Capability to variably apply agronomic products in the field A new use of precision agriculture technology could save cotton producers significant dollars as early as next growing season.

The components of the technology are the capability to variably apply agronomic products in a field, the Global Positioning System, a mission plan and a field map of plant vigor variability.

According to precision agriculture educator Tim Sharp, all these technologies are on the market today, at a reasonable cost. All that's needed is the human touch - engineers to rig the application vehicles and crop consultants to develop the mission (application) plans.

One important piece of the puzzle recently came on the market - plant vigor maps. These maps are generated from aerial photography. John Williams, president of Global Positioning Solutions, Inverness, Miss., provided Sharp with the images he has been studying. They were shot with a Duncan Technologies 2100CIR digital camera.

The camera produces at half-meter accuracy, multi-spectral images in green, red and near-infrared bands. In layman's terms, the camera picks up the reflectance from the crop in ways that can't be seen with the human eye. These particular multi-spectral images provide an excellent snapshot of plant vigor. Dark green areas in the geo-referenced image represent a higher level of plant vigor, while the lighter shades of green represent lower levels of plant vigor.

The image can pick up all sorts of irregularities in a crop, including fertilizer streaks and insect damage. But the most important image is created by an image analysis tool within a computer software program called SS Toolbox. This function groups all of the plant vigor data into five ranges of value - essentially creating a plant vigor variability map.

The first time Sharp saw a map generated by this function, numerous possibilities came to mind. But first, he wanted to see if the plant vigor map correlated with eventual yield. To do that, Sharp had his precision agriculture students at Jackson State Community College, in Jackson, Tenn., investigate a 48-acre, west Tennessee cotton field shortly before harvest.

The students randomly selected five plants from 10 sample sites within high, medium and low plant-vigor levels in the field. To guide them to the sites, they used a map generated from a multi-spectral image of the field taken Aug. 12.They hand-harvested the plants and carried the results back to the college.

While Sharp hasn't computed the yield data yet, it's obvious to the naked eye that the pile of cotton taken from the high vigor zones is larger than the pile taken from lower vigor zones. In other words, he proved that plant vigor, as seen by the multi-spectral image, does indeed have a strong correlation to cotton yield.

In terms of resolution, the image is superior to a yield monitor, according to Sharp. "The resolution of a yield monitor is based on head width and sample interval. If you're set on a two-second sample interval, that's four rows wide and two seconds of forward travel. That may be 30 to 40 square meters. This is half a meter. It's tremendously more precise."

On the other hand, "The yield monitor is really good as a reality check to make sure that what we seeing out here is real. One downside of this data is that we are inferring yield. It's not actual. It's going to predict yield provided you manage it right."

The plant vigor maps are also strongly related to soil type and to other factors which may or may not be correctable. But correcting problems in fields is not the best use of this technology at this point in time, according to Sharp.

Rather, growers can simply accept what's going on in a field, divide it into so-called management zones - based on the plant vigor map - then manage each zone according to its potential yield and profit. Sharp says the payoff could be immediate and significant.

For example, since each management zone would have a different yield potential, growers could in effect create a different budget for each zone. In other words, if the plant vigor map indicated that the yield potential in a management zone is only 200 pounds of lint per acre, a mission plan can be created to reduce agronomic inputs drastically on that part of the field, says Sharp.

The SS Toolbox software program will also generate the amount of acreage in each category in the field. "In the 48-acre field image, there were 2.3 acres of poor cotton and 7.8 acres of fair cotton," Sharp said. "So we have two zones out there, 10 acres out of a 48-acre field, where we're losing money. But the rest, we're doing real well on.

"The bottom line is that a bad spot is a bad spot," said Sharp, looking at a plant vigor map on a computer screen. "Even without knowing why it's bad, you can make the decision not to spend money there. In all the yellow areas on this map (of the 40-acre field), we're bleeding financially."

Sharp pointed to a study in which inputs were varied according to these management zones. "We could easily cut back to $50 an acre in total inputs on the low-yielding areas with 200-pound yield potential.

"At the very least, we want to break even on the low-yielding spots and make money on the high-yielding. Otherwise you would be spending $400 on a management zone that's not going to make 200 pounds."

Sharp says engineers could assemble GPS-based application equipment for varying the rates of Temik, Pix, single-product defoliants like Finish, nitrogen, cotton seed. "Anything that is one product at one rate, we could do that tomorrow." In fact, Sharp and lab instructor Greg Evans, who also owns a fabrication business, are working on building such an implement.

However, developing a mission plan is much more complicated.

"The farmer cannot do this without a really good consultant in the loop, to bridge this technology from the computer to the farmer," Sharp said. "The person has to be good agronomically and good on the technology side to put this into a usable form for a grower.

"Consultants have been struggling to find their role in precision agriculture," notes Sharp. "It's been focused on the retailer with the fertilizer issues. But the consultants are in the knowledge business. The technology is here, but nobody is doing anything about it."

On the other hand, not all consultants may be sufficiently trained on computers and the software required to farm by management zones. That's where JSCC and other colleges come in, according to Sharp. "I think JSCC has a role in continuing education in taking what we are learning and training the consultants to use this technology in ways that will make them money.

"If everything works out, we would like to start that process, we would like to do two to three work training sessions on using this technology. They're going to need the computer skills, GPS, GIS and remote sensing skills. Right now, consultants are agronomic wizards, but they're not computer wizards."