This is a guest post by John Gear.

A friend recently posed this question:

So maybe using food crops to produce ethanol or biodiesel isn’t such a good idea. What about using grass clippings and other “yard debris” currently trucked to landfills? What about using “crop residue” not used for food? Doesn’t that change the equation?

There’s a seminal article by Alice Friedemann titled Peak Soil: Why cellulosic ethanol, biofuels are unsustainable and a threat to America that answers that question. It is one of the more important articles available on the internet.

Here’s the supercondensed summary:

Just like operating factories need a constant flow of raw material inputs (roughly the same as their productive output + any wastes disposed of externally), soils need constant replenishment in roughly the same mass as is being removed as a crop, plus more because of the time lag for biologic availability (the time needed for materials to break down and be consumed by the microflora and microfauna that form the base of the food web in productive, living soil).

Of course, we should never be trucking clippings and yard debris anywhere – it’s needed where it is, and we’re wasting energy twice by removing the organic matter and then bringing back replacement matter to make up for the removal.

Similarly, there are no “crop residues” that can be safely removed from land intended for steady farming.  Just by taking a crop off the land you are already putting the soil in deficit, which is why you cannot maintain soil vitality without fallow periods and some kind of fertility treatments, such as manures.  The more concentrated and fast-growing the crop, the more the crop consumes the soil, and the more replenishment is needed.

If you remove what you call “residue,” you are simply adding another crop being taken from the same soil at the same time, which means you have to add even more inputs back into it, or exhaust it that much faster.  Mining soil “residues” is simply a way to burn a candle at both ends — it burns brighter, for a much shorter time.

The issue with all agrocrops is not the nature of the feedstock, which is essentially irrelevant. The issue is land, topsoil, water, fertilizers, and energy gain.

High quality land suitable for agriculture is very limited. Agrofuel backers talk about using “marginal land” now that people realize that using cultivated land to grow fuel for cars means that fuel for people has to be grown elsewhere — in other words, you push people into using marginal land or, worse (and this is what actually happens), into converting rainforest to cropland. But you cannot make money trying to crop marginal land, that’s why it’s marginal land. The only way it works is if food and energy prices climb enough to make the expense of cropping marginal land pay off.

This is why all agrofuels end up with a negative effect on climate — the huge amount of greenhouse gases released through land use changes negates any small gains in annual greenhouse emissions (compared to petroleum) from use of agrocrops for decades. We cannot invent a way to make more land, and all techniques for getting more yield from land involve MORE energy inputs, not less. In other words, chasing our tails faster . . .

As for the climate impact, needless to say, we don’t have decades. We have months in which to respond meaningfully — maybe 100 months. Quite possibly less. Releasing massive quantities of greenhouse gases now (that remain in the atmosphere for many decades) for the possibility of slight annual reductions later is suicide. You cannot both have an uncultivated crop and a cultivated crop.

Agrofuel boosters like to talk about using “weeds” Except that “weeds” is a non-biological label. There are no weeds. There are simply desirable plants and undesirable plants. As soon as you intend to cultivate a weed, you just turned it into a crop. Whether switchgrass or corn (for ethanol) or soy, camelina, palm, or canola (for biodiesel), agricultural use to make motor fuel means intensive cultivation, which means mining the topsoil, removing the nutrients much faster than they can be replaced and destroying the web of microorganisms that make dirt into soil.

Agrofuels are intensive water users. Fresh water is already limited, even in the rainy northwest. We cannot afford to put more fresh water into the service of autos than we already do. As our climate destabilizes further, we are going to see more and more droughts (we already are) intermingled with severe flooding bouts. We cannot afford to use our tiny reserves of fresh water as motor fuel.

Fertilizers and energy gain are really the same issue, since 99% of our fertilizers are derived from natural gas. Many have defined modern agriculture as “the use of land to turn fossil fuels into food” — but at least humans get food from it! If we start cultivating agrofuel crops, then we’ll have modified the saying into “The use of land to turn fossil fuels into fuel for cars, while pushing food crops onto marginal land and starving great numbers of the world’s poorest people through food price hikes (as food prices and energy prices are linked through the gas tanks of our cars).”

As the saying goes, let’s live on the planet as if we intend to stay.  That means taking care of our soil, first and foremost.