New technology will offer farmers the ability to pinpoint specific subsoil compaction areas in fields and then provide global positioning system (GPS) information to deep till only in compacted areas which could result in fuel and labor savings.

SOIL COMPACTION research conducted by the University of Arizona measures and records compaction data in fields prior to planting. The information could help farmers know when to deep-till or minimum-till fields, which could reduce fuel and labor costs.

Subsoil compaction is a major problem across the Sunbelt. Most compaction is caused by tractors and implements in fields.

In the southeast coastal plains soil compaction occurs naturally so tilling is required. Western soils have low organic matter and when combined with irrigation and equipment traffic for mechanized operations the soils become tightly compressed. Deep-tillage before planting is the only solution.

Farmers cannot see soil compaction because it occurs in the soil profile beneath the ground surface. Farmers typically deep till entire fields since soil compaction is invisible to the naked eye.

“Soil health depends on air and water movement,” says Pedro Andrade, precision ag specialist and assistant professor with the University of Arizona.

“When soil is compressed, void space is reduced. Plant roots grow sideways instead of vertically down. Water does not infiltrate since the compacted soil acts as a barrier. Compaction also limits oxygen movement to the root zone.

“Soil compaction also reduces crop fertility. When crops are sidedressed with fertilizer, compacted soil limits the nutrient uptake ability of the plant.”

Literature suggests subsoil compaction can reduce yields from 5 to 50 percent, Andrade says. With tight operating margins on many farms, lower yields can mean the difference between profit and loss.

Andrade and UA Research Specialist John Heun are testing technology at the Maricopa Agricultural Center (MAC), Maricopa, Ariz., and at several commercial farms to pinpoint the exact location of compacted soil up to 18 inches deep.

The technology to accomplish this fete includes a cone penetrometer, a sophisticated soil sensor panel, GPS, and other equipment.

GPS-based compaction maps generated from the tests could soon allow farmers to deep-till only the ground where soil compaction is identified and minimum-till uncompacted ground. This technology would save diesel fuel and labor costs, plus reduce equipment wear and tear.

Heun designed and built an apparatus for soil dynamics studies. The frame resembles a farm implement and is pulled behind a tractor to allow Andrade and Heun to test two systems.

The first is a stainless steel standard probe approved by the American Society of Agricultural and Biological Engineers. The probe (penetrometer) is attached to a hydraulic ram.

When the tractor is stopped, the 18-inch cone probe is pushed into the ground at a steady rate and the data acquisition system records penetration resistance every one-half inch down to 18 inches. That is deep enough to determine the soil area that influences the growth and development of rooted plants.

“The cone index is the best reference value we can obtain,” Andrade says. “The limitation is it’s a static-point measurement. With the cone mounted on the frame, the tractor stops, the frame is lowered, and the cone probes the ground to gather compaction data. The probe is lifted and the tractor is moved to another location. It’s a stop-and-go process.”

Electronic compaction data is gathered and recorded in a Campbell Scientific data logger mounted on the frame or inside the tractor cab. Generally three probe measurements are conducted and averaged per point location. Depending on the field variability, the ground is probed in one to three point locations per acre.

The second method, dubbed the “UC Davis soil compaction profile sensor,” was invented by Andrade and University of California, Davis Professor Shrinivasa Upadhyaya in 2001 while Andrade was completing his PhD work at Davis. UC holds a patent on the sensor, but the device is not yet licensed for commercial production.

The soil compaction sensor is a subsoiler shank mounted on the frame, lowered into the soil up to 18 inches deep, and then dragged continuously across the field.

Five force transducers on the sensor panel collect data at various blade depths. Ripping once through the center of a field is adequate to gain good soil compaction data.

“The benefit of the sensor is it’s a continuous measurement,” Andrade says. “The sensor is continuously generating data from the soil while the tractor is moving.”

The Campbell data logger simultaneously records the cutting resistance of the soil at five depths. Generally the instrumentation collects this data every one to three feet apart, and then geo references the position in a GPS location map.

Both methods have been tested at MAC before planting cotton. The systems are also under study in chile pepper fields and pecan orchards in southeastern Arizona.

“With these systems we are interfacing the hydraulics with the electronic measurement and control equipment to capture the soil compaction data in the field,” Heun says. “The data is invaluable.”

Which system is more accurate? As far as detecting the location of compaction, Andrade uses the cone penetrometer. As far as the practicality, the UCD-SCPS sensor is superior, Andrade says. The tractor travels through the field gathering real-time data faster.

Will this technology trickle down to commercial agriculture? Yes. In the short term Andrade and Heun can deliver the systems to farms to gather research-quality results. Down the road the technology could be installed on new tillage implements. Farmers would receive the compaction data in the tractor cab and lower and raise tillage tools as the GPS-positioning data indicates.

Andrade’s goal is to save farmers money. He understands that mechanization in agriculture is necessary. Sometimes heavy equipment must be operated in less-than-ideal conditions. This new technology would give farmers a new tool in their toolbox to improve efficiency and reduce production costs.

“There are significant energy savings that can be accomplished by avoiding compaction,” Andrade says. “There can be fuel savings from working the soil properly and avoiding deep soil tillage. New technology can improve tillage management.”

Andrade offers these suggestions which farmers can utilize now to reduce soil compaction:

■ Lower tractor tire inflation pressure — new ultra-flexible tires on the market require lower air pressure which reduces the concentration of stresses;

■ Use wide tires to increase flotation;

■ Reduce the implement load, use narrower implements but till faster;

■ Limit in-field traffic;

■ Work dry soil; and

■ Incorporate plant residues.

“We want to see energy savings through reduced soil compaction,” Andrade says. “It takes a lot of energy to break the soil. In the end we want to save fuel, labor costs, and wear and tear on equipment. It’s all about making mechanized operations more efficient.”

The UA funds Andrade and Heun’s soil compaction research.

e-mail: [email protected]