Effects of Homeowner-Applied Fertilizers on Water Quality

By Patricia Lunn Adsit, Master Gardener Extension Volunteer with Walton County

You might wonder why you and your family, with your “pride-and-joy” landscape and possibly an “envy-of-the-neighborhood” vegetable garden, should be concerned about the effects of your small-scale horticultural activities on water quality. 

You probably know that applying the correct fertilizers (especially the macronutrients nitrogen, phosphorus, and potassium) at the appropriate time and at the recommended rate is a suggested practice for maintaining a healthy lawn, vigorously growing shrubs and flowers, or productive vegetable garden. And you may even know that having strong, healthy plants means less reliance on pesticides, since pests will attack weak plants more often. But were you also aware that fertilizers, like pesticides, can also be sources of pollution of to our water? 

The major reason for concern is that the soil on your property, as well as on that of your neighbors, is a conduit to our groundwater, which is water that accumulates beneath the earth’s surface, filling fissures and other openings in rocks and soil. When contaminants reach the groundwater, they can travel great distances with the water, thereby spreading the contamination that can eventually clog surface water sources like lakes, rivers, and ponds, making them unsuitable for recreational activities like fishing, boating, and swimming.

So, why is fertilizer considered a contaminant? When nitrogen is applied in excess, it can be wasted and eventually end up in groundwater or surface water. Nitrogen along with phosphorus can degrade water quality by encouraging algae blooms. Too much nitrogen and phosphorus along with carbon surface water cause eutrophication, or an increased growth of algae and aquatic weeds, which harms aquatic life in rivers, lakes, and ponds. According to the United States Department of Agriculture, “[e]utrophication…is the number one cause of impaired water quality.”

Here’s what you can do to help manage this threat. Prior to applying any type of soil amendments or fertilizers, know the requirements of the plants being grown by doing a soil test on the yard, garden, or flowerbed; then only apply the needed amount of fertilizer. Your soil test report will give a recommendation of type and rate of amendments to apply, but you may need to do a bit of math.

If your soil test recommends that you apply 1 pound of nitrogen per 1,000 square feet, divide the first number on the fertilizer bag into 100. For example, a 16-4-8 fertilizer should be applied at a rate of 6.25 pounds per 1,000 square feet (100 ÷ 16 = 6.25). To apply 1⁄2 pound of nitrogen per 1,000 square feet, divide the first number on the fertilizer bag into 50. For example, a 10-10-10 fertilizer should be applied at a rate of 5 pounds per 1,000 square feet (50 ÷ 10 = 5).

Here are some more tips from the University of Georgia Extension about applying fertilizer to help maintain good water quality:

  • Whenever possible, apply fertilizers that are composed of slow-release sources of nitrogen. These sources are made so that the nitrogen is metered out slowly to the plants. 
  • Use a drop (gravity) type spreader rather than centrifugal (rotary) type spreaders near water to minimize the possibility of fertilizer particles entering the water.
  • Make sure you shut off the spreader when passing over unplanted or bare ground surfaces. Clean up any spills so the material can be used at a future date rather than enter the groundwater.

Still not sure you need to worry about water? Here’s a fun fact for you to consider: how much water is used during the growing and production of one tomato?  Answer: 3 gallons.

Want to learn more about what to do in your garden this Spring? The Walton County Master Gardeners will be offering a series of talks at the O’Kelly Memorial Library, 363 Conyers Rd in Loganville 30052 (reservations 770-466-2895) from 2:00-3:00 on Wednesdays and at the Monroe-Walton County Library, 217 W. Spring St, Monroe 30655 (reservations 770-267-4630) from 10:30-11:30 on Saturdays in April and May.

Have home gardening questions? Need a soil test kit? The Master Gardener Help Desk is staffed on Mondays (9:00-12:00) and Wednesdays (1:00-4:00). You can also email us at waltonmg@uga.edu or call 770-267-1925. Look for our Ask a Master Gardener booth on Saturday mornings at the Farmers Market in Monroe, May-October.

Patricia Lunn Adsit is a Walton County Extension Master Gardener Volunteer as well as a member of the Garden Writers Association (GWA). She lives and gardens in Loganville, GA

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