Subsoil drainage, mitigation strategies, replacement crops and workshops were among the NGN-driven projects that tackled waterlogging impacts during the consecutive La Niña years.

Western Australia : subsurface drainage

By Sophie Willshire, South Coast Natural Resource Management

Strategies to improve the management of waterlogging are being investigated to lift the economic sustainability of grain growing in Western Australia’s south-eastern cropping region.

Some three million hectares of agricultural land are prone to waterlogging, with the Esperance region particularly at risk due to its sandy, duplex soils and wet winters. Adapting farm management systems and employing tools such as subsurface drainage could alleviate the effects of waterlogging, improve unproductive soils and provide additional water sources for future drought-proofing.

While subsurface drainage opportunities are being explored in many agricultural landscapes, a limited understanding of the economic efficacy of this management tool poses a significant barrier to adoption.

Meanwhile, the issue of waterlogged crops is becoming increasingly important for southern growers. The need for effective management solutions was raised with GRDC through the National Grower Network (NGN). In response, GRDC contracted South Coast Natural Resource Management (South Coast NRM) to investigate the profitability of subsurface drainage.

The first drains were installed in February 2020, attracting a large crowd of curious growers to the trial paddock. Since then, South Coast NRM has been collecting and monitoring field data to support the return-on-investment analysis due for release in April 2024.

GRDC grower relations manager (west) Luke Dawson with growers from the Esperance port zone watching subsurface drainage installation in action at the Dalyup Demonstration Day on 16 February 2023. Photo: South Coast NRM

This work was guided by the project’s technical advisory group, which includes local growers, hydrology and earthmoving experts, and research representatives.

Preliminary results show that the subsurface drainage system is effective at moving water away from the root zone and maximising yield potential. This indicates that well-designed drains can effectively create normal soil conditions in previously inundated land.

The project found it is critical to use experts when designing a drainage system. These include an experienced drainage contractor, catchment or Landcare group, Department of Primary Industries and Regional Development representative, or Natural Resource Management group. The adverse effects of a poorly designed drainage systems are severe and can have impacts far beyond the farm gate.

Downloadable resources developed in this project are available at the South Coast NRM’s Southern Soils website.

More information: Sophie Willshire, [email protected]

Southern HRZ: mitigation and crop options examined

By Greta Duff, Southern Farming Systems

When wet conditions in 2021 caused waterlogging at trial sites in western Victoria, Southern Farming Systems (SFS) seized the opportunity to run reactive trials that explored waterlogging mitigation strategies and replacement crop options.

The crop replacement trials were spring-sown canola, barley, chickpeas and field peas at Streatham and Hamilton in Victoria. Two varieties for each crop were trialled. The trials, however, suffered from slugs, followed by summer heat stress ahead of a February harvest.

The best-performing spring-sown crop was barley, delivering a positive gross margin and yields averaging 3.13 tonnes per hectare. Field peas broke even but canola and chickpeas had a negative gross margin return (Table 1).

Table 1: Gross margins and break-even yields across the crop replacement trial.

Overall, favourable spring conditions, rainfall, few heat events at critical growth periods and reduced disease pressure all play a role in the success of spring-sown crops.

These crops, however, can provide other benefits such as soil cover over spring and summer, reduced weed pressure and the potential of drying the soil profile for the next crop.

The mitigation option involved crop nutrition trials, given that waterlogging causes nitrogen loss through denitrification and leaching while also diminishing the crop’s ability to take up nutrients, resulting in yellowing of leaves.

This trial tested whether additional nitrogen (and trace elements) can be used to minimise losses in wheat (Hamilton, Victoria, and Hagley, Tasmania), canola (Streatham, Victoria), and faba beans (Vite Vite North, Victoria).

Three types of nitrogen products were tested alone and in combination: liquid nitrogen, urea and sulfate of ammonia.

The applied nutritional products did not influence grain yield except at the Hagley wheat trial, where a yield response was observed with different rates of nitrogen. In Tasmania, the average yield was 9.5t/ha. The two highest-yielding treatments were urea and sulfate of ammonia at full rate with 10.3t/ha and urea at full rate with 10.28t/ha.

Additionally, the crop growth stage at waterlogging was found to have a large influence on yield. Established plants are most affected when they are rapidly growing, making waterlogging during warmer spring periods the most damaging to yields.

This means crops in the trial that presented with waterlogging symptoms were nonetheless able to yield exceptionally well: faba beans at 7t/ha and canola at 4.1t/ha.

Additional information and digital resources regarding these trials are available, including:

Trial reports are available at the SFS website and at the GRDC website.

More information: Greta Duff, [email protected]

Storm recovery workshop

By David Foxx, AgCommunicators

In January 2022, the Upper Eyre Peninsula region of South Australia received its entire average annual rainfall in a single weekend. Growers in the Kimba district were the hardest hit. Run-off flowed across cropping land, eroding topsoil on farms in elevated areas before gouging deep channels through downstream paddocks.

Many kilometres of fencing and roads were destroyed and there were significant issues with widespread debris, paddock trafficability and road damage inhibiting vehicle access.

Despite these difficulties, it was also recognised that this was a once-in-a-lifetime event offering full soil moisture profiles across the district. To help growers manage the multifaceted impact of this unprecedented flood event and take advantage of the seasonal opportunity, GRDC recognised the need for information support.

Front of mind was the need to prioritise paddock repair in time for sowing in 12 weeks so the upside yield potential would not be lost. Working with Grain Producers SA (GPSA) and the Department of Primary Industries and Regions (PIRSA), GRDC supported a series of ‘Cropping after the storm’ workshops.

In partnership with GPSA, PIRSA staff led by Mary-Anne Young were quickly able to assess the flood damage, tour affected farms and provide insights into what needed to be done. GRDC representatives took the team to see the damage first-hand and consult with growers.

The NGN provided local connections and contacts who could explain growers’ needs and ground-truth the planned support.

GRDC grower relations manager (south) Courtney Ramsey says grower input was vital for making sure the workshops delivered targeted, relevant advice.

“Having a network that connects us directly with growers allowed us to consult on the ground. This helped define the information we needed to provide and the range of speakers we invited to contribute,” she says.

“We were able to hear what they felt they needed and sound out our own recommendations on areas they may not have considered.”

The team was able to stage the ‘Cropping after the storm’ workshops just four weeks after the flood, with presenters addressing the potential effects on soil structure, paddock restoration and soil amelioration. Soil constraints, nutrient management, weed pressure and redistribution, nitrogen management and farm finances were also covered.

The NGN was also instrumental in providing input from Western Australian growers Peter and Lena Daw, who experienced a comparable 300-millimetre rainfall event on their Ravensthorpe farm in 2017. The Daws provided a viewpoint from five years on, sharing the importance of task prioritisation and recognising that some jobs would have to be left for later.

Ms Ramsey says that growers they met were often overwhelmed by the amount of work to be done and unsure where to start. “But there was also a strong undercurrent of excitement about the potential for the season ahead,” she says.

“We deliberately made the workshops in-person events so there was a community-strengthening, social aspect. It gave growers a chance to get together and talk about their shared experience.”

She says that hearing presenters such as Peter and Lena reinforce the message that the recovery process extends across years helped growers to focus on what needed to happen first to get the next crop in.

“From there, the more practical advice around managing crops for high yield potential and understanding changes to weed and nutrient distribution was designed to help growers prioritise through the season.”

In the end, virtually every affected grower was able to establish a cropping program in time and reap the benefits of a significant rain and stored soil moisture after several tough years. For Ms Ramsey, a key takeaway was how responsive the NGN allowed GRDC to be:

"The NGN allowed GRDC to be much more than an industry research and development corporation in this situation, with the two-way interaction contributing to our overall strategy and informing our reaction to grower needs on the ground," she says.

"'Cropping after the storm’ was a great reflection on the value of that two-way engagement between growers and GRDC. It has also given us a response template that can serve a wide range of situations – from climate emergencies to biosecurity events, to new market and crop opportunities.”

PIRSA’s ‘What to do after a flood’ guide can be downloaded.

More information: Courtney Ramsey, courtney.ramsey@grdc.com.au