Farm Horizons, February 2001

Less waste, more accurate fertilizing possible with GPS

By Lynda Jensen

Treat the cow, and not the herd. That's the theme for a new kind of fertilizer application known as precision farming, which uses a global positioning system (GPS).

GPS involves the use of satellite technology to give farmers an acre-by-acre account of a field's soil composition, said Jeff Lorentz, agronomist at Lake Region Cooperative, Cokato.

This means that farmers can apply specific amounts of fertilizer according to the needs of each area in a field, instead of giving the entire field a blanket dose of fertilizer, Lorentz said.

New way to farm

"When I started farming, you'd farm with your heart," commented Gene Lorentz, a lifelong farmer and Jeff's father. "Now, you do it with your head."

There are about a half dozen farmers currently using GPS now in the area, including Gene, who decided to try it this year; conservatively testing half his field.

Yield was the primary motivator, Gene said, since farmers nowadays have to operate like a business.

The initial statistics he looked at showed an increase in profit of about $25 per acre, Gene said.

With two agronomists in the family, Gene thought he would give precision farming a try.

"It beats throwing 300 pounds (of fertilizer) all over the place," he said. "Time will tell."

The preliminary cost may be prohibitive, Jeff Lorentz said, since GPS cannot be used with traditional spreaders and requires soil testing.

"We keep our growers on a three-to-four year schedule," Jeff Lorentz said. This means the data collected on soil samples is good for at least three years.

There are several reasons why precision farming is a good investment, Jeff Lorentz said.

It is better for yield because the fertilizer can be applied in whatever formula necessary to answer the needs of the soil in each specific area, which also saves money in fertilizer costs because farmers are not buying fertilizer they don't need.

In turn, this helps the environment because the soil isn't saturated with unneeded fertilizer, and cuts down on runoff, Jeff Lorentz said.

HLWW ag department on the cutting edge

Last year, ag teacher Jim Weninger wrote for - and received - a $10,000 grant to purchase GPS equipment for Howard Lake-Waverly-Winsted High School.

The department purchased 14 handheld units, two laptop computers and navigation software.

Senior Andy Sorsoleil used the GPS equipment on the farm owned by his parents, David and Sue Sorsoleil, as part of his hands-on project for FFA. Sorsoleil helps operate his parents' 80-acre farm.

He plans to use the system on two FFA test plots this summer.

How it works

The process starts with soil sampling, in conjunction with mapping on a grid, which is linked to satellite technology, Sorsoleil said.

A farmer would probably start by contacting a local agronomist, since a special spreader is needed for GPS technology, Sorsoleil said.

A farmer interested in the process would need to purchase equipment for the soil testing as well, he said.

To sample a field, it would be necessary to drive a pickup truck around the perimeter of a field, stopping every 2.2 acres or so to stick a probe into the ground. The probe would be used to pull out several soil samples to create one composite for that location on the grid, Sorsoleil said.

As the truck moves along, the navigation software can display the truck's exact location by longitude, latitude, and elevation, as well as the truck's speed, Sorsoleil said.

For example, if an area in the field is low in lime, this is recorded, Sorsoleil said.

When the time comes to spread fertilizer, as the spreader passes over that area, it will be programmed to drop extra lime over it to make up the balance, he said.

"It's really interesting, once you soil sample," Sorsoleil said. "You can tell if this spot is lacking in this or that," he said.

The visual rendition of soil sampling shows mounds of different minerals, Sorsoleil said.

Once this is done, a differential signal is used to correct any misguided signals. The signal used for mapping is within 10 feet of accuracy, Sorsoleil said.

The field is completed when all the points around the field have been mapped and locked into the computer. This information stays the same over the next few years until annual crops and fertilizer applications change the soil enough to sample again, Sorsoleil said.

The actual coordinates stay the same, Jeff Lorentz said.

Soil samples are sent in and tested, with each being marked by a different grid number on the field.

A lot of farmers in southern Minnesota use GPS technology, Sorsoleil said.

The concept itself has been in use for several years by other industries, such as over-the-road trucking companies, who use it to track drivers, Jeff Lorentz said.

When researchers initially looked at fertilizer spreading, it was discovered that areas around the house and barn were heaviest with fertilizer, since the weather made farmers want to stick closer to home, Sorsoleil said.

Cabs added to tractors helped correct this problem, he said.

Soil sampling is done in the fall, with the fertilizer spreading done in spring.

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