Stubble management is one of many complex issues that farmers must contend with.
Traditionally, grain growers have burnt stubble to manage weeds, diseases and reduce biomass to make sowing easier.
There is now less burning, less soil cultivation and increased retention of crop stubble.
Retaining stubble, rather than burning or cultivating, protects the soil from erosion.
It also conserves soil moisture and organic matter to sustain crop production. This is particularly beneficial in dry areas or in dry seasons.
Benefits of retaining stubble
Soil properties in Victoria’s crop growing regions have improved due to increased stubble retention. The main impacts are less erosion and moisture conservation.
Stubble provides groundcover, which protects soil from wind and water erosion by slowing wind speed at the soil surface and reducing run-off.
To protect soil:
- Stubble needs to be at least partially anchored.
- At least 70 per cent groundcover minimises water erosion risk and at least 50 per cent ground cover minimises wind erosion risk.
- Stubble height should be at least one-third of the width of crop rows. In general, the shelter provided by a barrier is approximately three times its height; 10cm tall stubble will protect the adjacent 30cm of topsoil.
- Maintain sufficient stubble for six to eight weeks after sowing.
Retaining crop stubble can improve soil moisture content by reducing evaporation and increasing rainfall infiltration rates.
Saving more surface soil moisture after autumn rains helps farmers to sow crops on time. This maximises grain yield potential and water use efficiency.
Other benefits of retaining stubble:
- Promotes nutrient recycling. It can contribute to a very gradual improvement in soil organic carbon and the soils’ microbial biomass.
- Significantly lower fuel costs and less labour.
- Lentil crops sown between cereal stubble rows are more easily harvested; plants grow taller and pods are higher.
Disadvantages of burning:
- Drier surface soils.
- Increased risk of topsoil loss from erosion.
- Loss of nutrients.
- A faster decline of soil organic carbon and soil microbes and fauna, with repeated burning.
- Poorer soil structure, for example, reduced soil aggregate stability and hydraulic conductivity and higher bulk density.
- Risk of escaped fire.
- The potential, or perceived, impact of smoke as an air pollutant and its impacts on rural communities and industries.
Strategic removal
Many Victorian farmers take a ‘flexible’ approach and are willing to reduce stubble loads if they are likely to cause problems with sowing, establishment or weed management.
- Legume and oilseed crops produce lower stubble loads. Their inclusion in the rotation may help with managing stubble.
- Livestock can help remove old stubble. Dry ewes or wethers can be useful in removing two-year-old stubble to enable inter-row sowing. Small mobs of sheep in large paddocks often only reduce stubble loads in parts of the paddock.
- In some years, stubble can profitably be removed after harvest by baling straw. Baled straw has uses in animal bedding, mushroom compost and in some years, livestock feed. It has other potential uses, such as for bioenergy.
- Strategic stubble burning in autumn can sometimes be a valid option when based on sound agronomic principles. Cool, late burns may successfully remove high stubble loads while leaving sufficient cover for soil protection.
Reasons to burn
While the long-term benefits of retaining stubble generally outweigh those of removing stubble, some growers choose to burn strategically for reasons such as:
- Ease of sowing and better establishment of small seeds, such as canola.
- A less suitable habitat for many crop seedling pests.
- Managing certain weeds, particularly herbicide-resistant weed populations.
- Low-cost way to remove stubble and control weeds, speed and convenience.
- Reduced reliance on agricultural chemicals.
- Better weed control due to a more even distribution of herbicides and effective incorporation of pre-emergent herbicides.
- Less nitrogen tie-up (immobilisation).
- In some instances, less frost damage to crops.
- Less inoculum for certain crop diseases (if stubble is completely removed).
Farmers opting to burn stubble should do so as close to sowing time as possible, to maximise soil moisture and reduce the erosion risk during summer.
Farmers must ensure they comply with all relevant regulations or laws.
Heavy stubble
Burning is often used as a last resort to manage heavy stubble loads, invasive weeds or pests. Stubble burning may be a reasonable option in particular circumstances.
Effective management of heavy stubble can begin with cutting the stubble at harvest as short as possible, ideally to no more than the row width, with the chaff evenly spread.
In general, if you can run your foot through the heaviest stubble, early on a dewy morning, you should be able to sow with a tyned seeder.
Some growers chop and spread stubble behind the header while retaining standing stubble.
Particularly heavy stubble can be cut higher and mulched after harvest. This helps to shorten stubble, retain soil moisture and accelerate decomposition.
If sowing the next crop with a disc seeder, rather than tynes, stubble can be cut higher. The straw and chaff need to be spread uniformly.
Straw can be baled after harvest. In some years, this is profitable, especially when feed is in short supply.
Inter-row sowing allows stubble to be retained when crop rows are more than 22cm wide.
– Agriculture Victoria