Phosphorus-Free Fertilizers
Introduction
If you have lawn and apply lawn fertilizer, you should be aware that phosphorus— represented by the middle number describing the fertilizer blend—can end up in Lake Tahoe after a rain storm or excess irrigation. Too much phosphorus turns Lake Tahoe and our streams and rivers green, supports invasive fish and weed growth, and ultimately depresses our tourism-based economy.
Phosphorus-free fertilizers can be compatible with green and vigorous lawns. They are an easy alternative to using traditional high-nutrient, fast-release fertilizers. Many soils in the Lake Tahoe Region already have enough phosphorus. You can test your lawn by having a soil test done to determine whether or not you need a fertilizer that contains phosphorus. See Resources for Residential Homeowners below.
Soil testing is key to applying the correct amount and kind of nutrients – not just for lawns, but for gardens and other parts of your home landscaping as well. Phosphorus-free fertilizers should also be used in these areas if soils already have sufficient phosphorus.
This is algal growth in Lake Tahoe’s nearshore. Phosphorus lawn fertilizers can help turn our blue lake green by supporting invasive aquatic weeds and organisms.
Fertilizers are always represented by a formula consisting of three numbers in the same order: Nitrogen (N) is the first number, Phosphorus (P) is in the middle, and Potassium (K) is the last number. Look for a “zero” in the middle for phosphorus-free fertilizer blends.
Background on phosphorus and its impacts
Lake Tahoe is naturally ultra-oligotrophic (nutrient-poor) due to the geology in the Basin. This contributes to the Lake’s remarkable water clarity. Increasing amounts of both phosphorous and nitrogen into the Lake over time by human development is reducing water clarity, which could impact this tourism-based Region.
Because Lake Tahoe’s clarity is declining, scientists have developed the Lake Tahoe Total Maximum Daily Loading (TMDL) to figure out why this is happening and how to fix it. The TMDL is a calculation done with the latest science and modeling to determine the key pollutants affecting the Lake, and how much the Lake can accept of each pollutant and still be clear and in good health.
According to the Lake Tahoe TMDL, phosphorus is one of the three key pollutants reducing Lake clarity (in addition to fine sediment and nitrogen). The TMDL calls for stringent controls and restrictions on phosphorus to reduce its impact on Lake Tahoe and its streams and rivers. Phosphorus from fertilizers applied on urban upland areas- primarily lawn/turf on residential properties and recreational facilities like golf courses and ball fields-is a main contributor of phosphorus runoff into the Lake.
Fertilizers are often used to maintain non-native vegetation, which increases erosion in SEZs, shorezones and other sensitive areas, supports invasive aquatic and terrestrial plants, and increases water consumption. Fertilizers are also used for native and adapted plants’ establishment, but not for their maintenance.
Invasive Asian clams can concentrate nutrients such as phosphorus that is available in the water to create algal growth around beaches and other shallow-water areas in Lake Tahoe that people enjoy. Marla Bay in July 2008. Photo credit: Dr. Marion Wittmann, UC Davis
Resources for residential homeowners
Tahoe Resource Conservation District (Tahoe RCD) offers free vegetation consultations on-site for property owners living on the California side of Lake Tahoe. To learn about landscaping and irrigation for your home or to get advice for a landscape project, call (530) 543-150, extension 113.
Turf Fertilization at Lake Tahoe is a fact sheet providing guidance on the type of and amount of fertilizer to use, how to apply, and turf types. This information is useful following soils testing to determine how much nutrients are in your soils.
Soil Testing: Typically, a homeowner will take one or more soil samples from the lawn or garden and send it to a Cooperative Extension or a soils laboratory for an analysis of the nutrient content of the soil. Home soil testing kits are available at home and garden stores and results will give you a general idea of the nutrients in the soil, but are less reliable.
• Soil Testing Guide for Nevada Home Gardeners from the University of Nevada Cooperative Extension. Information is provided on how to sample soils and where to get soil testing done.
• Nevada Tahoe Conservation District: See Nutrient Tip Sheet which contains soil testing information, including how to take a soil sample.
Fertilizers applied to lawns that get into the water fuels the growth of invasive Eurasian watermilfoil at Tahoe Keys.
Fertilizers applied near water can be particularly damaging. Rain or excess irrigation can wash fertilizers off lawns and into the water to grow a “garden” of invasive plants and animals. Efforts are underway at Tahoe Keys, a subdivision in South Lake Tahoe, to develop best management practices such as minimizing fertilizer use to combat invasive plants and fish.
Supporting Science and related materials
Lake Tahoe Total Maximum Daily Loading Report, supporting documents, and references:
Truckee Meadow Water Authority has information on soil testing and soil improvement. You can have your soil tested at the UNR Cooperative Extension at (775) 784-8484. There is a fee for this service.
Phosphorus Fertilizer Laws: State Legislation and Local Ordinances limiting phosphorus fertilizers for established lawn/turf
Minnesota became the first state in the nation to regulate phosphorus fertilizer use on lawns and turf in 2002.
Maine restricts the sale of fertilizer containing phosphorus in 2008 and continues banning cleaning agents containing phosphates.
Wisconsin passed a state law in 2009 restricting the use and sale of turf fertilizers containing phosphorus unless soil test indicates need for phosphorus. Examples of local ordinances include
Dane County and
Door County
Michigan in 2010 passed a law prohibiting phosphorus-containing turf fertilizer. It also bans turf fertilizer application near surface waters, and on saturated or frozen grounds.
New York passed a law in 2010 banning phosphorus in lawn fertilizer and in detergents. This article indicates that up to 50% of phosphorus in stormwater is attributed to fertilizers.
Virginia passed a state law in 2011 prohibiting the sale, distribution and use of phosphorus-containing lawn maintenance fertilizer and the sale of de-icing agents containing phosphorus, nitrogen, and urea. Training and technical assistance is provided for fertilizer applicators and golf courses.
Maryland passed a state law in 2011 prohibiting the sale, distribution and use of phosphorus-containing lawn maintenance fertilizer and the sale of de-icing agents containing phosphorus, nitrogen, and urea. Training and technical assistance is provided for fertilizer applicators and golf courses.
Vermont passed into law in 2011 prohibitions for phosphorus and nitrogen lawn fertilizers.
Washington State passed a law in 2011 prohibiting the sale and application of turf fertilizers containing phosphorus.
In New Jersey
over 100 towns will be required to adopt ordinances banning the use of
fertilizer containing phosphorus (scroll to page 12 in link).
Florida Works to Ban Phosphorus. Florida has several county ordinances that prohibit the use of phosphorus in fertilizers. This is an article discussing the proposal to make this a State wide initiative.
A healthy and beautiful Lake Tahoe. Photo credit: Toni Pennington, Tetra Tech
Contact
For questions or comments, please contact the Stormwater Management Team at
bmp@trpa.org, 775-589-5202.