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Lawn Fertilizer Doesn't Just Fertilize Lawns

Excess lawn fertilizer and nutrients can be carried by runoff into storm drains.

Lawn fertilizer, especially when applied incorrectly, fertilizes a lot more than just your lawn. Excess nutrients are carried by runoff into ponds and lakes. The same nutrients that help grass grow also help algae and pond weeds grow, leading to algal blooms and excessive aquatic plants that are not only unpleasant to look at and to swim in, but also affect food quality and habitat for fish and other organisms. 

Does this mean environmentally aware citizens are doomed to have unattractive lawns? No. By following a few simple recommendations, you can make sure that you're not contributing excess nutrients to your streams and lakes.

Shoreland homeowners and businesses should also consider the water quality and wildlife benefits of a more natural setting for lakefront property. 

Responsible Fertilizing Practices

1.        Start with a  soil test.

Make sure your lawn needs fertilizer, and find out how much you should be applying.  Your test results will include recommendations on what nutrients you should add to your lawn

When you buy fertilizer the package will be labeled with three numbers.

The first number indicates total nitrogen (N), the second indicates phosphorus (called available phosphate (P2O5) and the third, soluble potash (K2O).

Look for a middle number of zero, which indicates phosphorus free fertilizer.

2.        Choose the correct product.

If you had a soil test, be careful to read the labels and buy the correct fertilizer. If not, consider using phosphate-free fertilizer (and therefore phosphorus-free). WHY?

Lakes and streams may be phosphorus limited. When excess phosphorus from lawn fertilizer and other sources enters streams and lakes, algae and other plants have all they need (read more about the role of phosphorus in your watershed below).

3.         Apply the product correctly.

The following tips are taken from "Mugaas, R.J., 1995. Responsible Fertilizer Practices for Lawns University of Minnesota Extension, Publication #FO-06551-GO.

• Fill granular fertilizer spreaders on a hard surface where any spills can be easily cleaned up. NEVER wash off fertilizer spills into the street or other hard-surface areas where they can easily enter storm sewers and ultimately surface water areas. Wash off granular fertilizer spreaders over turfed areas to prevent runoff of fertilizer from hard surfaces. Fill and clean liquid fertilizer applicators over turfed areas for similar reasons.

• Close the gate on the fertilizer spreader when crossing hard-surface areas or go back and sweep up the material. Reuse it another time or put it back into the spreader.

• Try to use a drop spreader, which is more precise but slower than a rotary type spreader near surface water. Next to shoreline areas, apply fertilizer around the perimeter of the property with a drop spreader to create a safety zone. The rest of the area farther away from the shoreline can be fertilized with a rotary spreader. Since the perimeter has already been done with the drop spreader, it is not necessary to hug the shore because fertilizer may get into the water. The same kinds of precautions should be taken when using liquid fertilizer.

• Avoid getting fertilizer into natural drainage areas or pathways on a property. These areas may not necessarily be hard-surface areas, but they can carry fertilizer directly into the surface water before having the chance to infiltrate into the surrounding turf/soil area.

• Leave grass clippings on the lawn area to decompose and recycle nutrients back to the turf area. They should not be blown or raked into street gutters or onto sidewalks and driveways where they may be carried with runoff water to surface water. Nutrients released in water through decomposition may cause undesirable algae and vegetative growth.

Natural inputs
Phosphorus (P) is relatively sparse in natural soils and exists primarily as the phosphate molecule that tends to stick to soil as water moves through it. Therefore, in the absence of human-caused impacts, P concentrations in the surface and groundwater that flows into streams and lakes tends to be very low and so usually regulates the potential amount of algal growth in the system. In pristine parts of the world, there is also very little phosphorus in precipitation and in the dry portion of atmospheric inputs referred to as dry fallout.

Human inputs
Human activities lead to increased inputs of P in streams and sometimes in groundwater and even in atmospheric inputs. The most obvious sources are from municipal wastewater (sewage) treatment plants and from industry and are called point sources that are regulated by monitoring loads at the ends of their discharge pipes and setting strict limits. Diffuse, or non point sources, are much more difficult to measure and to control. Agricultural fertilizer-P is a major source of phosphorus pollution in streams throughout the US.

The major sources of P to most urban streams and lakes are non point, are all controllable to a large extent by homeowners and/or local community agencies and typically include:

* soil-P from erosion (construction sites, road banks, shoreline disturbance, lawns & gardens)
* road runoff (street sweepings of crud that accumulates between rainfalls)
* roof runoff
* lawn clippings
* excess lawn fertilizer runoff
* sewage from leaky sewer lines or from improperly constructed or maintained on-site septics drainfields

Lake internal inputs
Over long periods of time, urban lake sediments become greatly enriched in phosphorus and then release a portion back into the water. This internal release can occur sporadically and may exceed annual inputs from surface waters.

In productive, moderately deep lakes that stratify thermally in summer and become anoxic (no oxygen) in their hypolimnetic bottom waters, large amounts of this historically deposited phosphorus is released from the sediments into the water. It can then be mixed into sunlit surface waters during windstorms and fuel algal blooms. Turbulence from the wind can also resuspend high-P sediment from shallow areas, as can boat and jetski wakes. This latter source is worsened when the shoreline and nearshore zone submergent and emergent vegetation (weeds) have been removed since they stabilize the bottom sediment and act to dissipate wave energy.

(Graphics for this article are from http://www.duluthstreams.org)

Links

Fertilizing Florida Lawns

Source: G. Shannon Smith, Former Assistant Professor, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville

How well do lawns filter runoff? Dig deep for the answer
Source: John Barten, Water Quality Mgr. Hennepin Parks. Written for Focus 10,000-Minnesota's Lakeside Magazine

Where does the phosphorus in my watershed go?
Supplement what you've learned about nutrient movement in your watershed with this short video presentation by the city of Golden Valley, MN.