Does harvesting corn residue hurt soil health?

If you harvest the leftover parts of corn plants to make cellulosic ethanol, are you depriving the soil of nutrients that it needs for long-term health? 

It’s a reasonable premise — while corn biomass is a renewable resource, humans seem to have a propensity for exploiting renewable resources beyond renewability (see also: fisheries, aquifers, and I’m sure you can think of more). How is soil health affected by harvesting corn stover (leftover cobs, leaves, husks, and stalks) instead of leaving it on the field?

The answer, it seems, depends on how much you harvest. New data from an Iowa ethanol project supports the assertion that stover can be harvested in a way that does not hurt long-term soil quality. According to a recently updated set of data analyzed by Iowa State University and funded by ethanol giant POET, conservative harvesting levels (about 25% of above-ground crop residue) at an Emmetsburg, Iowa pilot project showed no yield loss over successive years and resulted in no significant difference in soil carbon. Some fields where stover had been partially harvested showed a moderate increase in productivity, possibly because less cover helps fields warm earlier in spring.

Brendan Jordan, who works on bioenergy issues at the Great Plains Institute in Minneapolis, emphasized that acceptable removal rates will vary depending on geographic location, soil characteristics, slope, crop rotation, and more, but indicated that the POET study’s results appeared to be consistent with other studies he has seen and that the 25% harvest rate was on the conservative side relative to other projects. 

He also mentioned that corn produces a very high amount of residue, more than many other crops, and therefore it is possible to get high yields of stover while still leaving a significant amount on the fields.

This information is supported by other research as well, including studies from Cornell and the University of Nebraska, which indicates that while full-scale harvesting of corn stover may deplete nutrients, partial harvesting generally does not harm the long-term viability of soil.

Photo by Andy Arthur via Creative Commons

4 thoughts on “Does harvesting corn residue hurt soil health?

  1. Isn’t there a dried byproduct used as cattle bedding in the ethanol from corn stover process? If this gets applied to the soil it can also help fertility. The cattle manure can also be best used for methane digestion thru large digesters. In WI there are two such large digesters rated at two MW each. One is on line, one being built this year.
    Still in all, the Ag industry must take better care of the soil it depends on. Highly extractive and depleting (profit motivated) methods are rapidly wasting the rich topsoil of this formerly agricultural land. It seems to have a “one step up/two steps in the hole” conservation history. I see you have data supporting your assertions, but not many farms use those methods.

  2. Phil: I think you are referring to the fiber from anaerobic digesters that is separated from the effluent with a screw press and used for bedding. But your bigger point is well taken: how can we get renewable energy AND enrich the soil we depend on. The innovative dry digester that is in startup at UW-Oshkosh will use food waste, yard waste, and some manure-saturated bedding to produce energy and compost. Recycling these nutrients enriches the soil and can offset fossil-based fertilizers. The magazine Biocycle is all about this approach and they are having a major conference in Madison, WI, on Oct 31-Nov 2 of this year.

  3. It seems to me that there are unanswerable variables here about the historical organic matter in the soil under native vegetation and the more precise chemistry of that organic matter. Soil degradation can be short-term, but it also is a long-term process. I doubt we can even compare soil organics in cropland this year to the organics in 1920 on the same acres, under non-hybrid corn, timothy grass, red clover, or any of the diverse crops we once grew in the Midwest. I will speculate that tallgrass prairie soils usually warmed slowly under a heavy residue, which would have inhibited many of the invasive cool-season grasses that are now noxious weeds.

  4. “Organic” material in the soil does very little for soil fertility. Organics that can be metabolized by bacteria can tie up some nitrogen liberated by dying roots so it doesn’t leach in the fall, but that nitrogen has to be mineralized before plants can take it up in the spring.

    Plants don’t need anything organic, all they need is NPK and trace minerals and the right soil structure to maintain porosity for air and water.

    Converting those cellulosic and lignin residues into biochar does aid in soil fertility, and biochar is much more stable in the soil than is unmodified residue. There is very little nitrogen in stubble, and what ever P and K there is stays with the biochar.