Crop Sensors to Control Variable-Rate N Applications: Five Years of On-Farm Demonstrations

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