Questions about Nitrogen and Corn?
By Justin Petrosino, ANR Extension Educator
OSU Extension, Darke County
For
some, planting this season is just wrapping up with the final fields of
beans being planted. For others things are in full swing. If you are
like old Hank Kimball here in the office, things are getting
piecemealed in one plot at a time. One of the big questions floating
around is, “How much nitrogen do I include in a sidedress application
for corn that is planted late?” There is not a simple answer to that
question.
Let’s start with where our nitrogen recommendations come from. N (lb/A)
= -27 + (1.36* Yield Goal) – N Credit. Simple right? Total pounds
of nitrogen to apply equals 1.36 times your yield goal, minus 27, minus
any nitrogen credits. The two big questions arise around yield goal and
nitrogen credits. Do we need to decrease our yield goal, and do we need
to adjust for any nitrogen credits?
There have been many recent teleconferences, late night email
exchanges, and phone calls made to our State Corn Specialist, Dr. Peter
Thomison, and to Purdue’s own Dr. Bob Nielsen. Both agree that yield
loss from late planting depends on what happens later in the season.
Will we see ideal rainfall and optimal temperatures or will it turn off
hot and dry for the rest of the summer? In recent years with late
planted corn yields were as high as 8 % above average to as low as 20 %
below average. In most research studies corn planted mid-May faced a 10
% yield loss which increased to 20 % if corn was planted early June. So
bringing that yield goal down some may be warranted. It all depends on
the weather!
Nitrogen credits are a hot topic, mostly in the form of cover crops and
manure. Manure, if you could get any out and incorporated this spring,
applied at a rate based on a soil test and manure analysis is fairly
easy to account for. The question arises when it was applied last
summer after wheat. Will any nitrogen be available?
Cover crops can provide some nitrogen, whether fixed by bacteria in the
roots of leguminous cover crops or taken up by a rye cover crop. This
nitrogen can be quite finicky in its release and timing. Nitrogen
release from residue is a biological process, so environment plays a
major role. This is further complicated by the cover crops growing
season. To fix nitrogen the Rhizobia bacteria found in a legumes root
nodules need an optimal habitat and time. Typically a full growing
season is needed to generate a significant amount of nitrogen. However,
without bacteria fixing nitrogen, a legume will act like any other crop
and take up available nitrogen from the soil.
So
how big is the nitrogen credit from manure or a cover crop? An accurate
way to determine what is available before a sidedress application of
nitrogen is made is to take a pre-sidedress nitrogen test (PSNT).
Pulling 10 to 20 cores per field depending on field size, 12 inches
deep, combining into a single sample, air drying, and submitting to a
testing lab can help you know what nitrogen is available. Once the
results come back you can consult with your fertilizer company or local
Extension office to determine how much nitrogen to apply in a
sidedress. The tests need to be taken as close to the time of nitrogen
application as possible. It is recommended to contact your testing lab
ahead of time to determine the turnaround time on the samples.
Determining an optimal rate of nitrogen for corn is complicated enough
without late planting. But if we wanted a simple job we wouldn’t be in
agriculture. A little extra time spent in a corn field that received
manure or had a cover crop last season may pay dividends! If you have a
surplus of manure in a pit that needs to be emptied, consider
sidedressing your corn with it! Just ask Putnam County AgNR Educator
Glen Arnold! It can work.
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