Unless no-till, ridge-till, or strip-till planting systems are used, it’s a tradition in Minnesota to use major tillage on the top 8 to 10 inches of the root zone. Except for sandy and highly erosive soils, most major tillage is completed in the fall. Recently, however, growers are asking about the effect of zone tillage on crop production. This type of tillage has also been referred to as the Rawson system. All deep tillage systems are not the same. In previous years in Minnesota, deep tillage was thought to be random and not necessarily parallel to the rows. With a zone till system, the deep tillage is parallel to existing rows and the intended crop is planted directly into the deep tilled zone.

The concept of deep tillage has been evaluated in Minnesota. Trials with corn were conducted at the Southern Research and Outreach Center, Waseca and in Olmsted County. The yields from a Port Byron silt loam at the Olmsted County site measured from 1997 through 2000 are summarized in the following table. The Rawson system uses deep tillage. The “one-pass” system for planting corn can be considered, many times, as a conservation tillage practice. In this system, there is no fall tillage and the corn crop is planted following a previous crop of soybean with seed bed preparation by use of a field cultivator.

Yields were lower when corn was planted following corn in a no-till planting system. Otherwise, tillage system had no significant effect on yield regardless of the previous crop. There was no advantage to the use of the Rawson system for corn production.

Another study was conducted on a Webster/Nicollet clay loam soil to measure the effect of tillage systems on yield of corn following soybeans. Those grain yields are summarized in the following table.

An explanation of the rip-strip treatment is needed. This tillage system involves the use of in-row subsoiling/ripping using the implement shown in Figure 1. The depth of tillage is 14 inches on 30 inch centers. This deep tillage is completed in the fall followed by planting directly on the ripped strip zone the following spring without any secondary tillage. The strip till treatment was similar except that a mole knife (much like an anhydrous knife) was pulled to a depth of 8 inches to create the tilled zone.

Yields were slightly lower when the no-till and one pass planting systems were used. The rip-strip system tilled to 14 in. did not produce yields higher than those produced by the use of the strip-till system where tillage was at a depth of 8 inches. In other words, the use of the extra deep tillage had no positive effect on corn yield.

There is also a risk associated with the use of deep tillage. The field shown in Figure 2 is one example. Deep tillage had not been used where the corn is green. A deep tillage implement had been used where the corn is yellow. The cause of the yellow corn is related to denitrification and probably reduced root growth.

Although deep tillage is thought to alleviate subsoil compaction, there may be an increase in resistance to root growth when deep tillage is used where the subsoil has a high clay content. When a knife or shank is passed through soil that is wet with a high clay content, the soil separates and is compressed. This can result in sidewall compaction and reduced size of the air-filled pores in the soil. These two factors can have a large negative effect on root growth, nutrient availability and nutrient uptake especially under drier or wetter-than-normal conditions. When the soil comes together again, the point at which the separated soil joins together is frequently more resistant to root growth than the original soil. In this situation the “soil strength” has been increased rather than decreased by the use of deep tillage.

There’s nothing new about the concept of deep tillage. This management practice has been used successfully on soils in the Eastern and Southeastern part of the United States. Those soils, however, are quite different from those in the northern and western Corn Belt.

Various modifications of the deep tillage concept have been evaluated by several universities in the region. The results, as illustrated by those from the Southern Research ad Outreach Center, have not been positive.

Additional information is being collected this summer. That information will be summarized after fall harvest.

For those that are interested, the zone tillage practice is being evaluated at the John Illiss farm east of Elrosa (more information). The zone tillage was completed in the fall of 2002. The Field Demonstration will be featured at the farm located ½ mile east of Elrosa on County Road 13. Corn growth as well as root growth can be viewed on August 28 starting at 1:00.

Figure 1. Deep tillage implement used at Waseca.

Figure 2. Impact of deep tillage on corn growth in the Red River Valley.