Farm trials confirm IMG effectiveness on dairy farms

Our latest farm trials of the soil amendment Iron Man Gypsum (IMG) are continuing to build confidence in the effectiveness of IMG to improve soil nutrient retention.

Spreading to set up the IMG rate trial on a dairy farm in the eastern Scott River catchment

Results of three trials through the State Government’s Healthy Estuaries WA program have again confirmed that a single top-dress application to pastures can significantly improve retention of phosphorus.

Phosphorus (P) is an essential nutrient for plant growth, but many of our soils in Western Australia have limited capacity to hold P. This means it is easily lost to waterways where it fuels algal growth.

Since 2018 we have been trialling IMG as a soil amendment to prevent P loss on farms. In 2022, we began additional trials on farms in the Scott River catchment and in the Vasse-Geographe catchment.

“These new on-farm trials are all on sandy soils that are particularly poor at holding phosphate,” said Dr Brad Degens, senior soil scientist at the Department of Water and Environmental Regulation.

“We applied IMG at a rate of 20 tonnes per hectare in Autumn 2022. Since then, we have been conducting soil and plant tests to measure how the soil amendment performs.

“Soil test results show that top-dressing with IMG greatly improves capture and holding of phosphate in the surface few centimetres of the soil. This keeps it available for plant growth, whereas it would otherwise be lost to waterways.

“Pasture productivity on the Scott River trial was also greater where the IMG was spread compared with an equivalent untreated area in the same paddock. This is a win for the production system as well as the environment.”

Dairy farmer Robin Lammie said he had been impressed with the early results of the trial on his farm in the Vasse-Geographe catchment, having found that improvement in P retention was possible while maintaining pasture production.

The trial on Robin’s farm also included a dairy effluent application, where the IMG enabled the effluent to be recycled for its potassium and nitrogen fertiliser value while preventing the P from becoming a risk to waterways.

Taking plant samples to assess nutrient uptake by pastures at the on-farm IMG trial site

Brad said the recent findings matched those found in experimental trials set up five years ago, where ongoing monitoring shows the IMG is still working, providing assurance that the same results can be achieved in different farming conditions.

IMG also improved the uptake of some other nutrients such as copper, cobalt and manganese by ryegrass and clover ‒ a result independent agronomist Brooke Anderson, who works with Scott River farmers, said was interesting to see.

Brad said another trial was set up in the Scott River catchment this season to see whether 10 tonnes per hectare of IMG could be as effective as 20 tonnes per hectare.

“Exploring this will help us determine recommendations for growers and continue to assess the cost-effectiveness of using IMG as a soil amendment,” said Brad.

These trials are a part of Healthy Estuaries WA – a State Government initiative to improve the health of our South West estuaries. The trials have been implemented in partnership with host farmers and the Lower Blackwood Land Conservation District Committee.

Disclaimer: Reference to specific commercial products in this article does not constitute an endorsement or recommendation by the Department of Water and Environmental Regulation. Professional advice should be obtained before applying the information to particular circumstances.