High-horsepower forage harvesters have drastically shortened the time needed to get silage corn and haylage off the field. But time is exactly what’s lacking in packing, said University of Wisconsin ag engineer Brian Holmes.

“Nobody’s going to reduce the harvest rate,” said Holmes at the January Wisconsin Custom Operators’ annual conference in Wisconsin Dells. “So you’d better be prepared at the bunker or pile” to make packing adjustments.

Silage stores best at packing densities of 44 lbs as fed per cubic foot or higher, Holmes said. “But if you increase harvest rate and/or dry matter content and don’t compensate for it, then silage bulk density will likely decrease.”

Someone with a forage harvester chopping at 60 tons/hour, for example, may need only one properly weighted tractor and one minute per ton of packing to ensure the silage is at the right density.

But if he upgrades to a machine that harvests at 180 tons per hour, three packing tractors will be needed to maintain the same one-minute-per-ton packing rate and get the same density, Holmes said. Some custom harvesters are chopping at 300 tons/hour, which would require five packing tractors to achieve that density.

Rather than adding tractors, some producers add weights to existing tractors – “some of which have research behind them and some of which we’d like to have some more information on,” he said.

“Some add front-end weights and wheel weights, put three-point-hitch weights on and possibly put fluid in tires.” He suggested, however, that producers first check with dealers about the maximum added weight their tractors are designed to carry.

Holmes has seen concrete and steel weights attached to the back of a tractor, front-end weights rigged to a tractor blade when there wasn’t the clearance between tractor and blade, and metal plates bolted to tractors to add weight.

It’s getting more common to see industrial equipment on silage piles. They offer heavier packing per horsepower, but some industrial machines don’t have the kinds of transmissions needed for the constant shifting needed in packing silage, Holmes warned.

But to get an accurate picture of how much weight and time you need to adequately pack silage, he recommended using a University of Wisconsin-Extension spreadsheet. It calculates what weight is needed to get specific bunker densities.

“It’s a fairly simple spreadsheet. You need to put in the height of the wall of the bunker, the height of the peak, the delivery rate from the field, the packing layer thickness and the dry matter content. And you are allowed to put in as many as four tractors, the weight of those tractors and the percentage of time that they’re packing. It estimates the bulk density, porosity and dry matter density you are likely to achieve.”

That spreadsheet – there’s one for piles, too – allows producers to try “what-if” scenarios to help determine if the number of tractors,  the weight applied and the layer thickness will allow them to achieve  their density goals.

Download the bunker spreadsheet or the pile spreadsheet.