The state of Amazonas, as well as the whole northern region, has great power of agricultural production. However, the low soil fertility of this place does not contribute to the healthy and quality development of crops grown in the state. In this sense, nutrient deficiency, mainly macronutrients, such as phosphorus, has been a research subject to evaluate the chemical interactions that occur in the soil-plant system. P is a very important mineral that participates in various processes in the growth of various cultures, and it is not possible to replace it with any other nutrient. Thus, the present work aimed to determine the available P content in two predominant soils classes in the Amazon, Oxisol and Argisol. The samples were submitted to drying, destroying and sieving to obtain the TFSA. Then the samples were extracted with Mehlich-1 solution for 24 h. Subsequently, ammonium molybdate acid solution and ascorbic acid powder were added to the extract for spectrophotometric determination of available phosphorus. Four concentrations with variations between samples were obtained, which were correlated to the clay contents obtained by particle size analysis. The results obtained in this study showed low available P concentration in both types of soil analyzed, confirming the low availability of this nutrient in characteristic Amazonian soils, as verified by other authors.
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