Agronomic Services — Mehlich-3 Extractant

 

0.2N CH3COOH + 0.25N NH4NO3 + 0.013N HNO3 + 0.015N NH4F + 0.001M EDTA

 

Function of components

Acetic acid (CH3COOH)

• buffers the extracting solution to pH 2.5 when all reagents are added and mixed, thus preventing calcium from being precipitated as calcium fluoride.

Ammonium nitrate (NH4NO3)

• facilitates extraction of basic cations such as calcium, magnesium, sodium and potassium &
• reacts with acetic acid to form ammonium acetate.

Nitric acid (HNO3)

• extracts a portion of calcium phosphates &
• its acid component [H⁺] aids in extraction of basic and micronutrient cations.

Ammonium fluoride (NH4F)

• the fluoride extracts iron and aluminum phosphates &
• the NH4⁺ ion complements ammonium nitrate in extracting basic cations.

Ethylenediaminetetraacetic acid (EDTA)

• chelates micronutrients (particularly copper) &
• prevents precipitation of calcium fluoride.