More silage managers are covering bunkers and piles with plastic films, yet many do lousy jobs of sealing them well enough to prevent spoilage and maintain silage quality. Although those aren't his exact words, that's the message Brian Holmes, University of Wisconsin ag engineer, wants to convey.
"They're not always getting it covered as well as they could," says Holmes. "Wherever there are opportunities for air to leak in around the plastic, that's where we have more spoilage going on than you might anticipate."
Sealing plastic at the edges of bunkers or piles is challenging, he admits. "How do you seal plastic to concrete when it comes down next to a bunker wall – so you don't get air and water going through? And if you don't do a good job of sealing plastic where it meets the ground on the silage pile, then you get air getting in under the edge."
Even during feedout, if the plastic isn't held down, it tends to "billow in the wind," and that causes air to suck in underneath the plastic, he says. To keep air out of a bunker or pile while feeding off its face, use tires just taken off the bunker or pile to double up on the weight at the plastic's edge. You may then want to cut excess plastic off the edge so it doesn't get caught in the wind, he suggests.
Distribute a uniform weight across the bunker or pile covers, he says. "We usually recommend covering with tires because they are cheap." But many times, he'll see too few tires covering the plastic to keep it from blowing. To seal well, full-casing or bias-ply sidewall tires should be touching each other, as shown in the photo at right.
"Gravel-filled bags are a fairly effective way to help seal the edges because they're more uniform than tires at that point," Holmes adds. Sand or soil can be piled on the edges to hold down plastic as well. "Even lining your bunker wall with plastic and rolling the wall plastic up on top of the silage and overlapping it with a top cover is a way to seal bunker corners, oftentimes referred to as 'shoulders.' It tends to shed the water away from silage, too." (A silage slideshow of one farmer's way of lining bunkers can be viewed here.)
"On larger storages, where you need to lap two pieces of plastic, use a 4-6' overlap to limit oxygen movement through the joint. Consider doubling up the weighting at that joint to help provide a better seal."
Also take a few minutes each week to check plastic for holes made by rodents, birds or other critters. Patch those holes to keep air out and reduce spoilage, says Holmes.