It’s been clear for some time that the biofuels industry needs to wean itself off of the corn ethanol spigot. Numerous studies show that utilizing the kernels of corn to distill fuel are playing havoc with food and feed prices, while contributing to a devastating plow-up of grassland, hayland, wetlands and just about any perennial part of the landscape. That’s why a bill recently introduced in the Minnesota House that would promote an alternative— cellulosic energy production—is so promising. Unfortunately, if House File 536 is passed in its current form, it could have a devastating impact on our soil and water quality.
First a primer: cellulosic energy production relies on lignocellulose, a structural material that comprises much of the mass of plants. Popular sources of cellulosic feedstock are switchgrass, woodchips and the byproducts of lawn and tree maintenance; even native prairies have been considered a possible source. Because it’s reliant on stems and other plant material we don’t usually use in food production, cellulosic biofuels production could go a long ways towards not only creating a homegrown source of fuel, but supporting a system that gets more continuous plant cover on the landscape, something we sorely need at a time when our corn-soybean system is leaving the soil vulnerable to erosion and chemical runoff at least half of the year.
But House File 536 could make things worse, not better, for the landscape. That’s because it doesn’t do enough to differentiate between plant materials we can afford from a soil conservation standpoint to process into fuel, and materials that play a critical role by being left on the land. The bill would provide incentive payments to biofuel producers who utilize a wide array of cellulosic products, and it’s no secret that in the Midwest the biofuel feedstock generating the most excitement these days is corn stover—the stalks, shucks, etc., left in the field after corn is harvested. POET-DSM launched a major corn stover biofuels plant in Iowa last September, and at full capacity, company officials say it will convert 770 tons of biomass per day to produce ethanol at a rate of 20 million gallons per year, later ramping up to 25 million gallons annually.
The firms invested in crop residue energy production are promising their ethanol process will result in 80 percent to 90 percent fewer greenhouse gas emissions when compared to conventional gasoline derived from fossil fuels. One study by the U.S. Department of Energy and the USDA estimates that biomass produced by forestry and agriculture could replace over one-third of our current petroleum consumption. Fulfilling such a role would require a major tooling up of how much plant material such as corn stover is recovered. That’s one reason there have been serious proposals, including the one represented by House File 536, to provide government subsidies for utilizing crop residue for biofuels.
At first blush cellulosic stover fuel appears to be the ultimate in recycling and making sustainable use of every last resource. After all, crop residue is unapologetically called “trash” by tillage experts and is considered a nuisance when putting in the following year’s crop. But it turns out that just because we don’t eat it, doesn’t mean it’s a waste product. Stover plays a major role in cutting erosion, building soil organic matter and helping fields store carbon.
The importance of that latter service was highlighted in a paper published in the journal Nature Climate Change. The University of Nebraska study found that removing corn residue for biofuel production could result in such a carbon deficit in fields that it would produce a net increase in greenhouse gas emissions over five years when compared to conventionally-produced gasoline. Crop residue stores carbon dioxide, and it also creates a better environment for the soil itself to sequester greenhouse gases by building organic matter and protecting the field surface.
Some scientists and biofuel industry experts fault the Nebraska study for the amount of residue removal its authors assumed would take place in a typical cornfield—they looked at removal rates as high as 75 percent or 100 percent. POET-DSM wants farmers to utilize a baling system that harvests no more than 20 to 25 percent of what’s available and recommends monitoring soil conditions to make sure stover isn’t being removed at an unsustainable rate.
But it’s unclear what if any enforcement of residue removal rates or conservation tillage practices biofuel firms will impose. The photo featured at right was taken on a central Iowa field where stover was harvested for biofuel production. There is a whole lot of bare soil visible.
What is clear is that harvesting more than 25 percent of a field’s corn stover can cause significant harm to soil biology. A paper published in the Soil Science Society of America Journal found that removing more than a quarter of a field’s stover had negative impacts on structural stability and soil fertility.
And replacing that fertility with petroleum-based nutrients like nitrogen fertilizer may help produce a bumper crop in the short term, but it won’t build the kind of soil health needed to sequester carbon in the long term. Research out of the Morrow Plots in Illinois shows that nitrogen fertilizer speeds up the decomposition process in soil, resulting in a net decrease of soil organic carbon.
This sets up a vicious cycle: more nitrogen means less carbon in the soil, which reduces biological activity, requiring more nitrogen to maintain yields. And all that fertilizer requires energy to produce. So when one considers that removing residue produces more greenhouse gases directly by impoverishing our soil on the spot as well as indirectly (requiring more production of synthetic fertilizer), it’s clear that stover is not something to be taken lightly.
The authors of House File 536 (Senate File 517 is its companion bill) make some effort to make it more soil friendly. Under the provisions of the bill, a 20 percent bonus payment would be made for agricultural biomass that is derived from perennial crops, or from acres where cover crops are used.
That’s a laudable step, but the bottom line is it won’t go nearly far enough to make up for the large amount of cover material our cornfields will lose when stover is harvested on a massive scale. Why pay an incentive to harvest a product that’s already ubiquitous? The point of tax-funded incentive payments should be to encourage practices we need more of, not less.
If cellulosic biofuel production is truly to be a sustainable alternative to corn ethanol, we need programs that put more cover on the land, not ones that provide one more incentive to leave it bare and vulnerable. That means making the growing of perennials and soil-friendly cover crop systems the center point of any incentive legislation, not an afterthought.
Brian DeVore is the editor of the Land Stewardship Letter.