Page 26—Com Talk, Lancaster Farming, Saturday, October 12, 1996
PSNT FOR CORN
Doug Beegle
Pertn State
Soil Fertility Specialist
The Presidedress Soil
Nitrate Test (PSNT) for com
has been used successfully in
Pennsylvania for several years.
This nitrogen soil testing ap
proach is based on taking soil
samples just before sidedress
ing after the spring wet per
iod but before the period of
major nitrogen demand by com
and determining the nitrate
nitrogen available in the soil at
that lime.
If the test level is greater
than 21 parts per million
NO,-N, no sidedress nitrogen
is recommended. If the test is
below this level, the results of
the test are then used to make
sidedress nitrogen recom
mendations.
This test is primarily recom
mended for use on fields where
there are significant organic ni
trogen contributions such as a
history of manure applications
or forage legumes in rotation.
It does an excellent job of veri
fying when these organic sour
ces of nitrogen are adequate for
the crop. This lest is of limited
value on most fields without
organic nitrogen contributions,
because these fields generally
have low levels and thus the
standard recommendations are
suitable.
Since this test is somewhat
unique compared to regular
soil tests, it is probably worth
while to review the procedures
for using the PSNT since it will
soon be time to test. The PSNT
procedure is as follows:
1. Only apply a minimum of
fertilizer nitrogen in the spring.
(Starter fertilizer and/or nitro
gen used as a herbicide car
rier.)
2. Apply manure based on
the history of the field, a man
ure analysis, how the manure
will be handled, and on crop re
quirements for nitrogen esti
mated from the expected yield
and crop history.
3. Take soil samples when
the com is 12 inches tall or at
least a week before planned
sidedressing.
4. Sample the fields by tak-
ing 10 to 20 cores to a 12-inch
depth if possible. If not sample
as deep as you can. Avoid start
er bands and other atypical
areas. Because of sampling
problems, this test cannot be
used on fields that received in
jected fertilizer or manure.
5. Combine and crumble the
cores and dry as quickly as
possible. Spread the samples
out in the sun or under a heat
lamp in a well ventilated area
to dry. The samples must be
dry within 24 hours.
6. The sample can be sent to
a reputable soil testing lab for
soil nitrate-nitrogen analysis.
A reliable field test kit for soil
nitrate-nitrogen can be used to
determine the nitrate-nitrogen
level in the sample.
7. Calculate the adjusted ni
trogen recommendation from
the worksheet below.
There are several areas that
seem to cause the most prob
lems with the PSNT. First,
many people try to take the test
too early. It is important for the
test to work properly that the
com be at least 12 inches tall at
the top of the whorl when you
sample. A second problem re
lated to timing of sampling is
taking samples immediately af
ter a heavy rain. Experience
has shown that the test works
best if you allow 2 to 3 days
following a heavy rain before
sampling for the PSNT.
Sampling too soon after a
rain can give a false low read
ing indicating that there is less
nitrogen available than there
really is. Third, and this is the
tough one, for the test to work
the best the samples should be
taken to a 12-inch depth.
Unlike phosphorus and po
tassium, nitrate will readily
move deeper into the soil.
Everyone complains about this
deep sampling but it could be
worse because taking deeper
samples would be even better.
Some states recommend two or
even four-foot deep samples
for nitrogen testing.
This 12-inch depth seems to
be a reasonable compromise
between optimum accuracy of
the test and sampling practi
cality. Finally, the samples
need to be dried immediately.
They should be completely dry
within one day of when they
are taken. I have seen sample
nitrate nitrogen levels increase
by a factor of 2 to 3 times just
from sitting around damp over
a weekend.
Agronomy Factsheet #l7
“Presidedress Soil Nitrate Test
for Com,” which explains the
PS NT in detail, is available
from Penn State Cooperative
Extension offices.
Statewide Com Checkoffs
What Is a Checkoff’
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NCGA-NCDF
Pennsylvania Corn, Soybean
GRANTVILLE (Dauphin
Co.) Plans are nearly com
plete for the 1997 Com and
Soybean Conference scheduled
Feb. 7 at the Holiday Inn at
Grantville.
This year’s program prom
ises to be a good one and will
feature Dave Cruse, an enter
taining ag broadcaster from
lowa, who will provide us with
his forecast for the 1997 com
and soybean markets.
The program will also fea
ture a recap of the growing sea
son for com and soybeans by
agronomist Mike Brubaker,
president of Brubaker Agro
nomic Consulting Service. Dr
Jim Bierlien from Penn State’s
R.K.IAIOGT
1225 >
Colebrook Rd.
BUYING BAR CORN.
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(717) 653-2510
1 (800) 654-2510
Spot or contract prices available
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Ag Economics and Rural
Sociology Department will
take a look to the future in
another presentation and ask
producers if they are ready for
managing farms in the 21st
century.
Other topics on the program
include the performance of Bt
com hybrids this year, a report
on the activities of the Mary
land Grain Producers Utiliza
tion Board, a review of some of
the new uses of soybeans, and
Marietta, PA
17547
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an update on some of the added
value soybean varieties that are
being developed.
The conference will also
include ag industry exhibitors,
Five Acre Com Club and Soy
bean Yield Contest awards, and
reports from the Pennsylvania
Master Com Growers and the
Pennsylvania Soybean Board.
More information on registra
tion will be available soon.
Mark your calendars and plan
to attend.
ATTENTION FARMERS:
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with a
H ROLLER
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It
are machine cut from a continuous length
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