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 representing 21 soil series, with varying cultural operations, were compared using Mehlich 3 (M3), Mehlich 1 (M1), ammonium acetate (NH4AOc), pH = 7.0 (AA), 0.2M ammonium chloride (NH4Cl), and ammonium bicarbonate-DTPA (AB-DTPA) extractants. Soil pH (0.01M CaCl2) varied from 3.57 to 7.28. The concentrations of Ca or Mg extractable by M3, M1, AA, and NH4Cl were strongly correlated with soil Ph (r2 = 0.381-0.482). Weak but significant correlations were also found between AB-DTPA extractable Ca or Mg and soil pH (r2 = 0.235-0.278). Soil pH relationships with extractable K were rather weak (r2 = < 0.131) for M1 and NH4Cl 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 NH4Cl extractants. Mehlich 3-P was significantly correlated with P extractable by M1 extractant only. Mehlich 3 versus AB-DTPA relationship was strong for K (r2 = 0.964), weaker for Mg and P (r2 = 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.
