Dr. Bill Weiss, Dairy Nutrition Specialist, The Ohio State University
Because of dry conditions, soybeans may not mature adequately to justify harvesting the crop as beans. An alternative is to chop the entire plant and make silage out of it. If harvested at correct stage of maturity and good silage making practices are followed, soybean silage can be a good feed for cattle.
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The crop must contain adequate water for fermentation. The best fermentation usually occurs when soybeans contain 35 to 45% dry matter (wetter silages for bunkers and drier silages for upright silos).
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Excessive fat (oil) in the seeds can inhibit fermentation. Soybeans at the R-6 stage usually do not contain enough oil (6 to 9% of the whole plant dry matter) to cause problems. Under normal growing, R-7 stage beans contain about 10% fat (whole plant) which can cause some fermentation problems, but under drought conditions, R-7 may still ferment adequately. If your soybeans contain much more than about 10% fat, they should be blended with other crops (corn plants) at the time of ensiling.
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Silage must be chopped relatively finely to encourage consumption of stems. A theoretical length of chop (TLC) of 3/8 inch should be adequate, but chop length should be evaluated at the time of cutting. Chop several feet of material and look at the forage. If several long stems remain, reduce TLC, if you cannot find any stem pieces that are about an inch long, increase TLC (not all the pieces should be 1 inch but you should be able to find some).
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Nutrient value of soybean silage chopped at the R-6 stage is similar to early to midbloom alfalfa. Average concentrations (dry matter basis) of some nutrients are: crude protein - 19%, neutral detergent fiber (NDF) - 40%, and fat - 6%.
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Certain herbicides that are used for soybeans may not be approved when harvesting the crop as silage. Check with your chemical supplier.