Evaluation of Mehlich‐III extractant to estimate the available P in Quebec soils

Abstract The Mehlich‐III method used for the determination of available P in 82 Quebec soils was compared to five other chemical methods (Bray‐II, Bray‐I, Mehlich‐II, Mehlich‐I and Olsen) and to two anion exchange resin techniques (F‐ and HCO‐ 3) In general, very good correlations were found between Mehlich‐III, Bray‐II and Bray‐I methods on acid soils (r=0.95** and 0.98**). The Mehlich‐III‐P content is somewhat the same as that determined by Bray‐I and corresponds approximately to 80% of Bray‐II‐P. The Mehlich—III extractant was found to be more reliable than Bray‐II and Bray‐I on very acid spodosols having high P‐sorption capacity. The Bray methods, with high NH4F concentration, extracted strongly fixed Al‐P in these soils and may overestimate the available P. In some acid soils containing apatite and in calcareous soils, the Bray‐II and Mehlich‐I (double acid) easily dissolved these Ca‐P compounds and gave exaggerated high P values. The Mehlich‐III and the other methods were less vigourous for these co...