Sensor Based Variable Rate N Management in Mid-Atlantic Cropping Systems
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Transcript of Sensor Based Variable Rate N Management in Mid-Atlantic Cropping Systems
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DEPARTMENT OF ENVIRONMENTAL SCIENCE & TECHNOLOGY
Laboratory for Agriculture and Environmental Studies
Sensor Based Variable Rate N Management in Mid-
Atlantic Cropping Systems
Joshua M. McGrath, UMD
Wade Thomason, VT
Steve Phillips, IPNI
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Background on the Mid-Atlantic
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Nitrogen Management Basics(since early 1990s in MD)
Corn:• Apply N based on
realistic yield goal – 1 lb N/bu expected yield
• Split-apply N fertilizer on corn– apply 30 – 40 lbs/A at
planting– remaining N as sidedress
• When utilizing manure or following leguminous cover crops use the
Pre-Sidedress Nitrate Test
Wheat:• Apply a total 70 – 120 lbs
of N• 20 – 40 lbs at planting• Split top-dress 80 – 100
– Green-up– Feekes 5 - 6
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What makes us special?
• >90% side-dress N in Corn on Delmarva
• Yields vary widely 120 – 220 bu/ac
• >90% no-till corn• 50 – 60% irrigated on the
lower shore• In Maryland farmers cannot exceed University recommendations
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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
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VIRGINIA APPROACHVIRGINIA APPROACH
Generated calibration models for wheat and corn grown in the Mid-Atlantic
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Predicted Yield Index
Yie
ld,
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0 0.001 0.002 0.003 0.004 0.005 0.006 0.007
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VIRGINIA APPROACHVIRGINIA APPROACH
Generated calibration models for wheat and corn grown in the Mid-Atlantic
y = 6.7825e367.41x
R2 = 0.9752
y = 8.5528e244.11x
R2 = 0.95
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0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009
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YPI
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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
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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
0.0000
20.0000
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0.00 0.20 0.40 0.60 0.80 1.00
N Rate
Constrained
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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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0.00 0.20 0.40 0.60 0.80 1.00
N Rate
Constrained
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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.
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In-season N management
1st topdress based on estimated tiller #
2nd topdress based on Tissue N concentration
30 to 40 lb N/ac preplant
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Zadoks stage, in parenthesis
In-season N timing
Days From Planting
1st topdress based on estimated tiller #
2nd topdress based on NDVI and DFP
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Validation in VA, MD, DE
• ~60 sites across Virginia since 2000
• 12 sites in DE and MD (2008, 2009)
• Irrigated and non-irrigated
• Conventional and no till• Various rotations,
hybrids, varieties, and soil types
• Wide range of pre-plant, 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
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Validation in VA, MD, and DE
• RCBD; 3-8 reps• Plot size: 60 by 250
to 500 ft• In-season N:
– 4-5 Fixed Rates– 1 Standard Rate– 1 Variable Rate
Spra Coupe 220 w/ 60 ft boom and
GreenSeeker RT200
Raven 440 flow rate controller
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Recommended vs. Applied Rates
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gal/a
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Prescribed
As Applied
• 55% are within 2 gallons of prescribed rate• 88% within 5 gallons
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Wheat: Applied N GreenSeeker vs. Tissue
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GS
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 AVG
N r
ate,
kg
ha-1
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Average Wheat Performance
Farmer Practice
Farmer Practice
GS
GS
0102030405060708090
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Grain Yield, bu/ac GS 30 N Rate Applied, lb/ac
NS
7% less N with GS
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Corn Algorithm Performance
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N R
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Average Corn Performance
Grain Yield, bu/ac Sidedress N, lb/ac
NS
21 % (21 lb/ac) less N with GS
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Limitations and Challenges
• Corn: V-7 versus V-4• Wheat: Herbicide in
second spring top-dress?• Check strips• How to tell if the system
was “right” – Skepticism• When parameters are
entered the application graph often needs tweaking by faking parameters
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Honest Answers Don’t Always Work!
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Can’t just plug and chug (spray)
Farmer would apply 46 gal/acre
N_pre = 0This has been corrected in the software
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Part of the Adaptive Management Toolbox
• Systems approach– Manage soil N
• Focused on in-season N management– PSNT– Active Crop sensors– LCM
• End of season assessment– CSNT– Yield monitoring
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The Future in the Mid-Atlantic
• The Chesapeake Bay and cost of fertilizer have us poised for rapid adoption– A few major farmers and ag service companies– Environmental Groups
• Likely to be covered through various cost share mechanisms soon
• Need to continue to refine algorithm to address– Accuracy of input values– Expand side-dress window– Straightforward user interface
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