SOIL amelioration practices, such as deep ripping, leave the soil surface soft and uneven, however a weighted roller, either towed behind the ripper or used in a separate pass, can level the surface to ensure good sowing depth control and crop establishment.
The use of a roller can also break up clods brought to the surface during ripping, conserve soil moisture, improve trafficability and flotation of the seeding bar and firm the surface.
They can also reduce inter-row ridges from the tynes before seeding for better sowing depth control and seed-soil contact to improve seed imbibition and germination.
Independent consultant Wayne Pluske, who leads a Grains Research and Development Corporation (GRDC) investment on soil constraints, said rollers can be classified into five broad types, based on characteristics such as width, diameter, weight, material, teeth and alignment.
"Each type is designed to achieve a specific result and soil finish depending on soil type, moisture content and stubble levels," Mr Pulske said
"Some are bought off the shelf, especially those that are built into the ripper and designed to both assist with ripping and soil surface preparation.
"On the other hand, a lot of independently-towed rollers are home made."
The GRDC project led by Mr Pluske is based on maintaining the longevity of soil constraints investments and increasing grower adoption through extension in the western region.
The project is extending practical findings to grain growers from the five-year Soil Constraints - West suite of projects, conducted by the Department of Primary Industries and Regional Development (DPIRD), with GRDC investment.
Mr Pluske said most growers would compromise and use one roller for all situations, so their 'right' roller is one that worked for most situations on their farm.
"Rollers will not miraculously fix the results of poor soil amelioration, such as when clods have been brought to the surface by ripping when the soil is too dry, or if there was very dense subsoil," he said.
"In these cases, mixing the soil surface first by ploughing, cultivating and even stubble crunching is usually beneficial.
"Growers with clods of densely packed sand, need to break them up or they will hinder seeding, establishment and probably herbicide efficacy."
In general, flatter and lighter rollers, such as a coil packer or drum roller with limited ridging/teeth, are effective on sandier soils.
However Mr Pluske said the exception was on sandy duplex soils where, if the soils are dry and you pull up hard clods, it can be tricky to crush them.
"Because the clods are harder than the surface soil, the roller might push them back into the ground instead of breaking them up," he said.
"The finished surface will look flat but the hidden clods will cause establishment issues and reduced chemical performance.
"An option is to break up the clods with a speed tiller or offset disc first and, if you can, wait until you have had some rain so the clods are easier to break."
In variable paddocks, the key trait to look for is a roller with the ability to change packing pressure as it means it can be used on multiple soil types.
A hydraulic roller, or a drum roller which can be filled to control the weight, are therefore both good options.
But Mr Pluske said adding weight from the ripper frame could cause the tynes to lift up and not rip as deep.
"It becomes a balancing act between ripping depth and keeping enough weight on the roller," he said.
"Some hydraulic rollers have accumulators on their lift cylinders to float the roller, so ripping can be deeper and the roller will not bulldoze the soil."
If erosion is a concern, it's necessary to consider roller weight and finish.
When there is low stubble cover, heavier rollers will do more damage to the standing stubble and increase the erosion risk, whereas with high stubble cover, the roller might just flatten it but leave it intact.
Mr Pluske said the best soil surface finish is a matter of conjecture.
"Rollers that leave a smoother finish, such as a drum roller, are generally thought to make the soil more prone to erosion, while rollers that leave ridges or do less damage to the stubble (such as a coil packer) will reduce erosion potential," he said.
"Specific finishes, for example golf ball dimples or herringbone, are likely to be beneficial for reducing erosion and/or improving water infiltration.
"On undulating surfaces, very wide, rigid rollers can result in uneven packing, as the roller won't always be in contact with the soil along its full length, so in those conditions Cambridge-style rollers, where the rings move individually, are better."
Some rollers are simply unsuitable for certain conditions and bulldozing the soil instead of rolling over it is a clear sign that the roller is either too heavy or too small in diameter.
Rollers that are too small will tend to sink in, pushing the soil in front of them and making ridges out to the side, while rollers that are part of the machine are more likely to bulldoze than towed rollers.
Mr Pluske said the only effective way to see how well a roller is working is to get out and check.
"Signs it is not heavy enough are clods and rocks still on the surface, clods not being broken up and just pushed under the surface or a very uneven surface.
"Sinking machinery, using more fuel than expected or pulling clods back to the soil surface are all signs you should have had more pressure."
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 break clods when set up correctly and if soil moisture is adequate.
TYPES OF ROLLERS
- Drum roller - In its simplest form, a smooth cylinder like an old piece of pipe. Many are hollow so you can add weight (for example water) to make them heavier. They leave a smoother surface than other rollers. Variations have teeth or bars to help crumble clods and push rocks back into the ground.
- Hydraulic cage roller - A cage-type construction which is hollow in the middle. Bars can be parallel 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.
- Coil packer - A coil packer is one coil on an axle. It leaves a herringbone pattern to control wind and water erosion. It also leaves more stubble than heavier rollers.
- Ring rollers - Ring rollers are a series of rings on a single axle. The rings do not move independently. Variations in ring shape (eg U or V) and materials leave a different finish. The rings leave ridges on the surface which help with erosion control and moisture retention.
- Cambridge roller - A Cambridge roller is a series of cast rings on a single axle. Each ring moves independently. It leaves a series of V-shaped tracks that help with wind and water erosion.
