Putting a value on paddock drainage

image of drainage pipe
Sub-surface slotted drainage pipe being installed at the Cranbrook trial site. Photo: GRDC

Heavy opening season rains in Western Australia, coming after above-average summer falls, have caused widespread waterlogging problems, particularly in south-western areas of the State’s grainbelt.

Left unmanaged, waterlogging can lead to soil structural decline and has the potential to create nutrient deficiencies and toxicities, cause root death or reduced plant growth, or worst case, result in death of the plant.

The Grains Research and Development Corporation (GRDC) has initiated new sub-surface drainage investments in WA to help growers manage the effects of waterlogging.

In total, the GRDC invests about $2 million nationally in projects addressing waterlogging, with work ranging from the new sub-surface drainage projects through to genetic research.

The aim of this suite of investments is to help growers implement strategies that help to realise crop yield potential and increase profitability by addressing the impacts of waterlogging.

The new investments in WA will explore the potential return on investment of sub-surface water management options for waterlogged areas in the western region, with one demonstration site established near Cranbrook in the Albany port zone and another at Neridup in the Esperance port zone.

GRDC Grower Relations Manager – West Rachel Asquith says the projects will help growers and advisers compare the yield penalty in undrained areas with the capital investment and gains of installing drainage.

“Subsurface drainage is widely used in other industries and for high-value crops, but the returns have not been established for cropping in WA’s south-western grainbelt,” she says.

“We want to demonstrate that a strategic drainage investment can add real value.”

The projects originated from discussions initiated through the GRDC Grower Network and grower participation is a key part of planning, developing, monitoring and maintaining the trials.

Project partner Stirlings to Coast Farmers (SCF) has installed a weather station and soil moisture probes at Cranbrook and mapped the site to establish water flows and water accumulation locations.

South Coast NRM is coordinating delivery of the Esperance demonstration and has undertaken the ground works at Neridup. South Coast NRM will share capacity and resources with SCF, which is managing the remote sensing for both sites.

Monitoring throughout the 2021, 2022 and 2023 growing seasons will record soil volumetric water content, weed and disease pressure, plant establishment and tiller counts, and biomass using satellite normalised difference vegetation index (NDVI) imagery.

Yield analysis, plant density analysis and basic gross margins will be measured annually before the final return on investment analyses are completed by South Coast NRM.

It has been estimated that approximately three million hectares of land may be subject to waterlogging or inundation across the South West agricultural region of WA.

Ms Asquith says most cereal varieties are poorly evolved for waterlogging, which is a highly seasonal issue and creates a lot of risk around investing in effective mitigation.

“This year, the costs to manage waterlogging or deal with issues such as bogged machinery will be much more significant than in 2020,” she says. “Our aim is to give growers data that lets them assess the cost of installing subsurface drainage against the potential to recover some of those losses by improving yields.”

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