Farmers can break up soil compaction with deep tillage, called subsoiling, based on measurements that indicate when compaction may have become severe enough to diminish yields.

Those measurements are made by manually pushing a probe, called a cone penetrometer, into the soil at several points around fields, says Sreekala Bajwa, assistant professor of biological and agricultural engineering at the University of Arkansas. Bajwa and graduate student Subodh Kulkarni are studying two instrument methods for quickly detecting and mapping soil compaction in cotton fields.

They use electromagnetic instruments that induce electrical currents at a depth of 13 in. and 39 in. The instrument readings are compared against traditional cone penetrometer readings.

“The advantage of using soil electrical conductivity is that the instrument can be towed around the field behind a tractor or all-terrain vehicle, taking measurements in a fraction of the time of traditional methods,” Bajwa says.

Another method uses reflected light from the leaf canopy to measure plant performance relative to soil condition.

Kulkarni uses a handheld sensor connected to an instrument pack on his back and a laptop computer to measure sunlight reflected from both a reference reflector, called a Spectralon panel, and the leaf canopy.

The health of plants is related to water and nutrient stress, Bajwa says. If all the plots are receiving the same amount of water and nutrients, and some of them exhibit more stress, then something is restricting water flow to those plants. All other factors being equal, the culprit must be roots stunted by compacted soil.

“Reflectance can be measured by aircraft or even by satellites,” Bajwa says.

The data from both instrument methods can be mapped using global positioning system (GPS) technology and used to guide variable subsoiling equipment, under development by other engineers, that would deep-till only those areas of a field where soil compaction was a problem, Bajwa says.

Bajwa is also trying to determine just how often subsoiling is necessary. She and Kulkarni measure the biomass and yields of plants in the test plots, which are subjected to varying degrees of intentional compaction.

“There is conflicting data on the effects of compaction,” Bajwa says. “We want to provide more accurate information that can prevent unnecessary and costly subsoiling trips over the field.”