Narrow windrow burning offers farmers an opportunity to reduce a paddock’s weed burden by capturing weed seeds at harvest and burning them before they can germinate next season.
However, this weed control practice is not as simple as it sounds; planning and forethought are required to maximise success.
If windrows are not set up appropriately there is the risk that the whole paddock will burn or windrow fires won’t be hot enough to destroy the weed seed. Windrow set up at harvest time is crucial to success.
For the best results:
- Cut the stubble at ‘beer can’ height and make sure the header knives are sharp so that they cut instead of pull the crop and lay weeds down.
- Keep rows 50-60cm wide, make sure chutes capture all chaff and weed seeds into windrow.
- Don’t over thresh your crops, this will lead to reduced airflow which makes the windrows smoulder not burn, therefore not achieving adequate temperature.
- Make sure your chute doesn’t restrict airflow from the cleaning fan to the harvester.
- Do not drive over the windrow with headers or chaser bins, this will compact the windrow and reduce temperatures.
- Slow down the harvester speed at the end of a run before you turn so that the sieve empties at the same time as the rotors. This will prevent grain from being mixed in with the straw for windrow burning.
Peter Newman from Weedsmart in Western Australia, says as a general rule, aim for 20t/ha minimum of biomass in the windrow. Less than this and you risk not getting an effective burn. But be cautious of heavy stubble loads too because the whole paddock may burn.
The desired biomass range is normally achieved by a 2t/ha crop with a windrow chute that has an opening 500mm wide. Growers can mount a chute at the rear of the header to get the desired windrow dimensions.
Chute design
To avoid blockages in the chute, the design must have minimal brackets, bolts or sharp edges that will hinder the trash flow through the chute. You should also aim to keep the bottom of the chute open and avoid any horizontal edges which will catch the chaff.
The best chute design is one which can be easily attached and detached from the header if you do not intend to windrow all paddocks. Make sure the chute doesn’t restrict airflow from the cleaning fan otherwise blockages will occur.
Burning
To achieve adequate weed control the chaff trail must burn for 20 seconds at 400°C to kill ryegrass and 30 seconds at 400°C to kill brome grass. A ‘white ash residue’ generally means the burn has been hot enough.
Burn windrows with a light cross-wind of 5-15km/h and burn the two outside laps first to create a firebreak.
Light windrows every 200m so that windrows burn out in reasonable time.
Don’t burn windrows after a summer rain. Windrows should be dried for 10-14 days after a rainfall event.
For more information on windrow burning and other stubble related topics visit: https://thestubbleproject. wordpress.com/wimmera-and-mallee-weeds-2/
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