More Dirt on Biofuel

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aerial view of farm fields
Intensive farming requires careful planning to avoid exhausting the land.
(cc) lemoncat1

As if biofuel didn’t have enough of a bad reputation, there are now indications that intensive farming of crops for cellulosic ethanol production may harm the very soil in which they’re grown.

Scientists with Agriculture and Agri-Food Canada in Saskatchewan have been studying the effects of various harvesting techniques on levels of organic carbon and nitrogen in the soil. Their findings suggest that those techniques designed to reap the maximum return from the crop may not leave enough of these essential elements behind for future growth. Findings may vary according to type of soil and climate, but there are certain techniques that work best in general. It is important to take care of the soil in order to reap as many good harvests from it as possible.

Crop residues — those portions of the plants typically left in the field after the edible portions are harvested — are not mere waste. When allowed to remain in the field and decompose, this residue returns valuable nutrients to the soil. It’s a simple concept with roots dating back to ancient times. The Mosaic Law dictated that fields were to lie fallow one year out of every seven. In the centuries since, farmers have reaped the benefits of letting their fields rest periodically to replenish their nutrients.

Today it’s well known that careful crop rotation — alternating dissimilar crops with complimentary nutritional requirements — can reduce strain on the soil and inhibit the spread of crop-specific pests. Legumes, for example, have nitrogen-fixing bacteria in the nodules on their roots. If other crops which require nitrates — such as cereals — are grown in the same field the following year, they benefit from this exchange. On the other hand, failure to rotate crops, or harvesting so much from the field that nothing is left behind, will eventually exhaust the soil.

This is of particular importance with regard to biofuel because most crop residue — as much as fifty percent of crop production — is cellulose, and therefore valuable in producing cellulosic ethanol.

At first glance this provides a solution to the food versus fuel quandary. One crop can be used for both purposes; harvest the corn cob for food, and the corn stalk for ethanol. Unfortunately, this means there’s nothing left to give back to the soil, increasing the need for fertilizers and pesticides which themselves consume valuable resources.

Of course, this is not a problem unique to biofuel production. Intensive farming is often practiced simply to extract every last bit of value from the land, whatever the crop.

This also doesn’t mean that biofuel itself is a bad idea. There are different types of biofuel and many different ways of producing it, not all of which require making a choice between food and fuel. (See our article “Food versus Fuel: Biofuel’s Bad Rap.”)

One thing is certain; if we’re going to continue growing biofuel crops, we’ll need to take the health of the soil into consideration, possibly sacrificing short-term profits for long-term gain.

Read Biofuels and Bioenergy: Processes and Technologies from Amazon.

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