Oxygen-barrier films used to cover stored silage can improve dry matter recovery at the top and near bunker walls by as much as 15 percentage units. So says Rich Muck, a U.S. Dairy Forage Research Center researcher in Madison, WI.

But traditional white plastic tarps held down by tires can do a good job, too, he says.

“I know the product works very well,” says Muck of Silostop, a silage-covering system he has studied for more than five years. “But I also know that you can get a long ways just by using white plastic, putting it down the bunker sidewalls and bringing it over the top.”

The key to both methods, it appears, is having good-quality plastic and a tight seal, he adds.

Muck has completed several studies of the two-step Silostop system, manufactured by Bruno Rimini Corp. It uses a clear polyethylene plastic film treated to keep oxygen from silage. Only about 1.8-mil thick, the film is spread down bunker sidewalls and overlapped at the top once silage is packed. A woven, plastic reusable tarp is placed on top of the overlapped film and held in place by 3’ bags filled with pea gravel.

Compared with the traditional 6- to 8-mil white polyethylene plastic secured with tires, Silostop recovered 17 percentage units more alfalfa dry matter and 13 percentage units more corn silage within the top 6” and about 2’ from bunker walls, Muck reports.

The woven-mesh tarp provides ultraviolet protection, is strong enough to resist damage from rodents and other animals and “really helps to hold the plastic film tightly against the crop. I would say it does a better job than tires do in terms of providing a good seal.”

The downside is that the tarps have to be reused to justify the system’s cost, which is about double that of traditional silage coverings. “The tarps have to last about five years in order to make a reasonable payback on the system. We’ve been reusing some of those tarps for maybe five years, and they hold up.”

But preserving the tarps isn’t convenient for producers, he says. “When you get a foot of snow or so on top of your silo and have to clear the snow off to save the tarp, it starts to become an issue.”

So Bruno Rimini Corp. has come out with a one-step plastic film that Muck is studying. “We compared its film with just gravel bags holding it in place vs. regular white plastic and tires. That didn’t turn out to be quite so favorable.”

Plastic was laid down bunker walls using both methods, so Muck mainly studied what happened on the tops of the bunkers.

“We didn’t see any benefit in terms of improved quality,” he says of the one-step product. “The reason is because, with just that white plastic film being held by gravel bags, we were seeing it blow around in the wind. So even though you can have the highest-quality film in terms of keeping oxygen out, if that plastic film moves around a lot in the wind, it can act as a bellows and draw oxygen under the edge of the cover.

“The gravel bags weren’t enough to hold it tightly against the crop.”

Rodent damage can be more significant in bunkers covered with the one-step product, Muck thinks. “If you have a small hole in one portion and have tires covering everything up, the tires keep damage localized. But if the whole sheet moves up and down and you have a hole, that can move oxygen to a wider area.”

Muck just started a second study of a new formulation of the one-step film.

“We’re using that film with gravel bags but also with tire sidewalls in between to help hold the film in place. We’re still using gravel bags around the seams and walls. Then we have another treatment where we’re using a mesh material to help hold the film in place.” Those treatments will be compared to bunkers covered with the traditional covering method and with Silostop’s two-step system.

All four treatments will include plastic laid down the sides of bunker walls, he says. “Our farm manager has become sold on putting the film down the walls. If there’s anything that has come out of this research, it’s that the film down the walls is a tremendous benefit in terms of keeping water out of silage and keeping spoilage down.”

Very little silage should have to be pitched if bunkers or piles are managed correctly, Muck says. The traditional white-plastic-and-tires method won’t give as good of results as Silostop, but will be fairly close.

“With our farms, since we moved to a fairly heavy-gauge (7-mil) white film, that actually improved things quite a bit. But the Silostop system has given another boost and primarily that boost has been to the sidewalls. That’s propelled us to the point where we can say we don’t have silage to pitch except for a bit when we open a silo.”

For a slideshow presentation of one farmer’s experiences with putting up silage in plastic-encased bunkers, go to hayandforage.com, click on Silage Slideshows.

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