Crop Sensors to Control Variable-Rate N Applications: Five Years of On-Farm DemonstrationsPeter Scharf, Kent Shannon, Harlan Palm, Ken Sudduth, Newell Kitchen and Scott Drummond, Univ. of Missouri and USDA-ARS
Introduction• Optimal N rate often varies
widely within & among fields• Weather has a large influence on
optimal N rate•Static properties can’t predict
• Color & reflectance of crop is strongly related to N status & need
Methods• Identify producers/retailers with:
• Interest• Sidedress/topdress equipment• Controller with serial input
• Develop algorithm to convert sensor values to N rates
• Develop control software• Make sensor brackets• Apply high-N reference area• Apply in-season N
• Producer rate and sensor variable-rate side by side
• Minimum 3 replications
sensorssensors
Computer in cab reads sensors, calculates N rate, directs controller
Controller runs ball valve to change fertilizer rate
Locations of sensor demonstration fields 2004-2009
Period#
Fields
Effect of sensor N management* on:
Yield N rate Profit
Mg ha-1 Kg N ha-1 $ ha-1
2004-2007 41 0 -27 +302008 12 +0.6 +18 +72*Effect is calculated relative to an in-season N application whose rate was chosen by the producer
Lessons learned• A good high-N reference
area/value is critical• Sensor values drift—need a
solution• Timing is the biggest issue to
producers
0
50
100
150
200
250
0.8 1 1.2 1.4 1.6 1.8
Visible/near infrared relative to high-N plots
Opt
imal
sid
edre
ss N
rat
e
Turning a sensor reading into an N rate
Cropscan, Crop Circle V6-V7(line basd on data points shown)
Crop Circle V8-V10
Greenseeker V8-V10Greenseeker V8-V10Greenseeker V6-V7Greenseeker V6-V7