If you want to play a major role in stopping the pollution of the Chesapeake Bay, the Potomac and Shenandoah rivers and other waterways, consider growing healthy stands of grass to trap sediment before rainwater carries the particles into catch basins, storm sewers and then into the Chesapeake.

Such is one of the many recommendations of agronomy experts at Pennsylvania State University who have spent the last six years conducting exhaustive tests on groundwater pollution of rivers and streams, and the effects of turfgrass in preventing soil erosion and sediment pollution.

Thomas L. Watschke, professor of turfgrass science at Penn State, conceived and coordinated the program that sheds welcome light on how our waterways are being polluted, largely by sediment.

Watschke received technical support from the full Penn State agronomy team, including academicians overseeing water quality, soil conservation and pesticide programs.

Events a half-century ago laid the foundation for Penn State's groundwater pollution test program.

During President Franklin D. Roosevelt's first term, some acreage on the university campus was set aside by the Works Progress Administration to conduct extended tests on soil erosion on cultivated land. Until the mid-1980s, the old test acreage lay fallow; its rediscovery seven years ago by agronomists created an ideal foundation for the new tests. Penn State's soil was silty-loam.

Site preparation began in 1983, with separate plots created for the seeding of Kentucky bluegrass and another for bluegrass sod.

Concrete catch basins were built to catch water flowing from the test plots. Basins were set six inches below the turfgrass to provide for accurate groundwater measurement.

Buildings adjoining the test plots held the sophisticated instrumentation that monitored water flow, water pH, particulate matter, nitrate fertilizer, insecticides and fungicides flowing into the catch basins.

Initial test results were misleading. Automatic sprinklers were geared to apply three inches of water an hour for an hour or two each day; however, no water flow was detected whatever from sodded plots while a small flow was found in seeded plots. Sprinklers were then reprogrammed to apply six inches of water an hour to assure a steady water flow from test plots.

Agronomy students maintained the plots along the same lines as homeowners manage their own lawns.

In April 1985, the students applied a water-soluble fertilizer via hose-end sprayer to the plots, immediately followed with an application of a pre-emergent crabgrass preventer; with thorough soakings following each application.

In July, plots received identical applications of an inorganic fertilizer. In September and November, students applied a balanced inorganic lawn fertilizer. Soil pH was maintained above 6 at all times via applications of dolomitic limestone.

The Penn State test reveals how waterway pollution occurs:

The primary pollutant of groundwater flowing into storm sewers and rivers and streams is sediment, particles of organic matter washed from the land.

As sediment flows in moving water, it retains many of the materials in which it has come in contact, among them effluent from fossil fuels, heavy metals in the atmosphere, petroleum derivatives from cars and trucks.

Turfgrass serves as a unique filtering or buffering agent for water cascading over it. As water flows over turfgrass, the soil captures and retains sediment and other particles, thereby acting as a catch basin for groundwater pollutants.

Groundwater is essentially purified as it flows across grassy areas.

Turfgrass also retains inorganic plant materials applied to it. Despite repeated applications of nitrate fertilizer to both plots in successive years, no trace of fertilizer was found in groundwater at any time.

No trace of the pre-emergent crabgrass control product was found in the groundwater. Less than one part per million of an herbicide applied for weed control was found in the groundwater.

Subsequent tests conducted on swales on interstate highways verified initial test data. In one test, groundwater flow was reduced by more than 65 percent by turfgrass growing in the swales.

If we would profit from the Penn State tests and reduce pollution of the Chesapeake, Potomac and other waterways, we should incorporate some of the following actions into home and commercial landscape management programs:

Always maintain existing lawns in good condition. If you have a strip of soil between the sidewalk and the street, grow grass there as a buffer to trap sediment flowing off the sidewalk or driveway.

Engineer downspouts from the house so water is discharged over grass before it cascades onto the street. Remember, sediment in water from rooftops will stay in the grass if you direct water there.

Inorganic fertilizers that break down slowly cannot pollute the groundwater. The fertilizer isobutylidene diurea (IBDU) is a perfect example of a slow-release turfgrass fertilizer not contributing to groundwater pollution because it breaks down over 16 weeks, regardless of the time of year or environmental conditions.

Even on sandy soils, IBDU offers the same pollution-free performance.

Remember that IBDU was first created as a slow-release fertilizer for rice plants growing in water.

If you have bare soil and signs of erosion, make an honest effort to grow some grass there, even if it's not acceptable in the landscape.

The popular Kentucky 31 tall fescue ranks among the worst of the cultivated grasses on the face of the earth, but K-31 is more acceptable than seeing sediment from bare soil wash down the street.

Commercial developers, shopping malls, parking lots and the like should consider reengineering surfaces where groundwater pollutants wash into catch basins and storm sewers.

In the last 20 feet before a catch basin, a properly maintained strip of turfgrass (turf-type tall fescue or Meyer's Z-52 zoysia) is a solution.

Asphalt or concrete should be ripped up and a large grass strip installed to serve as a trap for sediment and pollutants in groundwater.

Here are other priorities for the garden week:

Fertilize azaleas and camellias if you haven't done so already. Hollytone has been the standard fertilizer over the years, so perpetuate your own tradition. Apply Hollytone to bare soil and cultivate lightly at the drip line; if the soil is mulched, rake the mulch to the side, fertilize, then rake mulch in place.

Cottonseed meal (7-2-2) is a good substitute; apply at 10 pounds per 100 square feet, scratched in.

If you have a zoysia lawn, apply IBDU Turf Assurance now at the high rate on the label (setting No. 6 on the rotary Cyclone or Spyker spreader) which applies 1 1/2 pounds of slow-release nitrogen to the lawn. Cut the zoysia first, then apply the IBDU.

Treat the border of your zoysia lawn first, then the rest. Come Father's Day, make a second application of IBDU, again at the high rate. Fall zoysia feedings of IBDU at the high rate are scheduled for Sept. 1 and Halloween.

According to the zoysia turf manager at Pursley's Turf Farms in Sarasota, Fla., six pounds of IBDU nitrogen over the course of the year on sandy or hardpan soil will produce a spectacular zoysia lawn free of disease.

Also, lay in a supply of granular Diazinon to apply to the zoysia lawn next weekend, watered in, to control female billbugs before they deposit eggs in the turf.

Even if you have never encountered billbugs before, granular Diazinon now is your best insurance policy.

Protect iris by spraying leaves with liquid Thiodan to control borers. Spray in the evening when no rain is forecast to maximize uptake of Thiodan.

If troubled by invading bamboo, begin eradication efforts now by fertilizing with any water-soluble plant food (applied via the hose-end sprayer), then painting the bamboo with glyphosate the first weekend in May. We'll update at that time.

Spray pyracantha foliage with powdered Bayleton to prevent scab disease from ruining the bright orange berries starting to develop. Spray in the evening when no rain is forecast.

Jack Eden is the host of "Over the Garden Fence" Sundays from 10 a.m. to 1 p.m. on WTOP Radio (1500 AM).