Harvesting Soybeans for Forage

Mark Sulc, OSU Extension Forage Specialist and Bill Weiss, Extension Dairy Specialist, The Ohio State University

The drought conditions this summer have led some producers to consider using their soybean crop for forage. Whole plant soybeans can be excellent forage for cattle. Soybeans with little pod development can have about 18% crude protein and 40 to 45% neutral detergent fiber. In other words, whole soybean plants are similar to good quality alfalfa in nutritional value. Good soybean silage can be made under the following conditions:

1. Check the pesticide labels of chemicals used to verify that the crop can be fed to livestock after their application, and observe any pre-harvest intervals. For example, for glyphosate-resistant soybeans with Weathermax Roundup, wait 14 days between the final Roundup application harvesting the soybeans for grain, forage, or hay fed to livestock.

2. Under normal conditions, the optimum time to harvest soybeans for forage for optimal yield and quality is when seeds are filling the pods and the lower leaves are just beginning to turn yellow. At this stage, soybeans will yield from 2 to 3 tons of dry matter per acre (lower yields can be expected if planted late) with a composition of 17-18% CP, 0.56 Mcal/lb NEL (55% TDN), 45% NDF, and 34% ADF. If seeds are present and are reasonably well developed, soybeans should be mixed with corn in the silo to achieve acceptable fermentation (high oil content of pure soybean silage with good seed set will prevent good fermentation). Mix one part soybean with two or more parts of corn in the silo. If soybeans are to be ensiled alone, they must be harvested before seeds are formed.

3. Under dry conditions when seeds did not develop or are small, soybeans can be ensiled alone, provided the dry matter content is in the right range (see item 4 below).

4. Prior to chopping soybeans for silage, check the forage dry matter content (use a microwave oven or Koster tester). If the plant contains less than 45% dry matter (at least 55% moisture), the plants should ferment fine in upright and bag silos and will usually ferment OK in bunker silos. If the plant contains more than 50% dry matter (less than 50% moisture), fermentation quality will probably be poor in bunker silos. When dry matter is much higher than 55%, fermentation will be poor in all types of silos except sealed structures. If plants do not contain enough moisture for fermentation, water can be added but it takes a lot of water to change the dry matter content. To increase the moisture content of 1 ton of material by 4 percentage units (for example 55 to 51% dry matter), you have to add about 190 lbs of water (24 gallons per ton).

5. Whole plant soybeans can be harvested for hay but generally the nutritional value is much lower than soybean silage. Leaf shatter is severe when soybeans are baled so protein is much lower and fiber much higher in soybean hay.

6. Because excess fat from soybeans can depress fermentation in the rumen, the maximum amount of soybean forage that can be fed should be based on its fat concentration. If seeds are well developed the forage will have about 10 or 11% fat, and the maximum concentration of soybean forage to include in the diet is 20 to 25% of the dry matter fed. If plants have little pod development, soybean forage can comprise the same proportion of a diet as can alfalfa. If soybeans and corn are mixed, fat concentrations are usually around 5% and rumen problems caused by fat are not expected to occur.