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Land Applied Chemicals

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Land-applied chemicals, fertilizers, herbicides, and insecticides have definite benefits. But they can also create serious water quality problems. Explore more about the relationship between these chemicals and water quality.

Chemical Benefits
Every land-applied chemical has a specific purpose. Fertilizers provide nutrients to enhance plant growth. They’re used on crops, on gardens, on lawns and golf courses—any place you want plants to thrive. Nitrogen and phosphorous are two nutrients common to fertilizers. Herbicides and pesticides have a much different purpose. They’re used to kill weeds or insects that interfere with the plants you’re trying to grow, like corn or flowers. To get the desired results and avoid water quality problems, these chemicals must be applied correctly. Properly applied chemicals stay on the land and out of water, where they can seriously damage aquatic environments.

Chemical Threats
How do the chemicals get into water? One answer is runoff. Runoff is part of the hydrologic cycle. Water, usually from precipitation, moves across landscapes and eventually winds its way to streams and rivers. If runoff moves across land where chemicals were applied, the chemicals can be swept up into the cycle. If the chemicals are not trapped before they reach streams and rivers, they can cause serious problems.

Chemical Consequences
What happens when these chemicals get into water? When fertilizers are swept into waterways by runoff, they provide nutrients to aquatic plants, increasing their growth. This increased growth can trigger a dramatic chain of events for aquatic ecosystems. Excess nitrogen in drinking water poses a serious health threat to pregnant women and babies. High concentrations of other chemicals, like herbicides or pesticides, can kill aquatic plants and animals as well as posing a health risk to people.

Spills and Kills
All chemicals need to be managed very carefully, but the risk is especially high on farms where chemicals are kept in large volume. Huge spills are catastrophic to waterways and the plants and animals living there. In Iowa, some of the state’s worst fish kills were caused by big chemical spills.

Controlling Chemicals
Because there are risks associated with using land-applied chemicals, should their use be controlled? There are some regulations in place for farmers, but not many. Should there be more? How would they be enforced? How about for homeowners?

All in the Application
What should you consider when applying chemicals to a landscape?

  • Soil conditions — What are the existing nutrient levels? (the quantity of nitrogen and phosphorous in the soil)
  • Predicted precipitation — Are you applying right before a rain? This increases the chances of runoff?
  • Time of year — will the plants use the nutrients now or will they be stored in the soil?
  • Are you applying an appropriate product? an appropriate amount?
  • Are there waterbodies nearby that could be contaminated if the chemicals become runoff?



Explore More: Water Quality
Copyright 2004, Iowa Public Television
The Explore More project is supported by funds from the
Roy J. Carver Charitable Trust
and the USDE Star Schools Program.




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