A properly adjusted forage harvester can save fuel and increase the realizable milk per ton of your corn silage.

Matthew Digman, Assistant Professor and Machinery Systems Extension Specialist

Before getting into the details of forage harvesters, I’d like to point out a bit of historical trivia.  As some of you may know, the feed-rolls, cylindrical cutterhead and blower found in today’s modern forage harvester were pioneered at the Fox River Tractor Company in Appleton, WI. Thus, Wisconsinites should take particular pride when ensuring their harvesters are properly set-up for fall harvest.

The first place to check for proper adjustment on your forage harvester is the feedrolls. The feedrolls have two primary functions. First, they compress the crop into a uniform mat to ensure precise cutting. Second, they meter the crop into the cutterhead to produce a uniform length of cut. Increasing the rotational speed of the feedrolls results in more material entering the cutterhead before being cut. Consequently, the outcome is a longer length of cut. Conversely, decreasing the speed of the feedrolls results in a shorter length of cut. On most pull-type harvesters, this adjustment usually results from changing the sprocket(s) that drives the feedrolls. Your desired length of cut is based on many factors, such as silo type, moisture content, and effective fiber needs of your ration.  Common lengths of cut for whole-plant corn silage are 3/8-inch for harvesters without a kernel processor and 3/4-inch when a kernel processor is used.

It is important to understand the difference between the length of cut setting, what engineers call theoretical length of cut (TLC) and actual particle size of the chopped material.  Average particle size of whole-plant corn silage is often quite close to the TLC because the crop can be fed uniformly into the cutterhead.  The average particle-size of haylage is often quite a bit longer than the TLC because the crop enters the cutterhead in a random, mixed fashion.

Now, on to the cutterhead. The helical shape of the cutterhead evens both the crop flow and the power requirement, cutting the crop from one side to the other against the shear bar (stationary knife), like scissors. As with a pair of scissors, if either the knives or the shear bar is dull, or the clearance between the two is too large, power requirements increase and the cut becomes less uniform.

Consequently, keeping the cutterhead’s knives sharp is an important piece of the harvesting puzzle. There are typically two types of knife sharpening systems – those where the knives are sharpened one at a time and those where the knives are ground as a group by rotating the cutterhead and dragging a stone across the knives.  Knives sharpened individually allow the knife bevel angle to be precisely maintained, but sharpening can be tedious and care must be taken to grind each knife by the same amount to maintain uniform clearance with the shear bar.  It is more common on modern forage harvesters to grind all the knives at once by rotating the cutterhead.   Some machines sharpen the knives by reversing the direction of the rotation of the cutterhead.  This helps maintain the proper bevel angle of the knives.  Each system has its advantages and specific sharpening procedure. See your operator’s manual for your machine’s design.

When it comes to cutting, it is often overlooked that the shear bar is doing a lot more work than an individual knife.  If your harvester has a 12-knife cutterhead, the shear bar is doing 12 times the work of an individual knife. So, it is important that it, too, remains sharp (square) and undamaged. Some shear bars will have designated wear surfaces, usually coated or hardened, while others will consist of a uniform bar of high-strength steel. There will be greater wear on the end of the shear bar where the crop tends to get squeezed or pushed by the helix angle of the knives. Depending on the design of your harvester, a worn shear-bar can be swapped end for end, flipped, or both.  Some forage harvesters have different shear bars for haylage and corn silage chopping.  The haylage shear bar is a little more ductile in the middle so that it can withstand impacts from stones entering the cutterhead without shattering the shear bar.  Corn silage shear bars are hardened throughout for longer life. Consult your owner’s manual to determine what type of shear bar you have and how to configure it for a new cutting edge.

One of the most important adjustments you can make is the clearance between the knives and shear bar.  Have you ever tried to use scissors, grass clippers or hedge shears with poorly adjusted blade clearance?  Frustrating, wasn’t it?  Now apply that experience to the cutterhead and shear bar.  Not only does too much clearance waste power and slow your harvest, but it will also produce long, ragged material in your feed. The shear bar should be adjusted at least after each knife sharpening, but should be periodically checked as knives wear between sharpening. So again consult your owner’s manual to make this adjustment.

Moving on from the process of maintaining your cutterhead, let’s take a look at the kernel processor. Corn fed into an ethanol refinery is finely ground to maximize the surface area available to the enzymes used to degrade the starch into fermentable sugars. Likewise, corn grain fed in corn silage requires that same level of processing to ensure the energy is realized by the rumen microorganisms before passing through the cow. In the past, and in some cases today, corn silage is finely chopped to 3/8-inch to maximize kernel damage and, therefore, energy available in the animal’s diet. More recently, the kernel processor has been employed to realize the nutritional benefits of a longer effective fiber while ensuring the energy from the grain in corn silage is available.  Nutritionists tell us that merely nicking the kernel is not enough for today’s high producing dairy cow.  It is important to break up each kernel and make sure there are virtually no undamaged kernels in the feed.

Proper kernel processor roll gap ensures each kernel of corn is cracked, increasing the energy potential and, therefore, milk realized per ton of corn silage. The kernel processor cracks corn kernels by passing the chopped crop through a pair of serrated, differential speed rolls. The roll gap of your kernel processor needs to be set so that 90% (9 out of 10) of the kernels in a handful of corn silage are damaged. Typically, the roll gap should be between 0.08-0.12 inches. Greater than this and kernels will be pass undamaged. Too tight and harvester capacity will be reduced. A feeler gauge will come in handy for this adjustment. It is also important to check that the rolls have a uniform gap from side-to-side.  When compared to 3/8-inch cut length without a processor, research has shown that a harvester set up with a 3/4-inch length of cut and a kernel processor can ensure more damaged kernels with similar power requirements. You can learn more about assessing kernel damage and kernel processing by visiting the team forage website at http://www.uwex.edu/ces/crops/teamforage .

The blower (crop accelerator) is the second most energy intensive process in forage harvesting, after cutting, amounting to 30 to 40% of the total energy. Properly adjusting each paddle minimizes the energy lost when conveying forage. The old rule of thumb is that the blower should pick up a nickel but leave behind a dime. That might be a good place to start, but be sure to check your operator’s manual for your particular machine. Also check the blower band (wear plate) for wear or damage before heading to the field. Changing a band or wear plate in the middle of harvest can cost time and money.  Some harvesters allow a simple adjustment to slow the blower speed in corn silage, which is easier to blow than haylage.  Slowing the blower will save fuel and increase capacity.

If we take the time to check over our harvesters and properly adjust the various parts of the machines, we can save both time and money throughout the whole process. While I can guarantee that these adjustments are needed and will help, the one thing I can’t guarantee is good harvesting weather. Best of luck in the fields!