NOVEMBER 30, 2003
WHAT DO 2003 CORN AND SOYBEAN YIELDS INDICATE ABOUT FUTURE YIELDS?
Yields on many Illinois farms
in 2003 can be summarized using six words: excellent corn yields,
poor soybean yields. In this article, we compare 2003 corn and soybean
yields to historical yields. This examination indicates that it
is unusual to have an above average corn yield in the same year
as a below average soybean yield. However, this examination does
not suggest that the long-term relationship between corn and soybean
yields has changed.
State of Illinois Yields
Figure 1 shows state-average
corn yields for Illinois in the years between 1972 and 2003. Actual
yields are shown by dots. Also shown by a line are trend-line yields.
Trend-line yields increase each year by the average increase in
yields between 1972 through 2002. The Illinois corn yield has increased
1.45 bu. per year.
The projected yield for 2003
of 169 bu. per acre represents the highest corn yield that has ever
occurred in Illinois. The 2003 yield is 21 bu. above the trend-line
yield of 148 bu. per acre. The last time the actual yield was above
the trend-line yield by more than 20 bu. was in 1994. In that year,
the actual yield of 156 bu. was 23 bu. above the trend-line yield
of 133 bu. Overall, 2003 is an excellent corn yielding year.
Figure 2 shows state-average soybean yields for Illinois in the
years between 1972 and 2003. Trend-line yields have increased an
average of .42 bu. per year between 1972 and 2002.
The projected soybean yield in
2003 is 37 bu. per acre, 7 bu. below the trend-line yield of 44
bu. While below average, the 2003 is not the worst soybean yielding
year. Actual soybean yields were significantly below trend-line
yields in 1974 (8 bu. below trend-line yield), 1983 (7 bu.), and
1988 (11 bu.). Since 1988, however, soybean yields have not exhibited
much variability. This long period of relative stability was finally
broken in 2003. What may be more unusual than the below average
yield in 2003 is the relatively stable period from 1989 through
Also unusual is that an above-average corn yield occurs in the
same year as a below-average soybean yield. Figure 3 shows yearly
corn yields divided by the soybean yields, hereafter referred to
as corn-soybean yield ratios. Between 1972 through 2003, this ratio
averages 3.24 and exhibits no trend up or down. This suggests that
corn yields relative to soybean yields have been stable over this
The 2003 ratio of 4.6 is well
above any other year's ratio. Some have suggested that corn yields
have increased relative to soybean yields. If this were the case,
the ratios in Figure 3 would be trending up over time. The 2003
corn-soybean yield ratio likely represents an unusual event that
will occur rarely in the future.
Corn and Soybean Yields in Crop Reporting Districts
Differences in the relationship
between yields exist across Illinois Crop Reporting Districts (CRDs).
While the corn yield has increased an average of 1.45 bu. for the
state, yields increases exhibit a range from a high of 1.66 for
the Northwest CRD to a low of 1.22 for the East CRD (see Table 1).
Yields appear to be increasing faster in the western part of the
state and slower in the eastern and southern portions of the state.
Soybean yield increases exhibit similar variability. The average
soybean yield increase for the state is .42 (see Table 1). Yield
increases range from a high of .51 for the Northwest and West CRDs
and a low of .24 in the Southwest CRD. Yields again appear to be
increasing faster in the western part of the state.
Over most of Illinois, the corn-soybean yield ratio has exhibited
no trend from 1972 through 2002 (see Table 1). Three CRDs located
in southern Illinois have a slight positive trend in the yield ratio:
West Southwest (.01 increase per year), Southwest (.02), and Southeast
Similar graphs to Figures 1 through 3 for each
crop reporting district are available here: http://www.farmdoc.uiuc.edu/manage/newsletters/fefo03_22/0322figures.html
In this article, 2003 corn and
soybean yields are compared to historic corn and soybean yields.
The 2003 corn yield is considerably above average and the 2003 soybean
yield is significantly below average. Having an above average yield
in one crop and a below average yield in the other crop is highly
Some have suggested that 2003
indicates that corn yields continue to outpace soybean yields. An
examination of historic yields questions this viewpoint. With exceptions
in the southern part of the state, corn yields relative to soybean
yields have been relatively stable in most areas of Illinois prior
to 2003. The 2003 corn-soybean ratio is considerably higher than
historical corn-soybean yield ratios. It is likely that the 2003
yield is an unusual event that will occur infrequently.
Issued by: Gary
Schnitkey, Department of Agricultural and Consumer Economics