South Coast NRM and Stirlings to Coast Farmers help develop waterlogging strategies

By Shannon Beattie
March 22 2022 - 2:00am
South Coast NRM's Neridup trial site in its first winter, showing the waterlogging that occurs in the trial paddock affecting crop yield potential.

THE first year of a joint project in the South West has provided impressive results in its goal to drill down into the return on investment (ROI) from subsurface water management options for waterlogged areas.

The project, being run by South Coast NRM in the Esperance port zone and Stirlings to Coast Farmers (SCF) in the Albany port zone, plans to help growers implement strategies to realise crop yield potential and increase profitability by addressing the impacts of waterlogging,

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While subsurface drainage is a well-known tool and has been widely used to alleviate waterlogging in the past, there's a significant knowledge gap about the costs and benefits of this drainage design.

The aim of the three-year trial, partly funded by the Grains Research and Development Corporation (GRDC), was to close that knowledge gap by conducting a return on investment analysis to enable growers and advisers to make better informed decisions about the profitability of subsurface drainage for their farm systems.

In 2021, the focus was on the establishment of the trial with the installation of three kilometres of subsurface drainage in the Neridup region and 2.5km of drainage in Cranbrook.

A good growing season and high rainfall, including a 99 percentile year in Cranbrook with 748 millimetres of rain, provided South Coast NRM and SCF with enough data to begin the critical analysis of the drainage system and its value.

South Coast NRM regional agricultural landcare facilitator east Sophie Willsher said the trial paddock grew canola in 2021 with the susceptible crop yielding 56 per cent more in the drained site compared to the paddock average.

"Accounting for yield penalties, we can estimate a preliminary yield benefit due to subsurface drainage of 25-50pc," Ms Willsher said.

"With canola currently priced at $980 per tonne, this has translated to an increase in profit of up to $745 a hectare.

"Over the following year, we will be taking this yield increase and comparing it against the costs of installation to assess a preliminary return on investment."

At Cranbrook, the amount of rain did cause some issues with weed control and fertiliser applications, as they weren't able to get on it to spray until August.

However, SCF smart farms co-ordinator Philip Honey said regardless of that, the data again spoke for itself.

"We planted a Flinders barley crop with the undrained areas yielding 2.21t/ha, whereas the drained was 3.2t/ha, so that's a one tonne yield benefit," Mr Honey said.

"It's a 100 hectare paddock, a third of which was prone to waterlogging, so at a 1t yield difference between the drained and undrained, you're looking at the 2.5km of pipe paying itself off within three years.

"It really shows how well it can work, especially in an incredibly wet year like the 99th percentile one we had, although it does bring in a few extra questions around what the potential yield could have been if we had installed even more pipe."

Based on the interest in the project, both South Coast NRM and SCF have expanded their trials for 2022 and 2023.

"We will be including two additional subsurface drainage systems into the Esperance trial which will cover different areas of the Esperance port zone, as well as test the subsurface drainage in different soil profiles, climates and farm management practices," Ms Willsher said.

"We hope that the expansion of the trial will make the results of the final ROI analysis more robust and applicable to a wider range of landholders across a wider range of landscapes."

Meanwhile, Mt Barker farmer Kieran Allison has installed about 10km of subsurface drainage, with the SCF and GRDC project to look after the analysis of its impact and the return on investment it offers.

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