1. Evaluation of Pre-Side Dress Nitrate Test for Corn in Minnesota
Brad Carlson, jeff vetsch, ryan miller
© Regents of the University of Minnesota. All rights reserved..

2. Background
There is considerable interest in using sidedress N applications to “fine-tune” current N recommendations, primarily for yield enhancement.
Typical practice is to apply 60-75% of N prior to planting and then sidedress remaining N.
The hypothesis of this study was a Pre-sidedress Soil Nitrate Test (PSNT) could be used to determine sidedress N rates in a variable rate system.
Vetsch 2015

3. additional background
Partnered with Central Valley Cooperative
Solum “wet” testing equipment
MN AFREC funded project
Previous U of M research was not able to calibrate PSNT, nor correlate to response

4. The objectives of this study were to:
demonstrate and evaluate soil-based (PSNT) methods for making in-season N rate adjustments (recommendations);
evaluate PSNT’s ability to integrate climate and landscape based variability at the field scale;
compare this PSNT approach for making N recommendations to a conventional preplant application by measuring grain yield, N removal, residual soil nitrate and economic return; and
determine if the PSNT approach could improve N management for corn in Minnesota.
Vetsch 2015

5. Methods/Treatments: N Application
Preplant N treatments applied as urea, UAN, or AA, all preplant N was spring-applied.
Three treatments: fixed sidedress (70%/30%), variable sidedress (CVC) and U of M MRTN all preplant.
2015 N rates for corn following soybean: lb, fixed; 100-lb + varied, variable; 120-lb, UM MRTN.
2015 N rates for corn after corn: lb, fixed; 150-lb + varied, variable; 165-lb, UM MRTN.
2014 N rates for sidedress treatments varied slightly.
Sidedress N applied as urea+NBPT at V6-8.
Vetsch 2015

6. Measurements: Soil Sampling
Took 0-6” soil samples on 2.5 acre grids to characterize each site (pH, P, K and SOM).
Took 0-1 and 1-2 ft soil samples (PSNT) at V2 and V4-6 from 2-4 locations in each strip plot.
Samples were kept field moist and cool until analyzed for NO3-N (Rapid nitrate, Solum). Samples were then dried and ground and analyzed for NO3-N and NH4-N.
After harvest, took 0-2 and 2-4 ft soil samples for residual soil NO3 from 2-4 locations in each plot.
Dried and ground samples analyzed for NO3-N and NH4-N
Vetsch 2015

7. Corn After Soybean Yields
Nitrogen Rate^
Locations
Method PP SD
WA15
BP14
---- lb N/ac ----
---- bu/ac ----
Fixed
100/105
40/46
210b
150b
Variable
100
101/120
221a
160a
U of M
120
206b
136c
^ N rates slightly different for fixed and variable both PP and SD.
Vetsch 2015

8. Corn After Corn Yields in 2015
Nitrogen Rate
Locations
Treatment PP SD
NF15
CG15
-- lb N/ac --
--- bu/ac ---
Fixed
150 50
215 a
217 a
Variable
64/113^
220 a
U of M
165
213 a
213 b
LSD – 2!
^ Sidedress N rate average for each site, NF15=64 and CG15=113.
Vetsch 2015

9. Another look – nf15 Fixed SD 203 5.00 U of M 202 4.53
209
Avg. Yield SD
Fixed SD
U of M
Variable
208
203
207
204
205
196
202
198
196
199
202

10. Yield Summary
A split application of N (fixed or variable) increased corn yields at 3 of 4 sites when compared to single preplant U of M rate.
However, at only 1 of 3 responsive sites was the yield increase large enough to give a return on investment (cost of fertilizer N and application); moreover, at that site (BP14) a supplemental N application would have been recommended for the U of M treatment but was not applied.
Vetsch 2015

11. Comparison of soil test methods for nitrate.
Vetsch 2015

12. Comparison of soil test methods for nitrate.
Vetsch 2015

14. Another look Iowa State Critical Values - <25 ppm – 8 lb. N/ ppm
V6 Rapid NO3 test (ppm)

15. Prescribed application rates
0 lb. N – 67 ppm (ISU recommendation)
35 lb. N – 25, 32, 39, 25, 24 ppm (0 lbs. N)
70 lb. N – 24, 23, 23, 22, 21 ppm (<25 lbs. N)
90 lb. N – 16 ppm (72 lbs. N)
120 lb. N – 6, 16, 8 ppm (70 – 160 lbs. N)

16. The rest of the story V2 vs. V6 – 8 days apart Percentage of V2 vs. V6
The points with the 120 rec had soil test values of 29, 37, 49, and 37 ppm at V2

17. Take home messages Murphy practiced on-farm research
PSNT may have increased yield, but didn’t pay for itself, and is probably no better than other predictive methods
Sample handling is problematic when dealing with wet samples
Soil nitrate data has extreme temporal variability

18. Brad Carlson – Extension Educator and Associate Extension Professor U of M Extension Regional Office – Mankato 1961 Premier Dr. – Suite 110 Mankato, MN (507)