1. Alternatives to Using a Reference Strip for Reflectance-Based Nitrogen Application in Corn (Presented at 8th International Conference on Precision Agriculture, July 2006)
D. Kent Shannon
Newell R. Kitchen
Kenneth A. Sudduth
Peter C. Scharf
Harlan L. Palm

2. Alternative Approaches
Small Sample Area
One Field Length Strip
Multiple Field Length Strips – Interpolated into a Reference Map
Using Soil Electrical Conductivity (EC)

4. Study Layout

5. Missouri Corn N Algorithm
Ratio Reference ≤ 0.25
60 ≤ N Rec ≤ 210

6. Small Sample Area
Ratio =

7. One Field Length Strip
Ratio =

8. Using Multiple Strips

9. Using Soil EC

10. Using Soil EC
y = x
R2 =
C Site

11. C Site – N Rec Using Ceiling Ratio Value of 0
C Site – N Rec Using Ceiling Ratio Value of 0.25 and Minimum N Rate of 60 lbs/acre
Sample – R2 = 0.79
One Strip – R2 = 0.94
Multiple Strips
Using EC – R2 = 0.94

12. W Site - N Rec Using Ceiling Ratio Value of 0
W Site - N Rec Using Ceiling Ratio Value of 0.25 and Minimum N Rate of 60 lbs/acre
Sample – R2 = 0.25
One Strip – R2 = 0.26
Multiple Strips
Using EC – R2 = 0.35

13. Comparison of Sites – R2 Site Sample Strip EC B 0.69 0.63 NA C 0.79
0.94 D
0.70
0.48
0.60 E
0.61 H
0.64 S
0.80 W
0.30
0.31
0.35
Ceiling and 60 min

14. Comparison of Sites – Mean Nitrogen Rate in lbs/acre
Sample
One Strip
Multiple Strips EC B
188.35
160.96
187.69 NA C
189.08
172.03
177.64
174.82 D
146.76
99.02
149.66
114.73 E
105.56
107.17
101.07 H
121.51
129.51
126.98 S
115.02
113.57
125.79 W
146.10
158.87
170.99
161.14
Ceiling and 60 min

15. W Site – N Rec Ceiling Ratio Value of 0
W Site – N Rec Ceiling Ratio Value of 0.25 and Minimum N Rate of 60 lbs/acre
Strip
Ratio
Mean
St Dev 1
0.3353*
112.12
55.86 2
0.2166
143.66
58.40 3
0.2582* 4
0.22
140.13
58.81 5
0.1989
162.61
52.89 6
0.1761
186.04
37.94
All
Variable
166.85
52.17
* Ceiling Ratio Value of 0.25 Used
Using a Sample at the Beginning of Each Strip

16. Conclusions
Spatial reference information is important for some fields.
A sample reference is sufficient in some cases, but the location of the reference can be critical.
We need to be able to determine where spatial information is most important.

17. Questions

18. W Site - N Rec Using Ceiling Ratio Value of 0
W Site - N Rec Using Ceiling Ratio Value of 0.25 and Minimum N Rate of 60 lbs/acre
Sample – R2 = 0.30
One Strip – R2 = 0.31
Multiple Strips
Using EC – R2 = 0.35

19. Comparison of Sites – Standard Deviation
Sample
Strip
Multiple Strips EC B
24.14
36.17
23.46 NA C
41.54
51.37
44.23
49.15 D
49.58
49.22
50.07
51.71 E
44.28
44.41
46.22 H
32.12
31.43
36.09 S
40.73
40.50
46.06 W
49.66
45.6
43.15
41.37
Ceiling and 60 min
River Bottom Fields

20. Missouri Corn N Algorithm

21. Missouri Corn N Algorithm