Corn Residue: A resource or a problem?
While there has been a lot of recent emphasis on “bioenergy” crops that could be burned to generate electricity or heat or used as a feedstock in the manufacture of liquid fuels. Cornstalks represent one of the major “biomass” sources that currently exist. Because today’s healthy, high-yielding hybrids leave behind stalks that present a management challenge, some people are wondering why we don’t help solve both problems – the need for biomass and the difficulty of managing residue – by harvesting off the cornstalks to use as fuel.
Corn residue is organic matter, and we have been taught to value the addition of organic matter to the soil in order to maintain its productivity. Some work done in Nebraska indicated that maintaining soil organic matter levels requires adding about 2 ½ tons of residue with no-till or conservation tillage in continuous corn, and more than 5 tons per acre if a moldboard plow is used in a corn-soybean rotation. If the moldboard plow is used in continuous corn or no-till in corn rotated with soybean, then about 3 ½ tons of residue needs to be returned from corn.
A 200-bushel corn crop produces a total dry weight of about 10 tons per acre, and the grain and residue each make up about half of this total, or about 5 tons each. So in continuous corn we could remove about half (2.5 tons) of residue with no-till and about a third (1.5 tons) of residue if we do tillage. We could remove some corn residue in the corn-soybean rotation but only if we no-till.
We initiated a study in 2006 to see what effect residue removal, tillage, and N rate have on continuous corn yields. After harvest in the fall we remove none, about half, or all of the residue, then we till half the plots. We plant with tillage or no-till in the spring, apply N rates from 60 to 240 lb N/acre, and measure yield.
Here is what we’ve found over ten Illinois site-years, 2006-09:
- At higher N rates, yield of continuous corn was not affected by residue removal if we used conventional tillage, but with no-till, yields increased as we increased the amount of residue removed (Figure 1).
- The N response was about the same for tilled plots regardless of residue and for no-till plots with some or all of the residue removed, but the amount of N needed is 35 to 40 lb higher and the yield is lower about 20 bushels lower for no-till plots with all of the residue left on the field (Figure 2).
These results indicate that removing some or all of the residue caused no loss in yield or change in N requirement in the short run, and that removing residue can even increase yields under no-till. We will take soil samples after five years to see if there have been any changes in the soil.
So if residue removal can be done without excessive compaction and without increasing loss of soil to erosion, then partial removal might make sense for those who can market the residue. We estimate that each ton of residue contains about 25-3-33 lb of N-P2O5-K2O, which at current prices would cost about $30 per ton to replace, or about $75 per acre if we remove half the residue from 200-bushel corn.