Comparison of Mehlich 3, Mehlich 1, ammonium bicarbonate-DTPA, 1.0 M ammonium acetate, and 0.2 M ammonium chloride for extraction of calcium, magnesium, phosphorus and potassium for a wide range of soils
Communications in Soil Science and Plant Analysis 24(7-8): 603-612
Extractants employed for routine soil analysis vary from one laboratory to another. Lack of a universal soil extractant is a serious limitation for interpretation of analytical results from various laboratories on nutritional status of a given soil. This limitation can be overcome by developing functional relationships for concentrations of a given nutrient extractable by various extractants. In this study, extractability of CA, Mg, P, and K in a wide range of soils (0-15 cm) from citrus groves in Florida (USA) representing 21 soil series, with varying cultural operations, were compared using Mehlich 3 (M3), Mehlich 1 (M1), ammonium acetate (MH4AOc), pH = 7.0 (AA), 0.2M ammonium chloride (NH-4Cl), and ammonium bicarbonate-DTPA (AB-DTPA) extractants. Soil pH (0.01M CaCl-2) varied from 3.57 to 7.28. The concentrations of Ca or Mg extractable by M3, M1, AA, and NH-4Cl were strongly correlated with soil pH (r-2 = 0.381-0.482). Weak but significant correlations were also found between AB-DTP extractable Ca or Mg and soil pH (r-2 = 0.235-0.278). Soil pH relationships with extractable K were rather weak (r-2 = lt 0.131) for M1 and NH-4Cl but non-significant for M3, AB-DTPA, and AA. Concentrations of Ca, Mg, and K extractable by M3 were significantly correlated with those by either M1, AA, or NH-4Cl extractants. Mehlich 3-P was significantly correlated with P extractable by M1 extractant only. Mehlich 3 versus AB-DTPA relationship was strong for K (r-2 = 0.964), weaker for Mg and P (r-2 = 0.180-0.319), and non-significant for Ca. With the increasing emphasis on possible use of M3 as an universal soil extractant, data from this study support the hypothesis that M3 can be adapted as a suitable extractant for routine soil analysis.