Manage stubble now to minimise frost risk later
Frost caused significant damage to crops in many parts of the WA Wheatbelt last season, highlighting the importance of having a comprehensive frost management strategy as part of annual farm planning in frost prone areas. It should include pre-season, in-season and post frost event management tactics.
Research conducted through the GRDC National Frost Initiative (NFI) has found that pre-season stubble management influences both frost severity and duration.
Frost stubble research findings
Rebecca Smith, a Living Farm Research agronomist, has conducted 18 stubble management trials as part of the NFI between 2014 and 2016.
The key research findings were;
- Reducing stubble load reduced the severity and duration of frost events and resulted in less frost damage and better yields under frost. No differences were observed between stubble height, orientation or composition. Data to date suggest it’s mainly a load issue.
- In frost prone parts of the landscape growers can minimise frost risk by reducing stubble loads back to grain yield potential, prior to seeding. This can be achieved by various approaches including cutting low, windrow burning/chaff carting, stubble mulching, raking and burning, strategic blanket burning and summer grazing
- Without frost, once off stubble reductions did not reduce yield and may give a slight improvement in yield due to reduced disease and less nitrogen tie up, depending on site, season and variety choice.
- With multiple severe frost events, stubble reduction did not increase yield
Please refer to Rebecca’s 2017 GRDC Research Updates presentation and paper for more detailed information.
Is stubble removal cost effective?
The research sites that did experience moderate frost damage, stubble management practices reduced severity, duration and damage. An example of this was shown in York 2015 and 2016 where there was between $60-$200/ha increase in gross margin by reducing stubble to below 2t/ha.
The sites where frost damage was too severe, there was no negative impact of stubble removal on gross margin.
Where sites experienced no frost damage, there was an economic cost of removing stubble, mainly associated with nitrogen lost. This cost is higher with higher stubble loads.
So what’s considered too much stubble and how do I calculate it?
In terms of minimising frost risk, a good rule of thumb is that stubble loads should match grain yield. For example, in a low production environment, 2t/ha grain yield potential = 4t/ha stubble and the stubble load needs to be halved at seeding, back to 2t/ha to minimise frost risk. In a medium production environment with 3t/ha grain potential = 6t/ha stubble, which needs to be reduced to 3t/ha to minimise risk. This calculation assumes a harvest index of 0.5. See Figures 1 to 3 to get a visual of stubble loads.
Take home message
Frost is difficult to manage and with seasons like 2016 it is hard to survive unscathed. Due to seasonal and spatial variability in frost, like all management practices, the ability of stubble management to manage frost risk is site, season and often landscape specific. Stubble management will only form one part of your frost management strategy so it’s important to consider pre-season, in-season and post frost event management tactics to customise your management plan. For more information on the other tactics please refer to GRDC's Managing frost risk Tips and Tactics fact sheet.
Acknowledgments
This project (DAW00241) is jointly funded by GRDC and DAFWA.
Further information
More information about frost management can be found in the GRDC’s Managing frost risk Tips and Tactics fact sheet and the GRDC 2017 Research Updates Stubble management recommendations and limitations for frost prone landscapes presentation and paper by Rebecca Smith (Living Farm).
For more information contact Dr Ben Biddulph, Research Officer (project manager), DAFWA, South Perth on +61 (0)428 920 654 or Rebecca Smith, CROPS Group Coordinator, Living Farm, York, +61 (0)409 684 818.