlate well with plant response to applied phosphorus in deficient Australian soils.

The University of Adelaide’s Dr Sean Mason’s GRDC-supported PhD project, completed at the end of last year, was the starting point in this technical advancement set to benefit Australian grain growers.

All growers should be able to achieve good fertiliser efficiencies through the improved decision making capacity that DGT will offer. However, growers with calcareous soil types may be the real beneficiaries of the new DGT test because it can differentiate between responsive and non-responsive soils.

Photo caption: “Dr Sean Mason prepares to test soil samples for available phosphorus”

Dr Mason found that DGT readings were more accurate than other tests in calcareous soil types in laboratory trials. Traditional soil tests use an extractant to measure plant-available phosphorus. However, the extractant can often solubilise phosphorus that is not available to the plant and hence overestimate phosphorus availability.

The modified DGT test measures plant available phosphorus by mimicking a plant root. The device contains a binding layer with ferrihydrite that acts as a sink, drawing only the plant available phosphorus to it when the device is deployed on the soil.

This year with further support from GRDC for a one-year project, Dr Mason is moving DGT development from glasshouse to field testing. Although the test was developed for assessing available phosphorus, Dr Mason says that it can also be used to test for zinc and manganese, and with further modification possibly potassium too.

Dr Mason’s research team are now calibrating the DGT at different stages of plant growth, from sowing to harvest. The next stage of this research could be to make this test readily available for growers across Australia.

Dr Mason will be presenting results from his research at the GRDC Update to be held in Lock on August 15. For more information on the GRDC Update series, contact Jon Lamb Communications on (08) 8362 5417, or visit


• For more information contact Dr Sean Mason on (08) 8303 8107

• Peter Reading is the Managing Director of the Grains Research and Development Corporation, phone (02) 6272 5525.

GRDC Project Code: JLC00011 

GRDC Project Code JLC00011

Region South, North, West