Illinois Soil Nitrogen Monitoring: Announcing A New Project
DR. FABIÁN FERNÁNDEZ
URBANA, ILL.
The low corn yields and early death of the
crop in dry areas of the state have resulted
in a great deal of N in Illinois soils, both
from fertilizer and from mineralization of soil organic
matter. Because soil microbes convert
ammonium to nitrate over time, we can expect
that nearly all of this N is in the form of nitrate.
Nitrate is a form of N that plant roots can take
up, of course. But it’s also a form that, unlike
ammonium, moves readily in the soil. With no
roots present in most fields to take up nitrate,
the nitrate in the soil now is subject to downward
movement with water. If it stays relatively
dry between now and next spring, some of this
nitrate may remain in the soil to be available for
next year’s crop. Having a lot of soil N present
now might help some producers decide to cut
fall N rates, in case the amount of N carried over
into the spring means less total N will be
needed. Also, knowing how much nitrate remains
in the soil next spring can help us finetune
N rates if corn in 2013 follows corn in
2012.
If there is enough rainfall to get tile lines to
run, we can expect some of the nitrate to leave
the field in drainage water or to migrate below
the root zone. In fields without tile drainage, wet
soil conditions (while soil temperatures are
above 50°F) can also result in conversion of nitrate
to nitrous oxide or nitrogen gas, both of
which will leave the soil. Knowing how much nitrate
is present this fall can help us know how
much loss there might be before corn or soybean
roots next spring start taking up what N is
left.
Knowing how much soil N remains in fields
now will thus provide valuable information from
both economic and environmental standpoints.
To start to gather such information, we are initiating
a project immediately to sample soils for
N measurements. Funding is provided by the
Council for Best Management Practices; there is
no cost to producers or to those who take samples.
The protocol for the sampling follows:
• After harvest of corn, identify a 20 ft by 20 ft
site where samples will be collected. This needs
to be a site you can return to for spring sampling,
and it must be one where you know that
N application for the 2012 crop was uniform
(not on a headland, for example). This should
also be a field where no manure was applied for
the 2012 crop, and it might be best to avoid
fields where manure has been applied in recent
years.
• Take GPS coordinates of the center of the
area to be sampled. This and other information
will go onto a short form we provide, and a copy
of the form will accompany the soil when it is
sent to the lab.
• Collect soil samples after harvest this fall,
preferably in the second half of October, after
soils have started to cool but before any fall NH3
is applied. This timing means that nitrate in the
sample should be close to the amount present
as soils cool down and freeze.
• In spring 2013, collect samples at or shortly
before planting (within 2 weeks). Samples can
also be collected earlier in the spring once the
soil has warmed to near 50°F, but the one close
to planting will indicate how much N might be
available to the crop.
• Samples should be a composite of 4 to 6
cores (0.75 to 1 inch diameter). If fertilizer N was
broadcast-applied or if tillage has been done,
take samples randomly from within the area. If
N was banded (anhydrous or UAN) in 2012 and
soil hasn’t been tilled, take one probe core in the
band (or center of the row), one core 7 or 8 inch
from the band, and one core near the row. Do
this in two places and composite for one sample.
• The most important information comes from
samples taken to a 1-foot depth. This can be
done using a regular probe as long as you can
take 0-to-6-inch and 6-to-12-inch samples and
combine them. A 15-inch probe works better. If
possible, a 1-to-2-foot sample (below where the
0-to-1-foot sample was taken) will also be of interest;
take this sample if soils are not too hard
to get it. If tillage is done prior to sampling and
the surface soil is fluffy, step on the soil surface
to firm it up, then sample in the footprint.
• Take the 4 probe samples (6 if sampling after
banded N) from each depth and combine them
in one bag. Label each bag, package soil samples
in the box provided, and send the box to
A&L Laboratory along with the information form
for each sample location.
If possible, we would like to have at least 10
samples (from 5 sites at 2 depths each) and up
to 40 (from 20 sites) shipped to the lab together
for efficiency. This will require a coordinator to
pull together samples from the sites. The coordinator
can be a producer sampling numerous
fields – his or her own or from other producers
as well – or a public or private employee who assembles
samples from producer fields.
Bags and boxes for sampling will be sent to
each coordinator by A&L Laboratory of Ft.
Wayne, Indiana. To request these, the coordinator
need only send an email to Emerson
Nafziger (ednaf@illinois.edu), including the coordinator’s
name and mailing address, the
number of samples to be taken (number of sites
times 2), and the county or counties where samples
will be taken. We will in return email a form
to be sent with each set of samples, and we will
request that sample bags and shipping boxes be
sent directly to the coordinator.
All of the samples put in the same box for
shipping should be taken over a 24-hour period
and shipped immediately to the lab. If any samples
need to be kept for more than 24 hours before
shipping, refrigerate them. Shipping should
be done on Monday through Thursday; do not
ship on a Friday.
Results as they come in will be placed on a
map with no identification of producers or GPS
coordinates; they will also be made available to
the coordinators of the sampling. Δ
DR. EMERSON NAFZIGER: Professor/Research
Education Center Coordinator, University of Illinois
DR. FABIÁN FERNÁNDEZ: Assistant Professor/
Crop Sciences, University of Illinois