Soybeans as Forage

By Jared Goplen and Craig Sheaffer et.al

The current drought in Minnesota is taking its toll on forage crops. Alfalfa has gone dormant in many areas with minimal regrowth, and corn silage yields will be poor on many dryland acres. With high-quality hay exceeding $350 a ton in some cases, many are trying to acquire alternative high-quality forages. 

Soybean was initially used as a forage crop when introduced into the United States in the 1800’s and can still be harvested as high-quality forage. Even grain-type soybean varieties can be harvested for hay or silage. Despite its forage value, there are some restrictions and management considerations to explore before putting soybeans up for forage.

Key Points

• Soybeans can be harvested for forage as hay or silage. Forage yield and quality are affected by stage of development.
• Consider the value of the grain versus the forage value.
• Weigh the cost of harvest versus the yield and quality of forage.
• There is high potential for field losses of leaves and pods during the harvest process. Use a mower-conditioner to speed drying, and minimize raking to preserve leaves and pods.
• Soybean can be fed to cattle and horses but feeding practices may need to be adjusted.
• Check pre-harvest intervals for all pesticides applied.
• Consult with your crop insurance provider before taking any action.

CHECK PESTICIDE LABELS!!!

Before cutting your soybeans for forage, check ALL pesticide labels from products that have been applied in the last year. Restrictions on using soybean for forage tend to be quite strict, with only a handful of herbicides, outside of glyphosate, permitting the harvest of soybeans as forage. 

Insecticide and fungicide labels are not much better, with many restricting the use of treated soybeans as forage. It is illegal to harvest treated soybeans if the pesticide labels are not labelled for forage use. This restriction may be related to health effects they cause in livestock, or it is possible they cause unsafe pesticide residues that end up in milk or meat products. The Wisconsin Pest Management Guide provides a reference for some grazing and haying restrictions of herbicides, insecticides, and fungicides. (Herbicides: page 126, Insecticides: pages 134-149, fungicides: pages 159-163). Checking individual pesticide labels is recommended to ensure soybean forage is safe to harvest.

What next if I used the right pesticides?

If you are one who used pesticides that allow for forage use, there are a few considerations to ensure your time is well-spent harvesting soybeans as forage. It is challenging to dry soybeans to <20% moisture to successfully store as dry hay because of soybean stemminess and presence of pods. Leaf loss and seed shattering can be extensive. Harvesting for silage or baleage at higher moisture levels will reduce field losses and is less risky. Standing soybeans should be cut with a mower-conditioner to crimp stems and decrease drying time. Raking should be minimized as leaves and pods shatter easily.

Dry soybean hay is not particularly palatable. When fed as the exclusive roughage source, cattle will actively sort out the stem material leaving 30 to 40% of available dry matter as wastage. Furthermore, dry soybean hay can cause bloat in cattle, particularly when fed as the sole roughage source. 

Altogether, making silage or baleage is a better fit for soybean forage harvest. The target silage moisture content varies with how it is being stored, but should be in the 55-65% moisture range for most storage structures. Ensiling soybean will maximize palatability, reduce wastage, and provide feeding flexibility. Similar to alfalfa, the buffering capacity of soybean silage is relatively high and can result in poor fermentation. A high-quality silage inoculant or mixing soybean silage with corn grain or silage will improve fermentation.

Forage Yield and Quality

The forage quality of soybean is often similar to flowering alfalfa. When harvested at the correct stage of maturity, soybeans will be higher in protein than corn and small grain silages and tends to be highly digestible (Table 1). The forage quality will change with maturity due to increased grain filling and changes in the proportions of leaf, stem, and pod fractions and leaf/stem ratio. 

Soybeans are typically harvested for forage from R3 (beginning pod) to R5 (beginning seed) stage, but earlier maturity at harvest is recommended (Undersander et al., 2007). Soybean forage at the R3 stage has high quality because of leafiness and higher quality stems. Soybean forage at the R7 (beginning maturity) growth stage has high quality because of nutrients in the seed components but has a reduced proportion of leaves. With seed formation and increased stemminess, drying of cut forage from plants in the R7 stage is challenging. Soybeans closer to maturity at the time of cut will also have greater losses of leaves and seed due to shattering.

Table 1.  Forage yield and quality of grain-type soybean cultivars at several harvest stages. 

^*Digestibility calculated from ADF concentration DDM% = 88.9-[ADF% x .779]
Source: Hintz et al., Agron. J. 1992, 1994.

Effects of drought on yield and quality

The forage quality of a drought-stricken soybean crop will be very similar to a normal soybean crop, except yields will be lower. Forage yields will be reduced due to shorter plants with fewer and smaller leaves. Protein levels in the soybean plants may be lower than normal as both nitrogen fixation and nitrate uptake will be reduced in dry soils. If soybean plants have been unusually pale green or yellow this year, it is possible that forage quality might be further limited due to the drought.

Forage yield and quality are unlikely to increase significantly after R5.5 (last soybean leaves emerge from the top of the plant) due to limited seed set in drought-stricken soybean. Delaying cutting after this stage exposes the producer to risk of the crop deteriorating under extended drought. On the other hand, if late season rains do occur, it is possible that the quality of the crop may improve slightly as the crop 're-greens.' 

For marginal soybean crops that have the potential to produce some soybeans for grain, delaying cutting until closer to R7 (beginning maturity) would allow the producer the opportunity to re-evaluate their decision to cut for forage or harvest for grain, though additional harvesting and quality concerns exist with harvesting maturing soybeans as forage.

Feeding to beef cattle

• Grind dry soybean hay and mix with other roughages like corn silage, corn stover, or grass hay to reduce wastage and eliminate bloat risk.
• Soybean silage should be introduced at an inclusion rate of <50% of the diet on a dry basis.
• Inclusion rates can be increased by 10% after several weeks of feeding.
• If greater than 50% of the diet is soybean forage with a large proportion of soybean seed in the feed, the large concentrations of dietary fat may lead to scouring, digestive upsets, and in severe cases ammonia toxicity.

Feeding to dairy cattle

• Limited research shows slightly lower dry matter intakes of soybean forage compared to diets containing alfalfa or corn silage.
• Soybean forage can make up 15 to 20% of a dairy ration without having a significant effect on intake or milk production.
• Soybean hay does have the potential to cause bloat, so it should be introduced slowly and mixed with other forages.

Feeding to horses

• Research conducted in the 1920s suggests soybean hay can successfully be fed to draft horses, but limited research has been conducted since.
• Soybean forage can be fed to horses in limited amounts in the diet. Chopping and ensiling soybean hay can improve palatability, but these options are rarely practical for horse owners.
• Soybean forage containing seeds should not be fed due to the presence of a trypsin inhibitor that can cause health issues.
• Transition horses slowly to soybean forage that is free of mold, weeds, and dust, and test for nitrate accumulation prior to feeding.