Types of silage harvesters

What are the different types of forage harvesters?

Forage Harvesters

Forage harvesters are designed to either pick up mown forage from a windrow, direct-harvest standing crops, or both. In the latter case, this is achieved by changing the pick-up mechanism on the front of the forage harvester.

Most forage harvesters on the Australian market are precision chop machines, which are capable of picking up mown forage from a windrow and/or direct harvesting, depending on the front attachment.

There are also a number of forage wagons available. Forage harvesters and forage wagons are discussed in this section.

Flail harvesters

• Outdated.
• Consist of a rotor with several banks/rows of free-swinging flails designed for direct cutting of forage. Some capable of picking up windrowed forage.
• Sucking action of the flails often picks up soil, contaminating the silage.
• Variable chop length – from about 100 to >250 mm.

Double chop harvesters

• Superseded flail harvesters but are now outdated.
• Mown swath is picked up by various flail arrangements on a rotor, and then conveyed to a flywheel type chopper for extra cutting.
• Chop length highly variable, shorter than flail harvester.

Fine chop forage harvesters

• Usually fitted with windrow pick-up front.
• In most models the cutting mechanism is a rotating cylinder with fixed flails that cut the forage against a shear bar.
• Require more power to operate than precision chop forage harvesters for the same throughput (t/hour).

Precision (metered) chop forage harvesters

• Can be fitted with various fronts for harvesting of crops or windrowed forage.
• Available as tractor-mounted, trailed or self-propelled units.
• Forage is delivered into the chopping chamber, at a steady rate, where knives fixed to a rotating cylinder cut the material against a shear bar. Chop length is uniform, and can be altered to suit requirements.
• Contain either two, four or eight knives or banks of knives.
• Can be fitted with ‘cracker plates’ or other devices to further damage grain.

These require increased tractor power to operate.

• Capable of high throughput.
• The most widely used forage harvester.

Forage wagons (self-loading forage wagons)

• Self-loading machines where the forage is picked up from a windrow and harvested into an attached wagon. The chopped forage is unloaded directly from the wagon at the storage site.
• Most wagons have chopping mechanisms that are only capable of producing longer chop length forage of highly variable length. However, there are wagons that have precision chop machines attached which are capable of producing chopped forage identical to precision chop forage harvested material.
• Because harvesting stops during unloading and travelling to and from the storage, work rate is relatively slow. These units are really only practical when the storage site is close to the paddock being harvested.
• Advantage – less labour and machinery is required.

Effect of knife sharpness and adjustment Regular sharpening of the knives and adjustment of the cutter bar is essential. Blunt knives and poor adjustment of the distance between the knives and cutter bar will:

• Increase the power required at the cutting chamber (see Figure 8.2); and
• Result in a less uniform chop length, with an increase in average chop length

Metal detectors

Foreign metal objects, broken machinery fragments and rocks can cause substantial damage to precision chop forage harvesters – chipping and breaking knives.

Large, solid objects can even damage the chopping chamber and knife holders.

Wire picked up during harvest will be chopped into small pieces. Damage to the knives may only be minimal and go unnoticed, but there is a potential health risk to animals that consume the contaminated silage.

Machines can be fitted with metal detecting units, which immediately disengage the feed and chopping mechanism when metal is detected. These units can be a valuable investment, preventing substantial machinery damage and downtime.

Most machines are now fitted with banks containing several knives rather than a number of individually mounted blades. Damage is often confined to one or two smaller knives, which is easier and less expensive to repair.

Grain processors

The high energy levels of maize and grain sorghum silages are due to a high grain content.

Machinery manufacturers have produced a range of add-on equipment that can be fitted to forage harvesters to damage whole grain, increasing utilisation of the grain component by cattle.

These include recutter screens and cracker plates. More recently, larger forage harvesters have been fitted with rollers.

Use of grain processors for maize silage is common in the United States, where the trend is for chopping at longer particle lengths.

However, when the forage harvester is set up to harvest maize with a short chop length, a significant proportion of the grain is damaged without the need for additional processing.

In Australian studies, the grain in maize silage which had been finely chopped (4.2 mm theoretical length of chop – TLC) was well digested by cattle.

There may be a benefit in using grain processors when harvesting grain sorghum for silage. Even at short chop lengths, much of the sorghum grain escapes damage because of its small size.

Reducing chop length or using a grain processor will increase the tractor power required to harvest maize for silage. The additional advantages of reducing chop length .

These advantages will help offset the additional expense.