nitrogen diagnostic tools in corn production diagnostic tools in corn production john e. sawyer...

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


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


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


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


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


Samples From Corn Zero-N Plots(J.E. Sawyer and D.W. Barker, 1999-2015 )


Sawyer and Barker, 2015

Samples From Corn Zero-N Plots(J.E. Sawyer and D.W. Barker, 1999-2015 )


Mean 10.7 lb N/ acre per LSNT ppm increase Sawyer and Barker, 2015

Soil Inorganic-N With Broadcast N


Sawyer and Barker, 2015SC: EONR 112 lb N/acrePre‐N sample: 5/13N app: 5/18V5‐V6: 6/18V10‐V12: 7/1R1: 7/23


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.


Corn Yield Increase to Fertilizer N and Liquid Swine Manure Rate2000 - 2003

-20

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.


Corn Stalk Nitrate Test

End of Season Sampling


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



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



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


Rakshit et al.


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


Corn Plant N Status Sensing

In-Season Management


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


No N applied inthis part of field

N applied inthis part of field


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


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)


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



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.


Active Sensor Wavelengths


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


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


Reference Corn?


??

??

What’sthis?

What’sthis?

Why Use Relative Index Values?


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


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


Nitrogen Applied at Planting and In-Season (UAN) Based on Canopy Sensing


Barker and Sawyer, 2011. In-season N applied at V10 corn stage.

Nitrogen Applied at Planting and In-Season (UAN) Based on Canopy Sensing



Nitrogen Applied at Planting and In-Season (Urea) Based on Canopy Sensing



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


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


nitrogen diagnostic tools in corn production diagnostic tools in corn production john e. sawyer...

Documents