Ordinance Banning Unnecessary Use of Phosphorus-Containing Lawn Fertilizer in Effect
April 04, 2005
Fertilizers containing phosphorus are no longer displayed on store shelves in Dane County. That’s because a Dane County ordinance went into effect January 1 that prohibits the sale of lawn fertilizer containing phosphorus unless buyers demonstrate that they meet ordinance exceptions.
“Our new ordinance means we can have green lawns and blue lakes,” said Dane County Executive Kathleen Falk.
“The likelihood that a lawn in Dane County needs phosphorus is extremely small,” says UW Limnologist Elena Bennett. “The average phosphorus level in area soils is 50 ppm—more than double what the plants need,” says Bennett, who has done extensive soil testing in Dane County.
“Every year we add a million pounds of phosphorus to the soil in the Lake Mendota watershed over the amount that agricultural crops and plants use. The unused phosphorus stays in the soil. A small percentage of the phosphorus runs off into the lakes, but the lakes are extremely sensitive to it, and it causes algae to grow rampantly. When plants and algae die and decompose, they smell bad and use up oxygen. Low oxygen levels mean that fish and other aquatic organisms have less available to them. Thus, low oxygen levels can reduce fish populations,” says Bennett.
Another concern is that some species of algae naturally produce toxic substances. Humans and animals may experience illness or other health effects if there is skin contact with algal toxins or large amounts of the algae are ingested while toxins are being produced.
The phosphorus ordinance includes exceptions for newly-established lawns and for lawns that soil tests have indicated need phosphorus. The ordinance still allows non-phosphorus fertilizers, but before you purchase or apply any fertilizer, make sure your lawn actually needs it.
“If you don’t test your soil, there’s a good chance you’re just wasting money on fertilizer that you don’t need,” says Bennett.
Many local garden centers provide free soil testing kits prepared by the UW’s Soil and Plant Analysis Lab. Collect a soil sample and mail it in or drop it off. The analysis costs about $15.
If you go shopping for fertilizer, look on the bag to identify its content. The numbers indicate the percentage of Nitrogen (N) —Phosphorus (P) —Potassium (K) in the fertilizer. The middle number should be 0, indicating zero phosphorus.
For more information on the ordinance and fertilizers, visit the Dane County Lakes and Watershed Commission Web site: http://www.countyofdane.com/lwrd/lakes/phosphorus.shtml
The UW’s Soil and Plant Analysis Lab Web site is: http://uwlab.soils.wisc.edu/ourindex.htm
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Sue Jones (267-0118), Elena Bennett (262-3088)
Land & Water Resources