Abstract

Particle size distribution (PSD) is a soil physical property influenced by organo-mineral complexes (or-mic) in silt and clay fractions. In Andosols, these fractions are underestimated due to the presence of or-mic in soil micro-aggregates. This study estimated quantitatively the organomineral fraction by comparing two methodologies of granulometric analysis (sequential dispersion and sieve-sedimentation) in Andosols and Fluvisols from southern Chile. Or-mic were calculated through specific dissolution extractions (Al, Si, Fe). In addition, pH(NaF), and soil organic carbon (SOC) were determined. Correlations between Al-o (0.74), Al-p (0.71), pH in NaF (0.41), and the ormic were found. Or-mic were higher in Andosols, varying between 1.5 and 5.2%, which led to an underestimation of silt and clay fractions of the soil in PSD analysis and, thus, an overestimation of soil texture due to the continuous formation of micro-aggregates. Therefore, to properly determine soil PSD, it is essential to estimate or-mic, particularly in highly reactive soils, which are readily capable of binding organic compounds in their mineral fraction.