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Corangamite Region   'Brown Book'   - How to optimise your soils to enhance productivity
How do I manage stubble?
Most relevant to cropping industries
Key Points
Understanding the question
Managing stubble
Case Study
Other related questions in the Brown Book
Resources
References

Source: DEPI Victoria
Key Points
  • The benefits of stubble retention are well known, but wet seasons have seen a shift in farmer attitudes towards stubble management
  • Managing high stubble loads requires careful planning to ensure effective sowing during the following season
  • Burning is not always the most profitable treatment
  • Occasional, strategic burning of stubble based upon sound agronomic principles can be a valid choice and farmers should have flexibility to use this option when appropriate

  • Many farmers are forced into stubble burning due to machinery limitations
  • Paddock conditions will dictate how best to achieve stubble retention objectives
  • Alternative options to manage stubble residues, particularly in high rainfall areas, are continuing to evolve
  • Some growers have had success with stubble digester products, but their benefits are not yet proven in scientific field trials
Understanding the question
Why is it important to me as a farmer?
  • Successfully developing a well-integrated stubble retention system brings financial and environmental benefits, particularly in the area of soil health and condition
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Background information on stubble
  • Reduced tillage and stubble retention, started 40 years ago, following development of the first knockdown herbicides. These practices meant a change from conventional cultivation, which at the time consisted of stubble burning and several passes with tines or discs to control weeds and produce a seedbed
  • Reduced cultivation and retained stubble led to improved soil structure and less soil erosion, and the environmental value of conservation cropping became more widely recognised
  • Many farmers adopted minimum tillage, which consisted of a single cultivation before sowing, generally with a tined implement followed by seeding with a combine.
  • Conventional cultivation, involving multiple passes, had largely disappeared by the mid 1980s
  • By the late 1980s, full cut direct drilling was being adopted in some regions but not in others:
    • Farmers in low rainfall areas could direct drill into light stubbles with few problems
    • In high rainfall areas larger stubbles, off the heavier clay soils, provided a more significant challenge with many farmers resorting to burning and sowing after a one-pass cultivation
  • Few took the additional step to direct drilling until air seeders became common in the mid-1990s and with the addition of GPS technology farmers looked at sowing at wider row spacing from a traditional 7” (180cm) to 10” – 12”+ (250 – 300+mm) which enabled them to both handle increased stubble with less blockages and also to inter row sow the following crop with minimal soil disturbance
  • Since many of these innovations were developed, stubbles have been light due to lower than average rainfall in many areas over the last decade and hence many stubble handling methods have not been tested under higher stubble loads
  • The 2009 harvest produced some disappointing yields, after a very promising start, due in part to a very hot period of weather which coincided with flowering and grain fill
  • Stubble loads however were still reasonably high due to good rainfall during the growing season
  • When this heavier stubble was combined with some good summer rainfall many sowing systems, using fully retained stubble management, had significant problems with blockages at sowing and as a result large areas of stubble were burnt

Stubble retention and soil health
  • Retaining rather than burning stubble increases both the amount and activity of microorganisms in soil, resulting in greater soil nitrogen supply in the long-term. Regular inputs of organic matter are required to maintain soil health and optimise biological functioning of the soil
  • Ground cover should be maintained at a level where at least 50% of the soil surface is protected (this will mean different stubble loads for different crops)
  • Retain as much stubble as possible to maintain soil structure, provide a store and source of plant available nutrients and promote a wide diversity of soil biota
  • The amounts of carbon and nitrogen in organic matter (C:N ratio) influences the rate at which residues decompose. Legumes contribute to the continued release of nitrogen during the growing season, but do little to build long-term soil organic matter as their residues, with relatively low C:N ratio, decompose quickly
  • Cereal and grass residues that have a lower nitrogen content (higher C:N ratio), breakdown more slowly and are more likely to contribute to stable soil organic matter pools. A diversity of residue types supports a greater diversity of soil biota and contributes to an increasingly resilient soil
  • Maintaining stubble on the soil surface and minimising soil disturbance protects the surface from soil collapse (due to dispersion), reduces the risk of soil loss through erosion, and can reduce evaporation
  • Incorporation of stubble residues into moist soil will increase the rate of breakdown and may also stimulate breakdown of previously protected organic matter
  • Where problems are being experienced with stubbles at seeding, consider adjusting stubble height at harvest or slashing/mowing residues to reduce the size of individual stubble pieces
  • Climatic conditions and soil type influence the ability of a soil to retain organic matter. Warm, moist environments promote microbial activity and rapid breakdown of organic residues. Regardless of stubble treatment, adequate moisture is required for organic matter to breakdown. Clay in soils helps to protect organic matter particles; soils with a significant proportion of clay should maintain a higher equilibrium content of organic matter than coarse textured sandy soils
  • The uptake of biologically derived N is dependent on the amount and quality of organic residues, the speed at which they are broken down, and timing, in respect to whether there are actively growing plants able to take up the N before it is leached lower into the profile
  • When moving from burning to cereal stubble retention, there can be an initial tie-up of soil nitrogen as the stubble decomposes, and starter nitrogen may need to be increased at sowing. Over two to three seasons the soil usually adjusts to the new conditions, and in the long-term is able to supply a greater amount of nitrogen for crop growth and yield
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Advantages of stubble retention:
  • Increases in soil water and plant available water (PAW)
  • Decreases in surface (slaking) and subsoil (sodic) issues
  • Increases in organic carbon percentages
  • Increases in soil biological functions
  • Decreasing soil erosion potential
  • Improved soil air and pore spaces for better plant root exploration
  • Decrease in off-site leaking/loss of nutrients and pesticides
  • Potential increase in the amount of available energy for grazing animals
  • Burning it will also have the following negative impacts:
    • Potential off-site issues
    • Increasingly frowned upon by the community
    • Valuable carbon and other nutrients including nitrogen, phosphorus, potassium and sulphur literally go up in smoke. Approximately four kilograms of nitrogen are lost with every tonne of wheat stubble burnt
Problems with stubble retention:
  • High stubble loads present as surface trash at seeding time have the potential to disrupt seeding and impact on crop establishment
  • Large volumes of surface trash will also reduce the efficacy of soil-activated preemergence herbicides
  • The management of large residues also has nutrition implications because nitrogen is required for cereal stubble breakdown
  • The volume of surface residues in many paddocks and the time available for stubble management may mean some growers will decide to burn
  • There may be better long-term options but burning is a quick, simple, cheap, and effective way of reducing surface trash
  • The degree of benefit will depend on the timing, temperature and thoroughness of the burn
  • Burning it will also have the following positive impacts:
    • Reduce residue volume
    • Kill some weed seeds
    • Lower the risk of stubble-borne diseases and reduce some pest problems, such as snails and mice
    Figure 1 - Wide row spacing to allow easier management of stubble loads - Source: Soil Types and Structures Module, DEPI Victoria
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Managing stubble
What is the best practice?
  • Stubble management requires an integrated management approach, combining several strategies
  • Estimating stubble loads before harvest will help identify the best management practices to use during and post-harvest, and pre sowing
  • If stubble cannot be retained due to heavy disease or weed burdens, adopt best management practices to achieve an effective burn to minimise the environmental impact
  • Some growers in the have had success with stubble digester products (see case study below), but their benefits are not yet proven in scientific field trials
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How can you achieve this?
At harvest
  • The main management decisions at harvest are the header cutting height and the spread pattern of the stubble. If using tramlines and inter-row sowing standing stubble will make sowing easier
  • If inter-row sowing is not used, the cutting height is determined by the sowing machinery used, the amount of residue the machinery can handle and the available options for stubble management before sowing
After harvest
  • The amount of stubble left on the paddock, stubble characteristics post-harvest and the amount of stubble sowing machinery can handle, all determine how to manage stubble after harvest
  • There are a number of options available to manage stubble including grazing with livestock, slashing, mulching or harrowing and strategic burning
  • Stubble can provide a useful feed source for livestock. It is important to monitor stocking rates to ensure paddocks are not overgrazed, exposing them to erosion
At sowing
  • The major challenge of stubble retention is the physical management of crop residues
    Figure 2 - Residue management systems - Photo: Southern Farming Systems
  • Tyned implements are often less expensive than discs and may also reduce the risk of rhizoctonia bare patch due to increased soil disturbance, but they handle less stubble
  • While disc machinery handles heavier stubble loads and disturbs the soil less, they can result in ‘hair pinning’ (that is, stubble is bent rather than cut and pushed into the sowing groove with the seed), which reduces seed/soil contact
  • Other equipment combinations including press wheels, coulter discs, trailing harrows,help to manage stubble at sowing
  • Inter-row sowing allows crops to be sown into standing stubble and relatively high stubble loads without needing to chop, spread or burn stubble
    Figure 3 - Inter-row seeding of barley at 300mm row spacing into 4t/Ha wheat stubble - Photo: Southern Farming Systems
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Managing stubble burning
  • Stubble burning is most common in the southern part of the state, in Glenelg-Hopkins and Corangamite regions. This reflects the higher stubble burden due to high rainfall in these regions and the lower commitment to investment in conservation cropping technologies
  • Stubble smoke in the atmosphere can adversely affect human health
  • Research shows that total particulate matter is greater with smouldering burns than flaming burns, but levels are influenced by oxygen supply, size and type of fuel load, fuel chemistry and moisture, alkali metal content and firing technique
  • If burning stubbles, adopt best management practices to achieve an effective burn, while minimising the impact of smoke
    Figure 4 - Stubble burning within close proximity to Geelong - Photo: Southern Farming Systems
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Other related questions in the Brown Book


Brown Book content has been based on published information listed in the Resources and References sections below

Resources
References
  • Stubble Management Factsheet. Grains Research & Development Corporation.
  • Midwood J. Managing Heavy Stubbles. Southern Farming Systems.
  • Stubble Management – an integrated approach. EH Graham Innovation Centre, Charles Sturt University.
  • Stubble - threat and potential (pp 8-10). Making the most of a wet summer in the Southern Region. (2011) - Grains Research & Development Corporation.
  • Peries R, Gill J. The synergy of raised beds, controlled traffic, minimum tillage and stubble retention deliver higher water use efficiency in South West Victoria, Australia. Australian Centre for International Agricultural Research.
  • Plan to succeed with stubble retention. - October 2006 Grains Research & Development Corporation - Southern Farming Systems.
  • To burn or not to burn?- Case study 1. - Land and Water Australia - Soil Health Knowledge Bank, 2005.
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This project is supported by the Corangamite Catchment Management Authority, through funding from the Australian Government’s Caring for our Country

Page Updated: July 2012
Produced by AS Miner Geotechnical