Field Crops 28.31-15
More Mileage from Corn Silage: Selecting Hybrids
Joe Lauer, Corn Agronomist
Corn is a versatile crop that can be planted from early to late spring. In the fall,
producers have the option of harvesting corn for either silage or grain. Corn silage
is an important source of forage, especially in the northern Corn Belt of the U.S.
Many producers are reevaluating their cropping systems and increasing their use
of corn silage in dairy and beef feeding operations.
Advantages and disadvantages
Corn can produce high dry matter yields with one harvest. Corn is a good crop to
recycle nutrients from manure and maintain water quality. Corn silage is easily
ensiled and results in palatable forage with relatively consistent quality and higher
energy content than other forages. Corn silage production requires less labor and
machinery time than other harvested forages. Thus, the cost per ton of dry matter
produced tends to be lower for corn silage than for other forages.
Offsetting these benefits of corn silage are some disadvantages relative to other
forages. There are few established markets and transportation costs are high, so
the crop must be fed on or near the farm where it is produced. Storage facilities
for corn silage can be more expensive than facilities for dry hay. In some locations,
where corn is not well adapted, production costs may be too high to warrant silage
production. On erodible soils, corn silage production may be limited because of
soil residue requirements for conservation compliance.
Corn silage quality characteristics
Any good forage crop should have high dry matter yield, high protein content, high
energy content (high digestibility), high intake (low fiber), and optimum dry matter
content at harvest for acceptable fermentation and storage. With the exception of
high protein level, corn silage exhibits these characteristics better than other
forages. Both hybrid selection and agronomic management influence silage yield and
Corn hybrid selection is one of the most important management decisions in silage
production. Selecting the correct hybrid can often mean the difference between profit
and loss. Even selecting the "best" hybrid might not be enough if some
aspect in agronomic management is lacking such as delaying harvest. Selecting hybrids
for silage production depends somewhat on whether a field is planted specifically
for silage or whether the field may be harvested for grain (dual purpose).
Many U.S. farmers and livestock producers grow corn for both grain and silage and
they decide at harvest, which fields are to be used for each purpose. This flexibility
is appreciated because at planting it is difficult to predict overall forage needs
later in the year or know the condition of the corn crop at harvest. Acreage of
silage production will increase in years when perennial forage legume production
is reduced due to winterkill or drought or when moisture stress or early frost limits
corn grain production. On the other hand when adequate forage from other crops isn't
readily available and corn grain yields are adequate, producers may prefer the option
of selling their grain production in the cash market.
How different are corn hybrids for silage quality?
Until recently there was little information about the extent of variation for nutritional
quality of corn germplasm in the U.S. Most concepts about nutritive value of silage
corn were the results of past studies of grain to stover ratios and genetic oddities
such as the brown midrib mutants. It is generally agreed that most single gene mutants
or germplasm stocks exhibiting radically altered morphology (profuse tillering,
barren or "sugar" corn, dwarf, etc.) will not have much use as forage
types due to their inherently poor productivity compared to adapted hybrids selected
for grain production.
Although little information is available for U.S. germplasm, in regions of significant
silage production such as Northern France, Germany and The Netherlands, corn germplasm
has been undergoing selection for forage yield and quality for some time. After
evaluating nearly 40 different corn hybrids that are typically grown in Wisconsin,
Coors (1994) reported that the highest yielding grain variety hybrids were not necessarily
the highest yielding silage hybrids. Furthermore, whole plant digestibility and
fiber ranges seem rather narrow. In a similar study using another set of commercial
hybrids, Carter et al. (1992) also reported a relatively narrow range for whole
plant digestibility. Whole plant digestibility estimates by Alan et al. (1990) were
slightly larger, while those of Hunt (1992) were even more significant. Data from
around the world such as Canada, Netherlands and France indicate larger differences
in stover and whole plant digestibility.
Predicting animal performance and relating it to improvements in corn silage quality
is complex. In numerous studies, differences in fiber and digestibility translate
into differences in animal performance. For example, researchers in Idaho have found
that high quality corn silage (low fiber and high digestibility) produced $315 more
beef per acre than low quality silage. The optimum silage composition can vary depending
on the type of cattle it's fed to and the other components of the ration. The best
estimates of animal performance responses can be obtained through forage analysis.
The University of Wisconsin, along with many other universities, evaluates corn
hybrids for silage yield and quality characteristics. A silage performance index
using milk per acre and milk per ton was calculated using a model derived from the
spreadsheet entitled Milk 95 developed by Drs. Dan Undersander, Terry Howard
and Randy Shaver at the University of Wisconsin. Milk per acre and milk per ton
approximates a balanced ration meeting animal energy, protein and fiber needs based
on forage quality. The model is based on equations predicting intake and animal
requirements from data derived from National Research Council tables on nutrient
requirements of dairy cattle. The values of milk per acre and milk per ton are based
on a standard cow weight and level of milk production (1350 lbs. body weight and
90 lbs. per day at 3.8 % fat).
A dairyman who buys his feed off-farm would be interested in feeding the best quality
silage he could purchase and would be most interested in milk produced per ton of
silage. A dairyman who grows his own feed on-farm would be interested in both producing
quality silage as well as high yields from the farm land base.
Relatively small differences in corn silage fiber and digestibility translate into
large differences in predicted animal performance. In southern Wisconsin, the ranges
among hybrid entries for crude protein, ADF, NDF and in vitro digestibility
were relatively narrow. However, the range among hybrids for milk per acre was 9000
pounds, while the range among hybrids for milk per ton was 500 pounds (Figure 1).
Figure 1. Relationship between milk per acre and milk per ton for corn hybrids grown
in Wisconsin. Dashed lines are hybrid averages.
Repeatable differences for whole plant fiber and digestibility were observed in
the "high" and "low" quality checks. Previously identified high
quality hybrids were above average for milk per acre and milk per ton, while low
quality hybrids were average to below average in this trial. Consistent performance
regardless of environment is important for making hybrid selection decisions for
Criteria for selecting corn hybrids
Hybrid selection should start with identifying a group of hybrids that are adapted
to the area in terms of maturity, standability, disease and insect resistance and
drought tolerance. Generally higher silage yields are produced with hybrids that
mature slightly later than those adapted for grain production (about 5-10 relative
maturity units longer season). In areas with short growing seasons hybrids should
consistently reach harvest maturity just before frost. Other factors such as feed
requirements, harvest timing and the potential of wet soils at harvest may dictate
the selection of early maturing hybrids.
Once a group of adapted hybrids is identified, evaluate them on the basis of yield
potential. For those fields that are planted for silage production, evaluate hybrids
based on silage yield performance. Many studies have shown that grain yield is a
good general indicator of whole-plant yield, that is high grain yielding hybrids
tend to have high silage yield. However, within the high grain yielding group there
can be differences in whole plant yield and fiber digestibility, reinforcing the
need to have silage data available on these hybrids.
The final consideration for hybrid evaluation should be quality. Differences exist
among commercial corn hybrids for digestibility, NDF digestibility and protein.
Many seed companies are developing forage quality profiles of their corn hybrids.
Silage hybrids should have high forage yields, high digestibility, low fiber levels
and stover that is highly digestible. The best silage hybrids have high grain yields
because grain is so highly digestible. However, ranking for top yielding hybrids
used for silage may vary based on differences in fiber digestibility and grain to
stover ratio. A dual-purpose hybrid should have both high grain and forage yields.