A few years ago, you carried your management map in your head. Past experience, the sound of the combine as you harvested and a soil map told you everything you knew about which spots yielded well, which ones yielded poorly and why.
Modern technology, such as yield monitors and Normalized Difference Vegetation Index (NDVI) mapping, lets you give your field a checkup at any time during the season. NDVI mapping uses common color photography and infrared photography to show differences in vegetation across a field. It lets you spot problems almost as they occur, sometimes in time to correct them before harvest.
NDVI technology is so new that even consultants, such as Ken Ferrie and his son, Isaac, of Crop-Tech Consulting, are just now learning how effective it can be. "NDVI mapping is about where yield monitors were 10 years ago,” Ken says.
This past season proved that the Ferries' optimism was not misplaced.
To test the NDVI concept, Jack Pitts of McLean, Ill., had NDVI photos shot of two of his corn fields in mid-August. "The concept of a timely snapshot of the plants' status during the growing season, rather than after the fact with yield maps, seemed a wise use of our money,” he says.
Sure enough, when Pitts and the Ferries reviewed the NDVI maps they saw "two rows of corn that were absolutely getting hammered,” Ken says. To find out the cause, Isaac downloaded the photo onto a handheld GPS unit and set out into the field.
"The ears in those two rows of corn were stunted and deformed,” Isaac says. "Soil nitrate tests showed those rows had run out of nitrogen. Eventually, we realized that one knife on the farmer's sidedress bar either got plugged or did not seal properly. He was applying anhydrous ammonia on 60" centers, so it affected two rows of corn.”
Yield loss confirmed. A hand yield check showed the two nitrogen-starved rows yielded 100 fewer bushels per acre than the other six rows in each eight-row planter pass. That averaged out to a 25-bu.-per-acre yield loss across the entire field. On top of that, the applicator continued to pump out just as much ammonia, so the nitrogen that should have gone on those two rows either was lost to the atmosphere or applied to the other six rows, which didn't need it.
The problem did not show up on Pitts' yield maps. "It was an eight-row applicator and an eight-row corn head,” Isaac says. "So every combine pass took six good rows and two bad ones, all the way across the field. The resolution on the yield map was not fine enough to reveal the problem.
"On a yield map, a pixel is 15', 20' or 30' wide (depending on header width) by one to three seconds of travel. In our NDVI aerial photo, a pixel was 3½'x3½', so the problem affecting only two rows showed up clearly.”
- Early Spring 2009