Two consecutive wet seasons in southwest Western Australia have put a renewed focus on waterlogged crops. It is estimated that approximately three million hectares of land may be subject to waterlogging or inundation across WA’s southwest agricultural region.

Grains Research and Development Corporation (GRDC) investments, led by South Coast Natural Resource Management (South Coast NRM) and Stirlings to Coast Farmers, are exploring the potential return on investment of subsurface water management options for waterlogged areas at four sites in the Esperance and Albany port zones.

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

A new video and podcast released by GRDC this week capture a recent subsurface drainage demonstration day in Dalyup, near Esperance, where as part of the project, local grower Rohan Marold is installing subsurface drainage in his paddocks.

South Coast NRM Regional Agricultural Landcare Facilitator Sophie Willsher says subsurface drainage can alleviate water logging conditions by moving perched water away from crop root zones. Photo: GRDC

Mr Marold says that during the 2022 harvest it was a problem getting harvesters across paddocks that had been deep ripped, with machinery bogged several times.

“We used a consultant to do some digital elevation mapping to see where the water was flowing and where we needed to get to with the drains,” Mr Marold says.

“We started out on some heavy clay paddocks where we thought subsurface drainage pipes would be beneficial, but we found that wasn't as successful at getting the water out of the profile because of the sodicity and the subsoil.

“We then tried some on sand over clay and that worked well, the pipe started flowing almost straight away, within 24 hours.

“It's pretty satisfying to see the water coming out of the pipes after you've installed them, and it's nice clear water. It's different to seeing water running off the top of your paddock with all that nutrient loss and erosion.”

The installation of subsurface drains involved the use of a tile plough attached to a tractor. The tile plough uses GPS technology to create a ripping point. The plough then creates a trench, lays the plastic slotted pipe and then buries it under the sub surface.

Mr Marold says that the aim was to lay the pipes at least 600-800 millimetres deep to avoid any impact from machines or deep ripping.

South Coast NRM Regional Agricultural Landcare Facilitator Sophie Willsher is leading the project in Dalyup.

Several growers in the Dalyup region attended a subsurface drainage demonstration day in March to explore the process for laying paddock drainage. Photo: GRDC

Ms Willsher says South Coast NRM was currently in the third of four years of a subsurface drainage return-on-investment trial.

“Project findings from 2022 support conclusions drawn in 2021, solidifying our understanding that subsurface drainage is effective at moving perched water away from the root zone, leading to maximised yield potentials,” Ms Willsher says.

“Yield data from the previous two years show an almost two-fold increase in yield for drained areas compared to the undrained waterlogged site at our Neridup trial.

“One of your most important factors to consider is the elevation of your paddock. It's always best to work with gravity. You also should consider your soil profile and the depths to the clay layer, which is the impenetrable layer where most perched water will sit.

“Considering soil type and of course other factors on farm, including salinity levels, are important in making sure that your drainage is designed best for your property.

Ms Willsher says the project had monitored the biomass, weed and disease presence and soil moisture conditions of paddocks in the trial to produce a final return-on-investment figure in 2024.

“We're looking forward to seeing the final return-on-investment figure and how we can apply this into to support broader scale adoption for growers,” she says.

GRDC grower relations manager – west, Luke Dawson, says that GRDC investment into projects addressing waterlogging ranged from subsurface drainage projects through to genetic research.

“This project will help growers and advisers compare the yield penalty in undrained areas with the capital investment and gains of installing drainage,” Mr Dawson 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.”

The project concludes in 2024 with return-on-investment data to be made available to growers through a project report and via GRDC’s Groundcover magazine.