GRDC stubble management guideline No. 4
- Stubble management starts at harvest.
- Effective chaff and straw spreaders are essential in a stubble retained system.
- There is an increased cost associated with cutting crops low.
A successful retained stubble farming system begins at harvest. When planning harvest logistics consideration needs to be given to the type of stubble that needs to be produced and how crop residues will be managed for optimum outcomes the following season.
To avoid issues associated with stubble retention, such as seeder blockages, poor crop emergence and reduced herbicide efficacy, stubble left standing in the paddock after harvest should be even and at the appropriate length (according to crop rotation and machinery capability) and chaff and straw should be spread evenly across the paddock.
A grower’s capacity to achieve this will be impacted by the type of harvest machinery they use, their stubble load and the cropping environment.
As part of the ‘maintaining profitable farming systems with retained stubble in Victoria and Tasmania’ project, findings from field trials and demonstrations, as well as previous research and anecdotal evidence has been collated to develop harvest process guidelines, including tips on machinery selection and set-up and operation for growers operating retained stubble farming systems. This guideline links closely with Guideline 3 which identifies the type of stubble growers should be aiming to produce according to their farming system.
Residue management at harvest
If stubble retention is a priority, stubble management should be a key consideration when planning harvest logistics. Planning should take into consideration likely stubble loads, cutting height, machinery capabilities, crop type and rotation and the paddock’s pest and weed burden. These factors need to be balanced against the need to harvest the crop within the appropriate harvest window.
Factors that will effect residue management at harvest include:
- Harvest height and crop length
- Crop type (canola, cereals or pulses)
- Harvest speed and material throughput
- Residue spreading width (chaff versus straw)
- Moisture content of residue
- Weather conditions
Header cutting height and the spread pattern of stubble is the first consideration when preparing for harvest.
Cutting height will vary according to crop type and yield, crop planned for the following season, harvest logistics and the capabilities of seeding equipment. This is discussed further in Guideline 3: Desired stubble characteristics for the Wimmera and Mallee.
If your priority is to cut crops high and harvest fast, stubble may need to be managed post-harvest, depending on the capabilities of the seeder. This may involve performing a second pass during the fallow phase, grazing or baling straw.
Cutting crops low will be slower (potentially putting ripe crops at greater risk from inclement weather) but will negate the need for post harvest stubble management to improve sowing efficiency the following season. However, less (shorter) standing stubble can mean more straw and chaff in between the rows which can hinder emergence and yield, particularly of smaller-seeded crops such as canola (GRDC Ground Cover, 2014).
There is also an increased cost associated with harvesting low due to a reduction in harvest efficiency and increased fuel use and machine hours. On average header speeds will be reduced from 9.5ha/hour to 5.7ha/hour, a decrease of 41 per cent, when harvest height is reduced from 60cm to 15cm (Barr, 2014). In economic terms, research conducted by SFS in 2014 indicated that higher harvest heights provide additional savings of approximately $7.50 per 10cm of extra height.
Importantly, when identifying the appropriate cutting height for the paddock and/or situation, ensure groundcover will be sufficient to minimise wind erosion over summer.
Straw and chaff
The goal is to maximise the spread of crop residues while maintaining harvest efficiency, but this will vary according to the crop type, the composition of the residue, the moisture content and the weather.
Shorter straw and finer the chaff are preferable as they will break down faster, but the finer residue the harder it is to throw the width of the machine. Straw will spread further than chaff, but it is necessary to manage both.
Spreading capability will also be influenced by weather and crop moisture levels. If the moisture is high, residue won’t spread correctly and can end up concentrated in certain areas of the paddock. Wimmera agronomist and VNTFA member Ben Cordes discusses this further in the video below:
Machinery options and modifications
Harvest machinery will vary in its ability to handle crop residues. Understanding the capabilities of machinery and how well this matches crop rotations and yield environment is key to ensuring stubbles can be retained in a manner that benefits the profitability, productivity and sustainability of the cropping enterprise.
New machinery with built-in ability to chop and spread crop residues requires a large capital outlay, but many growers have successfully modified their existing machinery to improve residue handling capabilities.
Other stubble handling tactics that can be used at harvest include straw choppers, harvesting on the diagonal and secondary cutter bars. Alternatively, it could be more beneficial (economically and logistically) to employ a contractor with appropriate machinery for certain crops.
Choppers and spreaders
As outlined in Guideline No. 3: Desired stubble characteristics for the Wimmera and Mallee, advice for handling crop residues is to “chop it, distribute it, and do it evenly”, except if planning to bale straw or windrow burn.
In the past, many standard straw choppers and spreaders have tended to concentrate chaff and straw directly behind the header, reducing crop establishment and herbicide efficacy. While this has been improved on many of the newer model headers, some units can also be retro-fitted to older models.
The chopper should chop the straw evenly and spread straw and chaff uniformly across the header width. This will ensure sowing efficiency is maintained and emergence is less effected by areas in the paddock where there might be heavy or concentrated crop residues.
To maximise spreading width growers can increase the height of their cutter bar to reduce the amount of residue to be moved (Figure 1 and 2). If conditions are windy, or in sloping paddocks, adjusting the rotor speed and vane settings will improve residue spread.
In 2015 the Victorian No-Till Farmers Association (VNTFA) held a demonstration day where farmers could assess a range of choppers and spreaders in action. In the video below Wimmera farmer Wayne Adler shares his experiences.
Using a stripper front header
The stripper header allows just the head of the crop to be harvested, leaving the rest of the plant standing in the paddock, thus reducing the amount of crop residue passing through the header facilitating faster harvest speeds.
Efficiency gains (less fuel, less time stripping a paddock) are the key benefits of this harvesting system. Other benefits of a stripper front include improved performance in down, lodged and hailed crops and in green, high moisture and weed infested crops. Video footage of the this system in action is available on YouTube or see the Shelbourne website for more information.
If weeds or resistance is an issue, growers may modify harvest machinery or alter cutting height to facilitate weed control strategies such as narrow windrow burning or weed seed collection via chaff carts or the Harrington Seed Destructor. In this case, the aim would be to set the cutter bar at a height below the majority of the weed seed heads so that they pass through the header.
More information on these weed control strategies in a retained stubble system will be explored in Guideline 12: Weed management in a stubble retained system. Information on narrow windrow chute design and how to harvest is available on the GRDC’s YouTube channel.
Barr, R., 2014, ‘Cutting height can improve harvest yields’, Ground Cover, issue 112. Accessed at: http://grdc.com.au/Media-Centre/Ground-Cover/GC112/Cutting-high-can-improve-harvest-yields
Corangamite region Brown Book, 2012, ‘How do I manage stubble?’, How to optimize your soils to enhance productivity. Accessed at: http://www.ccmaknowledgebase.vic.gov.au/shkb/brown_book/34_Stubble.htm#top
Jennings G, 2012, ‘Exploring the stubble management potential of headers’, The cutting edge, SANTFA, Summer edition, 2012. Accessed at: http://www.santfa.com.au/wp-content/uploads/Santfa-TCE-Summer-12-Exploring-the-stubble-management-potential-of-headers.pdf
This guideline was produced by BCG as part of the GRDC Maintaining profitable farming systems with retained stubble initiative (project BWD00024 ‘Maintaining profitable farming systems with retained stubble in Victoria and Tasmania’).