Switch grass beats corn for ethanol production but violates law of return

Staff report

WASHINGTON: The energy return of producing ethanol from switch grass is more than seven times greater than that for corn but has a hidden cost that is not being discussed.

Switch grass is a warm-season native grass that grows from the Gulf of Mexico to Canada in the USA.

An average acre of corn produces about 400 gallons of alcohol, while an acre of switch grass yields 1,150 gallons of ethanol.

The energy output/input ratio of converting corn to ethanol is about 1.2 to 1 but is 4.4 to 1 with switch grass.

Switch grass is heated to 900 degrees F for one second which liquifies the grass. This liquid can then be fermented into ethanol.

The primary advantage to switch grass is that it is a perennial and does not require annual planting.

It is also being touted as not needing nitrogen fertilizer as it can feed on naturally occurring levels of soil nitrogen.

However, this soil nitrogen is actually from the breakdown of soil organic matter placed there by previous plants’ residue.

The USA currently produces about 4.3 billion gallons of corn-based ethanol and experts believe this could grow to 12 to 14 billion gallons, which is just a fraction of the 140 billion gallons of gasoline Americans burn annually.

In contrast, experts say switch grass and crop residues could produce about 60 billion gallons or slightly under half of America’s annual consumption of gasoline.

What is being overlooked is that continuous whole plant removal will drain the soil of needed minerals and organic matter just as making hay does.

This violation of the agricultural law of return is also being ignored in the idea of hauling off corn stalks and other crop residues for ethanol production that help maintain soil organic matter.

The closest thing to a free lunch energy-wise in nature is the direct grazing of whole plants with animals as they return 95 to 98% of the minerals in the plant as manure and urine.

Perhaps, grazing more and growing less energy-intensive corn would yield a more sustainable reduction in petroleum energy use than using whole plants for ethanol.

© by The Stockman Grass Farmer

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