VIDEO: Pasture Care – Fieldmaster GMM 300 gear mower test

Recently, Brent Lilley had the opportunity to put the new-and-improved Fieldmaster Gearmower Multicut mulcher through its paces, and that he did! The results not only impressed him but had the neighbours talking too.

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I was wrapped when Patrick Murray at Fieldmaster offered me the chance to test the Gearmower Multicut mulcher. This machine is a three-in-one Multicut rotary mulcher/topper/slasher that comes in a range of five widths, from 1.8 to 3m, and is suitable for tractors up to 180hp. I imagine many farmers like me have, at some point in time, used a mulcher, topper or slasher.

We have an original HD-model Flailmaster slasher built by Fieldmaster back in the 70s and it is still going strong. This longevity is a real testament to the brand, as the unit has had a tough life clearing gorse, blackberry, rushes and other rough pasture. These days, the biggest complaint about the original Flailmaster is its width of only 1.5m, which can seem a bit tedious when using larger horsepower tractors.

Fieldmaster has gradually progressed from the Flailmaster, with the new Gearmower Multicut mulcher. In particular, its range of applications has widened, while still retaining some of the principles that make the brand’s mowers simple, reliable and economical.

Machine design

Fieldmaster uses a modular design concept on almost all its mowers, which I think is a brilliant idea, enabling the mower to be configured for a variety of situations and assembled quickly to keep costs low. A robust-looking A-frame headstock, with category-two linkage pins, is bolted onto the deck of the mower with enough pre-drilled holes, allowing it to be flipped then bolted back on, so the mower can be used as a front mower on a front linkage.

The mower deck itself is built using a heavy-duty twin 5mm steel skin, with reinforcing under the deck for extra strength where it is needed while keeping the overall weight down. The sides on the mower use a heavy-duty pressed concave skid on the bottom – 80mm wide and built from 12 mm steel for an extended lifespan and wide ground contact – and bolt onto the deck via four bolts on each side in a slotted hole. A coarse threaded adjuster allows the cut height to be adjusted relatively easily using a scale on the side of the mower. The deck and the skids once again have pre-drilled holes so a variety of extras, such as front or rear rollers, wheels, mulching shrouds, chain guards, etc, can be bolted on to suit individual requirements.

On the 3m three-rotor model I tested, the drive for the mower comes from the tractor through a drive shaft to the main central gearbox, which splits the power to the centre rotor, and through drive shafts to the left and right rotors, which have their own 90-degree oil-filled gearboxes. This is a very simple, reliable, low-maintenance system that transfers the power of the tractor to the rotors with very little losses. However, one key thing I believe is missing here is a clutch or even a shear bolt on the driveline to protect the tractor in the event of some large object being struck.

All the steel on the machine is garnet blasted, treated with a zinc undercoat and finished with an oven-baked powdercoat on the surface to give an extended lifespan.


The selection of blades that can be bolted onto the rotors is the key to the versatility of the mower. The triple-stack blades on the machine I tested are unique to the Gearmower Multicut mulcher (or GMM 300). They use a straight, flat blade in the centre, with two smaller blades above and below which are bolted onto the main blade to create a Y shape to finely chop and mulch the material.

The guys from Fieldmaster suggest that the GMM 300 is ideal for mulching a wide range of materials, including kikuyu, rough pasture and weeds, crop stubble and, as I was to find out, rats tail and rushes, too.

As well as testing the triple-stack blade, the Fieldmaster team also brought along a selection of other blades, which included an extra-heavy axe head flail for use on big scrub and gorse, a thin gold-tipped blade, ideal for clean-cut pasture topping, and a tungsten-coated blade for use in abrasive situations such as vineyards. With only two blade holders on each rotor that use only a single heavy bolt, the blades can be interchanged very easily and quickly.

The test

Finding a suitable location to test the machine, during what many say is the wettest winter in decades, was definitely a big challenge. Most of the kikuyu had been frosted and any area in and around the rushes was a bog – I could barely walk across the ground, let alone drive a tractor through it. So I settled for topping a few odd rushes and some thick rats tail grass, which for those of you that haven’t come across it is a very hardy plant with similarities to tussock. It grows into quite a solid clump and can be up to a foot high when it is under grazed. But with the machine set at a 35mm cut height, this was going to be far from easy.

First, we unloaded the mower from the transporter and set it up on a 6430 John Deere, which I hoped it would be ‘man enough’ for the job at 125hp. The mower runs at 1000rpm and when I dropped it down on the rats tail grass, the tractor certainly knew it was on there. I was mulching on a reasonable slope and had a forward speed of around 5kph going up and about 6kph coming back down, while still doing a good job. I would suggest that anyone thinking about a 3m model would want at least a 120hp tractor, but probably more if you’re planning on mulching heavy foliage or working on hills.

The machine achieved a clean, even cut under what I’d describe as trying conditions. The GMM 300 shore off the clumps of rushes and rats tail grass low to the ground, with the mulching shroud on the back of the machine holding the material under the mower until the triple-stack blades had cut it up very finely. Because the rotors counter rotate against each other, the material is spread evenly across the machine’s width out the back, not like older machines that tend to windrow the material to one side.

The GMM 300 was fitted with a rear roller to help prevent scalping on undulating ground, which worked reasonably well considering the contour, but I still had to lift the mower up on a few occasions.

I wasn’t overly impressed with the rear roller as it blocked up with material a little and it limits the operator’s ability to back into taller plants. However, Fieldmaster does have solution for preventing scalping without a rear roller, offering a concave saucer that bolts onto the bottom of the rotor, allowing the machine to ride over undulating ground on three points. Although I didn’t get to try these saucers out, I can see a lot of merit in the idea.


I was impressed with this machine as it is very versatile and built strong. A standout feature for me is the modular design, which can be configured so that parts operators dislike, such as the rear roller, can be removed and anti-scalping saucers, which I liked the idea of, can be bolted on very simply to customise the Gearmower Multicut mulcher for any specific preference or intended use.

I wasn’t the only one impressed on the day either: a couple of local farmers who showed up to see what was going on commented on what a tidy job the machine was doing and how quickly it could cover the ground to be mulched.

The list price for the machine also surprised me – only $13,500 – which I think is outstanding when considering the fact that rotary mulchers are much cheaper to run and maintain than conventional flail mulchers.

Overall, a good machine with plenty of merit at good price, offering real value for money.

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