Nitrogen Not Imminent Threat To Groundwater

10/4/2004 4:25:26 AM

Distributed May 2004

We fertilize our lawns and landscapes to keep plants attractive and healthy. But does much of this nitrogen pollute our groundwater? LSU AgCenter horticulturist Dr. Tom Koske relays some encouraging news.

A recent Florida study showed that a sodded St. Augustine lawn, even on a sandy soil with 10 percent slope, was very effective in retaining the applied N (nitrogen). Sod was fertilized with a standard 1 pound. N/1000 square feet. every other month during the growing season.

Researchers found less than 2 percent of the applied N was lost as leaching down through that soil. This loss occurred essentially with fresh applications and higher rainfall.

"The message is that a healthy sod covering is an effective bio filter," Koske says, adding, "Homeowners should maintain a good lawn right down to their backyard ponds and ditches." He suggests not fertilizing very close to the water, so that the sod will catch and use surface runoff before it gets to the water.

"Consider your needs and discuss them with your landscaper, if employing one," Koske advises. Some rich, heavy soils can do with very little extra fertilizers if you are satisfied with appearance, thickness and lack of weeds. Mulch-mow to recycle nutrients.

When fertilizer is justified, make sure it is what is needed by the turf type and soil fertility status. A soil test from the LSU AgCenter can help here. Use materials with slow or controlled release N, which is less likely to leach. Avoid fertilizing if a heavy rain is expected. Apply granules to dry grass and water in to trap the N. Use irrigation wisely by moistening to about 5 inches deep, but only when showing early drought. This may require watering in several short cycles to avoid irrigation water running into the street, etc.

"With the right approach, a lawn can be a very effective bio filter of fertilizer even with a sandy soil," the LSU AgCenter horticulturist says.

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