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.