To make good grass silage, producers must first harvest high-quality forage, use the right type and amount of inoculant, and pack and cover the product tightly and properly.

That’s the advice of Dan Undersander, University of Wisconsin Extension forage specialist.

“In either haymaking or silage making, we can never make the product any better,” says Undersander. “The best we can do is preserve what we cut.”

All silages – grass, legume or corn – should be chopped at about 65% moisture. Producers who move from harvesting alfalfa to grass may want to check the dry matter content of grass to avoid cutting it too dry, Undersander recommends.

The pH levels of each of those silage crops, however, should be different. Corn silage should be the most acidic, at 3.8-4.2 pH, and legume silage the least acidic, at 4.0-4.3. Grass should be at a pH of about 4.0-4.2. But in testing-lab summaries that University of Delaware and Wisconsin researchers have analyzed, grass silage’s average pH runs too high – between 4.3 and 4.7, he points out.

“That means we’re probably not getting the fermentation we should in a number of cases. We might be putting it up a little too late and don’t have enough non-structural carbohydrates (sugars and starches) for good fermentation.” Harvesting grasses earlier, at boot stage when they’re leafy and just heading out, should help lower pH to the 4.0 to 4.2 range.

Cut grasses to a 3.5-4” stubble height to promote regrowth and avoid contamination.

Second and third cuttings should be taken every 35-40 days, when grass is 12-15” tall. Cut length should be ¾-1”, with about 15% of the forage longer than 2” for a good scratch factor. Producers should use flail conditioners and make wide swaths so the crop dries quickly. Then they can make silage by the end of the day they cut it, Undersander says.

“The faster you dry it, the faster you shut down respiration and the more carbohydrates you preserve for fermentation,” the forage specialist says.

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Although there are multiple inoculant options that reduce the microorganism growth causing mold and spoilage on grasses, Undersander recommends lactobacillus plantarum. It will preserve crop quality because it promotes a high lactic acid content.

But lactic acid doesn’t prohibit spoilage. So producers losing silage quality due to poor feedout conditions may want to consider lactobacillus buchneri, which encourages acetic acid growth. Buchneri will cause some dry-matter losses and isn’t needed if producers take a foot per day off the face of their bunkers, bags or piles and had packed them well, Undersander says.

“I’d encourage people to pack well and just use the lactobacillus plantarum.”

To evenly spread inoculant onto grasses, apply enough – 100,000 colony-forming units/gram – at the chopper. Then fill bunkers within one or two days to minimize oxygen exposure. If making baleage, wrap bales within three to four hours.

There’s no such thing as over-packing silage, Undersander says. The ideal packing density is 45 lbs/cubic foot. To get it, spread 4”-thick layers and pack with weighted tractors. “Whatever packing tractor you have should have a big cement block on it,” he suggests.

When covering a bunker, pay attention to details. Line walls with plastic to keep air and water from filtering in through cracks. Don’t pack bunkers so the silage slopes toward walls or water will run down into bunkers. Cover with two layers of plastic.

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