Study stating “biofuels are worse than gasoline” is fundamentally flawed

BioFuelNet Canada Biofuels GasolineBioFuelNet Canada strongly disagrees with the findings of a recent study by Professor John DeCicco from the University of Michigan and colleagues which states that biofuels are worse than gasoline in terms of greenhouse gas emissions.

In the study, when DeCicco and colleagues calculate the CO2 emissions going into the atmosphere, they consider all parts of the plant: leaves, stalks, roots, grain etc. However, when they calculate the uptake or storage of CO2 in the plant, they consider only the grain. Therefore there is an imbalance in the calculations, which would lead the reader to think that biofuels emit more CO2 than they absorb.

The carbon accounting in the study is fundamentally flawed, which generates a skewed picture of the carbon-neutral biofuels by conveniently ignoring a fundamental biological truth – crops produce more than just grain!

When plants grow, they take CO2 out of the atmosphere and produce the stalks, leaves, roots, grains. In corn and soybean for example, leaves, stalks and other non-edible parts contain even more carbon than the grain itself.

BioFuelNet Canada Biofuels GasolineAlthough grain is harvested, the non-harvested residues are left in the field. This biomass contains stored carbon that is gradually decomposed in the next years, some of which is released as CO2 and the rest becomes part of the soil organic carbon.

Accounting for the ‘missing carbon’ will go a long way to bring the findings of this study in line with the prevailing scientific opinion that those who plant and grow crops – namely the agriculture and forestry sectors – should get credit for the carbon gained from photosynthesis in all crop biomass, not just the portion that is harvested for biofuel.

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For the complete scientific explanation of our findings, please read the article below:

Crops produce more than grain: the ‘missing carbon’ in carbon-neutral biofuel analysis

Author: Dr. Joann K. Whalen, Ph. D., agr., BioFuelNet Canada

A recent study by DeCicco and colleagues gives a skewed picture of the carbon-neutral biofuels by conveniently ignoring a fundamental biological truth – crops produce more than just grain!

DeCicco and colleagues make an egregious error when they equate net ecosystem production (NEP in their study) from crop yield data (in tons/acre or bushels/acre) with the carbon harvest (referred to as H), the mass of carbon contained in the harvested crop.

Net ecosystem production is the difference between carbon fixation through photosynthesis and carbon loss via respiration. Thus, we have to consider the biomass and bioproducts produced in all plant parts, including the roots and root exudates, stalks, leaves, cobs, pods, and so on – as well as the grain.

BioFuelNet Canada Biofuels GasolineThe classic study of Prince and collaborators published in Ecological Applications1 offers some insight into how crop yields reported by the United States Department of Agriculture may be used to calculate the production of all plant parts. Corn grain yield is 53% of the aboveground biomass, which includes the leaves and stalks, cobs, tassels, silks and husks that are needed for the grain to grow. The root system is essential for the stability, water and nutrient uptake of the crop, and represents 14% of the total above-ground biomass.

A corn crop yielding 150 bushels/acre will give close to 8 tonnes/ha of grain plus:

  • 7 tonnes of leaves, stalks and other non-edible parts
  • 2 tonnes of roots plus 1 tonne of root exudates2

BioFuelNet Canada Biofuels GasolineSimilarly, a soybean crop yielding 42 bushels/acre will produce about 2.5 tonnes/ha of grain plus

  • 5 tonnes of leaves, stems and other non-edible parts
  • ~1.5 tonnes of roots and root exudates2

Although grain is harvested, the non-harvested residues are left in the field. This biomass contains stored carbon that is gradually decomposed in the next years, some of which is released as CO2 and the rest becomes part of the soil organic carbon. Anyone who has ever stopped to look at a corn field after harvest will appreciate that the carbon in these residues does not “count” in the soil organic carbon measurement because they are clearly too big – and too much like plants – to be considered part of the soil.

BioFuelNet Canada Biofuels GasolineDeCicco and colleagues note in their paper that changes in soil organic carbon are on the order of 0.2 Tg C/year and highly variable, while the carbon harvest (H) levels were two orders of magnitude higher at about 200 Tg C/year. They assumed that changes in soil organic carbon were negligible, but they forgot to consider the huge amounts of carbon fixed into the non-harvested biomass that is left on the soil surface. Calculations above indicate that non-harvested carbon is in the same order of magnitude and exceeds the 200 Tg C/year that is removed with through carbon harvest.

Accounting for the ‘missing carbon’ will go a long way to bring the findings of this study in line with the prevailing scientific opinion that those who plant and grow crops – namely the agriculture and forestry sectors – should get credit for the carbon gained from photosynthesis in all crop biomass, not just the portion that is harvested for biofuel.

1 Prince, S.D., J. Haskett, M. Steininger, H. Strand, and R. Wright. 2001. Net primary production of U.S. Midwest croplands fromagricultural harvest yield data. Ecological Applications 11:1194–1205.

2 Jones, D.L., C. Nguyen, and R.D. Finlay, R.D. 2009. Carbon flow in the rhizosphere: carbon trading

at the soil. Plant and Soil. 321:5–33.

Photo credits:

Corn picture: http://www.robinsonlibrary.com/agriculture/plant/field/corn.htm

Soybean picture: http://aglabs.com/soybean-yield-barriers.html

Corn residue picture: http://www.angusbeefbulletin.com/extra/2011/02feb11/0211mg-corn-stover.html

BioFuelNet Canada Responds To Study Claiming “Biofuels Are Worse Than Gasoline” by BioFuelNet Canada