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

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

Study Layout

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

Small Sample Area Ratio = 0.2141

One Field Length Strip Ratio = 0.2736

Using Multiple Strips

Using Soil EC

Using Soil EC y = 0.0017x + 0.1838 R2 = 0.5348 C Site

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

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

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

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

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

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.

Questions

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

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

Missouri Corn N Algorithm

Missouri Corn N Algorithm