THE conditions for the first two years of South Coast NRM's subsurface drainage trial could not have been better, with rainfall well over the 99th percentile across the 2021 and 2022 growing seasons.
Interest in the trial, which is looking into return on investment of subsurface drainage, has been growing since the development of the initial site at Michael and Marnie Fels' Neridup farm in 2021.
A second trial was established in Dalyup last year, while a third trial site is set for Wittenoom Hills early next year.
High rainfall has created the perfect testing ground for subsurface drainage, where the slotted tile drains are effectively moving perched water away from the root zone, thereby reducing crop yield loss due to waterlogging.
Having tried everything from raised beds and deep drainage to mitigate waterlogging, Mr Fels said subsoil drainage was the first thing that looked like it would allow them to grow solid crops every year on their high rainfall country.
"There's still a lot to learn, particularly the interaction between tile spacing and soil types and whether we also need to use mole drainage in our heavier soils for maximum benefit," Mr Fels said.
"I think this South Coast NRM project could possibly be the next major milestone in unlocking the potential of the broad Esperance high rainfall sandplain."
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In the lead up to the second harvest of the trial, South Coast NRM project officer Sophie WiIlsher was keen to look at yield differences observed since the drains were installed in February, 2021.
"The drained site, growing canola, yielded an average of 1.26 tonnes per hectare in 2021, despite rainfall being in the 99th percentile during the growing season," Ms Willsher said.
"This is an outstanding performance for the site.
"In 2020, prior to the installation of drains, the same area yielded less than 1t/ha in a lower rainfall year."
This yield increase translated to an estimated additional $750 per hectare in 2021, accounting for yield penalties and calculated for 2021 canola prices.
These results are encouraging for the profitability of using subsurface drainage as a tool to alleviate waterlogging.
However, there is still another two years of monitoring until the final return on investment can be calculated.
Understanding the amount of time to return on investment will help growers and advisers across the region make better informed agro-economic decisions around managing onfarm waterlogging and the benefits of subsurface drainage.
