1. Crop-based Approach for In-season N Application
USDA-ARS, Lincoln NE
John Shanahan, Jim Schepers, Dennis Francis, Kyle Holland, Ricardo Inamasu, Steve Payton

2. Plant Development and Corn N uptake

3. 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

4. “As Needed N Treatments”
Impact on Grain Yield
“As Needed N Treatments”

5. Visible Short-wave Non-visible NIR Longer-wave
Notice difference among N rates in green and red
Nitrogen Rates

6. Sensitivity of Vegetation Indices Across Chlorophyll Levels
Adapted From Gitelson et al. (1996)

7. Imagery Data and Vegetation Indices
NDVI = (NIR-RED)/(NIR + RED)
GNDVI=(NIR – GREEN)/(NIR + GREEN)

8. Correlation of GNDVI With Yield

9. Correlation Vs Growth Stage
Soil Background
V-T
R-2
V-6
R-5
V-T
V-6
Tassel Structure

10. “On-the Go System With Crop Circle Sensor”
GPS
Downward Sensors
Upward Sensors
Drop nozzles delivering N solution

11. Sensor Data Observations
One Hybrid
C.V. for within plot sensor-derived values of GNDVI is ~ 3.5%

12. Association Between Spectral Bands and Chl Readings

13. SPAD Vs. GNDVI
98% Sufficiency Index

14. Summary of Sensor Work GNDVI more sensitive than NDVI
Still have issues with less than full canopy closure
Need to develop VI’s that are more sensitive to variation in canopy vigor and greenness

15. Additional Research Efforts
Small Plot and On-farm Research

16. Hybrid and Plant Density Effect on Chlorophyll Content
Low Density
12 Hybrids
Med. Density
High Density

17. Chlorophyll Meter Readings

18. On-farm Sensor Research
Goal is to establish sensor threshold for triggering fertilizer applicator.
Develop practical system

19. Possible systems With or without: GPS sensors +GPS
Regional satellite view
With or without:
GPS
sensors
SAM or
+GPS
One-Time
Multiple Applications
-GPS