Inorganic phosphorus fractions extracted by sodium dithionite-citrate-bicarbonate and determined using the malachite green method

Abstract

Phosphorus (P) fractionation is a common tool used in studies on soil P dynamics. However, the P fraction extracted by sodium dithionite-citrate-bicarbonate (DCB), occluded in iron oxides (P-occluded), is difficult to quantify. This study presents an alternative and simpler method for the quantification of the P-occluded fraction extracted by DCB. Samples were collected from a clayey Oxisol at a depth of 0-0.2 m. The extraction method followed the procedure described by Zhang and Kovar and malachite green method was used for determination. The malachite green method produced satisfactory quantification results, and it revealed a pattern that represents extract P concentrations according to the absorbance level. The method is suitable for simple determinations of P occluded in extracts of DCB. RESUMO: O fracionamento de fósforo (P) é uma das principais ferramentas nos estudos sobre a dinâmica de P no solo. Entretanto, a fração de P extraído por ditionito-citrato-bicarbonato de sódio (DCB), ocluso em óxidos de ferro (P-ocluso) tem apresentado problemas para a sua quantificação. O objetivo foi propor método alternativo e mais simples para a quantificação