Crop-based Approach for In-season N Application

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Crop-based Approach for In-season N Application

• USDA-ARS, Lincoln NE
• John Shanahan, Jim Schepers, Dennis Francis, Kyle
  Holland, Ricardo Inamasu, Steve Payton

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Plant Development and Corn N uptake
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Use of Chlorophyll Meter to Schedule N Application

• 1991-present
• Corn/Soybean rotation
• 4 corn hybrids
• 6 N treatments
• 0,50,100,150,200 kg-N/ha at planting
• As needed N application scheduled with
  chlorophyll meter

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Impact on Grain Yield
As Needed N Treatments
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Visible Short-wave
Non-visible NIR Longer-wave
Notice difference among N rates in green and red
Nitrogen Rates
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Sensitivity of Vegetation Indices Across
Chlorophyll Levels
Adapted From Gitelson et al. (1996)
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Imagery Data and Vegetation Indices

• NDVI (NIR-RED)/(NIR RED)
• GNDVI(NIR GREEN)/(NIR GREEN)

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Correlation of GNDVI With Yield
r0.21
r0.93
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Correlation Vs Growth Stage
Soil Background
V-T
R-2
V-6
R-5
V-T
V-6
Tassel Structure
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On-the Go SystemWith Crop Circle Sensor
GPS
Downward Sensors
Upward Sensors
Drop nozzles delivering N solution
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Sensor Data Observations
One Hybrid
C.V. for within plot sensor-derived values of
GNDVI is 3.5
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Association Between Spectral Bands and Chl
Readings
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SPAD Vs. GNDVI
98 Sufficiency Index
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Summary of Sensor Work

• GNDVI more sensitive than NDVI
• Still have issues with less than full canopy
  closure
• Need to develop VIs that are more sensitive to
  variation in canopy vigor and greenness

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Additional Research Efforts

• Small Plot and On-farm Research

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Hybrid and Plant Density Effecton Chlorophyll
Content
Low Density
12 Hybrids
Med. Density
High Density
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Chlorophyll Meter Readings
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On-farm Sensor Research

• Goal is to establish sensor threshold for
  triggering fertilizer applicator.
• Develop practical system

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Possible systems
Regionalsatelliteview

• With or without
• GPS
• sensors

SAM
or
GPS
One-Time
-GPS
Multiple Applications