• Acid ammonium oxalate (Tamm's reagent / Grigg's reagent, 0.2 M ammonium oxalate + oxalic acid adjusted to pH 3.3) is universally recognized as the best extractant for available molybdenum in soils.
• Formulated by J.L. Grigg in 1953, the oxalate ions under acidic pH complex iron and aluminum sesquioxides, releasing adsorbed molybdate (MoO4^2-) anions into solution.
• Extracted molybdenum is subsequently determined spectrophotometrically as a colored thiocyanate complex.
• DTPA (pH 7.3) is used for cationic micronutrients (Zn, Fe, Cu, Mn), while ammonium acetate is used for exchangeable cations.

The hot water extraction method developed by Berger and Truog (1939) is the most widely used standard test for available boron in soils.

• Johnson and Nishita (1952): Classic reduction distillation method used for the determination of total and available sulfur in soils and plants.
• Williams and Steinberg (1959): Method designed for available sulfur fractionation in soil.
• Berger and Truog (1939): Developed the hot water-soluble boron extraction method, where boron is extracted by boiling with water and determined colorimetrically using azomethine-H or curcumin.
• Lindsay and Norvell (1978): Developed the DTPA micronutrient soil test for zinc, iron, copper, and manganese in neutral and calcareous soils.

Boron is uniquely absorbed by plant roots primarily as an uncharged, neutral boric acid molecule (H3BO3).

• Zn: Readily absorbed as the divalent cation Zn2+.
• Ni: Absorbed by plants in the cationic form as Ni2+.
• Mo: Absorbed as the divalent molybdate anion (MoO42-).
• Boron exists predominantly as undissociated neutral boric acid (H3BO3) at common soil pH values, enabling passive uptake across plant membranes.

Copper matches with azurite, iron with olivine, manganese with rhodonite, and molybdenum with powellite.

• Cu matches with (II) Azurite: Azurite is a basic copper carbonate mineral [Cu3(CO3)2(OH)2].
• Fe matches with (I) Olivine: Olivine is a magnesium-iron silicate mineral [(Mg, Fe)2SiO4].
• Mn matches with (IV) Rhodonite: Rhodonite is a manganese inosilicate mineral [MnSiO3].
• Mo matches with (III) Powellite: Powellite is a natural calcium molybdate mineral [CaMoO4].