Soil available phosphorus by Mehlich-1, Mehlich-3 and anion exchange resin and its sensitivity to soil clay content

摘要

Mehlich-1 is the most used chemical method to determine soil available P in Brazil, but its efficacy is affected by variations in clay contents due to the exhaustion of the extractants and readsorption of P by the soil particles. Thus, other methods have been tested in Southern Brazil to replace the Mehlich-1. The objective of this work was to evaluate the ability of Mehlich-1 (Ml), Mehlich-3 (M3), and anion exchange resins in strip (AERst) or in sphere (AERsp) forms, to extract P from soils with a wide range of clay contents. Samples were collected from the B horizon of a Brazilian Oxisol were mixed with different amounts of sand in order to get artificial soil samples containing 200, 400 and 600 g/kg of clay, in addition to a pure sand (with no clay) and a pure soil (800 g/kg of clay). Phosphorus rates (0, 100, 200, 400 and 600 mg/kg) were applied to each one of these experimental soils that were subsequently incubated for 1, 30, 90 or 180 days. After each incubation period, available P was quantified by the four methods. All methods, extracted less P as the clay content of the samples increased. The amount of P extracted also decreased with increases on the incubation time. Thus, the evaluation of soil P availability to plants determined by alltested methods need to take into consideration the amount of clay.