Michigan's Phosphorus Fertilizer Law
Phosphorus is the nutrient that most often stimulates excessive growth of aquatic plants, leading to a variety of problems known collectively as eutrophication. Elevated phosphorus levels are causing premature aging of many Michigan lakes.
In an attempt to address this problem, Michigan passed legislation several years ago that limited the phosphorus content of laundry detergents and more recently extended the ban to dishwater detergents. However, phosphorus in fertilizers remained a problem. Phosphorus is a key ingredient in many commercial lawn fertilizers and is commonly applied at rates well in excess of what is needed to maintain a healthy lawn. Excess phosphorus can run off into lakes and streams where a single pound of phosphorus can generate hundreds of pounds of aquatic vegetation.
The Minnesota Experience
Minnesota was the first state to enact a phosphorus fertilizer law. Between 2002 and 2005, Minnesota phased in a state-wide phosphorus fertilizer ban similar to Michigan’s new law. In enacting the law, the Minnesota legislature required that research be conducted to evaluate the effectiveness of the fertilizer restrictions. The research culminated in a report entitled Effectiveness of the Minnesota Phosphorus Lawn Fertilizer Law. Report findings indicate the following:
Water Quality Benefits
One of the challenges in evaluating the impact of the new phosphorus law on water quality will be to design sampling protocols and programs that can differentiate between natural variability and actual trends in water quality. While additional studies over several years will be required to document the impact of Michigan’s phosphorus fertilizer law, the law is certainly a positive step toward protecting water quality.