Variable-Rate N Fertilization of Wheat and

Corn in the Mid-Atlantic

Variable-Rate N Fertilization of Wheat and

Corn in the Mid-Atlantic

Wade Thomason, VTSteve Phillips, IPNIPaul Davis, VCE retiredMark Alley, VTMark Reiter, VT

Wade Thomason, VTSteve Phillips, IPNIPaul Davis, VCE retiredMark Alley, VTMark Reiter, VT

• Match Timing of Fertilization with Crop Demand But… if it’s been a wet early summer…

… if it’s been a dry early summer…• More Knowledge of Crop N Need

– 1 lb N/bu of expected yield

INCREASING N FERTILIZER EFFICIENCYINCREASING N FERTILIZER EFFICIENCY

TEMPORAL VARIABILITYTEMPORAL VARIABILITY

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TEMPORAL VARIABILITYTEMPORAL VARIABILITY

60 acre field in Caroline County

Wheat yields: 44 to 80 bu/acre

Corn yields: 85 to 178 bu/acre

Bojac 2AWickham 3A

Wickham 4ABojac 1A

SPATIAL VARIABILITYSPATIAL VARIABILITY

ADDRESSING THIS VARIABILITYADDRESSING THIS VARIABILITY• Temporal

– Shoot from the hip– PSNT– Tissue tests– Chlorophyll meter– Precision Ag Technologies

• Spatial– Soil map– Yield/History map

Why?

RED light absorbed = Green light reflected

Normalized Difference Vegetative Index

NDVI => Calculated from Red and NIR Reflectance

Sensor Function

Lightgeneration

Light signal

Lightdetection

Valve settings

? Calculate NDVI? Lookup valve setting? Apply valve setting? Send data to UI

“Sensor”

Valves and

Nozzles

Measures spectral reflectance in a 3/8” x 24” area

Samples at a frequency of 60 times/sec

Average reflectance measurements calculated every second

OPTICAL SENSORSOPTICAL SENSORS

The vigor of the leaves and the ratio of plant to soil affect NDVI values

The vigor of the leaves and the ratio of plant to soil affect NDVI values

What the Sensor “Sees”What the Sensor “Sees”

Note that the biomass of each plant is observable in NDVI value

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~60 sites across Virginia since 2000

Irrigated and non-irrigated Conventional and no till Various rotations, hybrids,

varieties, and soil types

BACKGROUNDBACKGROUND

Wide range of preplant, starter, and in-season N rates (including VR)

Collected spectral measurements and an assortment of plant physical and chemical characteristics at various growth stages

Determine grain yield

VIRGINIA APPROACHVIRGINIA APPROACH

Generated calibration model for Mid-Atlantic wheat

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Gra

in Y

ield

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YPI

Painter, VA, 2000

Painter, VA, 2001

Suffolk, VA, 2001

New Kent, VA, 2001

Culpeper, VA, 2001

Stuarts Draft, VA, 2001

Port Royal, VA, 2000

New Kent, VA, 2000

Warsaw, VA, 2000

Charles City, 2002

Painter, VA, 2002

Suffolk, VA, 2002

Painter, VA, 2003

New Kent, VA, 2003

Oklahoma

y = 0.74076 + .1021e 577.66x Oklahoma, Lukina et al., 2001Virginia, 2000-2003, y = 0.512 + .104e 579.45x

VIRGINIA APPROACHVIRGINIA APPROACH

Generated calibration models for wheat and corn grown in the Mid-Atlantic

Developed N fertilization algorithms for both crops

In-season N management

1st topdress based on estimated tiller #

2nd topdress based on Tissue N concentration

30 to 40 lb N/ac preplant

Zadoks stage, in parenthesis

In-season N timing

Days From Planting

1st topdress based on estimated tiller #

2nd topdress based on NDVI and DFP

Wheat N Rate Algorithm

Rate (kg/ha) vs. NDVI

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0.00 0.20 0.40 0.60 0.80 1.00

N Rate, kg/ha

Constrained NRate, kg/ha

What’s Needed

• Reference Strips– Difference between:

• High N reference (best possible with more than adequate N)

• Low N reference (0 N applied)

And• Area currently in sensor’s view.

VIRGINIA APPROACH - WheatVIRGINIA APPROACH - WheatTARGET NDVI

LOW REFERENCE HIGH REFERENCE GS 25 N DAP MAX YIELD MAX N NUE N RATE

0.60 0.50 0.80 50 150 85 80 50 80lbs/N dap bushels max constraint% lb/ac

87.1361 N fertilizer required23.5681 N required for additional grain46.0133 Bushel/A expected yield increase due to fertilizer

coefficients Define these units SI units ?ka 0.74076kb 577.66kc 1000kd

NUE 50%CONVERSION 0.0149

0.220.230.240.250.260.270.28

Rate (LB/ac) vs. NDVI

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N Rate

Constrained

VIRGINIA APPROACH - CornVIRGINIA APPROACH - CornNDVI Low_Ref Hi_Ref N_preplant DFP MAX YIELD MAX N N RATE

0.82 0.50 0.90 60 63 175 100 85lbs/N dap bushels max constraintgal/acre

kg/ha85.27

coefficients Define these units SI units ?ka 56.479kb 67.626kc 56kd

NUE 60%Pn 0.0125

0.220.230.240.250.260.270.28

Rate (gal/ac) vs. NDVI

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140.0

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N Rate

Constrained

Entering Required InformationEntering Required Information

VIRGINIA APPROACHVIRGINIA APPROACH

Generated calibration models for wheat and corn grown in the Mid-Atlantic

Developed N fertilization algorithms for both crops

Validated these rate equations for performance

EXPERIMENTAL PROCEDURES

EXPERIMENTAL PROCEDURES

Spra Coupe 220 w/ 60 ft boom and GreenSeeker RT200 Raven 440 flow rate controller

Diverse locs; RCBD; 3-8 reps

Plot size: 60 by 250 to 500 ft

In-season N:4-5 Fixed Rates1 Standard Rate1 Variable Rate

Grain Yield

0 – 75 N kg/ha: (numerical rates): Predetermined Nitrogen rates applied in lb/acres

Average: Single N rate determine using Greenseeker® (VA algorithm)

Variable: Variable Nitrogen rate determined using Greenseeker® Virginia Algorithm

Standard: Nitrogen rate determined based on GS 30 tissue test ( Standard Virginia recommendation system )

Greenseeker ® : Variable N rates determined using default Greenseeker ® wheat algorithm

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Mean

GS

30 N

Rat

e, lb

N a

c-1

VWA

STD

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STD

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-7%

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-0.8%

Comparison with Economically Optimum N Rate

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VWA -EONR

STD-EONR

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The Rx rate prediction map and real time map demonstrate the small trend in values – SW to NW values almost normal distributed: in the real time map those values ranged from 17 to 20 in the prediction map (interpolation) the recommended rate in that area still normal but decrease to 10 – 12 gal/acres

Corn Algorithm Performance

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N R

ate,

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/ac

STDGS

162

120

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151134

155

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173184

151161

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92

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132150

136

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191

148

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Yie

ld,

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STDGS

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STD

GS

Corn Algorithm Performance

Grain Yield, bu/ac Sidedress N, lb/ac

NS

21 % (21 lb/ac) less N with GS

Ridge and Valley Sites

2008 20090

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Farmer Practice

GreenSeeker

Gra

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InjectedManure

Surface-appliedManure

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61 lb N/ac

72 lb N/ac

Challenges

• Timing– Size of the corn

RX vs. Applied Rates

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1 201 401 601 801 1001 1201 1401 1601

gal/a

cre

Prescribed

As Applied

Challenges

• N rich strips– Timing– Same Field– Same Hybrid/Variety– Mark it!

• N “poor” strips

NDVI Low_Ref Hi_Ref

0.65 0.60 0.79

Challenges

• Herbicide Applications

Challenges

• Skepticism• How to tell if the system

was “right”• Risk• Cost

– EQIP cost share– Tax credits

Questions?