With harvest proceeding quickly this fall, agricultural producers have had time to consider performing some fall tillage. Since the preceding two fall harvests were fairly wet, many producers might be considering deep tillage to alleviate compaction, said DeAnn Presley, K-State Research and Extension soil management specialist.

Whether deep tillage will prove beneficial depends on soil conditions, she said.

“In research studies, it is commonly concluded that deep tillage is only beneficial if the zone of compaction is truly root limiting. If it isn’t, deep tillage probably won’t be of much benefit,” Presley said.

The only way to know if compaction limits root growth is to leave about three to five untilled strips through the field and then compare yields in those areas to the tilled parts of the field next year, she explained.

If tillage is performed when the soil is too wet, the zone of compaction could be moved even deeper.

“To know if the soil is too wet for tillage, try to make a ribbon out of the soil without wetting it. If you can make a texture ribbon, it is too wet. Alternatively, if you can roll out a ‘snake’ of soil by rubbing it between your palms, it’s too wet,” Presley said.

This is called plasticity and if the soil is plastic, or bendable, it can smear and compact easily. Producers will need to test this to the entire depth they want to till, she said.

Fracture is goal

“Your goal is to create fracture, so the soil has to be dry enough to shatter, not smear. To see if you’re achieving this, dig between the shanks with a spade and see if the soil is loosened. If you bring up huge clods, the soil isn’t shattering and it would be better to wait until it’s drier. Straight shanks are going to cause the least amount of soil disturbance,” Presley said.

Also, keep in mind that certain areas of the field are more compacted than others, she said. Those areas might not be ready for deep tillage at the same time as the rest of the field because compacted areas tend to stay wetter, longer.

“A case in point is a recent trip I made to a producer’s farm. I observed soil shattering from deep tillage across the entire 30 inches between the shanks in the average part of the field, but in the end rows where the grain cart was driven, I dug up clods that were about one cubic foot in size, most likely because the more compacted areas were wetter.”

Is deep tillage economical? “Only if a root-limiting layer is really present, and even then this is a costly operation (because) it requires a lot of power to go deep. Deep tillage is slow-going and the implements are not very wide. As a result, deep tillage requires a lot of operator time, diesel fuel, and usually a few shear bolts!” Presley said.