Mehlich 3 soil test extractant: A modification of Mehlich 2 extractant

TLDR

The study aimed to modify the Mehlich 2 extractant to include copper, broaden soil applicability, and reduce corrosiveness. The authors replaced chloride with nitrate and added EDTA, creating Mehlich 3 (M3) with a specific acid–ammonium nitrate–EDTA composition, and compared it to M2, Bray 1, and ammonium acetate across 105 soils. M3 extracted 20 % more fluoride than M2 and 4 % more than Bray 1, increased Cu extraction by 170 %, Mn by 50 %, Zn by 25 %, and showed high correlations with other methods.

Abstract

Abstract The objectives of this study were to modify the Mehlich 2 (M2) extractant to include Cu among the extractable nutrients, retain or enhance the wide range of soils for which it is suitable and minimize it's corrosive properties. The substitution of nitrate for chloride anions and the addition of EDTA accomplished those objectives. The new extracting solution, already designated Mehlich 3 (M3) is composed of 0.2N CH3COOH‐0.25N NH4N03‐0.015NNH4F‐0.013NHN03‐0.001M EDTA. Extractions from 105 soils using M3, M2, Bray 1 (Bl) and Ammonium Acetate (AA) were compared to evaluate the new extractant. The quantity of F extracted by M3 exceeded that by M2 20% and that by Bl 4% but the results from all extractions were highly correlated. Extractions of both K and Mg by M3 were 6–8% higher than those by AA and 3–4% higher than those by M2, but, again, there was high correlation among methods. Addition of EDTA increased Cu extractions by 170%, Mn by 50% and Zn by 25%. Cu extractions by M3 correlated with those from the Mehlich‐Bowling method. High correlations between Mn, as well as Zn, extracted by M3 and M2 were shown.