Minnesota Crop News > 2001-2008 Archives
Look at Minnesota Corn Yields over Time
Agronomy and Plant Genetics
University of Minnesota
Corn yields in Minnesota have been excellent for the past
few years and have exceeded the expectations based on weather
and growing conditions during the growing seasons. Whole
field yields during the past three years have exceeded
200 bushels per acre for many growers in the central to
southern regions of the state. As a result, we may begin
to wonder if these high yields are now normal and should
we expect them in the future or have they been blips on
the yield profile? It may not be very accurate to use the
past to predict the future, but it is one method to look
forward to corn yields of the next few years. That’s
the objective of this paper.
I used the 1968 to 2004 state average corn yields to determine
both a linear trend line and a curvilinear trend
line and then used those to predict the 2005-state
average corn yield. Both models (linear and curvilinear)
had similar fits to the data (the degree of fit is determined
by the R2 value for each model and the R2’s
were not statistically different). But, the curvilinear
trend line turns upward for the past few years, which shows
a better visible fit to the increasing yields of the last
few years. The linear trend line for the 1968-2004 period
predicted a state average yield of 147 bu/a for 2005 and
the curvilinear model predicted a state average yield of
158 bu/a for 2005. The last crop report pegged the Minnesota
state average corn yield at a whopping 171 bu/a! The curvilinear
model better predicted the 2005 corn yield.
What can we expect for 2006; will these high yields
I’ve updated the trend lines
including the 171 bu/a state average yield for 2005
and re-calculated both the linear and curvilinear models.
The linear is graphed in Figure 1 and the curvilinear
in Figure 2. The R2 values are again not
different statistically, so the long-term corn yields
fit both models equally well. However, the curvilinear
model is a better fit for the last few years because
it turns upward as I mentioned above. Based on 38 years
of Minnesota state average yields, a linear trend line
would predict a state average yield of 153 bu/a for
2006 while the curvilinear trend line would raise that
prediction to 164 bu/a.
Figure 1. Minnesota state average corn yields
for 1968-2005 with a linear trend line.
Figure 2. Minnesota State average corn yields
1968-2005 with a curvilinear trend line.
Is a state average yield of 164 bu/a doable?
the 2005 crop topped that. And yields for the next few
years will need to continue to go higher if we stay on
either a linear or curvilinear yield trend over time. But,
we should caution ourselves that a major factor driving
these high yields is the environment, which we can’t
predict very accurately. How much available stored soil
moisture do we have in the root profile going into the
growing season? When will the crop get planted? What will
the rainfall be--both the amount and distribution
during the growing season? What will temperatures be? Will
we have extreme temperatures at times when available moisture
is short? These are major environmental variables
that can make or break corn yields.
Deviations from the trend line do occur.
deviations (for either the linear or curvilinear model)
occurred in 1974 (Labor Day frost), ‘75, ‘76, ’83
and ‘88 (dry or dry and hot years), and ‘93
(late planting, cold and wet year).Corn
yields have been on or above the trend line (for both models)
for seven of the past nine years, which is one way of suggesting
that we may be due for a deviation from trend, and possibly
below trend line. The ‘74, ‘75, and ‘76
drops in yield were 20% below trend line and the ’83, ‘88
and ‘93 low production years were 20% to 50% below
the trend line, so major low yields have occurred.
A speaker at the recent Agri-Growth Council meeting was
asked if Minnesota corn production could continue to provide
grain for both the livestock industry and the expanding
ethanol industry in years when corn yields might be low.
The speaker’s response was, "Technology has
insulated us from disaster years." I don’t
believe that to be the case. It’s true that corn
breeders have provided us with high yielding hybrids that
appear to tolerate stress with a minimal effect on grain
yields (hybrids is only one of the technologies that has
contributed to high corn yields). We shouldn’t
be lulled to sleep expecting that high corn yields are
the norm. We need to remember that the weather we get is
the major yield limiting or non-limiting factor. Let’s
hope for a good growing season next year to continue this
upward yield trend for corn in Minnesota.
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