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..

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

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

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

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: 100 + 40-lb, fixed; 100-lb + varied, variable; 120-lb, UM MRTN. 2015 N rates for corn after corn: 150 + 50-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

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

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

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

Another look – nf15 Fixed SD 203 5.00 U of M 202 4.53 209 Avg. Yield SD Fixed SD 203 5.00 U of M 202 4.53 Variable 202 4.92 208 203 207 204 205 196 202 198 196 199 202

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

Comparison of soil test methods for nitrate. Vetsch 2015

Comparison of soil test methods for nitrate. Vetsch 2015

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

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)

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

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

Brad Carlson – Extension Educator and Associate Extension Professor U of M Extension Regional Office – Mankato 1961 Premier Dr. – Suite 110 Mankato, MN 56001 (507)389-6745 bcarlson@umn.edu