You may have never heard of it, or you or your neighbor might already be doing it. Making silage out of soybeans is highly possible, and may be a growing trend in homegrown dairy forage production.
Michigan State University Extension researchers share in this bulletin that soybeans actually were initially used as a forage crop in the United States. And more than two decades ago, University of Wisconsin Forage Professor Emeritus Dan Undersander published advice on utilizing soybeans for hay or silage.
Both of those documents focused on soybean silage as a rescue method to salvage a damaged crop; as an emergency option to address forage shortages; or to utilize prevented planting acres that were planted to a cover crop. But other dairy producers are actively planting soybeans with the intention of harvesting them for forage.
On a recent episode of the “Soybean School” podcast, Jim MacEwen with MacEwen Agricentre, Inc., Maxville, Ontario, Canada explained how dairy producers in his region regularly grow soybean silage. He said the flat, clay soils of eastern Ontario are not conducive to growing high-quality alfalfa, and soybean silage provides a worthy alternative for high-quality, high-protein dairy silage.
“We’re growing a forage crop; we’re not growing a grain crop. That’s a mindset shift we have to make,” advised MacEwen. “That means seeding is more like alfalfa and less like conventional soybeans.”
While solid seeding would be ideal, he suggested 15-inch rows provide a good balance between plant density and the ability to get through the field for fungicide and weed control applications. That fungicide is especially important to prevent white mold, which MacEwen warned will ruin the quality and palatability of forage soybeans because it will cause the stems to die prematurely.
The seeding rate is typically higher than that of grain soybeans. MacEwen said producers in his area typically seed silage beans at 190,000-205,000 seeds per acre.
He said compared to grain soybeans, growers of forage soybeans typically select varieties with longer maturities, ranging from about 2.7 to 3.2. Those longer-day beans will typically grow taller and yield more tonnage, but he said the harvesting window can be fussy.
“One big mistake we make with growing beans for silage is the harvesting of them – we wait way too long,” MacEwen advised. “Now that we’ve learned more, we can pretty much set our calendars by it – around August 20-25 is when we are cutting our beans, as soon as the top node is done flowering.”
Harvesting soybeans for silage is a bit of a cross between making hay and making silage. It requires cutting the wet plants and laying them down to dry for a few days before merging, chopping, and blowing into a bag or bunker. The Michigan State advisors recommended a 3/8-inch cut on the chopper.
Whole-plant moisture of about 65% appears to be the sweet spot for optimum ensiling. And like making hay, the cutting and ensiling window is highly sensitive to humidity and precipitation. In terms of yield, Undersander noted soybeans are capable of producing 4 to 5 tons of forage per acre.
Among the drawbacks of producing soybean silage are the fact that the high oil content of soybeans can interfere with fermentation if the crop gets too mature. Careful attention must also be paid to the crop protection products, including any seed treatment used before it went into the ground. Some chemicals are not approved for forage feeding at all; others have prescribed intervals between application and harvest.
Soybean silage is also not especially palatable to cows. This challenge can be remedied by ensiling or feeding it concurrently with a grass forage like corn or sorghum. On its own, it can make up 15 to 20% of a dairy ration without impeding animal intake or milk production, according to the Michigan State researchers.
Changes in soybean genetics also may be encouraging broader adoption of soybean silage. Bill Mahanna, Global Nutritional Sciences Manager with Pioneer Seeds, said the advent of high oleic soybeans creates more useful soybean silage hybrid choices because their fatty acid profile is more conducive to milkfat production. The result would be a more nutritionally valuable silage that could simplify dairy rations with fewer ingredients.
Mahanna added that with these benefits, “soylage” might become a more attractive crop to grow than alfalfa haylage. The only caveat is that oil is deposited late in the maturation process of the soybean, so high oleic soylage would not contain the same oil energy found in full-fat soybeans.
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