A Review of Midwest Laboratories Soil Test Methods

In 2014, clients in Iowa and Canada asked Midwest Laboratories to compare Mehlich III extraction of nutrients analyzed by ICP to Midwest Laboratories’ traditional methods which include P1 & P2 Bray extraction of phosphorus (P) with colorimetric measurement; neutral ammonium acetate (AA) extraction of potassium (K), magnesium (Mg), and calcium (Ca) with ICP measurement; and DTPA extraction of the micronutrients boron (B), copper (Cu), Iron (Fe), manganese (Mn), and Zinc (Zn) with ICP measurement[1] .   This study consisted of 139 samples: eighty-three from Canada and 56 from Iowa.

[1] Midwest Laboratories adds Sorbitol to the DTPA extract solution to capture boron