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Optimization of Crop Canopy Sensor Placement for Measuring Nitrogen Status in Corn

^a Dep. of Agronomy & Horticulture, Univ. of Nebraska, Lincoln, NE 68583
^b Dep. of Biological Systems Engineering, Univ. of Nebraska, Lincoln, NE 68583
^c USDA-ARS, Agroecosystem Mgmt. Res. Unit, Lincoln, NE 68583
^d formerly USDA-ARS, Agroecosystem Mgmt. Res. Unit, Lincoln, NE 68583

View larger version (13K): [in this window] [in a new window]   Fig. 1. Box-and-whiskers diagram of Chlorophyll Index (CI) base maps for Fields 1–8. The lower and upper limits of each box signify the 25th and 75th percentiles of CI, the lower and upper whiskers represent the 10th and 90th percentiles of CI, the large dots indicate the 5th and 95th percentiles of CI, the horizontal line in the center of each box represents the median, and the dotted line represents the mean of CI values.

View larger version (33K): [in this window] [in a new window]   Fig. 2. Lateral (A, B) and direction-of-travel (C, D) semivariograms of chlorophyll index for Fields 1 through 8.

View larger version (37K): [in this window] [in a new window]   Fig. 3. Theoretical and empirical mean square error (MSE) estimates when averaging CI values for the entire boom and assuming individual sensor measurements to represent entire boom sections in Fields 1 through 8 (A through H). Note different MSE scales for Fields 5 and 6.

View larger version (14K): [in this window] [in a new window]   Fig. 4. Percentage reduction in mean square error (MSE) versus increasing number of sensors (based on average across all fields of "one rate–theoretical" scenario in Fig. 2).

View larger version (40K): [in this window] [in a new window]   Fig. 5. Evaluation of mean square error (MSE) versus increasing number of sensors with split-boom N application scenarios in Fields 1 through 8 (A–H). Note different MSE scales for Fields 5 and 6.

View larger version (16K): [in this window] [in a new window]   Fig. 6. Relationship between chlorophyll index and row position based on three, eight-row strips (0 = next to the center of eight rows, 3 = outside row of eight-row strip).

View larger version (52K): [in this window] [in a new window]   Fig. 7. Actual and modeled distributions of row-to-row mean variability of chlorophyll index (CI) measurements for Fields 1 through 5. The CI was not modeled for Fields 6, 7, or 8 because no significant relationship between CI and row position was detected.

View larger version (24K): [in this window] [in a new window]   Fig. 8. Mean square error (MSE) of (A) single fixed N rate, (B) row-specific fixed N rate, (C) single variable rate (mean of 24 sensors), (D) single variable rate (3 sensor average), (E) 8-row variable rate (3 sensor average) for Fields 1 through 8, and (F) identification of row-to-row systematic pattern plus variable rate for Fields 1 through 5.