04-11-2001 Council Agenda - Laserfiche WebLink

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GREEN LAWNS - GREEN LAKES THE PHOSPHORUS CONNECTION Homeowners in the Twin Cities Metropolitan Area apply over six million pounds of phosphorus fertilizer to lawns each year. The fertilizer helps to keep lawns nice and green. Unfortunately, the phosphorus also helps to make lakes nice and green during the summer, which diminishes swimming, boating and fishing for many people. Recent studies have shown that 50 percent of the phosphorus in runoff from residential areas comes from lawns. Most of the rest comes from sources such as leaves, grass clippings and sediment on hard surfaces. It takes only one pound of phosphorus to grow 500 pounds of algae. tJa.p.,A V RESIDENTIAL 1\1J,.,v FF Total Phosphorus Sources SOIL PHOSPHORUS FERTILITY LEVEL n Medium Very High =P> 50 Ibs /acre High = P < 50 Ibs /acre Medium — O _ The unfortunate thing about all this fertilizer use, is that it is unnecessary. Soil tests have shown that most lawns, almost 70 percent, have very high levels of phosphorus and do not need any additional phosphorus fertilizer. The accompanying figure shows the results of 181 soil tests done on lawns in Plymouth, Maple Grove, Minnetonka and Eden Prairie. Similar results could be expected throughout the metropolitan area. When phosphorus fertilizer is applied to lawns with very high levels of phosphorus, much of it runs off of the lawn into the street where it can be carried into lakes, streams, and wetlands. The graph shows the concentrations of phosphorus in runoff water from lawns with different fertility levels and fertilizer application practices. As the graph shows, much more phosphorus runs off of very high fertility lawns than other lawns. This is not surprising, applying phosphorus fertilizer to high fertility lawns is like RUNOFF PHOSPHORUS CONCENTRATION pouring coffee into a full cup, some of it is going to spill out. ❑0500 E2000 i 1500 2 oao so a NF VIM Lawn Campary Page 16