With feed, fertilizer and bedding prices reaching new highs and cellulosic ethanol on the horizon, corn residue isn't just trash anymore, says Jeff Coulter, University of Minnesota extension corn agronomist.

If you remove too much residue you'll spend more on fertilizer and you'll lower soil productivity.

So how much can you remove sustainably?

Here's what Coulter says the research shows:

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 bushel corn crop. Thus, it is not sustainable to harvest corn residue in this system, and this system is actually reducing soil productivity over time.

In continuous corn is grown with moldboard plow tillage, the amount of corn residue that needs to be retained is about 0.84 tons per acre less than that produced with a 200 bushel corn crop. This leaves 0.84 tons of corn residue per acre (20% of the total residue production) that could be harvested annually, but this would require a 200 bushel yield level every year.

In no-till, strip-till or chisel-plow till with continuous corn, up to 45% of the corn residue could be harvested annually if grain yields are consistently 200 bushel per acre.

Tricky proposition

Harvesting only 45% of the corn residue is tricky, Coulter says, 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.

He suggests that you 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 and target manure applications rather than fertilizer for these fields if soil test levels indicate that phosphorus is needed, he advises.

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. This is especially important following dry years where uptake of nitrogen by the corn crop is lower than normal.

Cut rates

When residue is removed in continuous corn systems, reduce the nitrogen fertilizer rate for the next year's corn crop, Coulter says.

"Research that I conducted for my Ph.D. at three locations in northern and central Illinois on dark prairie-derived soils in 2006 and 2007 showed that the economically optimum nitrogen fertilizer rate in continuous corn is reduced by 13% when half or all of the corn residue is harvested," he says. "This was consistent for both chisel plow and no-tillage systems. In continuous corn, less nitrogen is needed for the following year's crop when residue is harvested because corn residue promotes tie up of nitrogen by soil microorganisms."

Source: U of M Extension Service