Evaluation of Mehlich-1 and Mehlich-3 extraction procedures for plant nutrients in acid mineral soils of Florida

Increasing number of soil testing laboratories in the mid-Atlantic and southeastern states of the United States are adopting Mehlich-3 (M-3) as the official extraction procedure in place of Mehlich-1 (M-1) or the dilute double acid method. Several studies have indicated that the M-3 has at least equivalent if not better extractability, particularly of micronutrients in the acidic and mineral soils in these regions. The objective of this study was to determine the correlation between the two Mehlich procedures and to provide conversion equations from M-1 to M-3 procedure. This is expected to serve as an estimate of nutrient availabilities particularly by the extension personnel and crop professionals evaluating different test procedures. A set of 519 mineral soil samples received at the UF/IFAS Extension Soil Testing Laboratory were selected and assayed with both M-1 and M-3 extracting solutions. The concentrations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn), manganese (Mn), and boron (B) in the extracted solutions were determined and comparative equations were developed. Highly significant linear correlation coefficients were found for all the nutrients extracted with both M-3 and M-1. Acidic to near neutral soil pH range of the soils had no influence on the efficiencies of extraction solutions. The equations developed showed that P, Cu, Mn, and B extracted were 47%, 94%, 101%, and 111% more with M-3 than with M-1 while for K, Mg, and Zn generally remained the same for both methods.