In most fields, corn residue remaining after grain harvest is incorporated into the soil with tillage or is left on the soil surface. But corn residue is also becoming a commodity. It's being harvested by some livestock producers, and there is interest in producing ethanol from corn residue in the near future.

However, soil productivity (synonymous with soil carbon) will be reduced if all corn residue in a field is harvested regularly and there is not another source of carbon being returned to the soil. Increased fertilization in fields where residue is harvested will help replace some of the nutrients removed in the residue, but it will not compensate for the lost carbon. Carbon is important; it is the backbone of soil organic matter.

In a corn-soybean rotation where corn residue is moldboard plowed, the amount of corn residue that needs to be retained is greater than the amount produced with a 200-bu. corn crop. Thus, it is not sustainable to harvest corn residue in this system, and this system is actually reducing soil productivity over time. The potential for residue harvest is much greater when a conservation tillage system such as no-till, strip-till or chisel-plow tillage is used.

Residue harvest is best suited to continuous corn systems that consistently have high yields and utilize little or no tillage. If corn residue is harvested, do not remove more than 45% of the residue. Harvesting only 45% of the corn residue is tricky, but it can be done if stalks are cut high during grain harvest and if stalks are not chopped prior to baling. If a rake is used prior to baling, make sure that the rake is set as high as possible to avoid collecting too much residue. Another useful idea when harvesting residue is to rotate residue harvest among fields. This ensures that residue is not harvested from the same field every year. In addition, think seriously about reducing tillage following residue harvest.

Also, target manure applications rather than fertilizer for these fields if soil test levels indicate that phosphorus is needed. Winter cover crops should also be considered for fields where residue is removed. In addition to serving as a carbon source, the roots from winter cover crops are extremely effective at scavenging residual soil nitrate.

When residue is removed in continuous corn systems, reduce the nitrogen (N) fertilizer rate for the next year's corn crop. Research I conducted in northern and central Illinois in 2006 and 2007 showed that the economically optimum N fertilizer rate in continuous corn is reduced by 13% when half or all of the corn residue is harvested.

While it is critical to maximize profitability from the land, we need to balance short-term economics with long-term sustainability. When removing residue this fall, use common sense to preserve soil organic matter and protect against erosion.