Potassium is an element essential for human and plant health. It is found in the environment in the form of natural salts and used heavily by plants. Potassium is easily depleted in soil, and is thus an ingredient in many fertilizers.

Potash is the term used to describe potassium chloride and other salt deposits that are mined for commercial used in fertilizers and other applications such as electroplating and melting snow and ice.  Potash can also be created by burning hardwood to harvest the potassium-rich ashes, as was once done in Potash Cove in Thompson Lake, near Poland, Maine. Today, Canada is the world's largest potash producer.

What is the "Available Potassium" test?

Available potassium is the amount of bio-available potassium in soil or other solid samples. Most of the potassium in soil cannot be used by plants.  Available potassium is sometimes used to determine how much fertilizer to add to farmland.

Health Limits:

Maine Maximum Exposure Guideline limit: not established

USA Primary Drinking Water Standard limit: not established

USA Secondary Drinking Water Standard limit: not established

Additional Resources:

Wikipedia: "Potassium"

Mindat.org, "The Mineralogy of Potassium"

Recently closed underground potash mine near Sussex, New Brunswick. Photo by PotashCorp.
Photo by PotashCorp.

MEL Test Method for Potassium:

Drinking Water – 200.7 (not regulated by SDWA)
Wastewater – EPA 200.7 R4.4 (NPDES Compliant)
Solids – EPA 6010B, 6010C (SW846) (RCRA Compliant)

Sample Requirements


Container: plastic, glass
Volume: 250mL
Hold Time: 6 months if preserved with HNO3 to pH<2, otherwise 2 weeks
Preservation: HNO3 to pH<2


Container: plastic, glass, baggie
Volume: a least 150g
Hold Time: 6 months
Preservation: n/a