The summer of 2012 was definitely one of water deficit. With the current weather pattern trends, there is concern as to what the soil moisture reserves will be for the 2013 crop. One thing that can be done to replenish and manage soil moisture reserves is to reduce tillage.
"Tillage reduces water infiltration by breaking large pores, and the small pores are clogged by the dislocation of soil particles," explains Mahdi Al-Kaisi, an Iowa State University Extension agronomist and soil management specialist. "When there is no crop residue on the soil surface, raindrops break the soil aggregates, which clog soil pores leading to slow water infiltration and increase in surface runoff. Additionally, subsequent rains result in more runoff because of potential soil crusting."
Studies show the more tillage you do, the less rainfall will soak into the soil
Research by Al-Kaisi and ISU Extension field agronomist Mark Licht has shown a significant decrease in water infiltration rate as the intensity of tillage increased as shown in the chart that accompanies this article.
Incorporation of crop residue can cause a significant loss of soil moisture, Al-Kaisi points out. Every tillage pass can cause the loss of approximately 0.25 inches of plant available water. Crop residue moderates soil temperature leading to a reduction in soil moisture evaporation, especially at the top 1 to 2 inches of soil. Crop residue also reduces the amount of wind at the soil surface and, subsequently, reduces soil moisture evaporation.
Another reason to skip fall tillage—you'll leave more crop residue to trap snow
Some farmers say they do deep tillage to reduce soil compaction. But it has been quite dry in 2012. "Under the dry weather conditions this season, soil compaction due to equipment traffic was minimal in these studies," says Al-Kaisi. "There is no reason to allocate your time and fuel for deep tillage. While tillage may temporarily help reduce soil compaction in the tillage zone, it is not necessary because shallow compaction can be alleviated with normal freeze/thaw cycles in the winter."
Another reason to avoid tillage is to leave more residue to trap snow. "Tillage reduces the quantity and quality of cornstalks that can trap snow," he notes. "Leaving standing corn residue stubble in the field can help catch snow that would otherwise blow across the surface and be deposited elsewhere. Eight- to 16-inch tall cornstalks hold more snow than bare soil. Additionally, the corn crop residue will reduce water runoff and increase infiltration of snow melt in the spring. By some accounts this could equal 1 to 2 inches of soil moisture."
Some farmers are convinced they need to do tillage to bury crop residue, in order to control corn diseases. Goss's Wilt, a corn disease that was a problem in a number of fields in Iowa in 2011, was not a concern in 2012. "Yes, it is true that this disease survives the winter on the corn residue, but because there was minimal presence this year, there is no need for tillage this fall to further reduce the risk of this corn leaf disease occurring in the 2013 growing season," says Al-Kaisi.