To reduce risk, producers should select multiple hybrids based on information from numerous sources including universities, seed companies and commodity groups. Data from individual on-farm trials should also be used if available.

When selecting hybrids, identify those which are consistently top performers over multiple sites or multiple years within a given region. The importance of consistency over multiple environments is critical, given the range of growing conditions from year to year. One of the first things to consider when selecting hybrids is maturity. Longer-season hybrids tend to have higher silage yields. A general rule of thumb is that hybrids planted for silage should be five to 10 days longer in relative maturity than the hybrids planted for grain. However, these later-maturing hybrids may not be the best choice for a producer wanting early silage or the option to harvest the corn for grain.

Consider planting hybrids with a range in maturity, as this reduces the probability that one’s entire crop will experience hot and dry conditions during pollination. This can also widen the harvest window, which is important for timely harvest at the appropriate moisture level. However, silage that is custom-harvested within a short period of time may require a narrower range in maturity to reduce variation in harvest moisture. Harvesting at the correct moisture level is key for producing high-quality silage, and if missed, this can negate the benefits of good hybrid selection.

Other important agronomic considerations when selecting hybrids include standability, drydown, herbicide and insect resistance, and tolerance to drought and disease. Hybrids with strong ratings for stay-green should be avoided because whole-plant moisture will be too high when harvested according to kernel stage.

Since corn silage is an energy source for animal performance, producers should consider both yield and quality when selecting hybrids. However, the numerous variables representing yield and quality can make hybrid selection a little overwhelming. From a practical standpoint, the two key variables for dairy producers to consider are milk per acre and milk per ton, both of which are calculated using the MILK2006 spreadsheet developed by the University of Wisconsin (www.wisc.edu/dysci/uwex/nutritn/spreadsheets/milk2006cornsilagev1.xls).

Milk per ton is an overall indication of silage quality, and it is estimated from forage analyses for crude protein (CP), neutral detergent fiber (NDF), NDF digestibility, starch and non-fiber carbohydrate. Milk per acre is a single term that represents both silage yield and quality. Milk per acre is calculated by multiplying milk per ton with silage dry-matter yield. When selecting hybrids based on milk per acre and milk per ton, consider the following:

• The goal is to identify hybrids with high values for both milk per acre and milk per ton. These hybrids produce high silage yields and high-quality forage, and are thus most profitable.

• Hybrids with a high value for milk per acre and a low value for milk per ton have high yield but below-average quality. Silage from these hybrids may be better suited for livestock with lower nutritive requirements than high-production dairy cows.

• Hybrids with a low value for milk per acre and a high value for milk per ton have below-average yield and high quality. These hybrids will have low profitability for dairy producers that grow their own silage, since gains in quality will not likely offset reductions in yield.

• Hybrids with low values for both milk per acre and milk per ton should be avoided. They have relatively lower yield and lower quality.

Once a group of hybrids with high values for milk per acre and milk per ton have been identified, further selection within this group can be based on specific agronomic and forage quality traits. In general, higher NDF values indicate lower intake and animal performance; while higher values for CP, starch, NDF digestibility and in vitro digestibility imply greater performance potential.

While small changes in forage quality can greatly impact milk production, differences in individual quality traits between hybrids that are less than 5 percent are probably not statistically significant or worth worrying about, especially since overall forage quality is summarized by milk per ton. PD

References omitted but are available upon request at editor@progressivedairy.com

—Excerpts from University of Minnesota Crop eNews, December 2008

Jeff Coulter
taCorn Agronomist
University of Minnesota
coult077@umn.edu

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