A rare win-win solution is being investigated on Western Australia’s south coast which could double local growers’ cropping capacity while cutting groundwater recharge.

In areas where significant summer rainfall can escape into the water table to draw saline water up the soil profile, warm season crops may be used as soaks to utilise that rainfall and limit recharge the following winter.

According to Grains Research and Development Corporation (GRDC) supported Department of Agriculture researcher, David Tennant, warm season grain and forage crops could reduce ‘soil water’ by around 10 – 30 mm.

“By drying the soil profile during summer, we could increase the capacity of those soils to retain winter rainfall and keep excess moisture from escaping into the water table.

“While this drying could stifle yields in lower rainfall areas, where good soil moisture is needed to optimise winter crop performance, it could be viable in wet coastal areas where excessive winter rainfall causes waterlogging,” he said.

CSIRO has helped develop a model which predicts summer crop growth and grain yield using historic climate data to assess the risk or return potential of specific summer crops at locations around the south coast.

Results indicate that production relates to soil moisture at the start of the season, making summer cropping a feasible option in Esperance once every five years.

“Sorghum grain yields would probably range from 0.5 to 2.0 tonnes per hectare depending on summer rainfall, while summer forage crops would generally produce 2.0 to 3.0 t/ha of biomass,” Dr Tennant explained.

“Sunflowers have delivered break-even returns despite receiving only 200 mm of growing season rainfall.

In addition to grain and fodder production, summer crops may be valuable for their contribution to farming systems, with south coast growers showing interest in biological soil ameliorants, such as pigeon pea, which can break open sub-soil channels for the roots of winter annuals.

Supported by growers and the Federal Government through the GRDC, the project will continue to appraise the agronomic and financial performance of different warm season crops while monitoring their impact on subsequent annuals and the water table.