Corn Illustrated Weekly: Mid-season Chlorophyll Readings Leave Questions

Higher nitrogen rates don't stand out.

Published on: Jul 9, 2007

Jim Facemire used the SPAD chlorophyll meter just as Bob Nielsen instructed him to do. Dave Nanda recorded the results. In the end, some things added up, others left questions at mid-season. It was all part of a mid-season evaluation of the Corn Illustrated plots sponsored by Farm Progress Companies.

Facemire, Edinburgh, Ind., is the cooperating farmer. Nielsen is the Purdue University corn specialist who has spent countless hours over the years trying to decipher what chlorophyll readings mean. The chlorophyll meter is designed to give an indication of a measure of greenness. The theory is that it should be tied to photosynthesis and how much N is in the plant. In fact, Nielsen and another agronomist, Jim Camberato, are experimenting with on-the-go sensors that mount on a high-clearance sprayer and basically measure the same thing, reflectance from the entire canopy, on-the-go.

Nanda is the consultant for Corn Illustrated plots. The long-time corn breeder is also president of Bird Hybrids, Tiffin, Ohio. He's been interested in chlorophyll measurement as a plant breeder because if he could find a correlation between chlorophyll readings now or even later in the season and yield, he could use that in his breeding program to make selections using a scientific, measurable criteria instead of just visual ratings and subjective analysis of looks and performance.

So far, there are trends, but the tie to yields at the end of the season remains elusive, based on previous trials Nanda has helped coordinate. Nevertheless, Camberato thinks there may be enough to the on-the-go sensing theory that it could someday be used to fine-tune nitrogen rates late in the season. But he and Nielsen still need to conduct many more trials to prove or disprove that point. Some are underway this year.

Facemire and Nanda tested the nitrogen plot last week, with corn at the 10- to -12 leaf stage, based on the leaf collar method. Nielsen suggests it's worth taking measurements at this stage to get a baseline for what's going on. They will test the plots again after plants set ears. Rates in the plot include 0, 50, 100, 150, 200, and 250 pounds of liquid 28% N sidedress injected, plus 20 pounds applied with dry fertilizer before planting. So approximate rates are 20, 70, 120, 170, 220 and 270 pounds per acre. Actual rates, recorded at time of application, will be reported when the plots are harvested.

Based upon Nielsen's recommendations, Facemire sampled 30 plants at random in each hybrid of each replication. He selected the uppermost leaf with an exposed leaf collar, and took the sample in the middle of the leaf. Consistency is important when trying to get good data, Nanda aays. The SPAD meter, provided for use by Spectrum Technologies, Plainfield, Ill., stores the 30 readings, then calculates the average. Facemire would call out the average for each hybrid in each rate to Nanda. The experiment is replicated once, and they tested both replications.

"I could tell which number would be higher and which lower between hybrids before he ever told me," Nanda says. "There is a distinct trend between hybrids. Some read higher than others. However, I have demonstrated in the past that a lighter-colored hybrid yielded more than one with darker-leaves during the summer in a plot, so I'm not sure how valuable the information is. What we can say is that there are differences between hybrids in chlorophyll readings during the season."

There were also differences between rates, but only to a point. The zero-rate plots obviously read lowest, with readings in the 30's range. The numbers themselves are only meaningful when compared to one another. The 50-pound sidedress plot delivered numbers in the 40's. From 100 pounds on, numbers were in the low 40's and 50's. "There was very little difference form 100 pounds sidedressed on," Nanda says.

Next to the plot is a third hybrid, not part of the plot. It received Facemire's normal regimen of 145 pounds sidedress plus 30 pounds N applied before planting. Those readings only turned out to be in the high 40's as well.

One theory that showed up last year was that population also matters, with thicker stands, especially very thick stands, tending to produce lower readings. Facemire and Nanda intend to test that theory when they check the high-yield plot at the normal time after pollination. Planting rates above 40,000 seeds per acre are included in that plot. Part of it is irrigated, part of it isn't.

Stay tuned for further updates.