- Rollers act to firm and level the soil surface after soil renovation. This is necessary for sowing depth control and good crop establishment.
- Generally, the deeper the rip, the heavier the roller needed to firm the surface afterwards.
- Rolling can increase erosion risk.
- Heavier and more ridged rollers do more damage to stubble.
- A smooth surface is more prone to erosion than a ridged surface.
Soil amelioration practices such as deep ripping can leave the soil surface soft and uneven.
A weighted roller, either towed behind the ripper or used in a separate pass afterwards, helps to:
- break-up clods that come to the surface during ripping;
- push rocks back into the soil (though where there are large rocks, it is best to pick them up before rolling);
- conserve soil moisture;
- improve the trafficability and flotation of the seeding bar (less sinkage and wheel ruts); and/or
- firm the surface (reduce inter-row ridges from the tynes) before seeding for better sowing depth control, seed-soil contact for seed imbibition (water uptake) and plant germination.
Types of rollers
Rollers can be broadly classified into five or six main types, with varying characteristics such as width, weight, teeth and material (eg. rubber versus steel).
These implements are all designed to achieve a specific result and 'finish' on the soil surface, depending on soil type, moisture content and stubble levels.
Some are bought 'off the shelf', especially those that are part of the ripper, and are designed to both assist ripping and leave the surface suitable for seeding into.
A lot of rollers that are towed independently of ripping are home-made.
Depending on the brand - or who you talk to - 'roller' and 'packer' are sometimes used interchangeably, or even together in the case of a 'roller-packer'. In this article, packer is associated with a coil packer and roller is generally used throughout.
1. Drum rollers
Drum rollers are cylinders with either a smooth or ribbed/ridged/toothed surface.
In its simplest form, a drum roller is a smooth cylinder, like an old piece of pipeline. Many are hollow, so you can add weight (for example water) to make them heavier. They leave a smoother surface than many other rollers. Variations have teeth or bars to help crumble clods and push rocks back into the ground. Home-made options include angle iron welded to large diameter steel pipe, either across the pipe or around it (to leave ridges on the soil surface).
Smooth - when to use it:
After sowing peas to remove ridges. Rolling stubble flat to seed into it. If it is all you have and doing something is better than doing nothing.
Ribbed/Ridged/Toothed - when to use it:
To break up clods. For example, a toothed roller can smash stubble and leave a pocked surface.
2. Hydraulic cage roller
This is a cage-type construction that is hollow in the middle. Bars can be perpendicular to the axle or on a slight angle. Pressure can be adjusted with hydraulics. These types of rollers leave a less ridged surface than a coil packer or spring roller. There can be mixed results when ripping to depths of 500mm.
When to use it:
When there are clods on the surface. In dry, non-sticky soils.
3. Coil packer
These rollers have a continuous piece of metal in a coil/spring shape and are, basically, a coil on an axle. They tend to leave a herringbone pattern to control wind and water erosion. They leave more stubble than heavier rollers.
When to use it:
When you only need a light pack and finish and don't have clods on the surface. Probably not heavy enough to use after ripping 300mm or in damp conditions.
4. Ring rollers
Typically, ring rollers are made from a series of rings on a single axle. Rings don't move independently (compared to a Cambridge roller below). There are many variations in ring shape (for example, U, V) and materials that leave a different finish. The rings leave ridges on the surface, which helps with erosion control and moisture retention. Spring rollers have flex - which helps crack clods. Tyre rollers have rubber tyres along the axle.
When to use it:
On sticky and/or stony soil. Tyre rollers suit most soil types and conditions. Can be used on loose sandy soil and sticky soil.
Cambridge rollers have a series of individual rings that can move independently along the axle. Examples include a Cultipacker and Agrowplow® Flexiroller. Each ring moves independently and it leaves a series of 'V' shaped tracks that help to manage wind and water erosion. Moisture is drawn into the 'V'. These rollers are good for working over pugged ground (lumpy ground caused by hooves).
When to use it:
Undulating terrain. Pugged ground.
6. 'Crumble roller'
This is a broad term used for rollers designed to crumble clods. These implements can be solid or hollow, the latter commonly called 'cage rollers', and have lateral bars (for example angle iron or pipe) that are perpendicular or at a slight angle to the direction of travel. Ideally, the bars have enough concentrated pressure to crush clods (like a high heel on a shoe has more downward pressure than a flat sole), but their effectiveness alters with roller weight and clod strength. The more clayey and drier the clod, the more pressure needed to break it. Depending on the brand or who you talk to, 'roller' and 'packer' are sometimes used interchangeably, or even together in the case of a 'roller-packer'. In this article, packer is associated with a coil packer, and roller is generally used throughout.
What roller should I use?
The ideal roller varies with soil type and how you have ameliorated the soil.
Most growers will compromise and use one roller for all situations. The right roller for them, therefore, is one that can work across most situations on their farm.
Rollers won't miraculously fix poor soil amelioration, such as in situations where clods have been brought to the surface because the soil was ripped too dry or where there was a very dense subsoil (that in many cases is best left as a subsoil). In these cases, mixing the soil surface first by ploughing, cultivating and even stubble crunching is usually beneficial.
If you have clods (or 'house bricks') of densely packed sand, you need to break them up, otherwise they will hinder seeding, crop establishment and - probably - herbicide efficacy. Use a crumble roller with lots of spikes or narrow diameter bars, as a smaller surface area has more concentrated pressure to crush the clods.
Larger diameter rollers, or flat rollers, have more surface area in contact with the soil and consequently less pressure to smash clods. The heavier (more clayey) and drier the clods, the harder the clods will be and the more pressure needed to crush them.
In some cases, you might need to break the clods up first with something like a speed tiller or offset disc. Rollers will not break most rocks-they will push them below the ground to reappear later at seeding.
On sandier soils, flatter and lighter rollers are effective - such as a coil packer or drum roller with limited ridging/teeth.
The exception is a sandy duplex soil - if you rip dry and pull up hard clods it can be tricky to crush the clods. The roller might push them back into the ground instead of breaking them (because the clods are harder than the surface). After rolling, the surface might look flat but the hidden clods will cause establishment issues and reduced chemical performance. One option is to break the clods with a speed tiller or offset disc and, if you can, wait until you have had some rain so the clods are easier to break.
If you have variable paddocks, the trait to look for in a roller is the ability to change pressure.
Being able to alter the packing pressure means you can use it on multiple soil types, adjusting as needed.
A hydraulic roller or a drum roller that you can fill to change the weight are good options. However, one consideration when adding weight from the ripper frame is it can lift the tynes up - so you are not ripping as deep. Then it becomes a balancing act between ripping deep enough and getting the necessary weight on the roller.
Some hydraulic rollers have accumulators on their roller lift hydraulic cylinders to 'float' the roller, so ripping can be deeper and the roller does not bulldoze the soil.
Where erosion is a concern, consider roller weight and finish.
Where there is low stubble cover, heavier rollers do more damage to the standing stubble and increase erosion risk. With high stubble cover, the roller might just flatten it but leave it intact. If stubble cover is low in summer/autumn and you rip, don't use a roller until closer to seeding.
The best finish on the soil surface is a matter of conjecture. The general thought is that rollers that leave a smoother finish (such as a drum roller) leave the soil more prone to erosion - and rollers that leave ridges, or do less damage to stubble (such as a coil packer), reduce erosion potential.
Specific finishes (for example golf ball dimples, herringbone) are likely to be beneficial in situations for reducing erosion and/or improving water infiltration. Angle iron rolled around a drum roller has been used to make ridges to reduce erosion.
On undulating surfaces, very wide, rigid rollers can result in uneven packing - as the roller won't be in contact with the soil along the length of the roller. Cambridge-style rollers, where rings move individually, are good for dealing with an undulating surface.
If the ground is wet, tyre rollers, spring rollers, or a ring roller with a U-shaped profile can work well. But if the ripper is leaving wide furrows, you will need a heavy weighted roller. If the ground is loose and dry (with few clods), consider a tyre or drum roller.
Some rollers are too heavy or unsuitable for the conditions.
Bulldozing the soil instead of rolling it is a clear sign the roller is either too heavy or is too small in diameter (see Figure 1). Rollers that are too small for the conditions tend to sink in, push the soil in front and make ridges out the side. Anecdotally, rollers that are part of the machine are more likely to bulldoze than towed rollers.
Currently, there is limited research on ideal pressures for different soil types and conditions. Anecdotal evidence and current thinking is the more weight the better. Go as heavy as you can successfully roll, without bulldozing or making the surface lumpy.
How do you know if it is working properly?
The only way to know how the roller is working is to get out and check. Signs it's not heavy enough are:
- clods and rocks are still on the surface;
- clods are not being broken up, just pushed under the surface (you will need to dig behind the roller to check this out); and/or
- there is a very uneven surface.
Sometimes you only discover that the roller wasn't heavy enough until later.
Sinking machinery, using more fuel than expected, or pulling clods back to the soil surface indicate you needed more pressure.
If the hydraulic roller isn't working as heavily as you thought it would, check with the manufacturer to make sure the roller is set up correctly. In a recent example, the manufacturer found that a critical part of the hydraulics hadn't actually been fitted to the machine.
No roller is perfect for every situation and rollers are not the only way to consolidate soil post-amelioration.
Smudge bars, levelling bars, and even shallow cultivation/stubble crunching can also break clods if set up correctly and if soil moisture is adequate.
However, these will not necessarily get the right soil strength to reduce seeding problems and crop establishment issues, so rolling afterwards is still likely to be beneficial.
GRDC Research Code PLT1909-001SAX
Note: This article was produced as part of the GRDC 'Maintain the longevity of soils constraints investments and increase grower adoption through extension - western region' investment.
Reviewed by Bindi Isbister and Glen Riethmuller, WA DPIRD.