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Soybean Silage as an Alternative Forage
Tim Griffin
Sustainable Agriculture Specialist
The questions started in 1997 – "Can we grow soybeans in Maine? What kind of
yield can we expect? Do they have to be roasted to feed to dairy cows?" I finally get
a handle on most of these and then…the questions change!! The most recent variation
is
Can we grow soybeans for silage,
instead of grain??
This interest is spurred by both the need for some alternative annual forage crops,
and probably the lack of grain harvesting and handling equipment on dairy farms. I have
been looking into the Soybean Silage alternative over the last month or so. Although not
an "Expert" by any stretch, I can provide some basic information here. Much of
the practical experience with Soybean Silage is not that far away, in northern New York
(especially at the Miner Institute in Chazy) and in Vermont. Some of the information below
is from these sources.
This interest is spurred by both the need for some alternative annual forage crops,
and probably the lack of grain harvesting and handling equipment on dairy farms. I have
been looking into the Soybean Silage alternative over the last month or so. Although not
an "Expert" by any stretch, I can provide some basic information here. Much of
the practical experience with Soybean Silage is not that far away, in northern New York
(especially at the Miner Institute in Chazy) and in Vermont. Some of the information below
is from these sources.
Production Basics:
Many of the basics are not that different from grain soybean.
Here is a summary of the important points:
- Variety selection is critical, as it is for soybeans for grain. The grain
varieties, forage yield is usually low (see Farm Report from Miner Institute, quoted
below). There are several long-season soybeans that have been evaluated (by USDA-ARS) for
forage production, including Donegal, Derry, Manokin, and Tyrone.
- Soybeans are usually drilled in narrow rows (5-8"), at populations of
200,000 to 250,000 seeds/acre. Populations are lower in wide (30-36") rows.
- Please inoculate seed for adequate nitrogen (N) fixation.
- Best results if planted into warm, moist soil. If the soil is cold, emergence can
be quite slow. Planting into wet soil, where crusting is likely, can be a disaster,
because soybeans do not tolerate crusting to any extent.
- Adequate P and K are important for a vigorous crop!
- Weed control can be either chemical or mechanical. (I can provide details.)
- Whole plant DM level should be 25-35% in September (from late May-early June planting).
Most likely, soybeans will need to be wilted before chopping.
Yield and Quality Potential of Soybean Silage:
Since I have no practical experience here, let me quote a few
people who have worked with this crop:
Bill Weiss, Ohio State University Bill Weiss, Ohio State University
"The concentrations of protein, fiber, energy, and fat depend on the maturity of
the soybeans when harvested. Soybeans that are just starting to develop seeds will contain
about 18% protein, 46% NDF, and 9% fat. Soybean plants that are starting to mature (one
pod has reached its mature color) will contain about 19% protein, 40% NDF, and 11%
fat."
Ev Thomas, Miner Institute
Farm Report, March 1999
"FORAGE SOYBEANS
"FORAGE SOYBEANS
There is plenty of interest in forage soybeans, or at least in using soybeans for
forage. USDA has been working for several years in developing forage varieties combining
high yield and quality. The first year of USDA research here at Miner Institute resulted
in 6+ ton/acre dry matter yields. Though we haven’t reached those yields since, 6
tons of DM really got farmers’ attention: "Where can I get seed?" Forage
soybean varieties weren’t yet available (they are now—Donegal, Derry, Manokin
and Tyrone) but some farmers planted grain-type soybean varieties. Here’s what we
know about soybeans for forage:
- Yield and quality—research trials: Forage-type soybeans yielded from 3-6
tons DM/acre, with crude protein 13-17%, NDF 44-48%. In one trial an early grain-type
variety (Pioneer 9071) yielded only 1.3 tons DM/acre with 22% CP and 36% NDF.
- Yield and quality—farmer experience: From Pete Barney, St. Lawrence
County Cooperative Extension: Farmers are planting forage soybeans and Group 1 soybeans in
7" and 14" rows. The Group 5 forage variety Manokin was 5-6 feet tall but
lodged. Yield and quality were fair at 2.5 tons DM/acre, 17% CP, 44% NDF, 2.7% fat and
0.58 net energy. Group 1 grain varieties Marathon and Sentry yielded 2.3-2.4 tons DM/acre,
averaged 22% CP, 42% NDF, 8% fat, 0.73 net energy. There were almost no beans on the
forage variety, lots of beans on the grain varieties. Pete’s going to blend the two
types this year in hopes of a better combination of yield, stand ability, and quality;
preliminary trials are encouraging. He recommends 220,000 seeds per acre and a good
inoculant such as Cell Tech 2000.
Moisture content: Planted in late May, forage soybeans are about 25% DM in
mid-September, at which time Group 1 varieties will be closer to 30% DM. Therefore, most
soybeans for silage will have to be wilted prior to ensiling."
Ev Thomas, Miner Institute
Farm Report, January 2000
"SOYBEAN SILAGE UPDATE
Forage soybeans were the topic of the day at a recent Vermont meeting.
While USDA has had forage soybean variety trials at Canton and Chazy, much of the soybean
silage action in the Northeastern U.S. is in Vermont and in Franklin Co., NY. Following
are some highlights:
Two experimental varieties grown at Miner Institute were
high-yielding but forage quality was modest at best: under 14% CP, 49% and 58% NDF.
Magnesium was very high at over 0.6%, while potassium was very low at 0.77% and 0.85%. Dry
cow forage? Hmmm.
Dry matter and NDF digestibility were horrid at 70% and 38%
respectively, but we may need more work on refining in vitro standards for forage
soybeans. Looking at the plants, though, it was easy to predict that digestibility would
be poor because the stems resembled trees, not forage.
Part of the reason the forage soybeans at Chazy were so woody may be
the 30" row spacing. It was suggested (based on farmer experience) that 7" rows
would be better: Smaller stems, less lignin, easier harvest.
Weed control is still a problem, but not an impossible one. According
to UVM agronomists there are a few decent weed control options. Unfortunately, Roundup
Ultra is not currently one of them. It’s labeled for soybeans, but not for soybean
forage.
Gordon Elder, a Franklin Co. grower who’s had as much experience
with soybeans for forage as anyone we know, says that silage fermentation isn’t a
problem when the crop is windrowed and wilted to 35% DM. He’s had good success with
and without an inoculant. Gordon has been happy with Marathon, an inexpensive early grain
variety. None of the farmers at the meeting reported palatability problems, but most
weren’t feeding soybean silage as a major portion of the diet.
Drought severely affected the Vermont crop in 1999. DM yields
generally ranged from 1.5 to 3.0 tons/acre, with CP and NDF similar to early bloom
alfalfa. As we have found in research here, lower quality generally accompanies higher
yields. (This is true for crops other than forage soybeans, of course.)"
Some people have grown soybeans along with sorghum or forage sorghum, and there is
mixed opinion about which is preferred. The presence of the grass will dilute the high fat
content of the soybeans, and may moderate the DM level as well. Sorghum-sudangrass is very
competitive, which some people favor because it helps keep weeds in check. Others are
concerned that the sorghum-sudangrass is too competitive with the soybeans, and they
don’t get the protein concentration they would like. My suggestion on this topic is
to try some of both (pure and mixed). I think the larger challenge is in producing this
alternative crop, not whether it is in a mixture or not.
A Couple of Comments:
Soybean silage can have high fat levels, compared to other
forages we use. Several sources of information that I looked at noted fat concentrations
of 10% or even slightly higher. It is important to know this for a couple of reasons, as
pointed out by Bill Weiss at Ohio State:
- "The high concentration of fat (about 10%) inhibits bacteria in the silage and
fermentation is slow and often incomplete. The silage may have a high pH and may allow the
growth of molds and other deleterious organisms." Mixing with silage corn going into
the silo is one way to add soluble carbohydrates.
- "The amount of soybean silage that can be fed is limited because of its fat
content. If the forage contained about 10% fat, the total amount of soybean forage that
should be fed to cows is 10 lbs of dry matter."
As with all new crops, don’t bet your farm on them! Try an acreage that you are
comfortable with, and pay attention to the details.
March, 2000
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