Dan Undersander, Professor, Kevin Jarek, Tom Anderson, Nick
Schneider, and Lee Milligan, Extension Educators, University of
Wisconsin, Madison 53706
Corresponding author: Dan Undersander. djunders@wisc.edu
Undersander, D., Jarek, K., Anderson, T., Schneider, N., and Milligan, L. 2007. A guide to
making soybean silage. Online. Forage and Grazinglands doi:10.1094/FG-2007-0119-01-
MG
Adverse weather such as drought or early frost sometimes raises the issue of
harvesting soybean fields for forage due to forage shortage and/or low yield
grain yield potential of the soybean crop. Soybean forage can be harvested as
either silage or hay. Harvesting as hay requires much longer field drying times,
increases shattering losses, and can be very dusty. No information was found
concerning production and feeding of soybean silage. Therefore, eight farmers
who had made soybean silage in Wisconsin during the fall of 2005 were
surveyed and the silage was sampled for analysis. Following are
recommendations for making soybean silage as reflected by the farmer
experience.
Soybean should be harvested for silage at the R3 stage [when one of the four
top nodes with a fully developed leaf has a 3/16 inch long pod (1)] for dairy
animals.
It is possible to harvest as late as R7 stage (one pod on main stem has
reached mature color; 50% of leaves yellow; physiological maturity, no more dry
matter accumulation). Yield at the later stage is increased compared to R3 and
R4 stages and plant dry matter is near to that required for ensiling (2,3,5). While
overall forage quality at the R7 is similar to the R3 or R4 stage and to alfalfa, the
plant is significantly different as far as the animal is concerned. The R3 and R4
stage soybean have high forage quality from green leaves and much more
digestible stems. The R7 stage soybean has high forage quality because of seeds
in the pods while having fewer leaves and much lower quality stems. Therefore,
seed shatter during harvesting at the R7 stage, resulting in loss of forage quality,
is a significant issue. Secondly, the high oil content of the beans at the R7 stage
may cause erratic fermentation in the silo, reducing palatability and forage
intake. Most of the farmers surveyed had harvested the forage at the R3 to R4
stage.
Standing soybean forage at the R3 to R4 stage was generally at about 80%
moisture and needed to be mowed and wilted to dry down to 65% moisture for
ensiling (Table 1). Farmers were able to mow and condition with their standard
mower/conditioners, though they often needed to go slower than normal.
Farmers also noted that flail conditioners caused more damage to the soybean
than roller conditioners. Drying time to 65% moisture generally took 2 to 3 days
in the late fall.
Forage yield averaged 1.5 ton/acre, ranging from 1.0 to 2.25 ton/acre. This is
significantly less than many published reports but reasonable when the soybean
is stressed from drought or late planting. Silage was made in oxygen limiting
silos, plastic bags, and bunkers. Forage should be chopped with a 3/8-inch
theoretical length of cut for good packing. Silage produced by the farmers
surveyed was generally in the correct moisture range (Table 1) and fermented
well. Forage quality was similar to alfalfa haylage as reported by others when
soybean is harvested at the R3 stage (2,4).
Some farmers mixed the soybean silage with other crops including 3rd crop
alfalfa, corn silage, sorghum-sudangrass, and triticale. Alfalfa mixed with the
soybean silage had no effect on forage quality. Sorghum-sudangrass, corn silage,
and triticale all lowered the quality of the silage by reducing crude protein
content and increasing fiber content (data not presented).
The farmer has the choice of mixing forages when ensiling or ensiling forages
separately and mixing them when feeding. Forages should only be mixed at
ensiling if the mixture will have better fermentation characteristics (proper
moisture, better substrate for bacteria, etc.) than either silage alone. When
forages are mixed at ensiling, often one is not at the optimum stage for ensiling
which reduces overall silage quality and/or yield. Further, ensiling the two
forages separately, gives the operator has more flexibility balancing the ration
according to needs of the animals being fed and quality of the ensiled material.
Farmers generally fed the soybean silage as 15 to 20% of the ration. They
were asked how animals consumed and performed on soybean silage. Of the
farms surveyed (Table 2), in only one case was feed intake decreased. Thus,
while soybean silage is less palatable than alfalfa or corn silage, it can be used as
a significant portion of the ration without influencing animal intake. There was
no problem with sorting stems from leaves, likely due to the fine chop used.
Most importantly, in no case was there any discernable difference in
performance when animals were fed soybean silage. Dairy cows are particularly
sensitive to their ration, so feeding soybean silage to other category of animals
should be no problem in a balanced ration. Some reports of feed intake
problems may have been caused by ensiling soybean at later stages, when high
oil content from the seed may have affected palatability.
In summary, making soybean silage may be a good opportunity for farmers
short of forage due to drought. The following recommendations will provide
successful soybean silage experience:
• Talk to your crop insurance adjuster before harvesting any insured
soybeans for forage to make sure that all requirements for insurance
are met.
• Make sure any herbicides used on the soybeans are cleared for
feeding to cattle.
• Harvest soybeans at R3 stage, when one of the four top nodes with a
fully-developed leaf has a 3/16-inch-long pod.
• Wilt forage to 35% dry matter before ensiling. Note: producers felt
soybean whole-plant moisture was difficult to judge in the field,
therefore testing is well worth the expense.
• Chop at 3/8-inch theoretical length of cut, pack well, and seal in
airtight, covered pile, tube, bunker, or vertical silo.
Literature Cited
1. Fehr, W. R., and Caviness, C. E. 1977. Stages of soybean development. Spec. Rep. 80.
Iowa Agric. Home Econ. Exp. Stn. Iowa State Univ., Ames.
2. Hintz, R., Albrecht, K. A., and Oplinger, E. S. 1992. Yield and quality of soybean
forage as affected by cultivar and management practices. Agron. J. 84:795-798.
3. Munoz, A. E., Holt, E. C., and Weaver, R. W. 1983. Yield and quality of soybean hay
as influenced by stage of growth and plant density. Agron J. 75:1457-148
4. Seiter, S., Altermose, C. E., Davis, M. H. 2004. Forage soybean yield and quality
responses to plant density and row distance. Agron J. 96:966-970.
5. Willard, C. J. 1925. The time of harvesting soybean for hay and seed. Agron J.
17:157-168.
Forage