Research paves way for new wave in crop data

OAKES, N.D. -- Farmers in the U.S. are starting to use multispectral meters -- either from the ground or even from the air -- to decide when and how much nitrogen to add to wheat and corn crops early- to mid-growing season.

Walt Albus, a research agronomist with the North Dakota State University at its Oakes Irrigation Research Site, envisions a day when farmers could get money-making information by attaching such sensors on their spray rigs or even to airplanes. This data would be juxtaposed with other GPS data and other map layers to improve economic returns for these crops.

Albus, describing recent work at the research site's July 26 field day, says he's been aware of precursors to this technology since 1992. Dr. Jim Schepers of the University of Nebraska-Lincoln did some of the early work using chlorophyll meters, which still are in use. Schepers (now retired and a consultant) used hand-held Minolta SPAD 502s to create a "nitrogen sufficiency index" for corn.

Using that technology, a researcher uses this at various stages of growth. On the corn crop, for example, just before it silks or flowers, greenness of the youngest mature leaf can indicate nitrogen sufficiency.

"You just clamp it on the leaf and it gives you a reading," Albus says.

In 1993, Albus became involved in a Management Systems Evaluation Area study, which uses this kind of technology. The main projects were in Iowa and Nebraska, as well as Missouri and Ohio. Minnesota also was involved in the study, and Oakes was a satellite site of the Minnesota MSEA.

The MSEA was designed to develop production techniques to lessen the impact of irrigated cropping on groundwater quality. Among other things, the MSEA study measured the effects of ridge tillage in a corn-soybean system on herbicide movement in soil and water, compared nitrogen management effects on water quality and described water flow and its effect on agrichemical movement. The study went from 1991 to 1999, and eventually included potatoes.

The research site decided to pursue the studies.

Green-reading corn

Corn is ideal for the green-reading technology, Albus says.

"With corn, you can create a 'high-reference' plot in the field, where you put on more nitrogen than you need," Albus says. "Say, if you believe you need 180 pounds per acre of nitrogen to grow a corn crop on particular field, you might add another 30 or 50 pounds more than you need for the reference."

Once corn hits its optimum nitrogen uptake level, it won't get any greener -- even if the maximum rate is exceeded. Similarly, farmers can use this "plot" technique as a reference to compare that spot bulk of the field. Albus has used this with volunteer farmer cooperators, and the technique must be repeated for different varieties, which each have their own green responses to nitrogen.

Nitrogen sufficiency is expressed as a percentage. The "reference" plot might rate at 40 relative units on the chlorophyll meter while the overall field might come in at 38 units. In that example, percentage is 95 percent.

"It varies, but with corn, if -- if it's at silking -- if you're 97 percent or 98 percent, you're probably optimizing your nitrogen," Albus says. "You wouldn't be adding any more through the system. But if you're at 95 percent or below, it's telling you that you're too deficient in nitrogen to get a maximum economic return. Getting it to 100 may increase the yield, but it wouldn't be worth the cost."

So far, the study suggests farmers might be dollars ahead by monitoring corn and maintaining sufficient levels of green in the early growing stages.

"If we under-apply early, we've capped our yields and our profits," he says. "We know over the course of years what the optimum nitrogen rate is, but -- that said -- if you get excessive rainfall and the nitrogen leaches out, or the type of year where the soil doesn't mineralize enough -- then we'll be short of nitrogen. Then we can compare the field to the reference plot and know that, so we don't cut ourselves short."

In an irrigation system, the supplemental nitrogen easily can be added to corn through the irrigation system -- "fertigation."

Launching field tests

In mid-1990s the MSEA program worked with three area farmers to try the techniques in field-level studies.

They hired an airplane to come in and take aerial pictures in corn fields with different nitrogen rates. With computer programs, they cut the red and green colors out of the picture to create a grayscale version, which was used to measure the greenness in the field. This was matched up with field data, which showed good correlation.

In 2010, the station acquired its own ground sensor system. There are several brands out there, but the Oakes station uses a "Holland Crop Circle ACS 430." active canopy sensor.

The "active-light" produce its own light, so technicians can go out -- even in the dark -- and get data. Three light sources emit three different parts of the spectrum -- near-infrared (NIR), red, and the so-called "red edge" area, which adds to the resolution.

The machine drives through and puts the sensor up 3 to 4 feet above the crop. Here again, a farmer later would compare this with his or her overlay maps, correlating the information with planting and harvesting data. The research station did correlating studies on its own site plots, using several experiments involving various crops.

Albus thinks this eventually will become commonplace. Albus says aerial photography or satellite imagery can be useful in parts of the country, but it won't necessarily come with the "red edge" spectrum. Images from air or space can run into weather or timing. But devices closer to the ground likely will become commonplace, he thinks.

"This could be a natural way for observing farm fields -- anything that affects crop growth -- insects, disease, green-snap -- it's all going to show up," Albus says. "It gives us a result that is a summation of green color and biomass."

While the information has obvious applications with irrigation, it also has nonirrigated application.

Ag Leader Technology, a precision farming company in Ames, Iowa, is one that offers this kind of technology on sprayers for nonirrigated crops. The variable-application system is guided by software which allows it to apply the needed supplemental nitrogen on-the-go, when the corn is about knee-high.

"They can go through a corn field and instantly read and apply the 'N' according to the readings," Albus says. "We feel we should be working with this concept more."

More resolution

Albus says he'd like to see experiments with a sensor mounted to the airplane, maybe taking pictures 10 to 60 feet off the canopy, Albus says. Some of the newer sensor technology allows researchers to get the readings from the lower heights, even at typical airplane speeds. There may be future potential using "drones" or radio-controlled planes or helicopters, but those systems so far have limitations such as weather, durability and other factors.

The human element still is important, he says.

"Chlorophyll indicators are more highly related to yield potential than nitrogen," Albus says. "If the corn is standing in the water, or in a salty area, for example, the system is going to show up as not seeing green. It'll assume it needs nitrogen, but putting more 'N' on isn't going to help. So we will want to run a reference strip through an area when something else is obviously a problem, other than nitrogen."

How long will it be typical grain farmers and their consultants will use these kinds of systems? Albus thinks it'll happen within the next five or 10 years.