Note DetailYield Estimate Reasonable but shaky
8/12/2008 11:41:00 PM

Yield Estimate Reasonable but shaky
The USDA yield estimate of 155BPA for US corn and
40.5BPA for soy based on a survey of crop condition
and stand counts is reasonable.  However, the
estimate assumes that the crop will
encounter “normal” weather throughout the remainder
of the growing season.   It must be remembered that
the estimate does not consider abnormalities of
growing degree units and some other hidden impacts
weather has taken on the crop to date (a condition
that resulted in an actual yield considerably below
the estimate in 2007).  Moderate temperatures have
benefited the development of a crop still highly
vulnerable to stress inflected by adverse planting
(and flooding) conditions.  Precipitation in August
has been below normal in the bulk of the Corn Belt
although there are conspicuous exceptions. Although
a final yield even higher than the estimate is
possible, the possibility of adversely hot
temperatures during the next 4 weeks constitutes
the very real risk that the US corn yield could
fall below the trend (150.6BPA).
   Historically crop condition observations become
meaningful after mid-August.  The 2008 crop to date
has persistently scored better than average for the
Corn Belt in general.    When more than 50% of the
crop is rated good to excellent the anticipated
yield exceeds the trend.   The current US corn
condition is 67% good-excellent.     -- Elwynn

Iowa State University Extension