May 2008
Field Crops 28.47-55

"Switch" Date Decisions for Corn Hybrids

 Joe Lauer, Corn Agronomist

As the 2008 planting season progresses, growers are becoming increasingly concerned about yield loss due to delays. Yield penalties start to become significant after May 10-15, but what growers really need to worry about is the increased drying costs that will likely happen in the harvest season if planting is delayed much longer.

Full-season corn hybrids have the greatest potential for maximizing grain yield. Figure 1 shows the grain yield relationship with planting date at Arlington over the previous 10 years. The planting date that produces maximum grain yield is May 1. On May 1, full-season hybrids will produce more grain yield than shorter-season hybrids. After May 1, grain yield decreases slightly at first, but then accelerates to 0.5 bushels per day delay around May 15 and by June 1 grain yield is decreasing by 2.5 bushels per day delay.

Beginning around May 23, shorter-season hybrids produce higher grain yield than full-season hybrids. Not only are shorter season hybrids better yielding, but they are also drier at harvest thereby increasing grower return through reduced drying costs. If drying costs are not a concern then switch dates should occur around May 23 at Arlington.

The date to switch  from full-season to shorter-season hybrids is influenced by grain price and energy costs associated with drying grain in the fall at harvest. Drying cost has more influence on this decision than grain price. Table 1 shows switch dates for various drying cost:corn price ratios. As energy costs increase from $0.00 to $0.07 per point bushel, then switch dates become 10 to 30 days earlier than May 23 depending upon corn price. As corn price increases from $1.00 to $6.00 per bushel, then switch dates become 8 to 20 days earlier than May 23. Other factors that will influence the switch date decision include:

1. Desire to accept risk: Full-season hybrids offer the highest yield potentials, but may also increase drying costs and/or delay harvest.
2.  Potential use of the corn produced: High moisture corn versus corn silage
3.  Field conditions: Although the penalty for late planting is important, growers also need to be careful to avoid tillage when soil is too wet. Yields may be reduced somewhat this year, but effects of soil compaction can reduce yields for several years to come.
4. Hybrid dry-down and grain quality characteristics: Longer-season hybrids within the latest acceptable planting dates should have fast grain dry-down and high test weight characteristics. Growing season, site and management influence a particular hybrid's actual days to maturity.
5.  Ease of trading original hybrids for superior shorter-season alternatives.

The amount of energy required to reduce a bushel of corn one percentage point will depend upon the efficiency of the corn dryer and the energy content of the fuel used for drying. Last year LP gas was selling for around $1.70 per gallon. Most inputs have increased this year. 

In southern Wisconsin in some years, farmers have the potential to switch hybrids maturities at most twice during a growing season with the last switch primarily intended for corn silage (maybe high-moisture corn in some years). In northern Wisconsin, only one switch day is possible and then growers should consider other crops. 

Figure 1. Corn grain yield relationship between full- and shorter-season corn hybrids grown during 1998 to 2007 at Arlington, WI. Full-season hybrids averaged 105 days Relative Maturity, while shorter-season hybrids averaged 95 days Relative Maturity.