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 quality.

Hybrid selection

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.

Animal performance

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 silage quality.

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.