Times are good for wheat farmers, but they should resist the urge to harvest their crop residue and sell it for ethanol production, a federal researcher says.

Leaving wheat residue on the ground helps preserve soil while harvesting the residue would speed erosion, said Ann Kennedy, a U.S. Department of Agriculture soil scientist.

Wheat is selling for more than $8 a bushel, double what it was a few years ago. That is injecting new money into farming areas like the Palouse, the wheat-producing agricultural area in the northwestern United States.

"In the more than 100 years that we have been cultivating soils in the Palouse, we have lost about half of the original organic matter," Kennedy said.

That organic matter, which consists of decomposed plant material and microbes, provides nutrients, holds water and helps prevent wind erosion, she said.

But farmers are rushing to cash in on the high prices. The amount of land planted in wheat in Washington has risen by 250,000 acres in the past year. Winter wheat acreage grew by 80,000 acres, to approximately 1.8 million acres. Spring wheat grew by 170,000 acres to about 620,000 acres.

The percentage of organic matter in soil varies from region to region, depending on climate, soil disturbance, moisture and vegetation. Kennedy said the soil in the Palouse should have about 3.5 percent organic content, but in reality it is closer to 2 percent.

Kennedy said at least a ton of residue per acre per year is needed to build organic matter over time. Leaving residue on the soil surface works best.

"It will tend to stay around longer, and the microbes will slowly invade it and convert it into organic matter," she said.

Proposals to bale the crop residue and sell it for biofuels are bad ideas, she said. "We need to constantly replenish organic matter," she said.

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FRESNO, Calif. (AP) _ Fresno County topped the $5.3 billion mark in agriculture production last year, holding onto its place as the No. 1 farming county in the country.

The county's 2007 crop report released Tuesday shows grapes, almonds and milk as the top three commodities.

The No. 2 county in the nation is neighboring Tulare, which recorded $4.9 billion in agricultural production value, with milk leading the way.

Agriculture officials say they worry that the current drought and rising prices for fuel, fertilizer and seed make the outlook less certain in 2008.

The drought has hit hardest on Fresno County's west side, where the most prolific farming takes place and some seasonal crops have been plowed under because of water shortages.