Mid-County Messenger Page 4
www.midcountycoop.com
Spring 2006
Mid-County Agronomy
How much nitrogen is needed to grow corn?
Participate in nitrogen study
Our University Extension, along
with most of the Universities from
the corn belt, have come up with new
nitrogen recommendations. The new
recommendations are typically lower
than the previous recommendations
by about 40-50 lbs/acre.
The real old nitrogen recommenda-
tions took into account yield goals and
organic matter of the soil. Figuring
that it takes 1.2 pounds of nitrogen
to produce one bushel of corn and
figuring that there is a minimum of 10
pounds of nitrogen for each percent of
organic matter, you would come out
with a recommendation of about 136
pounds of nitrogen for a yield goal
of 180 bushel corn and soil with 4%
organic matter.
The slightly newer recommendation
simply has a chart where you cross
reference the yield goal by the previ-
ous crop and the organic matter clas-
sification of the soil. In our above case
the recommendation would be 140
pounds of nitrogen under these recom-
mendations, which is pretty close to
the previous recommendation.
What the newest recommendations
do is look at the price of nitrogen
and the price of corn, and nothing
else. Using the parameters of 40¢ per
pound nitrogen cost and an optimistic
price of corn $2.60, the most economi-
cal recommendation is 89 pounds of
nitrogen. That’s about two thirds the
previous recommendations.
Why the difference? There are some
valid reasons why these recommenda-
tions have come down over the past
years. First and foremost is that we
have better hybrids that can produce
yields more efficiently. Part of that
Joe Forner
Agronomist
[email protected]
is Bio-tech traits like Corn Borer and
Corn Rootworm Bt that help protect
the yield. Traits like Roundup Ready
and Liberty Link improved weed con-
trol and have lessened competition
for fertilizer by these weeds. Throw
into the mix better drainage, planting,
and tillage equipment and yields have
increased without increasing inputs.
Is that enough to make up a 30%
decrease in fertilizer usage? In my
estimation it isn’t. Running the same
numbers for the price of corn and
price of nitrogen using the Iowa and
Wisconsin equations gives recommen-
dations of 109 and 101 pounds of
nitrogen respectively.
Iowa’s recommendations are 20
pounds higher than Minnesota. Illi-
nois’ recommendations are at 139
pounds of nitrogen; a whopping 50
pounds greater than Minnesota. Does
corn grow that much differently in
Minnesota compared to Iowa, Illinois,
and Wisconsin?
The new rates also concede that
about 20-25% of the time nitrogen
will be put on at less than economic
rates, meaning that about a quarter of
the time we could get substantially
more yield with additional fertilizer
applied.
The old recommendations were
insufficient about 5% of the time.
With the new rates we are about 4 to 5
times more likely to see reduced corn
yields due to insufficient nitrogen.
While there is some merit to bringing
the recommendations down, I believe
they have come down too far too fast
and are out of line with our neighbor-
ing states. The risk of shorting nitro-
gen is also too great since we have
little opportunity to sidedress nitrogen
after planting. If someone wants to use
these new recommendations all I can
say is “use at your own risk”.
Minnesota Nutrient Management
Initiative
The Minnesota Department Of Ag
has put together a program to encour-
age farmers from around the state
to put in strip trials to examine the
nitrogen and phosphorous recom-
mendations on large plots. The fields
should be in a co