Disc Mower or Mower Conditioner?

Earlier in the silage series we looked at the importance of wilting cut grass prior to ensiling. This wilting process starts at mowing but what type of mower should you use to optimise silage quality - straight mowers or a mower conditioner? Most manufacturers offer the option of adding a conditioner to a plain disc mower, but these add weight to the tractor and the price tag - so what are the advantages of conditioners over straight mowers?

It’s well known that as soon as the crop is cut, the available feed value of the crop starts to decline. Well almost immediately. If I’m remembering my school biology syllabus correctly, the gas exchange within the growing plant mostly occurs through the stomata on the underside of the leaf. If the plant is healthy and photosynthesising, and not suffering drought stresses, then these stomata will be open. The gases dissolve into the moisture on the cell walls inside these stomata openings.

So if the stomata are open, then the crop is losing moisture. If you mow in good weather conditions, then we can assume most of the stomata with be open. However the plant will close these stomata once drought stress begins, and this happens around 30-40 minutes after the mower has cut the crop. Once this has occurred, moisture losses - or wilting - will slow down considerably.

 So what is the conditioner trying to achieve?

The aim is to increase the amount of moisture loss out of the crop whilst minimising the in field losses. Early conditioners ,such as crimping and crushing rollers, increased the moisture losses by breaking the cell walls and allowing moisture to escape. The problem with these systems is that the breaking of the plant only occurs at intervals along its length and moisture losses only increase at these points. These systems can also increase the loss of soluble sugars that can also leak out of the crop once the cell walls are broken.

These issues led manufacturers to develop tine or bush conditioners. The tine conditioner works by scraping the waxy layers on the leaf surface and allowing moisture to escape. The scraping can be an action between the machine tine and the leaf but also between leaf to leaf rubbing past each other. This solution can result in greater moisture loss compared to rollers due to an increased area of action on the plant, but it can also lead to high leaf loss in delicate crops such as clovers and lucerne (alfalfa).

This explains the popularity of roller conditioners in parts of the world where legumes are commonly grown. Apart from setting the pressure limits between the rollers, and on some machines the roller speed, there is not much setting up to do. Check the crop coming out the back of the machine and make sure it’s ALL getting conditioned and check the amount of leaf loss on the ground.

Setting up a tine conditioner is a bit more complex. Of course you should always refer to the operations manual for setting up but these can sometimes be of little help in the real world. This results in most machines being adjusted very rarely, if ever, after leaving the dealership. Rotor speed is usually adjusted via a two speed gearbox or drive system, but the aggressiveness of the conditioning has multiple adjustments via the conditioner hood angle.

The action of a tine conditioner is harder to spot in the field than that from a roller.  That’s not to say it’s not as effective – far from it – but it’s not easy to see on the plants in the swath. Using a magnifying glass can help but, as ever, there is no substitute for experience. I would encourage every operator to keep records of the mower setting and cross reference these with the data from the harvester if available, or from the farm records of the incoming silage.

As a rough guide, in general, heavy crops need the hood opened up to allow for more space for the crop to pass through. Young crops, new leys and Italian ryegrass types need more gentle conditioning. Older traditional pastures, tougher grass species and lighter crops need the conditioning action to be ramped up.

But in a heavy crop many the consider the effect to be minimal, however almost the reverse is true, the more crop going through, the greater the effect (within reason). This works due to the different speeds of the material within the hood and the abrasion between the grass leaves. The crop closest to the rotor will be travelling the fastest though the machine. Even so, the grass will never travel as fast as the rotor so there is always abrasion between tine and leaf. The crop close up to the roof of the hood will be slowed by the friction of the metal so this moves slower and becomes abraded by the hood itself. Between these two zones the majority of the crop, is exposed to leaf to leaf abrasion.

So is the cut only mower a machine of the past? Not necessarily. These machines are suitable for mowing crops with high dry matter in the standing plants. The mowers are lighter on the tractor, lighter on the power requirement and lighter on the wallet. But to minimise the losses when making good silage, you should always be using a well set up mower conditioner. 

If you need further information or help on how to wilt your silage, or for any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com