– Jason Hartschuh, Extension Field Specialist, Dairy Management and Precision Livestock, Ohio State University Extension
Optimum time to harvest soybeans for silage is when pods are filled and lower leaves are just starting to turn.
Long before soybeans were cultivated as oil seed crops, they were first domesticated and used in the United States primarily as a forage. Soybeans harvested as forage are high in protein and lower in fiber than grasses making them an excellent forage if harvested and stored properly. Soybeans harvested as a forage can have dry matter yields as high as 5 tons per acre but are often much lower when the soybeans are planted late as a rescue forage or transitioned to forage due to drought.
Soybean feed value from Hintz et.al. from the late 1980’s showed that when soybeans were harvested at R7, crude protein values across 3 different varieties ranged from 18.1-20.5%. The NDF values for the soybeans ranged from 39.5-42.2. Dry matter yield ranged from 3-3.6 tons per acre. Row spacing and seeding rate had little effect on yield or forage quality. However, harvest timing affected all factors. When harvested at R3 soybean yields were 1.75 tons/ac increasing to 2.5 tons/ac at R5 and finally 3.3 tons/ac at R7. A statewide survey of soybeans planted in Ohio in late June or early July in 2019 had an average yield of 2.1 tons/ac when harvested between R5-R7. Crude Protein averaged 24% with a TDN average of 57 and a NDF average of 45.
The greatest limitation to using soybeans as an emergency forage is that few herbicides are cleared for use on soybeans that are harvested as forage. If soybeans are originally planned for grain harvest and the decision to harvest soybeans for forage is made after the application of a herbicide not labeled for use on soybeans harvested as forage it is not legal use them for forage. One such herbicide that does not allow for forage use is Liberty, which specifically says not to graze or cut for hay. However, many other herbicides such as Dual, FirstRate, Metribuzin, Roundup, Prowl, ect. allow the crop to still be used for forage, but you will need to check the labels on the specific herbicides you use and follow the preharvest interval.
The optimum time to harvest soybeans for silage to maximize yield is when the pods are filled and the lower leaves on the plant are just starting to turn yellow. This is just before the R7 growth stage, which is when one pod on the plant has reached a mature color. This is when the field has reached maximum dry matter yield and is beginning to decrease in moisture content. Soybeans harvested later will have a higher oil content which reduces their ability to ensile properly. While not ideal for harvest logistics mixing later harvested soybeans with a grass crop including corn silage will improve the forages’ ability to ferment properly.
Field drying is necessary before ensiling or making hay from soybeans. They will need to be harvested with a mower-conditioner, check the conditioner roll tightness to make sure it is not shattering the soybeans from the pods. Conditioning the stems hastens the drying so that the leaves and stems dry at a more similar rate and leaf loss is reduced during harvest. Harvesting as dry hay is not recommended as the increased drying time increases the chances of rain damage. More importantly, the increased leaf loss from dry harvest decreases the crude protein. Dry soybean bales are often dusty and the stems are brittle decreasing forage consumption and increasing feed bunk refusals. The seeds may still contain too much moisture when the plant is dry and may mold in the dry hay. If soybeans are harvested as dry hay, they need to be harvested at R1.
When harvested as silage or baleage the soybeans should be dried to 40-70 percent moisture. Baleage will need to be on the drier side from 40-60% moisture while chopped silage is better at 65-70 percent moisture. Baleage will need at least 4 layers of plastic wrap over the last stem that pokes through to ensure proper fermentation this will usually require a total of 6-8 layers of plastic wrap. Bales will need at least 4 weeks for proper fermentation with drier bales taking longer if they do even ferment properly.
Soybean silage is not the most palatable forage, consumption can be improved by mixing the soybean silage with corn silage or even low-quality grass hay. The soybean silage often has a higher crude protein than what your livestock will need. You will want to do a forage test to determine your feed’s nutritional value but a feeding rate ratio of grass crop to soybeans between 2 to 1 or 1 to 1 on a dry matter basis is often optimum. The best way is to mix these forages in a TMR mixer, the second best option is to use a bale chopper and mix the two forages with the least desirable option to feed them both as whole bales. If soybeans are in the R6 growth stage or later be cautious of the amount of oil that is in the forage, not only does it inhibit proper fermentation, but the high oil content can also cause digestive issues.
Soybean hay is similar in nutritional value to alfalfa hay, but it is less palatable alone to livestock leading to a reduced value per ton. However, fall soybean price is currently around $9.75 per bushel, and current hay prices for mixed alfalfa grass hay range from $140-385 per ton. Without including harvest cost the hay value of soybean at one ton per acre of dry matter is at least 14.5 bushels per acre and if you get 2 tons of dry matter per acre your soybeans yield needs to equal at least 28 bushels per acre for the soybean grain crop to be worth more than your soybeans forage value. Information on estimating soybean yields can be found here: https://agcrops.osu.edu/newsletter/corn-newsletter/2018-24/estimating-soybean-yield
If you use crop insurance for your soybeans be sure to talk to your crop insurance agent before starting to cut the soybeans to find out how it will affect your crop insurance. With some policies soybean hay can be harvested and still maintain this year’s soybean insurance. The process is similar to corn silage. A yield appraisal will need to be done before cutting the soybeans. This yield appraisal will be used for your insurance yield this year to determine if you had a loss that would trigger your policy coverage.
Be sure to communicate with your USDA Farm Service Agency office to see if harvesting the field for forage will affect your USDA program eligibility.