Evaluation of an Active Crop Canopy Sensor Using a Delta Yield Approach.

Whether variable rate N application technology, based on the spectral reflectance of the crop canopy, can improve N use efficiency and corn performance on a farm scale was evaluated in 2006 and 2007 in Ontario  A GreenSeeker RT200 Variable Rate Application and Mapping System (Ntech Industries, Inc) was used to measure NDVI on three starter nitrogen treatments:  1) four rows with 0 kg N ha^-1 relative to four rows in a fully fertilized reference strip,  2)  four rows with 30 kg N ha^-1 applied as a side band relative to four rows in a fully fertilized reference strip, and 3) two rows with 0 kg N ha^-1 relative to two  immediately adjacent rows with 60kg N ha^-1 applied as a sideband.  Treatments were replicated three times and were 150m in length.  Each treatment was subdivided into 10m plots and average NDVI measurements for each subplot were taken at the 7, 8, 9, 10, and 11 leaf stages of corn. In 2007 an additional measurement was taken at the 13 leaf stage.  To determine nitrogen responsiveness of each subplot, 0 and 150 kg N ha^-1 plots were placed on either side of each subplot, thus enabling a delta yield measurement.   NDVI was correlated with 0 Kg N ha ha^-1 plots in 2007, but was not correlated with delta yield in either year. This suggests that late season stresses may have a significant impact on corn yield response to nitrogen that cannot be predicted with early season NDVI measurements.