Maintaining profitable farming systems with retained stubble in the Riverine Plains region

WHY THIS PROJECT WAS NEEDED

Stubble retention can help protect soils from erosion, increase soil moisture retention and improve soil organic matter. However managing high stubble loads isn’t always straightforward, especially in no-till systems.

This project formed part of an overarching national initiative focusing on maintaining the profitability of stubble-retained systems. It was designed to investigate, demonstrate, and extend cultural practices to assist growers adopt no-till stubble retention (NTSR) in medium and high rainfall zones.

In short: This project focused on maintaining the profitability of stubble-retained systems. Multiple trials compared stubble management techniques used in the Riverine Plains region. Additional research on temperature and frost effects address growers' concerns, and contributed to local knowledge.

Project focus

The project established four focus farms with large, commercial scale trials at Coreen, Henty, Yarrawonga and Dookie. The trials compared crop growth, frost and disease risk and yield under different stubble management techniques, including burning, mulching or incorporation of stubble as compared to leaving stubble standing. Supporting small scale trials focused on specific issues such as row spacing and cultivar selection, nitrogen timing and disease management. The project built on findings from the previous GRDC funded Riverine Plains project Improving water use efficiency in no-till stubble retained systems.

This project aimed to increase the adoption of NTSR systems across the Riverine Plains region by increasing profitability and sustainability of NTSR cropping systems. The project also developed guidelines specific to the region, enabling growers and advisors to use rotational cultural control measures to enhance the sustainability of their NTSR farming systems.

This project was extended to include additional temperature and frost research, through links to the GRDC National Frost Initiative. As an addition to the Stubble Project, the frost research component aimed to understand the impact of stubble retention on in-canopy temperatures and associated risk of frost in cropping environments with high yields and stubble loads. This was driven by increased interest from growers and the need for more local knowledge.

Frost research stubble management trials were run at Coreen, Yarrawonga and Dookie and included tall stubble, low stubble, incorporated stubble and burnt stubble treatments (with the exception of Corowa where there was no low stubble treatment). Temperature data was gathered by Tinytag sensors at 50mm above the surface and 300mm above the surface, rising to 600mm during the season. At the Dookie site they were also buried at 50mm below the soil surface.

Project outcomes

Stubble retention in cropping systems of the Riverine Plains was published as a summary of project outcomes and learnings.

Major findings included:

Stubble management is not a key driver of yield. Recommendation: Retain stubble where possible, but use other tools, such as straw removal, mulching or incorporation, to manage stubble to optimise the efficiency of the farming system and machinery. Try to use burning as a strategic tool only when necessary.
Row spacing (22.5cm or 30cm) is less important in determining wheat yield in early-sown (mid-April) crops compared with later-sown crops (late May – early June).
During the four years of trials, applying a PGR did not deliver any positive yield effects or consistent quality effects.
Applying nitrogen increased yield potential, however the timing of the nitrogen application (split, single dose etc) did not influence yield. Recommendation: As there is no penalty for applying nitrogen in a split application, a high rate of nitrogen up front, or early, could be valuable under wetter conditions, while a lower rate of early nitrogen could reduce upfront costs when dry sowing, or where the break is late.
Applying either Prosaro (tebuconazole/prothioconazole) or Tilt (propiconazole) typically provided yellow leaf spot (YLS) control in the range 25–50%, which led to small, but consistent, positive yield effects. Recommendation: Use fungicides to control YLS during a wet spring, however sowing resistant varieties and employing rotations that include break crops, such as canola and pulses, also can help control YLS.
Long stubble shades the emerging crop, resulting in a delay in flowering and maturity. Recommendation: Growers can use this to their advantage by sowing crops earlier into long stubble and having them still flower in the right window, thus spreading the sowing window. If using two headers in a paddock, changing stubble height between headers will spread the flowering window of the following crop within the paddock over several days. This will reduce the risk of economic frost damage across a whole paddock/ variety.
Long stubble does not significantly increase the risk of frost in the Riverine Plains region. While in-canopy temperatures differences were measured across the Stubble project trials, these were not physiologically significant. Rather, the difference in flowering date due to shading in high stubble meant either the burnt or retained treatments had more frost damage during 2017, depending on which treatment was flowering at the time of the frost event.
Soil sampling should be conducted at repeatable GPS referenced locations across different soil types. Recommendation: Avoid the bulking together of soil samples that commonly occurs with transect sampling and instead adopt incremental sampling. This will provide a greater opportunity to detect changes in soil properties over time.
Variable rate nitrogen management is of highest value in seasons where water is limiting and when there are strong changes in clay content/CEC across a paddock. Recommendation: Zones developed through EM surveys need to be ground-truthed in order to determine which soil properties are likely to drive or limit production in each zone.

Summary: Comparable yields can be achieved in stubble retained and burnt systems. Even if full stubble retention is not feasible due to machinery, weeds or disease constraints, there are other options such as shallow incorporation, cutting short or straw removal which can provide flexibility, reduce the frequency of burning and address timeliness related issues.

This publication was made possible with funding from GRDC and the Sustainable Agriculture Victoria – Fast Tracking Innovation Initiative.

Stubble management guidelines

Stubble management guides were also produced:

Case studies

Stubble retention case studies with Steve Ludeman and Denis Tomlinson were recently updated, thanks to the Foundation for Rural and Regional Renewal (FRRR), and the William Buckland Foundation.

Results summaries

Results from this project have been reported in several editions of Riverine Plains research compendium, Research for the Riverine Plains, as well as having been presented at conferences or seminars. These reports can be downloaded via the links below: