For Esperance grower Rohan Marold, the major risk to cropping in his region is waterlogging.

Rohan farms at Dalyup, 680 kilometres south-east of Perth, with his wife Ruth and son Jordan. Jordan is the fourth generation to be involved in the family business.

“An annual average rainfall of around 600 millimetres means every one in three years we experience a waterlogging event,” says Rohan.

As the Marolds are cropping in a high-rainfall region, they apply higher inputs to chase larger potential yields but risk high financial losses when waterlogging occurs.

They often do not know if they are going to suffer a crop failure until there is a heavy rainfall event, typically later in the season in July or August. They also have soil profiles that fill from the bottom up, often from perched watertables, so waterlogging can take them by surprise.

But Rohan says their biggest risk is doing nothing about it.

The Marold’s is a mixed farm of 2100 hectares – 1800ha is cropped and the rest is under pasture for sheep. The farm is a 50:50 mix of sand plain and river type, and heavier clays with areas of sodicity. The area affected by waterlogging varies from season to season.

Over the past couple of decades Rohan has been deploying different farming practices to manage waterlogging. Raised beds, deep ripping and, more recently, subsurface drainage using 100mm filter-socked, slotted ag pipe has been installed.

“You need to address the entire system,” Rohan says.

“We are now also using hybrid canola varieties that perform better in these situations due to their vigour and more extensive root system. We look for robust disease tolerance in our varieties to combat higher disease load with high rainfall. For example, we have found that Brumby (PBR) has good resistance to powdery mildew. A high level of plant resistance also means we apply less fungicide.”

The Marolds also carefully consider their herbicide selection to ensure good weed management, applying a variety of modes of action and different herbicides that perform better on each soil type.

Rohan says of the drainage systems they have trialled, they are finding the subsurface drains the most effective and present the best long-term solution to waterlogging.

Trafficability is better with the subsurface drains compared to raised beds, and the hydrology of the system tends to work better. With raised beds we tended to still have surface run-off, which meant we could lose some of our inputs, like fertiliser.

Rohan bought a Soil-Max Gold Digger from the US in 2019 and has now installed 90 kilometres of subsurface pipe drains over 300ha. He plans to install 60 to 80ha a year going forward. His crop yields are increasing and the risk of crop failures is declining.

GRDC-supported research Rohan has been involved in with South Coast Natural Resource Management is also showing that, financially, the investment is worth it.

“Doing something about waterlogging and seeing the improvements certainly gives you confidence,” Rohan says.

Read also: Economics stack up for subsurface drains.