Stubble Burning
The Department of Primary Industries aims to help farmers make better decisions by providing options for successful whole farm system management.
We strongly encourage farmers to adopt conservation farming systems, including retaining crop stubble residues but also recognise that occasional, strategic burning of stubbles based upon sound agronomic principles can be a valid choice.
Farmers should have flexibility to use this option when appropriate. Alternative options to manage stubble residues, particularly in high rainfall areas, are continuing to evolve.
Key points
- Stubble management is one of many complex issues that farmers must contend with.
- There is no single, ‘one-size-fits-all’ solution for managing heavy stubbles.
- Stubble burning is not the preferred option for the majority of farmers.
- In particular circumstances, such as dealing with herbicide resistant weeds, stubble burning may be a reasonable option.
- Most farmers will only burn stubbles when absolutely necessary, having considered all available options and the potential implications of burning.
- To minimise negative impacts, farmers should rake and burn windrows or cool-burn just before the break of season.
- Stubble retention has many benefits, but requires a systems approach to manage disease, pest and weed pressure.
- A number of techniques, other than burning, can be employed to manage heavy stubble loads.
- Effective stubble management begins at harvest with even spread of residue and appropriate stubble cutting height.
- Decisions about stubble management may need to be reviewed annually. used this way, burning is not a significant carbon dioxide contributor.
Background
There are general community perceptions that the carbon (C) component in stubbles is lost by burning and that the process of burning stubbles even occasionally, seriously affects the organic carbon levels of the soil.Research clearly shows that around 80 per cent of the C in standing stubble will return to the atmosphere as CO2 in the short to medium term. Losses of carbon as CO2 to the atmosphere through burning are often only slightly greater than through natural decomposition, but they are of course immediate.
Actual nutrient losses caused by burning are also known. After harvest, a 3.45 t/ha wheat yielding crop left a residue of 5.4 t/ha of above ground dry matter. A cool burning of this stubble yielded 437 kg/ha of ash, the balance being lost as smoke to the atmosphere. The nutrients lost and proportion of straw (in brackets) were nitrogen 16 kg (80%), phosphorous 0.5 kg (40%), potassium 17 kg (60%) and sulphur 1 kg (50%). This nutrient loss is well understood by land managers and strongly influences decisions not to burn, except under extreme circumstances.
The 2010 season was exceptional with record crop biomass production combined with heavy rain and floods that tangled and lodged many crops, often before harvest. In many instances, burning became the only practicable management option (there was insufficient time between when flooded paddocks eventually dried sufficiently to allow machinery traffic and sowing activities in autumn).
Wimmera and Mallee crop transect surveys indicate a steady downward trend in the amount of stubble being burnt. While 2010 may be an exception due to the extensive flooding/water logging occurring through north west Victoria, there is a perception that the soil health messages delivered throughout Victoria by DPI (and others) are generating real practice change with a strong trend toward adoption of minimum/no-till, stubble retention and precision agriculture practices.
Surveys also reveal a growth in the intensity of cropping across Victoria resulting in healthier crops and more dry matter being produced on a regular basis. This increase in crop biomass is leaving behind a strong legacy of root material in the soil. It is this unseen carbon in the soil in root material, unaffected by burning, that provides the greatest potential for C retention. Up to 30 to 40 per cent of plant biomass can be located below ground.
Advantages of burning
- Cheap
- Quick and easy
- Can assist weed, insect and disease control
- Reduced nitrogen tie-up
Disadvantages of burning
- Loss of nutrients
- Loss of carbon
- Impact on soil microbes and fauna
- Reduction in soil structure (soil aggregate stability)
- Increase in erosion (wind and water)
- Can increase acidity over time
