This year’s corn crop will be a record and along with it we will produce a record amount of corn stover. Stover production has been increasing over time as corn yields have increased. These high levels of stover have generated many tactics for stover management to reduce the potential impacts of high stover levels. These tactics include stalk chopping, nitrogen applications, vertical tillage and fall tillage. Each of these tactics adds to the cost of crop production.
Another option some folks are using is a partial stover harvest. This provides some return and reduces the potential for slugs, cold soils in the spring and provides a better seedbed for sowing wheat following corn, if that is something that a producer is planning. It also reduces the need for tillage that some feel is necessary in these high residue conditions. Stover also provides a resource for bedding and mushroom substrate production.
A few management practices can really reduce the impacts of stover harvest on the soil and subsequent crop yields. In most situations, a partial (50% to 60%) stover harvest is best to leave some residue on the soil to reduce erosion and maintain soil carbon levels. A 200-bushel-per-acre corn crop will produce about 4.5 tons of stover, so a harvest goal of 2 to 2.5 tons for that crop might be a target, and less for lower yielding crops. Supplementing a partial harvest with no-till and other practices such as manure, mushroom soil or cover crops can help to continue the soil building process even while removing some stover. Some dairy farms have tried manure for stover trading options with grain farms to address this issue.
We recently completed a 5-year study and saw no negative effects related to soil carbon or corn yields from a 50% stover removal treatment in a no-till system. In some wet springs we saw a corn growth improvement with some stover removal. We managed potassium carefully and applied extra potassium to compensate for the removal. Potassium removal in our study averaged 18 pounds K2O per ton. One option in heavy corn crops is to delay stover harvest until the spring. The stover is dry then and the potassium removal dropped in our study to 7 pounds K2O per ton.
Stover harvest typically consists of a mow, rake and bale system requiring three additional trips across the field. POET, an ethanol producer in Iowa, has recently started a stover based ethanol plant in and has developed a one pass process called the EZ Bale system. It consists of modifying the corn head with stalk stompers or rollers, and having the combine discharge the residue in a 60-inch or less windrow. Then a round baler follows the combine and bales the material in the windrow.
This results in a partial harvest and the material is only the upper part of the corn plant that went through the combine, which turns out to be the best fraction for cellulosic ethanol production. Stover harvest yields are lower, but two additional passes are eliminated and the field has lots of residue remaining. More details can be found in the Biomass Program Overview document at the POET biomass site. There could be other combine options more suited for our conditions, but it provides an example of an innovation to reduce cost and improve sustainability.