Farmer yields and water quality could benefit from precision agriculture research being conducted in North Carolina.

Here, researchers are using aerial imagery to determine site-specific application of nitrogen on corn and wheat during the growing season. They’re also monitoring water quality on a field scale.

"In the future, nitrogen-management systems will be based on in-season analysis of the crop rather than pre-season guesses," asserts Ron Heiniger, North Carolina State University Extension corn and precision agriculture specialist.

The site-specific work has already pointed out the importance of 50 to 100 pounds of nitrogen up front in corn to maximize yields.

Using aerial photography, the researchers can judge the nitrogen needs of the crop by looking at the colors on the infrared and green photographs.

Hieniger believes this type of system will help farmers get a better economic handle on what their crop needs and if they should apply nitrogen.

The system is based on aerial photography, Hieniger says. Infrared color photographs measure the biomass of the crop. A green photograph measures how much chlorophyll is in the leaves.

By putting the two photos together, researchers have a good measurement of nitrogen uptake as it relates to the final yield. "We’re taking infrared and green color and relating it directly to nitrogen requirements," Heiniger says. "If you measure biomass and the nitrogen in the leaf, you have a good measure of the nitrogen uptake and the nitrogen leaving the plant."

Heiniger and other researchers have had particularly good success using the system with wheat.

There’s also an economic aspect to the photos. By using the infrared and the green photos, Hieniger is able to figure nitrogen needs based on price and the maximum yield. "We’re able to tell how the yield would be if the price of nitrogen isn’t a factor." This system lets farmers incorporate nitrogen and grain prices, Heiniger says. "The producer doesn’t have to guess, price wise, how much nitrogen the crop needs and if the return is worth the investment."

With wheat, the photos indicated a standard nitrogen application in late February or early March, at growth stage 5 (GS-5). "The aerial photography is taken at a time when you want to fertilize wheat, but it indicates the amount of nitrogen that is needed at the time to optimize yields," Heiniger says.

With corn, it’s a little more complicated, the researcher says. Typically, growers fertilize corn when it’s at V7 — 15 to 18 inches tall. "We’re finding that the photograph doesn’t make a good call at that time in corn," Heiniger says. "We have to wait until V10, when the corn is waist high to chest high, and that would require a Hi-Boy with drop nozzles. That’s an aspect of this system with corn we’re trying to resolve."

With corn, Heiniger believes a snapshot of the stress the crop is under is needed. That requires measuring the temperature of the canopy. "At V10, the crop is only two weeks away from tasseling and water is essential for development," he says. "Canopy temperature is a good way to measure the potential of the crop at a critical stage."

Using a thermal scanner, Heiniger maps the field, in much the same way a yield monitor does, getting a reading of the heat signature of the crop. With the information, he can predict the yield and irrigation and nitrogen needs of the crop.

Thermal maps are able to show sub-surface drainage, changes in the soil, as well as when and where the crop is under stress.

The mapping can be done either by airplane on mounted to a tractor.

Red on the map indicates that the crop canopy is hot and the crop is under stress. "It’s a good indication where there’s water stress and other problems," Hieniger says.

Dark blue indicates the crop canopy is cooler. In other words, the crop has received plenty of water.

"Thermal mapping can be used in other crops as well for making management decisions," Hieniger says. "For example, the farmer could use this to determine when to irrigate — you see the temperature differences long before you see the wilting. It’s a great tool for determining what your yield potential is for nitrogen or the economic thresholds for stresses."

While the study is looking at yield as it relates to nitrogen application, Hieniger and his colleagues are also monitoring leaching.

To date, theirs is the first large-scale research to look at water quality effects from site-specific nitrogen management, Heiniger says.

The N.C. State researchers are monitoring water quality on a 35-acre site in the eastern part of the state. On the site, they have wells every 100 feet on a grid pattern.

"The exciting part is we have the opportunity to show where nitrogen is being lost in the field, whether it be from soil changes, crop growth or other parameters," Hieniger says.

The researchers are using three systems to measure nitrogen management.

A conventional system uses the same rules as farmers in the Neuse River (N.C.) basin do, using the best three out of five yield records to determine nitrogen levels. In corn, that’s 120 to 140 pounds of N per acre. "We’re applying the nitrogen at V7 and calling it the current management practices," he says.

Another system uses aerial photography and determining N application later in the season on an average-rate basis.

The third system determines the N rate based on the site-specific condition of the crop every 30 feet, as fast as the sprayer can change rates.

USDA and NASA are funding the water-quality portion of the project, Hieniger says.

In its first year in 2001, Hieniger found reduced nitrogen losses with the site-specific system.

"We’re still pulling data apart, but it appears that the site specific application gave us higher yields in wheat and soybeans," Hieniger says. "This will be the first year we look at corn due to the rotation.

"Site-specific appears to be working," he says.