Dr. Dan Talks Agronomy

As spring arrives in the Corn Belt, farmers will be anxious to rush to the field and work their soil prior to planting. Just say whoa. That long, cold winter we just endured makes it more important to consider soil conditions and the depth of the frost line this spring.

In general, spring is not a good time to do aggressive tillage because the soil can be wet and the frost line shallow. Working with a disk or field cultivator to a depth of 8 inches will often pull up clumps of wet soil that will dry into clods. The tillage points will easily create horizontal and downward shearing forces that will likely increase soil density and could create a compaction layer.

On March 13, I went out into my field intending to spread dry fertilizer. I knew the soil was firm and appeared dry. It's been so cold, that I was confident I could pull a dry spreader.

Fortunately, I also took along a spade. On a north-facing slope, the frost line was from 0 to 1 inch and since the slope was steep and the soil held a little moisture, I spun out a few times. On a south-facing slope near a hilltop with no residue, the frost line was 6 inches deep. Other locations had frost lines between 0 and 6 inches.

Mahdi Al-Kaisi, soil management expert at Iowa State University told DTN that lack of snow, especially in the Western Corn Belt, drove the frost line deeper than normal this winter. "We have seen frost lines down to 48 inches this past winter, and it will take a lot of heat or heat and rain to warm those soils up," he said.

Al-Kaisi does not feel the extremely cold conditions were all bad. "The deep frost will re-orient soil structure. And the freezing and thawing will be very effective in making the soil mellower in the top 12 inches," he explained.

When it comes to spring tillage, Al-Kaisi recommended patience until thawing begins. On March 17, I observed two tractors with tracks and heavy disks working heavy, black bottom ground east of Fremont, Neb. These fields had been disk ripped last fall and looked rough after running the disk this spring. I had a roadside view, but I couldn't help wondering if they were pulling up wet clumps of soil.

"Wait to till until the soil is thawed to 12 inches," Al-Kaisi said. "If you till early, you will bring up frozen clods of soil. When these clods thaw, rain will cause some of them to disintegrate and others will harden. The fine clay particles will seal the surface creating a crust, and it will be difficult to get a good seedbed."

CAN YOU DIG IT?

Al-Kaisi recommended getting on the business end of the spade once the soil thaws to 12 inches. If your soil has a nice granular and stable structure, why till it and ruin it? Spring tillage tends to ruin good soil structure.

"If you didn't till last fall and your soil is in good shape, do not till it," he said. "And there is no benefit from doing deep tillage in spring. If you disturb the soil in the spring, you will do more damage than good."

Some growers want to do tillage in the spring to blacken soil so it warms and dries quicker and the seedbed is more even. "If you must do tillage in the spring, keep it light and use a finishing tool and run it only 3 to 4 inches deep and when the soil won't smear and glisten between your fingers," he said.

Deep tillage or surface tillage done under improper conditions in the spring can increase soil density or compaction, leading to poor root development that can greatly affect the growth and yield of corn and soybeans.

(PS/AG)

Copyright 2014 DTN/The Progressive Farmer. All rights reserved.