1. Eric Miller August 3rd, 2010 Dr. Camberato & Dr. Nielsen
Variability of Maize Canopy Reflectance within Field-Length Strips Fertilized With Low to High Rates of Nitrogen
Eric Miller
August 3rd, 2010
Dr. Camberato &
Dr. Nielsen

2. Research objective
Do “Virtual Reference Strips” occur in under-fertilized corn?

3. Virtual Reference Strip
OptRx calibration process
1/3 – 1/2 estimated total N consumed
Suggested pre-plant N rates:
kg N ha-1 Corn following Soybean
kg N ha-1 Corn following Corn

4. Virtual Reference scan consists of driving for five minutes over the tallest, greenest plants in the field
Vegetative Index Reference Value

5. Project Description 2006 - 2009 6 Purdue Agricultural Centers
32 site years 2006, 2007, 2008 and 2009: 19 CS and 13 CC
Plots range in size from 120 m – 550 m in length
Starter + sidedress with 28% UAN at six rates from 0 – 286 kg N ha-1
Crop Circle ACS-210 were run 14 – 25 days after N application
Single hybrid/near-isoline was planted

6. Relative CI well correlated with rel. yield over 23 site-years
2006: ACRE, DPAC, NEPAC, PPAC, SEPAC (all C/S)
2007: ACRE, DPAC, NEPAC (C/S and C/C)
2008: ACRE, DPAC, NEPAC, PPAC, SEPAC, TPAC (C/S and C/C)
* Normalized to values of highest N rate in each rep

7. Sensor Measurements 2 ACS-210 sensors
4 mph, 40,000 hz, 38,400 baud rate
Recording data every 18 cm
Partitioned data into 30 and 60 sec runs
Approx. 3, sec runs/305 m

8. Few 30 sec. runs of CI equal to RefCI
C/S rotation, sidedressed with 90 kg N/ha, V9-V10 sensor readings
Optimum N rate, kg/ha
167
169
190
204
225
232

9. Throckmorton Purdue Ag Center
305 m long plots, 12 rows, 76 cm wide
V-stage: V10
Sensor Data Collected: July 8th
Hybrid: Pioneer Brand ‘33F88’
Population Density: 81,500 plants ha-1
Dominant Soil: Throckmorton- Fine-silty, mixed, superactive, mesic Mollic Oxyaquic Hapludalfs
Precipitation during growing season: 25 cm
Planted: May 24th Previous Crop: Soybean
Fertilized: June 24th

10. Yield Response

11. 30 second runs = 53 meters of row Avg. CI = 4.77
Frequency, %
Avg. CI = 4.77
30 second runs =
53 meters of row
With 114 kg N ha-1 (68% of optimum N rate)
17% ≥ CI 4.77
Starter only (14% of optimum N rate)
2% ≥ CI 4.77

12. Location of CI = RefCI
114 kg N ha-1
24 kg N ha-1 77
131
130 77 84 67

13. Davis Purdue Ag Center 365 m long plots, 12 rows, 76 cm wide
V-stage: V10
Sensor Data Collected: July 9th
Hybrid: Pioneer Brand ‘33F88’
Population Density: 81,500 plants/ha
Dominant Soils: Blount- Fine, illitic, mesic Aeric Epiaqualfs Pewamo- Fine, mixed, active, mesic Typic Argiaquolls
Precipitation during growing season: 37 cm
Planted: May 26th Previous Crop: Soybean
Fertilized: June 15th

14. Yield Response

15. 30 second runs = 53 meters of row Avg. CI = 4.00 54% of optimum N rate
Frequency, %
54% of optimum N rate
38% ≥ CI 4.00
34 % of optimum N rate
16% ≥ CI 4.00

16. Conclusions
Few areas of a field fertilized with 50-70% of the optimum N requirement had CI equal to or greater than the reference CI.
Areas with CI ≥ ref. CI were small, generally less than 200 m and 2 minutes in length.
Could we have found these areas without previously running the sensors?
Would these areas identified in 2009 continue to be ≥ ref. CI?

17. Questions?