Let’s Not Forget Carbon Just Yet

Life-cycle modeling for ethanol needs to be updated to reflect big improvements in corn's GHG emissions profile, Alverson writes in the May print issue's Clearing the Air column.
By Ron Alverson | April 20, 2017

“Reports of my death have been greatly exaggerated.” The famous quote attributed to Mark Twain fits these days as it relates to the national interest in reducing carbon emissions. Without question, we are seeing a de-emphasis on lowering carbon at the federal level, but it does not mean the issue is going away or that low-carbon fuels have no value. While the pendulum appears to be swinging from one extreme to the other, it is likely to settle somewhere in the middle. Fuels that help automakers achieve efficiency standards are going to be important.

California and the “left coast,” as well as numerous other states have or will be adopting low-carbon fuel standards. Countries importing our ethanol that require a low-carbon pedigree and the potential for a carbon tax all remain drivers to reduce our footprint.

This is good news for ethanol, despite the myths, misinformation and prejudices that have dogged corn ethanol for years. Why does corn ethanol get such a bad rap?  What is it that makes U.S. EPA and many environmentalists cover their eyes and ears when we provide solid, scientific data that turns those myths and misinformation upside down?

For starters, the debits applied to corn ethanol for the use of fertilizer are based on numbers we left behind years ago. Similarly, dramatically higher corn yields and reductions in tillage over the past 30 years have reduced soil erosion and built soil carbon stocks in corn fields.  These two revolutionary changes have made old carbon intensity calculations obsolete.

Recently, Dr. Paul Fixen, the immediate past president of the American Society of Agronomy, penned a piece called “Progress in Agronomy: A Story Worth Telling.” Since the early 1980s, he writes, corn yields have increased by 70 percent, yet nitrogen fertilizer use per acre has only increased by 5 percent; cropland under conservation tillage increased from 18 to 42 percent; soil erosion declined by more than 40 percent; and more than a quarter million soil tests from multiple labs have confirmed that the long decline of soil organic carbon (SOC) has been reversed in the western Corn Belt due to those higher yields and reduced tillage. On average, SOC has increased 25 percent. 

So, what does all this good news about corn crop productivity, fertilizer use efficiency and soil health improvements have to do with the carbon intensity of corn-ethanol fuel?  Big reductions!  But only if the currently used models are updated to reflect these facts. The life-cycle greenhouse gas (GHG) emission models used to determine corn ethanol fuel’s carbon intensity do not consider a biofuel feedstock’s effect on SOC stocks.  Small annual increases in SOC mean big reductions in corn carbon intensity that, when accounted for in GHG models, reduce corn ethanol fuel’s CI by 40 percent relative to the GREET 2016 model’s latest assessment.

Currently, GHG emission models calculate that the manufacture and use of nitrogen (N) fertilizer to grow corn produces more than 40 percent of all GHG emissions during corn production, using decades-old emission factors.  In the 1980s and 1990s, corn growers routinely applied about 1.25 pounds of N to produce a bushel of corn.  Over the past five years, growers have used 0.9 pounds of N per bushel.  This means big improvements: far less surplus nitrogen is left in soil and far less is lost to the environment. In 2015, the Gulf of Mexico task force report to Congress indicated total nitrogen fertilizer in Mississippi River water quality tests has been reduced by 30 percent over the past 35 years. We are working with the Urban Air Initiative and others to get EPA to update its models with these facts, which would show nitrogen fertilizer related emissions would be reduced by 40 percent. 

Big improvements in nitrogen fertilizer use efficiency and soil carbon stocks mean big reductions in corn ethanol carbon intensity. The wait is over, the low-carbon, high-octane, economical, plentiful and home-grown renewable fuel is here today.


Author: Ron Alverson
President, American Coalition for Ethanol
rsalv@itctel.com