Typical strip-till unit with cutting coulter, residue managers, mole knife, and berm shapers.
Typical strip-till unit with cutting coulter, residue managers, mole knife, and berm shapers.

Selecting a tillage system requires consideration of many factors, including soil and water conservation, economic return, labor availability and management capability, all of which are specific to the individual farming operation. For a more complete discussion of soil and tillage management in southern Minnesota, see the University of Minnesota Extension Bulletin for South Central or for Southeastern Minnesota:

Soil and water conservation considerations

Many agronomic and environmental factors affect the impact of agriculture on soil and water quality in Minnesota. Annual row-crops like corn and soybeans do not protect the soil from direct raindrop impact until the leaf canopy closes, which is usually mid- to late June. Because the period from April through June is generally wet in Minnesota, and soil moisture conditions are at or near field capacity while transpiration rates from row crops are low, this period has the greatest potential for water runoff. When the impact of raindrops detaches soil particles, they can be carried in runoff to surface tile inlets and streams. Excessive soil erosion results in the loss of yield potential over time. It also degrades streams and lakes with phosphorus-induced algal growth and sediment, reducing light penetration and depleting oxygen necessary for fish. Maintaining crop residue cover until canopy closure reduces the impact of raindrops that dislodge soil particles, and can reduce the power of runoff water to move soil to streams. Residue is especially effective if left standing, anchored by roots.

Conservation tillage and previous research

Conservation Tillage is defined as tillage systems that leave at least 30% residue cover on the soil surface after planting. Reduced tillage systems have benefits other than soil conservation, such as increased water infiltration, increased or sustained organic matter content, increased water-holding capacity, and continued long-term productivity of the soil. They also require less capital investment in equipment and fewer field passes, which reduces the amount of labor and fuel used.

So why have producers in Minnesota been hesitant to switch over to a higher residue tillage system for corn? One of the biggest concerns is that increased levels of crop residue will result in cooler and wetter soils in the spring, which may delay planting of corn on poorly drained soils. These are typically the glacial till or lacustrine (lake sediment) soils of the state. Delayed planting can reduce yield potential and result in a higher moisture content in grain at harvest. Leaving a high level of residue on the soil has less effect on soybean emergence and growth, since soybeans are planted later, when soils are warmer and drier.

The University of Minnesota has researched several reduced tillage systems to assist farmers and agricultural advisors in making tillage decisions for corn following soybeans. This research showed that reduced tillage systems can enhance residue cover and soil conservation while maintaining or improving corn yields. Small-plot research performed at the University of Minnesota's Research and Outreach Centers, presented in the two publications cited above, has shown that no-till corn following soybeans on glacial till, heavy clay soils will reduce yields compared with systems that involve some tillage like spring field cultivation, fall strip tillage, or fall chisel plow. However, on the well drained loess soils in southeast Minnesota, research showed no-till corn yields were similar to those of the three reduced tillage systems for corn following soybeans.

On-farm research evaluating four tillage systems

The University of Minnesota and Monsanto Corporation, in cooperation with farmers across the state, compared tillage systems for corn following soybeans on farm fields in 2004 and 2005, using producer-owned commercial tillage equipment. Details of the research methods are presented in the box below.

Research methods
Ten on-farm trials were completed in 2004 and nine in 2005, with an additional site, Sibley-2, planted but lost to wind in 2005. All sites were on glacial till-derived soils except for those in Fillmore and Wabasha counties, which were on loess-derived soils. Plots were field-length strips ranging in width from 500 to 1,000 ft. and replicated three times in a randomized, complete-block design. The farmer cooperators performed all tillage, planting, spraying and harvesting operations. Generally, experimental sites were chosen that had high to very high levels of soil test phosphorus (P) and potassium (K), and therefore fertilizer P and K was not needed. Nitrogen fertilizer was spring-applied at University of Minnesota recommended rates. Weeds were managed with label rates of herbicides to minimize their impact on corn production. Corn grain yields were measured with a weigh wagon. Percent residue cover, stand counts, grain yield, and grain moisture were measured in each plot at each site. Four tillage treatments were compared at seven sites in 2004 and six sites in 2005. They were no-tillage, spring field cultivate, fall strip tillage, and chisel plow plus spring field cultivate. Two treatments, strip tillage and chisel plow plus spring field cultivate, were compared at an additional three sites each in 2004 and 2005. (See Table F, Table G, Table H, and Table I.) The tillage systems are described in the following section.

The four tillage systems for corn following soybeans compared in this study are described below in order of decreasing residue.

  1. No tillage (No-till): No-till systems leave the greatest amount of residue cover on the soil surface and provide the greatest erosion control. Fertilizers may be broadcast in no-till systems, but band applications at or after planting are preferred. No-till requires complete chemical weed control. Generally, no-till has been successful in regions of Minnesota where there is less precipitation and there are coarse-textured or otherwise well-drained soils.
    The no-till treatment received no fall or preplant tillage prior to planting corn. Planter attachments (row cleaners and/or coulters) were used on the planters at most sites.
  2. Strip tillage (Strip-till): The strip-till system is relatively new in Minnesota. Strip tillage creates a raised berm by tilling a zone 5 to 9 inches deep and 6 to 10 inches wide, but leaves the soil and residue undisturbed between the tilled zones. Since it leaves more than 30% residue on the soil (averaged across tilled and untilled zones) it is a conservation tillage system. Residue is removed from the tilled zone at the time of strip tillage and corn is planted into the residue-free area. Advantages for fall strip tillage include better warm-up of soils and a mellow seed bed due to freeze-thaw effect. While strip tillage is possible in the spring, the soil has less time to warm up prior to planting and the seedbed may be uneven. Subsurface banding or zone incorporation of P and K fertilizer may be combined in the same pass with fall or spring strip tillage.
    Strip-till implements used in these trials varied across farms, ranging from mole-knife with opening coulter and berm-shaping disks, to combinations of fluted coulters, to a large, toothed disk. All strip tillage was carried out in the fall.
  3. Spring field cultivate (One-pass): The one-pass system of this study had no fall tillage and only a single pass in the spring with a field cultivator before planting. Using this system, fertilizer may be broadcast and incorporated with tillage or applied with the planter. This system typically leaves about 30% residue cover after planting corn in a corn-soybean rotation, and therefore usually qualifies as a conservation tillage system. One-pass, along with strip-till, is also referred to in this publication as "reduced tillage."
  4. Chisel plow plus spring field cultivate (Chisel-plow-plus): The chisel-plow-plus system is generally considered conventional tillage for corn following soybean on the poorly drained glacial till soils in Minnesota. Fertilizer may be broadcast and incorporated with tillage or applied with the planter. The soil warms up fast in the spring but is left with less than 30% residue cover.

Rainfall and growing degree units during the trials

Climatic conditions varied across the state and between years during the study period. In 2004, cumulative growing degree units (GDU) were 5 to 10% below normal at three regional Research and Outreach Centers, and precipitation ranged from 47 to 57% above normal for the months of May through September. In contrast, 2005 was an ideal year for crop growth. Precipitation was 28 to 53% above normal and GDUs were 10% above normal. Crop producers experienced exceptional corn and soybean yields in 2005.

In addition to the cool and wet conditions in 2004, some Western Minnesota producers experienced a very early frost on August 21. The frost affected maturation, grain moisture, and ultimately crop yields, especially at the Grant County site in West Central Minnesota, where planting and harvest had been delayed.