Silage Management in Corn
Key Points
 To produce high-yielding,
good quality silage, you must
consider crop management,
moisture content at harvest,
and proper filling of silage
structures.
 Corn harvested at the proper
moisture level sets the stage
for effective fermentation and
helps to minimize losses from
heating and seepage.
Corn silage is an important forage source
used in dairy and beef cattle production.
Corn silage is palatable to livestock, relatively
consistent in quality, and carries a yield and
energy advantage over most other forages.
Corn silage is desirable to growers because
it requires less machinery and labor than
other forage crops. The keys to producing
high-yielding, good quality silage include:
good crop management, harvesting at the
appropriate moisture content, proper filling of
silage structures, and packing it in well.
Crop Management
Milky
Starchy
Product Selection. An important
consideration in corn product selection is
whether to use a dual-purpose product, one Figure 1. A cross section of a corn cob showing
that could be used for grain or silage
the milk line (indicated by the arrow) separating
production, or to use a product meant
the solid (starchy) and liquid (milky) areas of the
 Ensiling involves 6 phases and
specifically for silage production. In general,
maturing kernels.
begins once the corn is
dual purpose products will produce an ear
chopped and firmly packed
comprising 1/3 of the forage weight at harvest. Silage specific products should produce
high forage yields, high digestibility, low fiber, and highly digestible stover. When
into the silage structure.
narrowing the products for selection, know that good yielding grain generally equates to
good yielding silage. Therefore, examine trials in your region and choose products that
balance good yield with high quality. As with any product selection, you should select from products that match your scenario in
maturity, disease and insect resistance, and drought tolerance.
Soils and Fertility. In some cases, fields that may not be suitable for grain production may be suitable for silage. Wet soils, however,
are not the best option because early planting is important for silage and wet soils can delay planting. Special soil management
considerations during silage production include preventing compaction and
ensuring adequate residue cover if conservation tillage is used. With regards to
Table 1. Optimum moisture levels for
fertility, growers should be aware of the removal of available nutrients (especially
harvesting corn silage.
nitrogen and potassium) during harvest and make sure to conduct soil tests to
Storage structure
% moisture
% dry matter
ensure proper fertilization. Often, silage production goes hand in hand with
manure application, which can result in soils that carry an excess of phosphorus
Stack or pile
65-72
28-35
and potassium.
Planting Date, Row Spacing, and Populations. While early planting improves
quality and yield for silage production, the relative return is not as great as for that
of grain production. Therefore, if you are growing both, your grain should get first
priority. Population recommendations vary, but a general recommendation is to
plant at slightly higher (10-20%) populations than for grain. Furthermore, research
show that planting in narrow rows can provide a slight yield advantage.
Harvesting
Trench or bunker
65-70
30-35
Bags
60-70
30-40
Upright concrete
62-67
33-38
Oxygen limiting
45-55
45-55
Source: Kilmer, L. and S. Hoyer. 2012. Making quality corn silage.
Iowa State University Extension Dairy Team.
Moisture Level. Harvesting at the proper moisture content is the main goal during silage harvest. The target moisture varies by
structure (Table 1) but in general ranges from 60-70%moisture. Ensiling corn at the proper moisture level sets the stage for effective
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Silage Management in Corn
fermentation and helps to minimize losses from heating and seepage. If silage is packed too wet, seepage can remove nutrients and
could damage the storage unit. Silage packed too dry can have air pockets preventing an anaerobic environment and allowing
molds and spoilage.
Examination of the kernel milk line (Figure 1) is a common way to determine kernel moisture content. After corn dents, the starch
layer or milk line progresses from the top to the bottom of the kernel. Break an ear and look at the milk line on the developing
kernels. As a general rule, when the starch spans ½ to ¾ of the kernel, it is ready for silage harvest. If corn is allowed to reach black
layer, the silage may produce slightly more tonnage, but will be of lesser quality.
When corn reaches early dent, chop a representative sample and measure the moisture content. You can estimate harvest date by
using a 0.6% per day drydown rate, but may also want to reevaluate prior to harvest. One easy way to measure moisture content is
the microwave test. Collect a representative sample and chop it into 1-2 inch pieces. Weigh 3 to 4 oz or 100 grams – referred to as
fresh weight. Spread the sample uniformly and thinly over a microwave safe dish. Place this dish in the microwave with a cup of
water, heat for 1-2 minutes and weigh. Heat for 30 seconds and reweigh. Repeat until two weight recordings are the same
(indicating you have removed all the moisture). If sample chars, use the previous weight. With your measurements, you can calculate
percentage moisture:
[(fresh weight – dry weight)/fresh weight] x 100 = percent moisture
Harvest Height. Corn silage is traditionally harvested at a height above ground level, which helps maximize yield potential and still
keeps the desired quality (measured in the dairy industry as milk production potential per acre).
If the cutting height is raised, you will decrease silage yield, but improve forage quality because the lower stalks are typically higher in
fiber and lower in digestibility. Research has shown that an increased cutting height can reduce silage yield potential; however, by
increasing silage quality (milk per ton) the livestock productivity (milk per acre) may only be slightly reduced. If the crop has been
under drought conditions, nitrate levels in the stalks may be elevated. If nitrates are suspected, cutting higher at 18” will result in
material that is lower in nitrates since the majority of nitrates are found in the bottom 1/3 of the stalk.
Ensiling Process
The process of converting chopped corn into silage involves 6 phases and begins once the corn is chopped and firmly packed into
your silage structure:
1. Aerobic (oxygen using) bacteria begin to break down plant proteins and the pH begins to decline. Respiration from fresh plant
material and bacteria cause heating of the silage and releases water. This stage ends once all the oxygen is depleted, which can
occur in as little as a few hours under ideal circumstances. Rapid completion of this first stage is crucial to make a good silage
and relies on proper harvest timing, chop length, quick fill, good packing, and a good seal.
2. Once the oxygen is depleted, anaerobic bacteria ferment soluble carbohydrates and produce acetic acid, which continues to
drop the pH. Once the pH falls below 5, acetic acid producing bacteria decline. Phase 2 generally lasts from 24-72 hours.
3. During this transitional phase, which lasts only around 24 hours, falling pH enhances the growth of lactic acid producing
bacteria.
4. Lactic acid producing bacteria numbers increase and the fermentation of soluble carbohydrates occurs producing lactic acid,
the most desirable fermentation acid. It not only acts to preserve the silage, but can be used by cattle as an energy source when
consumed. This is the longest phase in the production process and continues until the pH is low enough to prevent bacterial
growth.
5. When a stable pH is established (usually around 4 in corn silage), the forage has reached a state of preservation where there is
very little microbial activity. During the storage phase, the ensiled crop must be kept anaerobic. If oxygen is able to enter the
silage, it will increase yeast and mold growth, resulting in reduction of quality, dry matter loss, and heating.
6. When you begin feeding out a silo, oxygen is once again introduced to the silage. The goal during feed out, is to limit the surface
exposure of silage to oxygen, which can help to minimize dry matter losses. Before feeding, laboratory analysis should be
completed on corn silage to determine dry matter content and nutrient levels for use when formulating rations.
Sources: Kilmer, L. and S. Hoyer. 2012. Making quality corn silage. Iowa State University Extension Dairy Team. www.extension.iastate.edu/dairyteam/ (verified 8/20/13); Lee, C., et al.
2005. Producing corn for silage. University of Kentucky Cooperative Extension Service AGR-79. www.ca.uky.edu/agc (verified 8/20/13); Roth, G. 2003. Maximizing corn silage yield and
quality. 2003 Four State Forage Conference Proceedings. www.ars.usda.gov (verified 8/20/13); Roth, G. and D. Undersander. 1995. Corn silage production, management, and feeding.
American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America; Schroeder, J.W. 2013. Silage fermentation and preservation. North Dakota State
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