Soybean vines reached the tops of corn plants last summer in South Dakota State University (SDSU) research aimed at identifying crop blends that improve silage yield and quality.
The soybeans were vining-type breeding lines developed by SDSU plant scientist Xingyou Gu. The corn was MasterGraze, a fast-growing, high-protein brown midrib variety from Masters Choice, Inc., Anna, IL.
Research is just beginning, but silage made from the corn-soybean combination will benefit dairy and beef producers, says SDSU dairy scientist Dave Casper.
“Soybean meal today is still costing almost $500 a ton,” he says. “So if I can produce a higher-protein-content forage that has very good digestibility, I can feed more of it in a ration and reduce my purchased feed cost.”
Gu developed vining soybeans by crossing a cultivated variety with a wild soybean. The Group II genotypes retained several traits of the wild one, including an indeterminate growth habit. The vines are more digestible than conventional soybean plants because the stems are finer.
“Conventional soybeans have a large main stem,” he says. “Many of the carbohydrates stored in a stem can’t be used because they’re not digestible.”
Growing soybeans and corn together increases the amount of nutrients produced on an acre of land and makes more efficient use of the sun’s energy for photosynthesis, says Gu. Also, he points out that soybeans fix nitrogen that can be used by the corn or added to the soil.
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Gu also intercropped the vining beans with a conventional corn hybrid, but Casper thinks the soybean-MasterGraze duo has more potential.
“I’m kind of fascinated with MasterGraze corn because not only is it higher protein, but it also is a very-high-sugar-content corn,” he says. “It never produces an ear, and within 60 days you’ve got really good forage yields.”
In 2012, he grew the corn alone and fed the silage to dairy heifers.
“We got the same performance at much less cost vs. a conventional heifer diet,” he reports.
The silage tested 14% protein, and Casper says soybean silage is about 20% protein. A 50-50 mixture of the two crops should result in silage that’s about 16% protein. That, he says, “is just about meeting the requirements of a growing animal or dry cow, and it’s certainly going to help towards a lactating cow.”
Future research will determine the best planting rates, fertilization levels, etc. The 2013 research was basically a demonstration trial to verify that the soybean vines would wrap around and climb other plants. No fertilizer was applied and planting rates weren’t recorded.
The corn and soybeans were planted in the same and alternate rows. Alternate-row planting worked best. Vining-soybean seeds are much smaller than conventional soybeans, and controlling planting rates was difficult when they were mixed with corn in planter boxes, says Gu.
The crop was planted in early June and harvested in September, when the corn was at optimum maturity – just before tasseling – and the soybeans had green pods.
If the dual crop proves viable, Gu will increase the supply of vining-soybean seed, make it available to farmers and begin to develop varieties with wider maturity ranges. He’ll cross vining soybeans with a tall-growing variety to increase the forage yield, and will add drought resistance and resistance to diseases that are problematic in South Dakota and surrounding states.
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