New trials to provide insights for best practice soil management on sandy soils

IMG spreading at a dairy farm in the Vasse-Geographe catchment.

Two new trial sites on dairy farms in the Vasse and Scott River catchments have been launched to demonstrate how top-dressing applications of Iron Man Gypsum (IMG) can keep phosphorus on farms where it is needed, instead of being washed into our estuaries where it can cause algal blooms and water quality issues. 

IMG is made up of small iron mineral particles that have a high capacity to hold on to phosphorus.  When IMG is applied as a soil amendment, it helps keep phosphorus in the soil.

Dairy farmer Wes Lammie is hosting the trial in the Vasse-Geographe catchment in partnership with the Department of Water and Environmental Regulation (DWER). This trial is on a paddock with sandy, low phosphorus-adsorbing soil which can only hold small amounts of the plant nutrient.

The trial will also look at how well IMG retains phosphorus following application of dairy shed effluent.

The trial in the Scott River catchment is hosted by LACTANZ 2 farm manager Josh White partnering with the department and the Lower Blackwood Land Conservation District Committee . This is the first trial on very low phosphorus adsorbing soils that are under irrigation.

The new trials are the latest in a series of ongoing studies through Healthy Estuaries WA and Revitalising Geographe Waterways, and the predecessor program Regional Estuaries Initiative.

DWER senior soil scientist Dr Brad Degens said that the trials to date on farms and sporting fields have shown positive impacts on holding excess phosphorus in soils and  reducing leaching to waterways.

“Our first series of farm trials have been running for three to four years now. So far, they show that the IMG applied several years ago is continuing to keep phosphorous in the soils and prevent losses to waterways,” he said.“Many grey sandy soils in coastal regions of WA lose nutrients like phosphorus very easily by runoff or leaching, so this is a great result for the ecological health of our waterways.”

The farm trials build the confidence of farmers and agronomists in the effects and opportunities of using IMG as a top-dress soil amendment. Site visits will be held in spring for farmers and agronomists to learn about how the trials are progressing.

“The new trials will provide more information about how IMG performs in different conditions. Along with data from the existing older trials, this will help to develop best practice guidelines for the application of soil amendments on coastal sandplains,” Brad said.

“The IMG application trials complement other new trials in the Hardy and Wilson Inlet catchments where sub-soil clays sourced from the farm are being applied as a soil amendment.

“A lot of farms won’t have subsoil clays or clays that are suitable – and this is where IMG might be the only amendment option available.”

This project is part of Healthy Estuaries WA and Revitalising Geographe Waterways. These State Government initiatives aim to support the long-term health of our south-west estuaries.