By John DeFore

Conservation minded farmers might naturally assume it’s wise to get the most out of what’s available; if post-harvest waste material can be used in biofuel production, it seems to make financial and ecological use to sell it.

Not necessarily, according to a scientist at Washington State University who is urging farmers in her region to leave the waste where it falls.

Ann Kennedy, a USDA-Agricultural Research Service soil scientist who serves as an adjunct professor at the school, studies the composition of soil in the Palouse region, an area in Washington, Idaho and Oregon where wheat is grown.

Specifically, she tracks the balance of minerals, microorganisms, and organic matter that constitute soil, determining how levels are affected by different farming practices and how they in turn influence a field’s productivity.

Kennedy has found that the farmers in her region should aim for around 3.5 percent organic matter — the mix of “well-decomposed plant material and microbes” that “is black and rich and gives soil its dark color” — in their soil, but that most of have only about two percent.

“Organic matter provides nutrients crops need; it holds water and contributes to aggregation,” Kennedy says, so she is focused on ways to replenish it where it’s low. One way she has found is to cut back on tilling, which can mix materials too quickly for microbes to process them effectively.

But another is leaving crop residue on the soil surface, where “it will tend to stay around longer, and the microbes will slowly invade it and convert it into organic matter.” Harvesting this residue for biofuel production, Kennedy believes, will only lead to decreased fertility and require farmers to find other means of boosting organic content. “We need to constantly replenish organic matter,” she says, “so removing valuable residue, especially in areas with low rainfall, may not be the best practice.”

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