WASHINGTON (AP) _ Soil scientists have discovered a new ''whey'' of stopping soil erosion: pumping cheese-making leftovers onto fields.

That technique can boost harvests, say Melvin J. Brown and Charles R. Robbins of the USDA's Agricultural Research Service in Kimberly, Idaho.

Whey, a leftover from cheese production, is a slightly milky, watery product containing sugar, protein, calcium, magnesium, potassium, nitrogen and phosphorus. The soil researchers used cottage cheese whey, which is acidic.

''We found that pumping cottage cheese whey onto sloped, furrow-irrigated fields can cut soil erosion losses between 65 and 75 percent,'' Brown said in a recent Agriculture Department news release.

Brown flooded furrows with whey at a rate of about 50 gallons per minute, until the liquid reached the end of the rows.

''On one field with a 4.4 percent slope, we lost about 75 percent less soil in the whey-treated furrows, compared to untreated ones,'' he said.

Cheese factories now pay to dispose of excess whey through local sewage treatment plants. About half of the 2 million tons of acidic whey produced annually in the United States goes to waste.

''Our findings suggest we've found a practical use for something that is otherwise a disposal problem,'' Robbins said.

Robbins came up with the idea of using whey to restore the productivity of high sodium soils where water tends to run off the surface, depriving plants of enough moisture.

But whey's calcium, magnesium and potassium ''actually replace the harmful sodium...,'' Robbins said. The soil's structure is improved by getting rid of excess sodium, water soaks in more easily and thirsty plants can drink, he said.

Whey's nitrogen and phosphorus also help nourish growing plants, he said.

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WASHINGTON (AP) - The Agriculture Department is extending by two weeks the deadline for farmers and ranchers in 10 states to qualify acreage as summerfallow under the Federal Crop Insurance Program.

Summerfallow is the practice of controlling weeds and grass on crop land to conserve soil moisture and improve absorption of precipitation. To qualify it for crop insurance purposes, producers are required to use continuous chemical and-or mechanical weed control programs. The process must begin by a specified date for the area.

Agriculture Secretary Edward Madigan said the deadline is being extended because of adverse weather conditions in parts of the 10-state area. It includes Colorado, Idaho, Kansas, Montana, Nebraska, Oregon, South Dakota, Utah, Washington and Wyoming.

Farmers and ranchers in the area now have until July 1 to qualify land as summerfallow. Acreage insured as summerfallow under the crop insurance program is used to produce crops every other year.

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WASHINGTON (AP) - Milk production during May in the 21 major producing states totaled 11.2 billion pounds, slightly lower than production last May.

The Agriculture Department also said the number of cows on farms in the 21 major states was 8.25 million head, 142,000 head less than May 1991.