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

Plant Development and Corn N uptake

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

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

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

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

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

Correlation of GNDVI With Yield

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

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

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

Association Between Spectral Bands and Chl Readings

SPAD Vs. GNDVI 98% Sufficiency Index

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

Additional Research Efforts Small Plot and On-farm Research

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

Chlorophyll Meter Readings

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

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