In 2008 University of Minnesota Extension launched an on farm research project evaluating continuous corn production under a series of different tillage systems on six farms across Minnesota. For the sake of brevity this article will only address one site in Southeastern Minnesota that is located near Faribault.
The tillage systems studied include a conventional moldboard plow system, a chisel plow system representing a traditional conservation tillage, and strip till as a higher residue conservation tillage system.
Among the challenges of growing continuous corn is residue management. Previous research has shown a yield advantage for moldboard plowing. While conventional tillage has been documented to produce higher yields, it is energy intensive and has the potential to have long-term environmental and productivity consequences due to increased soil erosion. Many producers report that their perception of the problem with mulch-till is that there is too much residue build-up in continuous corn systems leaving a "fluffy" layer on the surface that is cold and damp and not conducive to good seed-soil contact for full germination. Moldboard plowing solves this problem by burying the residue, but it is theorized that strip-till can accomplish the same growing environment by simply moving the residue aside. A primary goal of this project is to determine if corn grain yield can be maintained when utilizing conservation tillage systems.
One of the challenges produced from greater amounts of residue is cooler soil temperatures. The moldboard plow system accumulates more Growing Degree Units (GDU's) every week. In addition, diurnal variation in soil temperature tends to be greater with moldboard plow and more buffered with conservation tillage systems. The differences in temperature and GDU accumulation can be attributed to differences in albedo and water content. Greater residue cover increases albedo which means the soil absorbs less solar radiation. Finally, the greater amount of residue is correlated to increased water content, and increased water content buffers the soil from rapid changes in temperature.<
There have been some marked differences in the early growth of corn in different tillage systems. Corn in the moldboard system was taller and one growth stage ahead of the other systems at the time measurements were taken.
Even with early differences in corn growth the jury is still out on grain yield. In 2008 conservation tillage systems yielded well across the state. Additional benefits have been noted in conservation tillage systems, in particular this year we had a huge wind erosion event on May 20th. At the Faribault site little soil was being eroded from strip-tilled land while neighboring conventionally tilled ground was visibly losing soil. It is difficult to determine exactly how much more soil was moving off of conventionally tilled ground, but from a qualitative standpoint at times it looked like a blizzard. Other benefits to conservation tillage systems include a reduced potential for water erosion due to greater residue cover. Given the topography of this part of the state the reduced water erosion potential is a huge benefit.
Currently there is no reliable fuel use data for strip-till, therefore it is difficult to give exact fuel use savings. When you consider less of the ground disturbed by strip-tillage (25% vs. 100%) and less trips across the field (one to three) one can assume a 10-30% fuel savings. Farmers using strip-till verify this.
In addition to easily measureable benefits, farms that have a long history conservation tillage report many intangible benefits. These benefits include better overall "soil quality". Some of these factors include: increased soil organic matter leading to increased fertility levels, better water infiltration and water holding capacity, and increased soil structure leading to better crop root systems. The Southern Research and Outreach Center has documented that strip-till fields have been fit to plant 3 to 7 days earlier than other tillage systems in the last few years. Also, during spraying season some growers site the ability to get back in the field faster after a rain. Long term, there may be opportunities in the carbon markets for farmers using conservation tillage in continuous corn production.
It will be interesting to see how the summer develops and how these experiments end-up yielding. Regardless of what happens we should not forget about the many benefits of conservation tillage systems. For more information on tillage see the following links:
Ryan Miller, Extension Educator - Crops
Brad Carlson, Extension Educator - Rice and Steele Counties