In an emergency season, farmers desire to maximize forage yield often at the expense of optimizing forage quality. This article discusses some guidelines for producing the best forage quality possible in spite of a bad situation. Figure 1 describes an example of the trade-off between corn forage yield and quality during the life cycle of the corn plant (Darby and Lauer, 2002). Most corn planted around July 1 will likely only develop to the flowering stage (tasseling, VT and silking, R1).

First, some definitions regarding corn forage quality. Corn forage quality is calculated using the model Milk2000 (Schwab et al., 2003) and expressed as milk per ton which provides an overall estimate. Two important measurements used in Milk200 for calculating milk per ton are NDFD and starch content. NDFD measures the digestibility of the stover. Starch content measures the amount of starch in the forage and is considered 85 to 100% digestible by dairy cows.

Corn forage is unique among forages. Like most other forages, optimum quality occurs just prior to flowering (Figure 1E). Like other forages, quality decreases as harvest is delayed after flowering due to decreasing stover digestibility (Figure 1C). Unlike other forages, as corn nears maturity, quality improves due greater starch content in corn grain (Figure 1D). By maturity forage yield (Figure 1A), milk per ton (Figure 1E), and milk per acre (Figure 1F) are maximized. Harvest timing is dependent upon optimum moisture content (Figure 1B) for the storage structures.

In an emergency forage season where corn is planted around July 1, the objective of corn production changes to maximizing stover yield and quality. Corn stover yield is maximized at flowering (derived Darby and Lauer, 2002). Likewise corn stover quality is at a maximum just prior to flowering (Figure 1E).

At least three hybrid selection options exist: 1) ultra-short-season hybrids to produce some grain; 2) full-season hybrids or longer to flower around the frost killing date; and or 3) hybrids with improved stover digestibility traits. Whether one chooses an ultra-short-season hybrid or a full-season hybrid, the success of your decision hinges upon your ability to predict GDU accumulation for the remainder of the growing season and the fall killing freeze date.

Planting corn around July 1 results in good stover yield, but relatively low grain yield that is decreasing 2.5 to 3 % for each day delay (Lauer, 1997). Late-April and early-May are optimum dates for corn planting and by June 20, only 3 to 32 % grain yield is produced depending upon location. For most years planting corn July 1 or later will not produce grain, but your chances of producing at least some grain improve in southern Wisconsin when using ultra-short-season hybrids. For example at Arlington in 1997, a 75 day hybrid produced 41 bu/A when planted on July 1 (Oplinger and Lauer, 1997).

It may be more feasible to plant a full-season hybrid to maximize stover yield and not be concerned about grain yield. Selecting a hybrid that nears flowering prior to a killing frost will take full advantage of the remaining growing season. Like most forages, corn has high milk per ton prior to flowering (R1) that subsequently declines (Figure 1E). Greatest stover yield will be produced with full-season hybrids. Stover yield increases 0.5 T dry matter/A for every 10 RM units (derived from Lauer et al., 2001 and SELECT: 1990-1995).

Finally, selecting a hybrid that has improved stover traits might maximize forage quality. An example of a hybrid with improved stover quality is bmr hybrids, although seed companies have been very active in developing and identifying hybrids with greater NDFD. Visit with seed company representatives regarding NDFD traits of hybrids. Keep in mind though that little research is available regarding quality differences at silking between hybrids.

A significant challenge in managing emergency corn forage is timing harvest. Proper forage moisture is critical for fermentation and preservation. Corn planted around July 1 will likely only develop to flowering (R1) and be too wet for ensiling until after a fall killing frost (Figure 1B). After a killing frost forage moisture will have to be monitored closely. The problem is that all emergency planted acres on a farm will need to be chopped within a relatively short harvest window. Custom choppers will not be able to get to all late-planted fields in a timely manner.

In conclusion, corn planted around July 1 as "emergency" forage has relatively good forage production potential compared to other forages. During the life cycle of corn, forage quality is best at flowering AND at maturity. Successfully optimizing corn forage quality depends upon farmer objectives and matching hybrid flowering date with remaining GDU accumulation for the season.

Literature Cited

Darby, H. M. and J. G. Lauer. 2002. Harvest date and hybrid influence on corn forage yield, qualtiy and preservation. Agron. J. 94:559-566.

Lauer, J. G. 1997. Corn replant/late-plant decisions in Wisconsin . University of PC_ Wisconsin Cooperative Extension Publication, Madison , WI . A3353, 6 pp.

Lauer, J. G., J. G. Coors, and P. F. Flannery. 2001. Forage yield and quality of corn cultivars developed in different eras. Crop Sci. 41:1449-1455.

Oplinger, E. S. and J. G. Lauer. 1997. Studies on cultural practices and management systems for agronomic crops. University of PC_ Wisconsin Department of Agronomy 346 pp.

Schwab, E. C., R. D. Shaver, J. G. Lauer, and J. G. Coors. 2003. Estimating silage energy value and milk yield to rank corn hybrids. Animal Feed and Science Technology 109:1-18.