Shortening the length of cut and opening up the kernel processor roll gap on a self-propelled forage harvester could save some operators field time and provide their customers with the feed value they want, said Tim Meister, John Deere division marketing manager for self-propelled forage harvesters.

It also allows the cutterhead to do the work it's supposed to — and saves wear and tear on kernel processors (KPs), he told Wisconsin Custom Operators at its annual meeting.

“A lot of people — nutritionists — say, give me 1” length of cut. Then they go to the pit and see kernels, so they tell you to tighten the KP gap down so all the kernels crack. The problem is that the KP is doing all the work — not the cutterhead.”

That also gives a less-consistent product, he added. “It may be better for the chopper to go down a couple of millimeters in length of cut and open the KP up. You would get more consistency, and you might get a longer particle length.

“We have tried it in the field, and the sample doesn't always change. But the machine goes a mile per hour faster.”

Deere researchers shortened the length of cut and opened the KP on one of their machines as well as another brand of harvester. Crop samples were very similar. “All the KPs do pretty much the same work based on the same concepts from 1984,” Meister said.

That study also revealed that, when the KP was “crunched down to get all of those kernels,” only 3% of crop from one machine and 7% from the other came out at the correct theoretical length of cut. “That means that the KP resized 97% of the crop on one machine. Mean particle length was ⅜” on a machine set at ¾”.”

Meister thinks most operators try to adhere to a 19-mm length of cut and around a 2-mm KP roll gap. They should also take into account the moisture level of the crop and whether the settings are causing “juicing,” or squeezing out nutrients.

“Then you have to advise the customer that the KP is too tight. They may be sticking to that rule of 19 and 2, but do they want to lose nutrients?”

One of Meister's customers was chopping at 1” (25 mm) and processing crop through a 1-mm KP gap. “He was doing about 200 tons/hour with a machine that should be doing 280. We thought he had the KP set too tight — he was working the machine too hard in the wrong place. We took the KP up to 2 and the length down to 21.

“The customer said that his dairyman wouldn't accept this. So we went to the pit with the load and asked him (the dairyman), ‘What do you think?’ He said that the sample looked like the last load's crop.

“The difference to the custom operator was that the machine went half a mile an hour faster, which was about 75 tons/hour. So he improved his income by changing the settings.

“There are hundreds of crop conditions, moistures and varieties, but we want to adhere to one setting? This doesn't provide the best results.”

It doesn't work all the time, Meister said. He advised operators to check settings to optimize their machines — and keep customers happy.

Most forage harvesters with KPs are set to ¾” (19 mm) length of cut, agrees Matt Digman, University of Wisconsin ag engineer. The roll gap on a KP should be set so at least 90% of kernels in a handful of corn silage are damaged. That means 0.08-0.12”, or 2-3 mm.

“Greater than this and kernels will pass undamaged. Too tight and harvester capacity will be reduced.”