Nitrate Defined and Sources

What is nitrate and where does it come from?

Although nitrate is necessary, high levels can be harmful to humans, animals, and plants.

Nitrate (NO3) is a compound that contains nitrogen and water.  Nitrogen comes from decomposing organic materials like manure, plants, and human wastes. Often the nitrogen (N) comes from ammonia (NH3) or ammonium (NH4).

Basically, plants need nitrogen to make amino acids and proteins, which are essential for plant growth. Plants cannot use organic nitrogen directly. "Microorganisms in the soil convert the nitrogen locked up in crop residues, human and animal wastes or compost to ammonium (NH4). A specific group of microorganisms convert ammonium to nitrate (NO3)" 58.  Since nitrate is water-soluble, excess nitrate not used by plants can leach through the soil and into the groundwater.


The widths of the red arrows show relative amounts of nitrate leaching 
into groundwater.  The wider the arrow the more nitrate.

Nitrate is also found wherever biotic things are breaking down or decomposing like animal waste, and  septic system absorption fields or mounds.

The main sources of nitrogen in groundwater are highly fertilized crops and lawns, and large amounts of human and animal waste (septic systems, sewage, and manure).

Studies have shown that nitrate in Wisconsin's and Portage County's groundwater comes from:

  • agriculture-90%, 
  • septic systems-9%, and 
  • lawns and other-1%  7

The DNR website has more information on nitrate in drinking water.

Also pick up, "Nitrate in Wisconsin Groundwater: Sources and Concerns" (G3054) from your Wisconsin County Extension office.


Nitrate:  explanation  |  impacts  |  PC levels  |  testing  |   in drinking water  | actions

goals and strategies  |  nitrate  |  pesticides  |  quantity
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