The chaff lining technique is clearly the cheapest in terms of capital cost. Chaff lining involves making a simple chute to divert the chaff fraction (containing weed seeds) into a narrow row in the centre of the harvester instead of onto tramlines.
The chaff is then left to mulch while the residue can be chopped and spread to maintain ground cover.
Although suited to controlled traffic systems, chaff lining can work in non-CTF systems if the harvester operates along the same runs for consecutive years.
What can I do at harvest to reduce my future weed burden?
As crops mature and harvesters begin reaping, consider the potential fate of seeds ripening on weeds that escaped in-crop control measures.
Peter Newman, WeedSmart’s western extension agronomist, says harvest time is an important opportunity to assess weed burden across the farm and be proactive about driving down the weed seed bank.
“Harvest can either be a super-spreader or a weed suppressing event,” he says. “Small patches of weeds can quickly expand when seed is blown out the back of the harvester. On the other hand, the harvester can be a powerful weed management tool if any one of the harvest weed seed control options are implemented.”
WeedSmart’s western extension agronomist, Peter Newman says efforts made to reduce the spread of weed seed at harvest will soon pay off for growers.
Australian growers have led the world in inventing and adopting harvest weed seed control tools such as impact mills, chaff carts, chaff decks and chaff lining, all of which can reliably destroy over 90 per cent of the weed seed that enters the front of the harvester.
“In addition to harvest weed seed control there are several other actions in the WeedSmart Big 6 that growers can implement just prior to, during and immediately after harvest that will make a measurable difference to the weed burden in future growing seasons,” says Peter. “The WeedSmart Big 6 tactics are scientifically-proven to reduce the risk of herbicide resistance through diverse herbicide use and cultural control to prevent weed seed set.”
What can I do before harvest to manage late emerged weeds?
In brief: Scout for and map weedy patches. Consider sacrificing small areas of high density weeds. Swathing can be a very effective way to stop seed set of late emerged or resistant weeds. Collect weed seeds for herbicide susceptibility testing.
The details: Growers across Australia use a variety of methods to map weeds – from the simple to the sublime. ‘Dropping a pin’ using the tractor’s GPS mapping system as you travel through a weedy section when spraying or harvesting is easy and provides useful information about the distribution of weeds in the paddock. Many growers have their own drones and use them the collect images or video footage of the crop that can be viewed or analysed to identify high density weed patches.
Collect seed for herbicide susceptibility testing – knowing what still works is vital information for planning next season’s herbicide program. There are three herbicide testing facilities in Australia that are equipped to test weed seed samples – Plant Science Consulting, CSU Herbicide Resistance Testing and UWA Herbicide Resistance Testing.
Collecting weed seed before or at harvest is the most common method used. The collected seed must be mature, from green to when the seed changes colour. Before harvest, collect 30 to 40 ryegrass seedheads or several handfuls of wild oats seed. After harvest, it is common to find seedheads still in the paddock or samples of contaminated grain can be sent for analysis.
Keep samples from different locations separate and details noted on the bag. Only use paper bags (double layer) to collect and send seed samples. Ensure bags are sealed so that the samples don’t mix during transit.
Which harvest weed seed control tool is best for my situation?
In brief: There are six harvest weed seed control tools used in Australia – impact mills, chaff decks, chaff lining, chaff carts, bale direct and narrow windrow burning. Choose the one that best suits your system and budget.
The details: Impact mills are best suited to continuous cropping situations. Residues are retained and evenly spread. Chaff decks have lower capital cost and are well-suited to controlled traffic situations. Chaff carts are popular with grain producers who also run livestock. Bale direct is also expensive but has a good fit in locations where there is access to straw markets. Chaff lining is currently the best ‘entry level’ system and can be used in CTF or non-CTF systems, with best results where the harvester runs on the same track each year. Chaff lining has essentially superseded narrow windrow burning, overcoming the time required and risks involved in burning and reducing the loss of nutrients from the system.
If you haven’t used harvest weed seed control tools before, it doesn’t take long to build and fit a chaff lining chute ready for use this harvest season.
What should I be ready to do straight after harvest?
In brief: Spraying weeds immediately after harvest is fairly common practice. Weeds present may be close to maturity or fresh germinations of summer-active weed species.
The details: Some growers get in early with knockdown herbicide applied under the cutter bar when swathing barley or canola. Consider using the double knock strategy, heavy grazing pressure and possibly a soil residual herbicide that is compatible with your planned crop rotation. Pay particular attention to any weedy patches identified before or during harvest. Stopping seed set at every opportunity is the crux of an effective weed management program.
Give some thought to what might be the underlying cause of weedy patches – fixing problems such as pH and soil nutrition imbalances, waterlogging and spray practices that routinely deliver low doses of herbicide.
Central NSW growers investigate IWM options
Having completed a two-year demonstration of chaff decks with investment from the GRDC, Tim, along with cropping officers from adjacent LLS regions, are capitalising on the interest in integrated weed management tactics to counter the insidious rise of herbicide resistance in weeds.
“Annual ryegrass is one of the main weeds causing growers concern in-crop,” he said. “There is known resistance to Group 1 [A] and 2 [B] herbicides, and there are strong indications that glyphosate resistance is evolving on some farms.”
Tim Bartimote, Local Land Services (LLS) in Dubbo, says many grain growers in the Central West region of NSW are keen to see the benefits of integrated weed management tactics demonstrated in their area.
Harvest weed seed control has been commonly practiced in the region for many years, primarily as narrow windrow burning or simply broadacre stubble burning. Tim says there is a definite shift in interest toward technologies such as impact mills, although the price of these machines is a barrier to immediate and wide-spread adoption.
“Through discussions with grower groups we found that a few growers had moved into using chaff decks and chaff-lining, but these options were not well-known to others in the area,” says Tim. “We decided to demonstrate chaff decks, which are less expensive than impact mills and are well-suited to the controlled traffic systems used on a few properties in the region.”
The two growers who demonstrated the use of chaff deck systems both identified resistant ryegrass as their main weed target for harvest weed seed control.
“At the demonstration site at Parkes, the ryegrass population was evenly spread across the paddock at a density of 26 plants per metre square,” says Tim. “For the purposes of monitoring the effect of the chaff deck operation, we chose four sites within the paddock and found 4, 19 and 9 plants per m2 away from the wheeltracks and 68 plants per m2 on the wheeltracks.”
“This clearly demonstrated the shift of ryegrass seed from being spread across the paddock to being concentrated on the wheeltracks where seedlings can be controlled with other tactics as required.”
Chaff decks help concentrate the weed seed onto the wheel tracks during harvest.
At the second site, near Gilgandra, the weed population was found concentrated in patches. Tim and the grower, Daniel Volkofsky, GPS-marked sites within the paddock following the 2020 harvest and will monitor the shift in weed density over the next few years.
The growers used both commercial and home-made chaff deck systems in the demonstrations and found both options were effective. In addition to the traditional use of HWSC in winter crops, Daniel also tried using his chaff decks in a sorghum crop but ran into trouble with blockages on the leading edge of the baffle plate. Some growers have added cameras to help monitor stubble flow over the baffle plate and pre-empt blockages.
Tim says the LLS team wants to achieve a ‘weed management legacy’ from the investment of GRDC funds in the region.
“One of the outcomes of the GRDC-funded project was to build a network of growers with experience using different tactics in their integrated weed management programs,” says Tim. “We are now able to direct interested growers to speak to and visit growers in their region who can talk to them about what they have tried and what has worked well for them.”
“Some of the growers who have manufactured various harvest weed seed control devices on farm are willing to share their low-cost designs with others who are not ready to invest in the commercial models. There is also a pool of experience when it comes to the modifications to baffles and chutes required for different header makes and models.”
HWSC is one of the WeedSmart Big 6 tactics that under pin integrated weed management programs across Australia. Within each of the tactics growers are implementing a range of different methods that suit their own systems to keep weed numbers low.
Tim says they are capitalising on the interest generated through the project to now test and compare the efficacy of a range of pre-emergent herbicides on the market.
WeedSmart podcast with Tim Bartimote
Regional Update – Tim Bartimote, LLS NSW
Over the last two years, Tim has been working on a chaff decking paddock demonstration project which has GRDC investment.
Tim provides us with an overview of what this project is all about and gives us a regional update for his region.
Video on chaff deck project
GRDC IWM handbook
Weed management options during harvest article
Why chaff decks are a great option for harvest weed seed control
WeedSmart Southern Extension Agronomist, Greg Condon, who is a big advocate of chaff decks, joins us to give us some answers!
We also hear from Northern Region grower, Chris Berry. He has had a chaff deck for a number of years and while he likes the concept of the mill, is sticking with the chaff deck for now.
Effects on paddock from using a chaff deck. Photos supplied by podcast guest, Chris Berry.
Our next Regional Update will come out next Monday and we’ll be hearing from Norther Region expert, Tim Bartimote. Tim is a Senior Land Services Officer in the Cropping division for NSW Central West Local Land Services.
Over the last two years, Tim has been working on a chaff decking paddock demonstration project which has GRDC investment.
We’ve got great content on the WeedSmart website for you to check!
Make sure you check out our latest Ask an Expert. It looks at how you can maximise grass weed control using hybrid canola. EPAG Research agronomist, Andrew Ware provides the answers. Read it here.
Also, don’t miss our latest Case Study on the Single family, based in Coonamble, NSW.
We also hosted a webinar last week with WeedSmart Southern Extension Agronomist Chris Davey & ICAN’s Mark Congreve. They looked at considerations for pre-emergent herbicides with dry sowing.
You can watch it here.
Esperance growers using chaff decks and chaff lining
Ten growers from the Esperance region of Western Australia who have adopted either chaff lining or chaff tramlining to help manage weeds have provided insights into their experience with these harvest weed seed control tactics.
Each grower spoke to Planfarm Agronomist, Nick McKenna, who documented their experience as part of a GRDC investment into the practical adoption of HWSC in the area in 2018.
Adrian Perks – Esperence grower using an EMAR chaff deck system for harvest weed seed control.
Nick says the growers all felt that they needed to use HWSC tactics to stay ahead of the weed pressure on their farms. One grower indicated that he would need to return to a mixed farming operation if he did not take action to reduce the weed numbers in his farming system.
“Several growers in and around Esperance had used narrow windrow burning and chaff carts in the past but had found it was often difficult to get a clean and safe burn on the residue, either because summer rain had made them too damp, or because the risk of fire escaping meant it required too much attention to burn safely,” he says. “Changing to chaff lining or chaff tramlining was an easy decision for these growers because there is no further effort required after harvest to get a kill on the weeds.”
Experience with chaff decks
The chaff lining system involves dropping a narrow line of chaff, including weed seed, behind the harvester. A chaff deck directs the weed seed-laden chaff into the permanent wheeltracks in a controlled traffic system. In both systems the chaff is left undisturbed.
Two of the ten growers interviewed were using the chaff lining system and eight had installed chaff decks on their harvesters. Each grower was satisfied with the results they were getting with the system chosen and there were few differences between the two systems.
“The two growers with chaff lining chutes had both built their chaff chutes themselves at minimal cost,” says Nick. “One person had moulded plastic chutes with a hot air gun and some tek screws and the other was made of metal sheeting. Both were attached to the harvester with pins and R-clips, making them easy to drop off to access the rear of the harvester. The total cost for materials and labour was about $1000.”
Chaff decks are a more expensive option – usually around $15,000 to $20,000 when fitted to new harvests. The commercially available chaff decks have two conveyor belts running at an angle to the harvester to deposit the chaff onto the wheeltracks. Installation on the harvester involves moving the chopper a fair way back to make room for the chaff deck. None of the growers Nick spoke to had experienced any operational problems with their chaff deck systems.
“One grower had made his own chaff decks specifically for John Deere S670, S680, S690 harvesters,” says Nick. “His system had two conveyors running across the back of the harvester, and did not involve as much modification work at the back of the harvester. It looked to be a simpler system, and cost about $13,000.”
Chaff decks deliver the weed-laden chaff onto the harvester wheeltracks.
The growers Nick spoke to all considered annual ryegrass to be their main weed. When using chaff decks the growers had observed greater germination of weed seeds on the high traffic wheeltracks, compared to the low traffic wheeltracks.
“Growers using chaff chutes said that very little grass germinates in the chaff lines,” says Nick. “I think this was partly because there is very little seed soil contact in the fluffy chaff left in chaff lines, and the chaff lines seem to do a good job of shedding water.”
“Clearly it is not essential to have a full controlled traffic system in place, but it is best if the harvester runs on the same tracks each year,” he says. “Some might consider that having no disturbance and very little germination is better than having weeds germinating on a portion of the wheeltracks; but either way they are concentrated and not spread across the whole paddock.”
When it came to seeding, none of the growers had run into difficulties when seeding through chaff lines. Some growers were running disc units either side of the chaff to minimise disturbance of the chaff and maximise the crop competition, so that the crop would suppress any weeds that did germinate.
“One advantage of the chaff deck is that the quantity of chaff is split between the two wheeltracks rather than all going into the one chaff line,” says Nick. “The growers all said that using a chaff deck or chaff lining allowed them to sow early with confidence, knowing they wouldn’t have an excessive number of weeds germinating in-crop.”
Those using a chaff deck observed that the ‘carpet of chaff’ on the wheeltracks significantly reduced the amount of dust generated during spray operations, giving them better coverage behind the boom, especially in hot conditions. In the day or two after rain the chaff can cause wheel slip during seeding on some soil types.
The experiences of these ten growers are documented in ‘Investigating the harvest weed seed control tools chaff lining and chaff tramlining (chaff deck) in the Esperance area – Grower case studies from the Esperance Port Zone’. The project was an initiative of the Esperance Port Zone Regional Cropping Solutions Network and the report was prepared by Nick McKenna and Peter Newman, Planfarm.
Nick McKenna, Planfarm agronomist visited 10 growers around Esperance, WA who have adopted chaff decks or chaff lining for HWSC.
The growers featured in this report are:
Mick Shutz – EMAR chaff deck
Adrian Perks – EMAR chaff deck
Col de Gussa – chaff tramlining using chutes
Carl Rasich and Henry Barlow – EMAR chaff deck
Steve Marshall – EMAR chaff deck
Elliot Marshman – EMAR chaff deck
Con Murphy – EMAR chaff deck
Mark and Hayley Wandel – chaff deck (continuous conveyor at 90 degrees to the direction of travel)
Patty Barber – chaff line (metal chute)
Mic Fels – chaff line (plastic chute)
Does chaff in a chaff line suppress weeds?
with Annie Ruttledge, Weeds researcher, DAF, Queensland
In the wake of rapid adoption of chaff lining, the newest harvest weed seed control tool developed by Australian farmers, a substantial research effort has been made to validate the efficacy of this practice.
Chaff lining involves depositing weed seed-laden chaff in a narrow line behind the header. Some growers using this practice have suggested that as the chaff in the chaff line rots away, much of the weed seed also decays in the process. Researchers working across the northern grains region have now gained a deeper understanding of what happens to weed seed in a chaff line.
Dr Annie Ruttledge, DAF Qld weeds researcher has been investigating weed emergence from chaff lines.
Department of Agriculture and Fisheries, Queensland weeds researcher Dr Annie Ruttledge and several collaborating scientists have been looking into different aspects of weed seed decay and weed suppression in the chaff line.
“Non-herbicide tools like chaff lining are very important to help manage the onset and spread of herbicide resistance in weeds,” says Dr Ruttledge. “The idea with harvest weed seed control tactics is to collect any weed seed present at harvest height, usually above 15 cm. With chaff lining, these weed seeds are deposited in a narrow line of chaff behind the harvester.”
“Burial in the chaff line can suppress emergence in some weed species, but it does not guarantee that no weeds will emerge from chaff lines,” she says. “Harvest weed seed control tools like chaff lining and chaff tramlining concentrate the weed seed into confined zones where emergence can be monitored and action taken as required, without treating the whole paddock.”
Chaff lining (and chaff tramlining) deposit weed-laden chaff in a narrow line behind the harvester or directed onto the tramlines.
Does the chaff line suppress weed emergence?
Short answer: Yes, if the weed seed is buried deeply enough in the chaff. Many weeds in no-till and reduced-till farming systems prefer to germinate on the surface where there is plenty of light.
Longer answer: Our trials investigated the effect of chaff on germination rates of annual ryegrass and common sowthistle. The sowthistle seed was more readily prevented from emerging than annual ryegrass seed, probably due to the different requirements of the species for light. Maximum suppression of annual ryegrass emergence was achieved with a chaff load of 42 t/ha, which can be feasibly produced in a 3.5 t/ha cereal crop. In contrast a chaff load of just 12 t/ha of wheat chaff was sufficient to suppress emergence of common sowthistle seed.
Work done by our collaborator Dr John Broster, CSU found that chaff from cereal crops generally provided better suppression of annual ryegrass compared to canola and pulse chaff. For all chaff types the higher the rate per hectare the better the suppression.
One of the experiments involved determining the level of chaff required to effectively suppress emergence of annual ryegrass and common sowthistle.
What’s the difference in suppression in chaff lines compared to chaff tramlines?
Short answer: Chaff tramlining effectively halves the amount of chaff in each line, potentially reducing the suppressive potential of the chaff.
Longer answer: Placing a single line of chaff behind the harvester (or directing all the chaff from a chaff deck into one tramline) maximises the amount of chaff and therefore the level of weed suppression. Different crop types, sowing rates and crop yield all influence the quantity of chaff produced.
In addition to looking at suppression of emergence, we looked at weed seed decay under field conditions. In these trials there was no evidence that weed seeds rotted more rapidly in a chaff line than on the soil surface. However, we expect that environmental conditions play a large part in weed seed decay so the results could vary according to season, with more rotting likely in a wet year than in a dry year. The depth and persistence of chaff cover and the type of weed species are other factors that would influence seed persistence in chaff lines or chaff tramlines.
Harvest weed seed control tactics aim to collect weed seed at harvest and concentrate it in a small zone where weeds can be targeted at a fraction of the cost of whole-paddock treatments.
What are the options for treating the weeds in the chaff line or tramlines?
Short answer: Farmers are leading the way with practical solutions to manage weeds along chaff lines and chaff tramlines.
Longer answer: Some growers use an optical sprayer or a boom with nozzles only operating on the chaff line or tramlines to apply a mix of herbicides that may be too expensive to apply to the entire paddock. Weed seed that is collect at harvest and placed in the chaff line, may have survived in-crop herbicide applications and may be herbicide resistant. Susceptibility testing can help identify herbicides that can provide effective control.
Non-herbicide options are to wait for germination and chip or trample the weeds. In a mixed farming operation, sheep can graze the chaff lines rendering most of the weed seed unviable, and the sheep will benefit from an additional feed source.
Growers who have been using chaff lining and chaff tramlining for several years report that the high concentration of weed seed leads to a high level of competition between the weeds and this is compounded with competition from the following crop. Over time, seed set reduces and any weed seed produced will be collected and returned to the chaff line the following year. When chaff is deposited on the wheeltracks, weeds that emerge face dry, compacted conditions and are often subject to frequent passes with heavy machinery.
This chaff tramline was sprayed out using a shielded sprayer.
Does it matter if I use a draper or a stripper front?
Short answer: No, not in terms of amount of weed seed harvested, provided you set up and operate with weed seed collection in mind.
Longer answer: Our collaborators Dr John Broster, Dr Michael Walsh and Annie Rayner conducted trials with stripper and draper fronts at two trial sites. The results at one site showed that it is possible to achieve the same level of weed seed collection with the two harvester front options. At the other trial site, the stripper front was not as effective as a result of wider row spacing, higher operating height and faster operating speed compared to the draper front at the same site. The key to success with chaff-only harvest weed seed tools is getting the weed seed in the front and effectively separating the weed seed and chaff from the straw component. The WeedSmart website provides practical information about setting up different harvesters and operating them for effective harvest weed seed control.
Bear in mind that a stripper front will generate a lot less chaff than a cutter type front, and so this is likely to influence weed suppression and the rate of weed seed decay.
Setting up harvesters to capture weed seed in the chaff
Getting weed seeds into the chaff fraction
Separating the chaff (including the weed seeds) from the straw is a great way to retain more crop residue at harvest. There are several harvest weed seed control (HWSC) systems that manage just the chaff, including chaff decks, chaff carts and chaff lining. All these systems rely on the weed seed entering the front of the header and then being captured in the chaff stream.
Chaff lining – new, cheap, simple [but not fully tested]
Chaff lining is a new harvest weed seed control method that has sparked incredible interest from growers throughout Australia. Similar in concept to the chaff deck system (called chaff tramlining), chaff lining places the chaff fraction directly behind the harvester rather than on the CTF tram tracks.
It is a grassroots grower solution to HWSC that is cheap to try and seems to be a very effective tool. Essentially weed seeds are collected at harvest and dropped in a narrow line behind the harvester. There is no burning required and all the straw is spread behind the harvester so there is very little loss of ground cover.
Getting started involves the construction of a simple chute that is then fitted to the harvester. The chaff lining chute can be used in all crops and does not affect harvester operation. Like all harvest weed seed control methods, the harvester must be set up and operated, correctly to ensure the maximum number of weed seeds enter the front of the header and are contained within the chaff fraction.
Below are a number of videos and farmer case studies showing how to implement chaff lining. This method of HWSC is well suited to controlled traffic farming but it can also work in non-CTF systems provided the harvester runs in the same lines for a few years in a row.
Grower case studies
Mic and Marnie Fels have developed a farming system where herbicides are used to back-up their cultural practices, rather than the other way around.
Mic Fels has used a modified version of chaff tramlining as their harvest weed seed control strategy. The idea is that the chaff component is funneled into a narrow strip in the middle of the CTF runs behind the header.
In a controlled traffic system this means that the weed seeds collected through the header are concentrated into the same zone every year and any seeds that germinate through the mulch are subject to the full force of crop competition. Similar to the experience of growers using a chaff deck to channel the chaff into CTF permanent wheeltracks, Mic finds that the chaff and the weed seeds simply rot away and there is no need to burn the chaff to gain the benefits of this weed control measure.
Daniel (left) and David Fox are pleased with the chaff lining chute they have introduced as a harvest weed seed control method on their Marrar farm near Wagga Wagga.
Marrar farmer Daniel Fox is chasing higher yields across his 2100 ha cropping program while also driving down weed seed numbers. For a few years Daniel has been adding components to his system to conserve moisture and keep herbicide resistant weeds at bay.
Having used narrow windrow burning for a few years and seeing the benefit of capturing seed from late germinated weeds at harvest, the Foxes have now built a chaff lining chute for the header and are delivering the chaff component, including weed seeds, into a 250 mm chaff line in the middle of the 12 m CTF lap. This maintains most of the crop residue evenly across the paddock and avoids the need for burning. “Having the weed seed concentrated in a narrow band reduces the amount of seed that germinates and also reduces the chance of weed seed being buried and ‘stored’ underground at planting now that we are using a disc seeder,” says Daniel.
Setting up harvesters to capture the weed seed in the chaff
Andrew Boultbee, WA
Grazing chaff heaps solved two problems
For many growers burning crop residue to kill weed seeds collected at harvest goes against the grain. Along with the loss of nutrients and ground cover there is significant risk, stress and discomfort associated with burning, even in autumn.
Andrew Boultbee wanted to stop burning chaff heaps. His solution: first graze the chaff heaps, then lightly scarified before seeding right across them.
Andrew and Marjorie Boultbee run a predominantly cropping operation near York, Western Australia, with land they own and lease spread across their district. As annual ryegrass became increasingly difficult to control with herbicides the Boultbees adopted narrow windrow burning as a harvest weed seed control method. They soon saw how effectively this technique drove down weed seed numbers on their farm and decided to invest in chaff carts.
Andrew has seen many growers in his district adopt the use of chaff carts only to stop using them because of the costs and dangers associated with burning the heaps. “We soon found that burning the chaff heaps consumed all our attention and the smoke was unpopular with our neighbours,” he says. “Having properties spread out also caused logistic difficulties and with the heaps smouldering over several days we had a few close calls and sleepless nights.”
To keep the weed control benefits without all the problems Andrew and Marjorie decided to stop burning and to start using the chaff heaps as a feed resource for their sheep over summer.
Andrew has found canola and wheat chaff heaps to be very effective for weed control, even if the heaps are not burned. He allows sheep to graze on the heaps first which makes use of the feed resource while also knocking down the heaps to allow him to seed through them the following autumn. This works very well in canola however Andrew has found that running the scarifier lightly along the cereal heaps prior to seeding helps to spread the heaps more and minimises the chance of blockages at planting.
“The sheep eat down and flatten the canola heaps to the point where we can pass through with the seeding equipment and the crop grows through the remaining residue,” says Andrew.
The cereal chaff heaps are also well grazed, however Andrew always runs a scarifier along the row of heaps, knocking them down to about 30 cm in height. Doing this at right angles to the sowing direction means the seeder is able to seed through the chaff zone without blocking up.
“It is important to seed across the line of chaff heaps, not along them,” he says. “We make a habit of creating the heaps in a line across the paddocks at harvest.”
It takes a couple of years for the heaps to disappear altogether and return to full production but the heaps cover only about 1 per cent of the total cropping area. Once the heaps have disappeared there is a noticeable increase in the crop production in those patches, more than compensating for the small loss of production in the first year.
“The remaining residue in the 30 cm deep cereal chaff layer slowly composts during the winter rains,” Andrew says. “Two years after grazing a chaff dump we can notice the difference in that part of the paddock, with stronger crop growth and few weed issues.”
The Boultbees also choose crops and cultivars that they are confident will perform well within their weed management program. Andrew says they look for cultivars that are high yielding, very competitive in the early growth stages and have hard grain that is not damaged by the harvest settings that remove the most weed seeds.
“It pays to set everything up well before attempting to use harvest weed seed control tactics like chaff carts,” he says. “The paddocks must be free of rocks so that there is no impediment to cutting low to the ground and the header must have sufficient power and the correct settings so that weed seeds are taken in the front and end up on the sieve.”
Cutting low is particularly important for soft-seeded weeds like annual ryegrass that do not stay dormant in the soil for many years. Andrew says that leaving low growing or lodged weeds in the paddock in the first year effectively selects for the trait that exposes the weakness of this weed control method.
“It is important to harvest as low as possible right from the start and to have other strategies to deal with weeds that ‘survive’ collection,” says Andrew. “The next step is to make sure the header is set up for optimal performance and to collect as much seed as possible in the chaff.”
It is important to run at high rotor speed and to open the back of the concave up so that seed and straw is efficiently separated. The harvester needs to have the capacity to handle the increased amount of straw and must be set up so weed seeds end up on the sieve and not out the rotor. Andrew also avoids harvesting on cold damp nights where separating the harvested material efficiently is more difficult.
Annual ryegrass and wild radish no longer dictate the Boultbee’s cropping rotation as they once did. The chaff carts keep weed pressure low and allow the Boultbees to take advantage of seeding or marketing opportunities for their crops, with spin-off benefits for their sheep enterprise.
Australian Herbicide Resistance Initiative leader of communications, Peter Newman, says chaff carts capture about 75 to 85 per cent of annual ryegrass seeds and 85 to 95 per cent of wild radish seeds that are present in a crop, without slowing harvest operations.
In a cost comparison of harvest weed seed control methods, WeedSmart estimated that running a chaff cart, including the cost of nutrient removal, costs $14/ha (assuming 2000 ha wheat at 2 t/ha), or even less is a second-hand chaff cart is used.
In Andrew’s situation there is less nutrient removal costs and less costs associated with burning. He identifies rock-picking the paddocks as one of the major costs in his operation but estimates the cost of running the chaff carts is only $8/ha.
A few years after grazing, improved growth and crop productivity can be easily observed with the chaff heap zones growing larger crops.
Better results in barley
Barley crops play an important part in the Boultbee’s weed management program. Andrew chooses the most competitive barley varieties available to suppress weed germination and growth in-crop. When sown on 260 mm row spacing the tall dense stand lessens lodging in the annual ryegrass, keeping it erect and protecting the seed heads from shedding in the wind.
By swathing the barley they introduce more diversity into the rotation so that every few years each paddock will be cut early rather than later. Barley windrows maintain their shape well and are easy to pick up with the header. There is less shedding of barley grain and weed seed due to the early swathe timing.
“Swathing barley means there is a greater proportion of the cropping area that is cut early,” says Andrew. “With harvest potentially extending through to the end of December the weeds have quite a long time available to mature and shed their seed and so evading capture through any harvest weed seed control measure.”
Then graze and burn in-crop
There are some challenges that arise when barley chaff heaps are not burned. Barley chaff heaps are prone to thatching, which helps protect seeds on the soil surface from getting wet and composting during winter.
“Even after grazing, the soil under the chaff heaps stays dry enough to preserve both barley seed and weed seeds,” says Andrew. “Volunteer barley growing in our wheat crops became a problem that we had to solve and so we have tried in-crop burning of barley chaff heaps in winter.”
From their previous experiences with narrow windrow burning and burning chaff heaps, the Boultbees knew that burning was an effective way to drive down weed numbers quickly but they did not want to go back to the traditional autumn burning method.
“We are seeing good results from in-crop burning of barley chaff heaps when the winter crop has reached the mid-tillering growth stage,” Andrew says. “Unlike burning chaff heaps before sowing, these in-crop burns are very safe, with virtually no risk of escape. Because of the minimal risk involved, one person can easily set fire to heaps across 1000 ha in one day.”
The small fires are well contained and burn out within a day or two rather than continuing to smoulder for several days. Burning in winter makes it easier to predict the wind and Andrew takes the wind direction and location of their neighbours into consideration when burning. “There is no stress or urgency associated with burning in winter and there is much less smoke,” he says.
The Boultbees are using the same idea in high weed density wheat paddocks and Andrew thinks it could also work well in paddocks with a high burden of wild radish in canola.
In-crop burning of the barley heaps after grazing is very safe and has proven to be very effective in destroying the weed seed that can evade grazing and composting.
Extracting the feed value from chaff heaps
Grazing the chaff heaps over summer fills a feed gap for the Boultbee’s 3000 sheep, and has lifted the lambing percentage of the flock to over 100 per cent—quite an achievement for Merino ewes.
The ewes are put in to graze the canola heaps first and on mating they are moved onto the barley heaps. After mating the ewes are moved onto the wheat heaps where they will stay until planting. Once the lambs are weaned they remain on the cereal paddocks with access to barley in a lick feeder to finish them.
The grazing value of the chaff heaps enables the Boultbees to run more sheep over summer and the sheep do better than those that don’t have access to this resource. Andrew says that there is an opportunity to use the chaff in a lot-feeding situation but he has not done this as yet.
Sheep selectively graze the most digestible portion of the chaff heaps including fine leaf material, whole and broken grain and weed seeds, chasing the seeds to the bottom of the heaps. Annual ryegrass, wild radish and wild oats seeds along with some broken cereal grains constitute about nine per cent of the material in the chaff heaps. The sheep seek these seeds and fragments out and spread the remaining plant material as they feed and trample the heaps. The nutrients from the heaps are then redistributed in the paddock via the manure, particularly when the chaff heaps are located some distance from watering points.
To gain maximum nutritional benefit, the Boultbees put the sheep in to graze the chaff heaps soon after harvest, and move them to new paddocks when they have extracted all the feed value from the chaff heaps and stubble. Providing a protein-rich feed such as barley seed in a lick feeder is a great way to finish the weaners very cost-effectively.
The chaff heaps provide an additional feed resource and allow the Boultbees to increase the number of animals they can run over summer, especially in difficult years when there is more small seed left in the paddock at harvest.
There are risks associated with feeding chaff to livestock that farmers should be aware of. High levels of toxins such as the bacterium associated with annual ryegrass toxicity, phomopsin in lupins that cause lupinosis and ergot, which can cause illness and even fatalities in sheep and cattle. Monitoring the health of the animals while they are grazing, and testing for toxicity in the chaff will reduce the risk of disease.
Research has shown that less than three per cent of ryegrass seeds that the sheep consume from chaff heaps will survive digestion. In contrast, almost one-third of ryegrass seeds ingested by cattle remain viable in the faeces.
Research has shown that less than three per cent of ryegrass seeds that the sheep consume from chaff heaps will survive digestion. The sheep shown in this image are not grazing on the Boultbee’s property.
Want more? You can also watch the recording of the webinar where Andrew and Peter discuss the value and practicalities of grazing chaff heaps and stubble.