Phosphorus extractants for soils in the humid tropical region of Brazil

Abstract

Given the heterogeneity of soils in Roraima state, Brazil, and the need for a phosphorus (P) extraction protocol, this study aimed to assess the efficiency of the Mehlich-1, Mehlich-3, Bray-1 extractants and anion exchange resin (AER) in determining available P in soils representative of the state. The chemical, physical and mineralogical attributes of seven soil classes were determined. The experiment was conducted in a greenhouse, using a randomized block design in a 7 x 5 factorial scheme with four repetitions. The first factor was the soils (LA (ITÃ), LV (ITÃ), LA (SERRA DA PRATA), LA (CCA), PA (CCA), FT (BONFIM), SN (SURUMU)), and the second P doses, estimated based on the maximum P-adsorption capacity (MPAC). A polyethylene pot containing 5 dm3 of soil and five plants was defined as the experimental unit. The indicator species was corn grown in two 30-day phases. The P doses were applied using monopotassium phosphate. Soil samples were removed before planting to determine available P using the extractants. Corn dry weight was assessed at the end of the two-phase experiment. Correlation tests were performed for dry weight versus extractant and extractant versus extractant. The Mehlich-3 and Bray-1 extractants were the most sensitive to variations in soil attributes. The resin exhibited the greatest correlations with the different soils individually and combined, showing potential in determining available P in soils from the humid tropical region of the Brazilian Amazon.