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Soybeans for silage
Salvaging if crop hit by frost
By Beth Wheeler - Dairy Cattle Nutritionist, OMAFRA, Kemptville
An early frost may spell the end of the soybean harvest in some areas. In Kemptville, we have had 2 nights of temperatures below freezing, and producers are already inquiring about harvesting the soybean crop for silage. Soybeans require 30 to 40 days between the appearance of small pods at the top part of the plant to reach maturity. Frost prior to this could damage the crop, especially if less than 50% of the leaves have turned yellow.
Frost damaged immature soybeans can be harvested as hay or silage, but silage is preferred. Milking cows and growing heifers can perform as well or better on soybean forage as on alfalfa. Soybeans produce reasonable yields and are comparable in quality to alfalfa harvested at first-flower. If soybean plants are free of white mould and ensiled properly, palatability is not a problem. Cows may sort out and refuse to eat the coarse stems.
Precautions:
Many herbicides used on soybeans have label restrictions that prevent the crop being used as a forage. Check the labels of any herbicides used before harvesting and feeding soybeans as forage. If the label does not specifically state restrictions on beans intended for forage use, contact the manufacturer for clarifications.
For soybean hay, moisture must be below 25%. Extended drying time is required because the stems dry slowly. This increases shattering losses and the incidence of dustiness or mouldiness under cooler fall temperatures. Optimal harvest is when the pods have started to fill and the lower leaves are just starting to yellow (just before stage R7). Use a mower conditioner so that the leaves and pods dry at the same rate as the stems and to reduce leaf shattering and loss.
Soybeans can be harvested alone for silage. Problems with ensiling soybeans can be related to improper moisture content or to the high concentration of fat in the immature beans. Fat inhibits bacteria during fermentation. This slows the fermentation and increases the resulting pH and chance of mould growth. If equipment permits, soybeans can also be combined with corn silage by mixing 1 load of soybean silage with 2 loads of corn silage. Work on this at Ohio State showed that corn provides soluble sugars to speed up the fermentation and dilutes the fat content in the soybeans. Be careful to ensure relatively uniform mixing of the two in the silo, so that composition and intake will not vary at feedout.
Poor seed set obviously will dramatically reduce forage quality. Harvesting procedures and maturity will have a large impact on nutritional value, so a feed test is extremely important. Some southwestern Ontario soybean plants harvested during the first week of September showed protein levels varying from 12.8 to 21%, depending on pod formation and plant height. Be sure to sample at ensiling time and analyze using wet chemistry. Be sure to check the fat level (ether extract) so that energy value can be adjusted. Normal forage energy values are based on ADF (fibre) and will not account for energy from fat. Recheck soluble protein and heat damage at feed out.
If the soybean forage contains 10% fat, the total amount that should be fed to milking cows is 10 lbs. (4.5 kg) of dry matter. This keeps the total fat levels from soybeans under 1 lb. (450 g). Do not feed soybean forage in combination with other sources of vegetable fat (e.g. Roasted soybeans).
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Questions about soybeans for silage
