Taking Care of the Topsoil

Following my inclusion in the Top 10 list of ethanol enemies, I sought to Set the Ethanol Record Straight on my actual views on ethanol. I set out three broad tenets that shape my views. They are:

  1. Tenet One: We must transition from fossil fuels with a sense of urgency.
  2. Tenet Two: We need to develop systems and services with a much lower fossil fuel dependency.
  3. Tenet Three: We must take care of our topsoil.

The second and third tenets are where I usually run afoul of ethanol supporters, because I feel many of our ethanol policies simply maintain a high level of fossil fuel dependency. Further, the rush to turn corn into gold has led to practices that have depleted topsoil and aquifiers.

But my desire has never been to kill off the U.S. ethanol industry. To the contrary, I would like to see it grow along with the rest of the renewable energy sector, but grow in a way that is long-term sustainable, self-sufficient, and enhances U.S. energy security. That means producing and using ethanol as energy efficiently as possible, and taking care of the natural resources — like topsoil — that are required for ethanol production.

POET, the world’s largest ethanol producer, is engaged in an effort called “Project LIBERTY,” which plans to use biomass left over from corn production — corn cobs, leaves, husks, and stalks — to produce cellulosic ethanol. Of course biomass removed from the soil has the potential to negatively impact soil quality, so they have been conducting a study with researchers from Iowa State University and the USDA to examine potential changes in soil quality as some of the cellulosic corn by-products are harvested.

Here is an extended excerpt from their press release reporting on the study:

Data shows responsible biomass harvesting is part of good soil management

EMMETSBURG, IOWA (June 1, 2011) – POET’s contracted biomass removal rates with area farmers are conservative and consistent with good soil management, updated site data gathered by Iowa State University and USDA researchers indicate.

Iowa State University has completed analysis on data from the third year of an ongoing study for POET near Emmetsburg, Iowa to monitor how soil health is affected when crop residue is removed. POET’s planned 25 million-gallon-per-year cellulosic ethanol plant, dubbed “Project LIBERTY,” will use corn cobs, leaves, husks and some stalk to produce renewable fuel.

The newest data confirms previous assertions that removing about 1 bone-dry ton per acre (which is about 25 percent of the area’s above-ground crop residue) will not cause significant nutrient loss. In fact, corn yields continued to show no yield loss or moderate increases in fields with this rate of biomass removal.

“Based on this study, we conclude that 1½ to 2 tons/acre of corn stover can safely be harvested” from fields similar to those used in the study, according to the research summary prepared by Dr. Douglas L. Karlen with USDA-Agricultural Research Service and Dr. Stuart Birrell with Iowa State University. Appropriate removal rates will vary depending on how productive the soil is in a specific area.

The data also showed no significant difference in soil carbon after three years. That research will continue as well, including an analysis of deep core samples.

POET sent me the press release, which I found quite interesting and especially relevant to my core belief of taking care of the soil. So I followed up with a few questions, which they graciously answered. My e-mail to them:

I think this is good work; the kind of work that will blunt the sorts of criticisms you will encounter. However, I do have one question. I have frequently heard that we have overfertilized the soil over the years, leading to perhaps more than enough residual nitrogen. If that is the case, excess biomass might be removed for some period of time before yields started to decline. The press release says that there was no significant change in soil carbon. What about nitrogen? I presume this was monitored closely. Given that the recommendations don’t include nitrogen, I am assuming that nitrogen levels weren’t declining. But can you confirm?

I am also wondering whether soil erosion was monitored. That is another frequent criticism of corn ethanol in general, but will become a more significant issue as more biomass is removed.

And their response back to me from Matt Merritt, POET’s Media Relations Specialist:


I think your question can be answered in the research summary. Here’s an excerpt:

“The middle three columns (Table 4) show the average additional amount of N-P-K that is removed when the stover is harvested. The important information from this data is that although there is an increase in nutrient removal when stover is harvested, the grain is still the predominant removal mechanism for N and P. For K, however, stover removal roughly doubles the amount of K removed and this will cause the soil test K values to fall if they are not monitored routinely. Finally, the last two columns in Table 4 show that soil-test values for P and K, when averaged across all treatments and years, did decline. We conclude that these soil-test changes confirm that higher rates of fertilizer should have been applied and that the decline in soil-test was caused more by soil variation across the field than by the stover harvest treatments.”

The recommendation was that no significant increase was needed for Nitrogen or Phosphorus (beyond normal fertilizing rates). Potassium was about 15 lb per acre additional replacement for these fields. If you look at the table, you see that the stover has significantly less Nitrogen per pound than the grain. That was for at our removal rate. At some of the higher removal rates, more N was required.

Dr. Karlen said they actually might have been too conservative on fertilizing the fields in general; there was a year-to-year decline in all nutrients for the conventional field and the biomass-harvested fields, which is addressed in those last two sentences.

As for erosion control, that’s not the limiting factor in how much biomass can be removed, from what they’ve told us. The photo I attached shows that there’s still a lot of material on the field after biomass harvest.

POET is to be commended for doing this work. The last thing we want to do is to replace unsustainable fuel sources with other unsustainable fuel sources. I think everyone would agree that fuel that results in degradation of the topsoil is not a desirable source. Thus, research should certainly be done to determine the potential impact of biomass harvesting on soil quality — and act upon those findings as necessary.

But I don’t believe that sustainable corn ethanol has to be an oxymoron, any more than I believe that sustainable forestry is an oxymoron. I have this conversation frequently about forestry; there are good practices and bad practices. We have to weed out the bad practices and encourage the good practices. Forestry can be used to decimate a landscape and erode away the soil, or it can be used responsibly to arrest erosion and actually improve the soil quality over time. Studies similar to the one POET is undertaking have shown the way toward better forestry management.

No matter the source of our energy, there are going to be trade-offs. There is no perfect energy solution. But as we strive to replace fossil fuels, we must avoid trading one set of problems for another that is as bad or worse. The way to do that is to continue to do the sort of work that POET has reported on here.

Additional Resources

Stover Harvest Report – Summary by Dr. Douglas Karlen and Dr. Stuart Birrell for POET of three-year soil data from Emmetsburg, Iowa

Biomass Baling – A slide show recap of the learning process for farmers during the first large-scale biomass harvest in Emmetsburg, Iowa