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Illinois
AgriNews - July 2004
 
Understanding and Using USDA’s Weekly Report of Crop Conditions
Scott Irwin and Darrel Good
Department of Agricultural and Consumer Economics
University of Illinois at Urbana-Champaign
The USDA’s weekly report of
crop conditions is one of the most widely followed
indicators of corn and soybean yield potential. The
survey and estimating procedures for
this report are much different than for most surveys
conducted by the USDA. For
example, the monthly corn and soybean production forecasts
rely on a June acreage
estimate based on a survey of farmers and on a separate
area frame sample. Monthly
yield forecasts are also based on a survey of farmers
and objective yield estimates based
on an area frame sampling design where fields are randomly
selected for observation and
measurement.
In contrast, the crop condition surveys “are non-probability
surveys that include a
sample of more than 5,000 reporters whose occupations
provide them opportunities to
make visual observations and frequently bring them in
contact with farmers in their
counties.” These reporters indicate the percent
of the crop in five condition categories,
including very poor, poor, average, good, and excellent.
Reports reflect conditions, or
expected conditions, as of Sunday. Nearly two-thirds
of the reports are submitted
through a secure web site and about half of all data
are submitted on Monday morning.
The data are reviewed at the state level for reasonableness
and consistency and submitted
to the Agricultural Statistics Board which then releases
condition estimates each Monday
for each of 18 states and a weighted average of all
the states.
Analysts use the crop condition data in a variety of
ways to anticipate crop yields
and production. We have found that the percentage of
the crop rated good or excellent
for all states in the final report of the season is
reasonably correlated with the U.S.
average yield. Because there has been a trend increase
in average yield over a long
period of time, historical yield data must be adjusted
for the trend and then the adjusted
yield is correlated to the percent of the crop rated
good or excellent. For the current year,
then, all historical data are expressed in terms of
2004 equivalent yields in order to
calculate the correlation to crop conditions. Using
data over the past 18 years, the
percent of the crop rated good or excellent in the final
report of the year explains 86 and
83 percent of the variation in trend-adjusted yield
for corn and soybeans, respectively.
During the growing season, the forecast yield can be
calculated assuming that the
current weekly crop ratings are maintained to the end
of the season, or on the basis of
any other assumption about crop condition ratings that
the user wishes to make. For
example, 74 percent of the 2004 corn crop and 68 percent
of the soybean crop were rated
in good or excellent condition as of July 11. If those
ratings are maintained through the
end of the season, past relationships project to a national
average yield of 148.3 bushels
for corn and 41.9 bushels for soybeans.
There are limitations to using crop condition ratings
as an indicator of yield
potential, but they do provide useful information. The
trick is to forecast the end-of-year
ratings!!
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