Proper irrigation, tillage, and cover crops can help prevent compaction, improve root growth, and increase yields.
A panel of soil scientists at the recent Louisiana Agricultural Technology and Management Conference (LATMC) in Marksville, La., discussed the effect compaction has on root growth and nutrient availability.
Kip Balkcom, research agronomist and lead scientist with USDA ARS at the national soil dynamics laboratory in Auburn, Ala., and Stacia Davis Conger, assistant professor of irrigation engineering with LSU and the LSU AgCenter, focused on cover crops, conservation tillage, and irrigation.
Cover crops and tillage
"In Alabama, with its sandy soils, I do a lot of work in cotton, corn, peanuts, and wheat. In our region, coarse-textured soils have low organic matter and is very prone to compaction and erosion," Balkcom said.
Cover crops and conservation tillage help build up organic matter levels and reduce compaction.
"Cover crops and conservation tillage give us some resiliency against forces causing compaction," he said. "With sandy soil, weather cycles of rain and dry spells cause compaction, so we try to do a tillage operation every year."
Compaction also happens with large pieces of equipment going across a field, especially if it's too wet.
"Farmers don't need to be out in the field when it's that wet, but they're trying to do what they have to do to get the work done," Balkcom said. "Unfortunately, you'll have to come back and correct for that. We usually use something like strip-till to alleviate compaction. There are all different kinds of implements related to strip-till and conservation tillage.
"The main thing is we're trying to minimize the soil surface disturbance because we want to protect that soil surface with the residue; we have with conservation tillage, but we also want to maximize below-ground disruption."
Some farmers feel they must use some form of tillage every year since the weather is unpredictable.
"If we knew that it was going to be a wet year or a wet summer for us, we probably could get away with not doing tillage, but many people don't want to take that chance," Balkcom said.
Tillage is an expensive operation.
"There is no need to till as deeply as people usually think they need to," he said. "Using a penetrometer to detect soil compaction will show you how deep you need to be tilling."
"Unfortunately, irrigation often does not help compaction issues," said Davis Conger, irrigation specialist. "Furrow irrigation is going to cause the most compaction of any of our irrigation methods. You're putting a large volume of water — every gallon weighs 8.34 pounds — and we typically apply 3 inches with every furrow irrigation. When you calculate that for a 40-acre field, it is over 9 million pounds of weight you were putting on that soil."
Switching to a sprinkler system will minimize the size of the water droplets and hit the plants first.
"Even if the drops are below the plant canopy, you're still pixelating the water, so it's not going to have so much weight to it, and you're applying less per time," she said. "A pivot is going to apply a half-inch to an inch, whereas furrow irrigation, you're still doing that 3 inches just to get water across the field."
Drip irrigation is the best to reduce compaction because the drip tape varies for row crops and pushes the water up.
"You have no pressure on the surface of the soil from that water; you're actually pushing it up," Conger said. "Not only does it not cause compaction, but the water is being pushed, so it is creating macropores those roots can access, and water can flow through. Now, I'm not saying that drip is going to work in all situations, but for compaction management, drip irrigation might be something to consider."
Irrigation supplements rainfall, so rainfall is going to compact the soil first.
"Rainfall, of course, is not a controllable factor, which is why implementing things like cover crops is going to hold those macropores over the winter and help with any rainfall," she said. "You're still going to have pressure on the surface from rain, but the soil is going to hold in place much better. It all comes back to good soil health."