“These maps provide a snapshot of what’s going on in the growing season before the crop is harvest and sometimes before the symptom shown in the map disappears,” Ferrie says. “The key to using NDVI maps is ground-truthing the information they show.”

The limitation of the NDVI maps is that they only show you where to look, not necessary what is going wrong. Follow Ferrie to the field in episode 13 as he shows a surprising example of ground-truthing a problem area identified using NDVI.

“As we look at this example, we see red areas, and the first suspicion is that it looks like nitrogen deficiency. But this grower increased his nitrogen rates…”