Missouri algorithm for N in corn Peter Scharf, Newell Kitchen, and John Lory University of Missouri and USDA-ARS

Missouri Algorithm Based on direct empirical relationship between measured reflectance and measured optimal N rate Site characteristics Very compatible with current sensor group approach We will likely use the algorithms that will be developed from group activities

Missouri Algorithm Original calibration: Cropscan passive at V6 Green, Red edge, Blue-green best Green/Infrared best combination Optimal N rate = 330 * (G/NIR)target/(G/NIR)high N – 270 Works with either 0 or 100 N applied preplant Tentatively applied with Crop Circle active sensor Subsequent research agrees fairly well

Relationship between optimal N rate and sensor measurements Y = 330(X) – 270

Greenseeker Values swing more widely than Crop Circle over the same range of corn N status Need equation with smaller slope

Growth stages Original calibration was for V6 Also use for V7 Chlorophyll meter, sensor research show that slope decreases as season progresses Decreased slope to 3/4 for V8 to V10

Current Missouri Algorithms Sensor Growth stage Equation Crop Circle V6-V7 330 * (V/NIR)t/(V/NIR)hiN - 270 V8-V10 250 * (V/NIR)t/(V/NIR)hiN - 200 Greenseeker 220 * (V/NIR)t/(V/NIR)hiN - 170 170 * (V/NIR)t/(V/NIR)hiN - 120

On-farm demos using Missouri algorithms

21 with USDA Spra-Coupe

35 with producer-owned applicators

10 with retailer-owned applicators

Kansas producer 2006: 4000 acres of corn fertilized in six days using high-clearance spinner, sensors, & Missouri algorithm

On-farm demonstrations 32 on-farm demonstrations 2004-2006 with producer rate & sensor variable-rate side-by-side and replicated Average N savings = 31 lb N/acre Average yield loss = 1.7 bu/acre Yield & N economics $2 to $10/ac benefit depending on prices used Doesn’t count technology & management costs

On-farm demonstrations Complication: sensor values change during the day Probably mainly due to changes in: Canopy architecture Internal leaf properties External leaf properties

Leaf wetness effect on sensor values Dew Rain

Why diurnal changes in sensor values? Leaf wetness is the only reason we’re sure of Wet leaves are darker Need to re-measure high-N reference when leaf wetness changes Reference strips perpendicular to rows can make this feasible

Reference strips Perpendicular to rows? Tried in on-farm demo in 2007 Real-time update of high-N reference value Worked great Apply with 4-wheeler + spinner? Aerial?

Diurnal changes: other impacts We may consider changing to an algorithm based on NDVI Especially Greenseeker Less sensitive to diurnal changes in sensor values

Diurnal sensitivity of N recs: Greenseeker/cotton example NDVI-based VIS/NIR-based

Diurnal sensitivity of N recs: Crop Circle/cotton example NDVI-based VIS/NIR-based

Thanks!! Questions? Comments? Discussion?