With expectations of ending corn stocks for 2011-12 to be near pipeline levels, the size of the 2012 crop has substantial price implications, says Darrel Good, University of Illinois (UI) agricultural economist.

Although acreage intentions will be revealed in the USDA's March 30 Prospective Plantings report, much discussion will continue to revolve around the prospects for the U.S. average corn yield. Ask enough folks and you’ll find yield projections all over the board – and off the board.

Good says four yield factors receiving lots of attention are:

• The timing of planting,

• Magnitude and potential change in the trend yield,

• Expected summer weather conditions and

• Location and magnitude of acreage changes.

“The mild winter weather and early spring fieldwork suggests the 2012 crop will be planted in a very timely fashion,” Good says. “There is a general perception that early planting results in a higher U.S. average yield potential, all other things being equal.”

Agronomic research in the Corn Belt reveals a slight yield penalty for extremely early planting (March), a wide planting window for maximum or near maximum yield potential (early to mid-April through early May), and a yield penalty for late planting that increases with the lateness of planting.

“While there is a clear yield penalty for late planting, there is not a similar yield premium for early planting,” Good explains. “The majority of the crop is planted in the optimum window in most years.

“To have an effect on U.S. average yield potential, a substantially larger or smaller portion of the crop would have to be planted outside the optimum window,” Good says. “For 2012, a smaller-than-average percentage of the crop planted late might increase yield potential, but that impact would be quite small.”

By mid-March, there were already reports of corn planting taking place in parts of Illinois.

“Although there have been some fields planted this early in the past, this is the earliest we've ever had good planting conditions across so much of the state, and it's certain that we have never before had this many corn acres planted so early,” says Emerson Nafziger, a UI professor of crop sciences.

Widely varying opinions about the trend in U.S. average corn yields have emerged in recent years. According to Good, “the long-term increase in average yields is associated with the development and adoption of crop production technology and crop management practices.” The nature of those developments has varied over time, but there's been a steady flow of yield-enhancing technology and practices.

For the most part, Good explains that variation around the trend yield reflects variation in growing-season weather, although events such as pest infestations or early occurrences of freezing temperatures can have a yield effect. Confusion about the yield impact of technology and weather can occur if there is a string of years with very favorable or unfavorable weather. In that case, the impact of weather can be attributed mistakenly to technology and give the impression that the underlying trend yield has changed.

“That appeared to have happened from 2003 through 2009 when generally favorable weather led some to believe that the underlying trend yield was increasing at a faster rate,” Good says. The reverse may have occurred recently; poor weather in 2010 and 2011 resulted in low yields following the record yield of 2009. Overall evidence suggests that the trend in U.S. average corn yields has been linear since 1960.

As for weather, the debate is whether the nation is transitioning from La Niña to neutral conditions – associated with average trend value, according to Good – or transitioning directly to El Niño, which Good says would increase the odds for above-average yield.

U.S. corn plantings are expected to increase by 2-3 million acres in 2012. Some argue that the increase will occur in lower-yielding areas and therefore prove to be a drag on the U.S. average yield.

Good thinks that the yield implication of increased acreage is likely to be extremely small. “First, some of the increase in corn acreage may occur in the higher yielding areas of the eastern Corn Belt since acreage there in 2011 was below the recent peak of 2007,” Good says. “Second, a 2-3% increase in acreage has the potential to only marginally impact the U.S. average yield even if all the increase was in low-yielding areas.”