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UTILIZING THE LATE SPRING (PSNT)
SOIL TEST TO OPTIMIZE
NITROGEN MANAGEMENT FOR CORN
Reasons for Using the Soil Test
Nitrogen fertilization is essential for profitable corn production, but it also is a major cost of production and can
contribute to degradation of the environment.
Who Should Use the Test
Producers who do not sidedress can use this test in fields already fertilized to obtain feedback on their nitrogen
management.
Producers who normally sidedress can use the soil test to adjust nitrogen rates for all factors affecting soil nitrate
concentrations in late spring.
The use of this test requires higher levels of management, but the additional management usually yields significant
economic and environmental benefits.
Time of Sampling
Collect soil samples when corn plants are 6 to 12 inches tall (measured from the ground surface to the center of the
whorl). The test is called the "late-spring" soil test or Pre-Sidedress Nitrate Test (PSNT) to emphasize that the time of
sampling makes this test different than other soil nitrate tests.
Depth of Sampling
Samples collected for the late-spring soil test must be representative of the top foot of soil. Samples taken at a
different depth or timing could alter the interpretation of the data.
Methods of Sample Collection
Soil samples analyzed for this test should be derived from at least 16 to 24 cores collected within an area not
exceeding 10 acres. Areas with different soil types or management histories should be sampled separately.
Care should be taken to ensure that the soil samples are collected in a manner that is not biased by the presence of
corn rows or bands of fertilizer. At least 24 cores should be collected in fields having more than 50 pounds
nitrogen/acre applied as anhydrous ammonia.
Sampling in patterns relative to the corn row can help improve the accuracy and eliminate potential effects from band
applications. Move to the first sampling location and take a core 3 inches to the left. The cores from the second
location should be taken 6 inches to the left. Repeat this process moving an additional 3 inches each time until the
adjacent row is reached.
Handling and Shipping Soil Samples
Protect moist soil samples from temperatures above 75˚F and refrigerate the samples if they cannot be analyzed within
two days. Mailing usually poses no problem if the samples spend no more than two days without refrigeration.
Nitrogen Applications Before or Near Planting

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If sidedressing is not planned, the producer's normal rate should be applied unless previous use of the test has
demonstrated need for change.
If sidedressing is planned, apply only modest amounts of nitrogen before or at planting. This means no more than 70
percent of the total amount normally applied in a year. At least 30 to 50 percent of the amount normally applied is
recommended for unmanured fields in continuous corn. See attached table on page 3.
If sidedressing is possible, no more than a normal starter rate of nitrogen should be applied to manured soils, first-year
corn after alfalfa, or second-year corn after alfalfa. These soils often need little or no additional nitrogen to maximize
yields, so application of high rates of nitrogen before or at planting reduces the potential benefits of using the test.
Producers having fields that frequently receive animal manure are strongly encouraged to apply fertilizer nitrogen
only as a sidedressing or a topdressing after testing the field in late spring.
Where Caution is Required
The soil test may underestimate amounts of plant available N when (1) nitrification inhibitors or urease inhibitors are
applied with fertilizers, (2) more than 150 lb. N/acre are applied as anhydrous ammonia, and (3) more than 150 lb.
N/acre are applied as injected manure.
Midwest Laboratories can provide you with quick, accurate results for these late spring tests. Results can be
emailed, faxed or phoned back within 24-48 hours upon receipt of the samples. The fee for this service is $5.50
without recommendations and $6.00 with recommendations.
PSNT Iowa State University

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manured or corn on alflalfa corn on corn or corn on beans
excess precip normal precip average yield high yield
Nitrate ppm N lbs/ac N lbs/ac N lbs/ac N lbs/ac
1 90 90 192 232
2 90 90 184 224
3 90 90 176 216
4 90 90 168 208
5 90 90 160 200
6 90 90 152 192
7 90 90 144 184
8 90 90 136 176
9 90 90 128 168
10 90 90 120 160
11 60 60 112 152
12 60 60 104 144
13 60 60 96 136
14 60 60 88 128
15 60 60 80 120
16 0 30 72 112
17 0 30 64 104
18 0 30 56 96
19 0 30 48 88
20 0 30 40 80
21 0 30 32 72
22 0 30 24 64
23 0 30 16 56
24 0 30 8 48
25 0 30 0 40
26 0 0 0 32
27 0 0 0 24
28 0 0 0 16
29 0 0 0 8
30 0 0 0 0
Higher than normal rainfall can reduce the recommended rate by 20-40 lbs/ac
There may need to be some adjustment to the N recommendations for cornons when
high than average yield goals are desired on either manured ground or
corn following alfalfa.