Trials fine-tune gypsum rates

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Sodic soil at Ravensthorpe, WA, showing dispersed clay particles that prevent air and water movement in the soil.

New research is refining the rates for applying gypsum to improve yields on sodic soils, which account for nearly a third of Australia’s agricultural land.

GRDC-funded trials over three years north of Ravensthorpe in Western Australia show that gypsum applied at rates of between 2.5 and 3 tonnes a hectare could bolster yields on high sodium soils.

Sodic soils contain excess exchangeable sodium, which renders wet soils unstable. This often results in clay particles plugging soil pores and channels needed for air and water movement.

Department of Agriculture and Food, WA (DAFWA) senior researcher Dr David Hall says the poor water infiltration, surface encrusting, erosion and waterlogging linked to sodic soils can notably reduce crop yields.

To rectify the problem, Dr Hall urges growers to apply gypsum. He says the trials indicate there are large yield benefits in the first year after the mineral is applied, and these gradually increase over time. In the third year, yields were about 25 per cent better compared with untreated areas.

“We are looking at how gypsum changes the soil chemistry, production capacity of the paddock, and defining areas which benefit from particular rates of gypsum,” Dr Hall says.

He says although gypsum has traditionally been applied at blanket rates, use of EM38 technology has the potential to help growers use gypsum more effectively by applying it at variable rates.

Dr Hall says further research to gauge how often gypsum should be applied is required because growers apply it for different reasons, including as a source of sulfur and calcium.

“Gypsum is one of the few forms of sulfur that does not acidify soils,” Dr Hall says.

This research is part of the Agronomy Jigsaw project involving DAFWA, Precision Agronomics Australia and the South East Premium Wheat Growers Association.

GRDC Project Code DAW00193

Region West