Use of an N-Rich Strip and Ground-Based Active Optical Sensors for Detection of Sulfur Deficiency in Corn.

Yellowing in corn (Zea mays) can be caused by a number of factors including nitrogen deficiency. We found in our N rate trials using ground-based active-optical sensors that when our high N rate plots of 220 kg N ha^-1 were more yellow than the check (0 N) plots, S deficiency was the cause. The ground-based active-optical sensors used in our research verified that before S application, NDVI readings decreased with N rate, while a week following S application, NDVI readings increased with N rate. One of the implications of these findings is that a virtual reference recommended for use by certain active-optical sensor providers may give erroneous results when there is S deficiency in the field, and an N-rich strip is the only method that would prevent N fertilization on the area of the field with the most N already available.