Nitrogen Diagnostic Toolsin Corn Production
John E. SawyerProfessor
Soil Fertility Extension SpecialistDepartment of Agronomy
Evaluating Plant-Available N
Soil N mineralization / soil supply Indirect procedures (crop rotation) Plant vegetation
• Yield, N uptake, tissue N, plant sensing Laboratory microbial incubation Total soil N analysisChemical extraction
• Water, strong acids or bases, neutral salts– Analyze for C, N, distillable NH3, UV adsorption
Soil inorganic NO3-N (PPNT/PSNT)
J.E. Sawyer, ISU Agronomy Extension
J.E. Sawyer, ISU Agronomy Extension
Soil Nitrate Test
In-Season Sampling
Sidedress Soil Nitrate Test
Presidedress Nitrate Test (PSNT) and Late Spring Nitrate Test (LSNT)Take a 0- to 12-inch soil sample when
corn is 6 to 12 inches tallAnalyze for nitrate-NDetermine sidedress N rate
J.E. Sawyer, ISU Agronomy Extension
Sidedress Soil Nitrate Test
MeasuresResidual soil nitrate Spring mineralized nitrate
• Soil organic matter or manure organic N Applied nitrate or nitrified ammonium (LSNT)Nitrate present (top foot) at samplingNot ammonium-N
Sampling banded N difficult (LSNT)Best at indicating excess N situations
J.E. Sawyer, ISU Agronomy Extension
ISU Soil Test-Based N RecommendationsFor C - C and S - C
Set soil nitrate-N critical value 25 ppm NO3-N
If rainfall > 20% above normal between April 1 and sampling time 3 to 5 ppm lower
(Critical level minus soil test) x 8 = lb N/acre needed
J.E. Sawyer, ISU Agronomy Extension
Evaluation of Soil Nitrate Tests for Predicting Corn N Response In N.C. Region
NCR Publication 342 Summary Relative success of soil NO3 test strategies is
subject to variation in growing season that influence the potential for NO3-N loss, soil N mineralization dynamics, and crop N demand
Average failure rate for PSNT, 0-1 foot sample depth was 27%
• Most failures when test < Critical Level but no response to applied N
J.E. Sawyer, ISU Agronomy Extension
Samples From Corn Zero-N Plots(J.E. Sawyer and D.W. Barker, 1999-2015 )
J.E. Sawyer, ISU Agronomy Extension
Sawyer and Barker, 2015
Samples From Corn Zero-N Plots(J.E. Sawyer and D.W. Barker, 1999-2015 )
J.E. Sawyer, ISU Agronomy Extension
Mean 10.7 lb N/ acre per LSNT ppm increase Sawyer and Barker, 2015
Soil Inorganic-N With Broadcast N
J.E. Sawyer, ISU Agronomy Extension
Sawyer and Barker, 2015SC: EONR 112 lb N/acrePre‐N sample: 5/13N app: 5/18V5‐V6: 6/18V10‐V12: 7/1R1: 7/23
J.E. Sawyer, ISU Agronomy Extension
Poultry Manure - 18 Field Trial Sites
-20
0
20
40
60
80
100
0 10 20 30 40 50 60
Soil Nitrate-N (ppm)
Cor
n Yi
eld
Incr
ease
(bu/
acre
)
No ManureLow Manure RateHigh Manure Rate
Poultry Manure - 18 Field Trial Sites
-20
0
20
40
60
80
100
0 10 20 30 40 50 60
Soil Nitrate-N (ppm)
Cor
n Yi
eld
Incr
ease
(bu/
acre
)
No ManureLow Manure RateHigh Manure Rate
Ruiz Diaz et al.
J.E. Sawyer, ISU Agronomy Extension
Corn Yield Increase to Fertilizer N and Liquid Swine Manure Rate2000 - 2003
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0
20
40
60
80
100
120
0 10 20 30 40 50 60 70
LSNT (ppm)
Cor
n Yi
eld
Incr
ease
(bu/
acre
)
NoneLowHigh
Rakshit et al.
J.E. Sawyer, ISU Agronomy Extension
Corn Stalk Nitrate Test
End of Season Sampling
Corn Stalk Nitrate Test
Weather conditions can impact stalk nitrate concentrationDrought – result in high concentration
• Poor ear development (small N sink)High rainfall (N losses) – result in low
concentration Insect/disease damageStalk nitrate concentrations will vary from
low to high between years in relation to late-season corn N use, corn productivity, optimal need, and soil N supply
J.E. Sawyer, ISU Agronomy Extension
Corn Stalk Nitrate Test
Consistently low or high?Evaluate for several yearsUsually in low range:
• Increase N rateUsually in excess range:
• Decrease N rate
Best at indicating excess N situationsDoes not indicate optimal N rateDoes not indicate how much to change N rate
J.E. Sawyer, ISU Agronomy Extension
J.E. Sawyer, ISU Agronomy Extension
Corn Stalk Testing, Pm-1584. Sample stalk: 6 to 14 inch segment above ground1 to 3 weeks after black layerFifteen 8-inch segments per sample
J.E. Sawyer, ISU Agronomy Extension
Rakshit et al.
J.E. Sawyer, ISU Agronomy Extension
1
10
100
1000
10000
-240 -160 -80 0 80 160 240
Stal
k N
itrat
e, p
pm
Differential From Economic Optimum N Rate, lb N/acre
Stalk Nitrate at Maturity vs. Applied N Rate Difference from Economic N Response
1999-2002 C-S Sites
1999-2002 C-C Sites
Sawyer and Barker, ISU
J.E. Sawyer, ISU Agronomy Extension
Corn Plant N Status Sensing
In-Season Management
J.E. Sawyer, ISU Agronomy Extension
N Stress SensingAerial PhotoAerial Sensed Image
Multi-spectral reflectanceEquipment Mounted Sensor
Active Canopy SensorsGreenSeekerCrop CircleOptRxCropSpec
Hand-Held SensorsMinolta 502 SPAD MeterPhone Apps
Seeing Field Variability in N
Deficiency
J.E. Sawyer, ISU Agronomy Extension
No N applied inthis part of field
N applied inthis part of field
J.E. Sawyer, ISU Agronomy Extension
2003 LTN Five-Site AverageC-S
0.50
0.60
0.70
0.80
0.90
1.00
-200 -160 -120 -80 -40 0 40 80 120 160 200Differential from Optimum N Rate (lb N/acre)
RC
M V
alue
V8
V15
R1
R3N Deficient N Adequate to Excess
Sawyer and Barker, ISU
Corn Nitrogen Uptake and Composition
J.E. Sawyer, ISU Agronomy Extension
Grain
PMR 1009; Abendroth et al., 2011
Leaf GreennessChlorophyll Meter
Minolta model SPAD 502Read 30 plants per area
• Prior to VT: sample most recently developed leaf with color exposed
• After VT: sample ear leaf• Sample ½ distance from leaf tip to collar• Sample ½ distance between leaf edge and midrib
Read area of interest and well fertilized reference area
Calculate relative sufficiency index (relative greenness)
J.E. Sawyer, ISU Agronomy Extension
Leaf GreennessChlorophyll Meter
Does indicate N deficiency Relative index < 95% (Nebraska) or <97% (Iowa)
indicates N deficiency• Need for comparative reference area that is well
fertilized
Does not indicate excess available NMaximum leaf greenness not affected by
luxury N consumptionCan indicate rate of supplemental N required
J.E. Sawyer, ISU Agronomy Extension
J.E. Sawyer, ISU Agronomy Extension
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
-240 -200 -160 -120 -80 -40 0 40 80 120 160 200 240N Rate Difference from Economic Rate, lb N/acre
Rel
ativ
e C
hlor
ophy
ll M
eter
(RC
M) V
alue
Data From 1999-2005
RCM = 0.97 + 0.000614*ND - 0.000004897*ND^2 RCM = 0.99 for ND > 63 R2 = 0.73***
Figure 1. Relative SPAD chlorophyll meter (RCM) value versus N rate difference from economic optimum rate, R1 corn growth stage.
ISU Publication PM-2026
Yield Summary for 30 SC Sites, 2004-2006
EONR(0.10) for Pre-N rates = 132 lb N/acre
Number of SitesN Application Mean with Post-Sensing Relative Mean
Treatment Total N Applied† N Applied CM Value Yield‡
lb N/acre n bu/acre0 0 -- 0.82 141d
60 60 -- 0.93 177c60+ 115 28 --- 185b120 120 -- 0.97 192a
120+ 131 9 --- 193a240 240 -- 1.00 197a
‡ Mean yields are not significantly different when followed by the same letter (P < 0.10).
† Sum of Pre-N and Post-sensing N rate, averaged across all 30 SC sites.
Hawkins, Lundvall, Sawyer, 2006. Post-sensing N applied V15-VT corn stage.
J.E. Sawyer, ISU Agronomy Extension
Active Sensor Wavelengths
J.E. Sawyer, ISU Agronomy Extension
Gre
en
Ambe
r
Red
Wavelength (nm) 475 510 570 650 475 510 570 650 475 510 570 650
Gre
en
Sensor Visible, nm NIR, nm Other, nmMinolta SPAD Meter 650 (red) 940GreenSeeker 506 560 (green) 774GreenSeeker 505 656 (red) 774Crop Circle ACS-210 590 (amber) 880Crop Circle ACS-430 670 (red) 780 730 (red edge)Crop Circle ACS-470 various various variousCropSpec 800-810 730-740 (red edge)
Sensor Index Calculations
Most common active canopy sensor indicesNormalized Difference Vegetative Index
(NDVI)• (NIR – VIS) ÷ (NIR + VIS)
Chlorophyll index (CHL)• (NIR ÷ VIS) – 1
Relative values Sensor reading normalized to highest N rate
J.E. Sawyer, ISU Agronomy Extension
Why Use Relative Index Values?
Various canopy characteristics influence sensor readings and index values Leaf chlorophyllWhole plant biomassCanopy temperatureCanopy moisture contentHybrid Plant density (population)Other nutrient deficiencies
J.E. Sawyer, ISU Agronomy Extension
Reference Corn?
J.E. Sawyer, ISU Agronomy Extension
??
??
What’sthis?
What’sthis?
Why Use Relative Index Values?
J.E. Sawyer, ISU Agronomy Extension
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
-240 -200 -160 -120 -80 -40 0 40 80 120 160 200 240
GD
VI
Difference from EONR, lb N/acre
0.00
0.20
0.40
0.60
0.80
1.00
1.20
-240 -200 -160 -120 -80 -40 0 40 80 120 160 200 240
Rel
ativ
e G
DVI
Difference from EONR, lb N/acre
Barker and Sawyer, ISU
Active Sensor Calibration at Mid-Vegetative
J.E. Sawyer, ISU Agronomy Extension
0
50
100
150
200
250
0.50 0.60 0.70 0.80 0.90 1.00
N App
lication (lb
/acre)
Relative Sensor Index Value
CC‐210 Sensor
rNDVI
rCHL
Barker and Sawyer, ISU
In-Season N ResponseCorn Canopy Index
J.E. Sawyer, ISU Agronomy Extension
Nitrogen Applied at Planting and In-Season (UAN) Based on Canopy Sensing
J.E. Sawyer, ISU Agronomy Extension
Barker and Sawyer, 2011. In-season N applied at V10 corn stage.
Nitrogen Applied at Planting and In-Season (UAN) Based on Canopy Sensing
Barker and Sawyer, 2011. In-season N applied at V10 corn stage.
J.E. Sawyer, ISU Agronomy Extension
Nitrogen Applied at Planting and In-Season (Urea) Based on Canopy Sensing
J.E. Sawyer, ISU Agronomy Extension
Barker and Sawyer, 2013. In-season N applied at V10 corn stage.
Corn Plant and Canopy Sensing
Uses corn plant as indicator of N adequacy or deficiency
Corn plant able to integrate across timeProvides instantaneous feedbackWith active canopy sensors Electronic integration of sensing and N rate
application on-the-go• Requires recommended operation
Sub-field/continuous N rate adjustment
J.E. Sawyer, ISU Agronomy Extension
Corn Plant and Canopy Sensing
Considerations Sensors cannot detect excess NCorn must be N deficient to express N
stressDetecting small N deficiency difficultMust have an “adequate or N-Rich” in-field
references (create relative N stress value)• Sensors “see” any plant stresses
J.E. Sawyer, ISU Agronomy Extension