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Photo: Sharpley collects a soil sample from a test plot. Link to photo information

Read the magazine story to find out more.

Portable Rainfall Simulators Helping Fight Runoff

By Jan Suszkiw
October 12, 2001

With the pull of a cord, researchers can now simulate thunderstorms on demand with portable “showers” that allow for detailed studies of field conditions that promote phosphorus runoff into lakes, reservoirs and other water bodies.

This summer, 40 teams of scientists across the country used the portable rainfall simulators (PRS) to help standardize their collection of soil and runoff data in agricultural watershed regions. Until recently, such research has primarily been confined to the laboratory and carried out by scientists using different methods, notes Agricultural Research Service (ARS) soil scientist Andrew Sharpley.

With rainfall simulators, it’s now possible to coordinate such efforts and generate results for easier comparison, adds Sharpley, with ARS’ Pasture Systems and Watershed Management Research Laboratory, University Park, Pa. There, he helps coordinate the National Phosphorus Research Project, an ARS-led effort involving 21 ARS labs, 16 state universities, USDA’s Natural Resource Conservation Service, and the Environmental Protection Agency.

The project’s main objectives include determining how much phosphorus the soil can retain before losing the nutrient to runoff, creating a reliable indexing system to assess and rank a farm site’s vulnerability to phosphorus runoff, and devising new guidelines by which farmers can maximize their crop yields using manure and fertilizer while minimizing runoff.

Driving the effort is concern over phosphorus enrichment of fresh water, which can speed eutrophication, a natural aging process. One manifestation is the growth of aquatic weeds and blue-green algae that can clog filters, crowd out beneficial plants and deprive aquatic life of oxygen.

At field sites, scientists can simulate how it all begins on 20-square-foot plots by starting a gas-powered pump that forces water through the simulators' plumbing systems and into nozzles that convert it to “rain.” The plots are showered at a thunderstormlike rate of nearly three inches per hour. Once puddling and runoff occur, metal borders downstream collect the water and direct it to gutters that empty into plastic bottles for weighing and analysis.

A more detailed story in October’s Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's principal scientific research agency.