Subsurface drainage, the latest in the Marold family’s quest for long-term waterlogging solutions, has seen crop yields double over the past three years.

With a 30 per cent chance of crops being waterlogged during a season and a high risk of crop losses, Rohan Marold has spent 20 years striving for a long-term solution to provide greater resilience in his farming system and business.

Waterlogging decreases oxygen availability for root respiration, resulting in impaired nutrient uptake. Wet conditions also promote soil-borne pathogens such as fungi and bacteria, leading to increased disease impacts. The worst-case scenario is complete crop failure.

Soil compaction and loss of soil microbial activity can also be a long-term effect of waterlogging, further reducing a cropping system’s sustainability.

Rohan farms with his wife Ruth and son Jordan 40 kilometres west of Esperance in WA. Their property is a 50:50 mix of sand plain and river type–alluvial– and heavier clays with areas of sodicty and areas with a perched watertables. An average rainfall of 600 millimetres means waterlogging is a regular event that can cause partial or complete crop loss.

Initially Rohan looked to the Victorian experience with raised beds systems in its high-rainfall regions, then surface drainage, deep ripping and, more recently, subsurface drainage.

We installed raised beds over 600 hectares with some success, but the beds allowed surface run-off, which took nutrients from the crops and ponded in furrows and low points. They also presented trafficking challenges on headlands and required regular maintenance, especially if we ran stock on those paddocks. The beds have now been filled in.

Rohan also noted that raised beds did not solve the perched watertable issues. Often paddocks could incur waterlogging from below as these tables filled.

Equipped with a degree in environmental science from Murdoch University, Rohan has a thorough understanding of the environmental issues he has to manage. This expertise was expanded during an honours project that entailed a detailed environmental analysis of an area in Cascade, north-west of Esperance, where he determined there was a perched watertable. Rohan had also gained an understanding of the region’s soils from two years working as a soil surveyor for the WA Department of Agriculture before returning to the family farm in 1997.

After some online research into growers’ experience in the US and Europe, where subsurface drains are deployed, the Marolds bought a Soil-Max Gold Digger pipe layer from the US in 2019 and started work on their subsoil drainage programme.

The Marolds have found the most cost-effective design is to use 100mm filter-socked, slotted ag pipe, installed at a minimum depth of 600mm and spaced every 36 metres.

“We have found during a waterlogging event that this design allows the soil profile to drain to the depth of the pipes within four to five days,” says Rohan.

The pipes were installed in parallel to the Marold’s controlled-traffic system to avoid damage to the pipes, and were mapped with GPS for accurate ripping to 1m to optimise water movement. Open drains were used at the paddock ends with subsurface drains positioned at a minimum of 600mm and falling at 0.1 per cent across the landscape. The collected water drains into creeks on the property or into an old clay pit.

Over the past three years, this drainage system has significantly increased yields on the drained areas, with wheat yields rising from 3t/ha to over 7t/ha and canola yields from zero to 400kg/ha to more than 2t/ha.

Rohan and Jordan more recently have been involved in a GRDC-supported National Grower Network project with South Coast Natural Resurce Management evaluating subsoil drainage. The project has determined both a high level of efficacy and sound economics of investing in subsurface drains.

The Marold’s first pipe instalment covered 300ha with 90km of pipe. They are now planning to lay pipes in 60 to 80ha each year going forward.

Rohan says they are working best in the shallow sandy soil over clay, and they will experiment with applying gypsum to the heavier clay to improve soil structure and see if the drain performance will improve.

“The effectiveness of the subsurface drains opens further possibilities for us for water harvesting to boost the climate resilience of our farm and business.”

Read also: Economics stack up for subsurface drains.