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New Equations Reduce Chance of Water Pollution From Dairy Manure

By Judy McBride
July 29, 1997

New, simple-to-use equations estimate how much manure a specific dairy herd produces. Developed by scientists with USDA’s Agricultural Research Service, these equations will help agricultural engineers design waste storage systems to prevent pollution of streams and rivers with nitrogen and other nutrients in the manure.

More jurisdictions now monitor water quality and hold dairy farmers accountable for polluting waterways. So farmers are storing manure in pits and other holding facilities until it can be applied to fields or recycled as compost. The trouble is, a herd may produce more manure than the holding facilities are designed to contain--especially with high milk-producing cows that eat more.

The manure production research at ARS’ Beltsville (Md.) Agricultural Research Center is part of a broad effort at the center to improve management of manure nutrients by studying their complete cycle--from the soil into the forage into the cow and back to the soil. A scientist at ARS’ U.S. Dairy Forage Research Center in Madison, Wis., collaborated on the equations.

Traditional methods for designing manure-storage facilities use an average value for manure output, gleaned from many scientific observations. The new ARS equations make for a more accurate estimate by plugging in the farmer’s own herd statistics. These include the animals’ body weight, milk production and composition, feed makeup and number of lactating cows.

Many farmers use manure for fertilizer to reduce spending on commercial nitrogen fertilizer. But some nitrogen in fresh manure vaporizes before it can reach the field. The new equations estimate the manure’s initial nitrogen content--encouraging design of storage systems that save more of the nitrogen and thus help farmers save more on fertilizer outlays. The new equations also can give policy makers a more accurate reading on nitrogen escaping into the atmosphere from dairy farms.

Scientific contact: Victor A. Wilkerson, ARS Nutrient Conservation and Metabolism Laboratory, Beltsville Agricultural Research Center, Beltsville, Md., phone, (301) 504-8620, fax 504-8744,