Extractor efficiency and critical phosphorus levels for establishing pasture in Amazonas

The Mehlich-1 extractor is the most used in Brazil, however it extracts low phosphorus (P) levels in soils with high clay levels and iron-bound (Fe) and aluminum (Al) fractions. Thus, we aimed to evaluate the P availability and fertility classes in Yellow Latosol (YL) and Gleysol Haplicum (GH) soils using Mehlich-1, Mehlich-3 and anion exchange resin extractors, as well as to estimate the critical P levels in the soil and in plants for establishing Urochloa humidicola cv. Common. All extractors were efficient in evaluating the availability of P in the soil, however the anion exchange resin showed a high correlation with the P accumulation in the shoot, which can be considered the most efficient method in P extraction. However, we recommend the Mehlich-3 extractor due to its high efficiency in extracting the P linked to the Fe and Al fractions, in addition to being a multi-element extractor. The critical level of P in the soil for establishing U. humidicola by Mehlich-3 in YL is 10.32 mg dm-3, while it is 7.46 mg dm-3 in GH. The critical P level in plants grown in YL is 1.20 mg dm-3, and it is 1.54 mg dm-3 in GH. The estimated phosphate doses can be recommended for cultivating U. humidicola and can serve as a reference for future research on correlating and calibrating P doses.