Gypsum can help mitigate losses in runoff

Centre for Sustainable Agricultural Technologies Ltd says gypsum has shown efficacy in phosphorus mitigation over a range of soil types and conditions.

It says attention should be paid to applying sufficient gypsum, allowing sufficient time for it to take effect, mimicking realistic rainfall conditions and to establishing sensible criteria for soil, slope and waterway characteristics when choosing appropriate study sites.

The company quotes Winstone, an importer of Australian gypsum, as saying the benefits of gypsum in soil treatment go beyond the above points.

Gypsum also helps mitigate the flow of nitrates and phosphorus in waterways and can be used to address the issue of sodium from applied effluent, the company says.

It also helps reduce surface runoff and drainage loss, reduces preferential flow of water run-off in soil, and assists with addressing high soil potassium levels.

"Rates vary per farm and soil type; applications can last for up to three years and can be used as a base layer in stand-off pads," the company says.

How gypsum works

Gypsum has long been used as a soil conditioner and fertiliser but only recently has gypsum's potential for reducing farm runoff to waterways been researched, says Centre for Sustainable Agricultural Technologies Ltd.

Gypsum (CaSO4.2H2O) can improve soil aggregation through calcium induced flocculation of particles and sulphate induced leaching of excess sodium.

Such effects can reduce surface runoff volume by improving water infiltration into soil. Improved stability of aggregates reduces the potential loss of soil particles to waterways over and through soil.

The calcium ions can also increase precipitation of phosphate ions either directly as calcium phosphate or indirectly by increasing availability of aluminium ions. Increased ionic strength of soil solutions due to dissolution of gypsum may also increase adsorption of phosphate ions and organic matter to soil particles.