Corn Illustrated Weekly: Chlorophyll Meter Will Unmask Differences - Hopefully!

Six nitrogen rates will be checked this week.

Published on: Jul 2, 2007

Rain has finally fallen on the Corn Illustrated plots devoted to testing nitrogen rates on two different hybrids. More rain is still needed, but at last count, the field received roughly an inch in different showers last week.

Differences in color reflecting differences in N rates continue to delineate themselves. The entire plot received 20 pounds per acre of nitrogen as starter fertilizer. Then the sidedressed rates were: 0, 50, 100, 150, 200 and 250 pounds per acre. These are approximate rates. Actual amounts applied will be detailed when results of the plot are reported this fall.

The zero-rate plots were very easy to pick out within a week of application, even before rain came. Nitrogen was 28% liquid N, applied just below the surface with a liquid nitrogen injection rig. Plots that received 50 pounds of sidedressed N were not as yellow. Other plots were greener, but it was difficult to pick out 150 from 200 from 250 pound per acre rates.

So this week, Tom Bechman, Dave Nanda, Corn Illustrated consultant for the project, and Jim Facemire, the farmer, will test each plot with a hand-held chlorophyll meter. Corn should be at about the V 12 stage, which means 12 leaf collars are exposed. Finished plants should have 16 to 18 leaf collars.

While it's most common to check chlorophyll readings after the corn pollinates, Bob Nielsen, Purdue university corn specialist, suggests doing it now as well. It will begin to allow plot organizers to get a handle on how well various plots are using N, he says. There's no doubt that the chlorophyll meter, also called a SPAD meter, will detect differences between the zero-rate, yellowish corn and the darker green corn. The real question will be how much difference, if any, it picks up between the three highest rates. The $1,200-plus meter is being provided for use this summer by Spectrum Technologies, Plainfield, Ill.

Chlorophyll testing in the past in other trials indicates that there may be differences in hybrids. The two hybrids in this plot have already exhibited large differences, one being taller with darker, upright leaves, the other a bit shorter, with leaves that showed vein striping at a younger stage. Nanda attributes that to a genetic trait of the hybrid, and attaches no yield potential significance to it.

Thickness of the sand has also affected readings in the past, with thicker stands tending to produce lower readings. Stand was checked on this plot, and is very uniform, with standard deviation for spacing less than 2.0. Nielsen notes that such performance is exceptional. Where the stand spacing was checked, over 50 consecutive plants in each of the 12 planter rows, the population was 34,000, slightly higher than intended. But the stand should be the same across the entire plot. All sidedress rates are replicated, meaning the same rate was used twice.

Organizers also hope Nielsen and Jim Camberato, a Purdue associate, will try out their light-sensing technology on this plot. Sensors are designed to mount on a high-clearance sprayer with corn at V-10 to V 12 stage, and determine how well N is being used. Think of it as an automatic chlorophyll tester on wheels.

Weather patterns, rain storms, believe it or not, are putting kinks in the researchers' schedules. It's not certain yet whether they will be able to try their equipment on the Corn Illustrated plot or not.

We'll bring you updates of hand-held chlorophyll testing next week.