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Computer model helps ensure clean water.

Computer Model Helps Ensure Clean Water

Farm families and city dwellers alike are increasingly concerned that agricultural chemicals may be contaminating ground water in both rural and urban areas.

About 50 percent of the total U.S. population relies on underground sources of drinking water. In rural areas, groundwater furnishes up to 90 percent of the supply.

"Groundwater contamination is a serious problem that has to be faced by everyone - farmers; urbanites; agricultural leaders; federal, state, and local governments; and agribusinesses.

Unfortunately, there is no band-aid that can be applied to this problem. Above all," says ARS soil scientist Marvin J. Shaffer, "everyone should be aware tht contamination of groundwater by nitrates and other chemicals is essentially irreversible. That makes its prevention critical. We must keep contaminants from reaching groundwater supplies in the first place."

It's an awesome responsibility that should not rest entirely with an individual farmer or homeowner - and help is at hand.

In the past, farmers have fertilized to ahieve high-yield goals and have paid less attention to nitrate leaching. A real possibility also exists that fertilizers used on lawns, gardens, and golf courses in urban areas may leach into groundwater supplies. Both rural and urban sources threaten groundwater contamination and require site-specific evaluation.

Nitrogen in the form of nitrate is often a contaminant in groundwater supplies. The process of carrying nitrate away from the root zone and closer to groundwater is known as leaching.

The season of heaviest leaching is variable throughout the country, and it's important for farmers to know when this occurs. Certainly, they want to avoid a buildup of excess nitrate in the soil profile just before the time of high leaching potential.

"If we can keep plant nutrients in their place - in the root zone where they have the most benefit - both city and farm populations will benefit," says Shaffer.

That's where help from a computer program called NLEAP comes into play. It's a screening package designed to help individual farmers, Soil Conservation Service personnel, farm advisers, and homeowners determine if they have a potential nitrate leaching problem on an individual farm or site.

NLEAP stands for Nitrate Leaching and Economic Analysis Package. The computer model was developed by Shaffer with the assistance of ARS soil scientist Ardell D. Halvorson and Michigan State University associate professor of soil science Francis J. Pierce.

The model, which is designed for personal computers, builds several types of information indexes to predict potential leaching of nitrate nitrogen and its impact on underlying aquifers.

Still in the testing phase, the model has been field-tested at sites in Iowa, Michigan, Minnesota, Nebraska, Ohio, Illilois, and Colorado. So far, the results indicate that the model can accurately identify potential nitrate leaching problems. Eventually, the model will be tested on at least 50 sites throughout the United States.

Included with the model is a national database that provides information on various soils and climates. Information in the database can be pulled up by the computer for any individual state. The information is organized on four diskettes that cover four goegraphical regions - western, upper midwestern, southern, and northeastern.

The program evaluates the underlying aquifer and ranks it according to its vulnerability to contamination from nitrates. Other, similar programs don't link the nitrate leaching to an aquifer vulnerability index, according to Shaffer.

Today, users of agricultural chemicals can call on the collective knowledge of experts and decision support systems like NLEAP. With this collective knowledge, they can decide on management alternatives, such as timing and rate of nitrogen application, tillage methods, irrigation, use of manures and other

organic sources of nitrogen, and crop rotations.

The data used in NLEAP is specific for individual crops, soil types, local rainfall and weather conditions, and practices like irrigation. Making use of this local data, NLEAP users can predict which combinations of conditions could result in groundwater contamination and nip the problem in the bud.

For example, a farmer growing corn each year on a sandy soil can tell if there is a nitrate leaching problem. NLEAP suggests options to the farmer on how to modify rates of fertilizer application, to reduce or redistribute irrigation water, or to grow a legume (such as alfalfa or soybeans) after corn.

Shaffer's work and other ARS projects are one part of the President's Water Quality Initiative, which is a long-term program of federal and state research. The initiative's planning adviser. C. Richard Amerman, who is with ARS, says, "nitrate in the form of nitrogen fertilizer is the main contaminant of groundwater."

The project coordinator, soil scientist Ronald F. Follett, is editing a book entitled "Managing Nitrogen for Groundwater Quality and Farm Profitability."

Chapters and appendixes explaining NLEAP and its use and the computer diskettes containing NLEAP are included in the book. Other chapters provide state-of-the-art concepts to minimize potential hazards of nitrate leaching. These concepts were the basis for the NLEAP model.

A related geographical information system project intended to supplement the NLEAP activity is underway that is using geographical information system technology to expand site data. This can be used for developing management plans for farms, watersheds, or entire regions.

The model is adaptable enought to be used by other federal, state, and local agencies, or by farm consultants and state extension personnel. USDA's Soil Concervation Service considers the NLEAP model one of its major tools.

In developing the model, Shaffer and co-researchers have worked closely with state and local agencies, the U.S. Environmental Protection Agency, the U.S. Geological Survey, the National Oceanic and Atmospheric Administration, and the Tennessee Valley Authority.

USDA's budget for all water-qaulity activities in fiscal year 1990 was $156.6 million, compared with $109.6 million in fiscal year 1989. The budget for fiscal year 1991 is $201.6 million, according to Amerman.

"Information gained from this research will help farmers comply with their state's pollution management programs authorized by the federal Clean Water Act of 1987," says Amerman.

PHOTO : Unpolluted streams, lakes, and groundwater wll be easier to maintain with the NLEAP computer model developed by ARS and Michigan State University scientists. (K-4013-11)

PHOTO : University of Michigan soil scientis Fran Pierce (left), and Marvin Shaffer review soils data from Ingham County, Michigan, for inclusion in the Nitrate Leaching and Economic Analysis Package. (K-4012-6)

PHOTO : At ARS's Crops Research Laboratory in Fort Collins, Colorado, soil scientists Marvin Shaffer and Mary Brodahl evaluate NLEAP-predicted leaching for a test plot located near Coshocton, Ohio. (K-4011-14)
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Title Annotation:Nitrate Leaching and Economic Analysis Package
Author:Cooke, Linda
Publication:Agricultural Research
Date:Apr 1, 1991
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