Precision Lime Application Pays Off
Soil mapping, soil testing and variable-rate application produce cost savings, better utilization of lime and fertilizer and more

Steve Grady says the returns he gets from Southern States precision- application services more than repay the program's cost. Steve Grady reaps the rewards of precision-application services provided by Mt. Olive Service employees Sammy Fields, left, store manager, and Russ Brock, right, assistant store manager. Russ Brock, precision-application specialist with Mt. Olive Service, works closely with farmer Steve Grady to keep his crops and pastures in top condition.

Steve Grady long ago learned the value of soil testing for providing his crops with adequate plant nutrition. But he began to reap even greater benefits when he began soil mapping using aerial photo imagery a few years ago.

"I was surprised at how much difference in plant food requirements there could be between different parts of a field," Grady says. "With conventional soil sampling, you tend to get a shotguneffect, overapplying in one part of the field to get the proper amount of fertilizer or lime in another."

Grady farms 3,500 acres of tobacco, cotton, corn, soybeans, wheat and hay near Mt. Olive, N.C. Russ Brock, assistant manager with Mt. Olive Service, Grady's local Southern States retailer, helped him develop soil maps for about 2,000 acres of cropland and pasture.

"We had the digitized county soil survey maps on file," Brock explains. "Aerial photo imagery based on GPS helped us establish the physical boundaries of each field. Through the use of a computer program, we were able to overlay those boundaries on the soil survey maps and create soil zones for each field.

"Then, through regular soil sampling, we determined the plant nutrient availability in the various soil zones," Brock continues. "From that, we can develop precision-application maps for lime and fertilizer."

Mt. Olive Service has two Terragators and one truck equipped for precision application. Information from the application maps is downloaded into a computer in the vehicle.

The computer, in turn, sends the information to a control box. The control box regulates a gear chain that slows down or speeds up according to the rate called for in a particular zone.

"We started this program in 1996," Brock reports. "Currently, we are servicing about 16,000 acres over a 30-mile radius in a five-county area.

"We start soil sampling about the first of September--as soon as corn is harvested--and continue right into March," he says. "Some growers test every acre every year, some do it every other year." So far, most of the Mt. Olive store's variable-rate application has been with lime.

"We have a wide variety of soil types," Brock explains, noting that it's not unusual to identify six to eight different soil types in some larger fields. The lime requirements can vary by as much as zero to 2 tons per acre.

"Through soil mapping and soil testing, we can zero in on those different soil types to get the soil pH to the desired level," he adds.

Brock explains that, in addition to correcting soil acidity, lime increases the availability of plant nutrients that are tied up in the roots and soil. As a result, less applied fertilizer is required. It improves the effectiveness of weed-control chemicals. It also improves crop growth and quality.

Brock concedes that some producers haven't bought into soil mapping and precision application because of the extra cost. But those who have been on the program for several years have realized major savings from not applying as much lime and fertilizer in fields where not as much is needed.

"I think the program saves us money over and above the extra cost of surveying, sampling and application," Grady says. He applies hog effluent to several hundred acres of hay pasture and cropland, which results in a large differential in plant nutrients in different fields.

Those differences, he notes, can be determined only through soil testing. "We've more than gotten our money back," Grady concludes.