Resumo

LA MANNA, LUDMILA et al. Determinaciones de granulometría en suelos volcánicos: comparación entre distintos métodos analíticos. Cienc. suelo [online]. 2016, vol.34, n.2, pp.355-364. ISSN 1850-2067.

Grain-size analysis is a key analysis in soil studies, so accurate determinations are needed for this variable. However, different analytical methods could show different results, even more in volcanic soils with high organic matter contents. The aim of this study was to compare the granulometric fractions of non-allophanic volcanic soils of the Andean Region of Argentina, applying different methods for particle size analysis (hydrometer, pipette and laser diffraction), following pretreatments and protocols commonly used for each technique. Feasibility of applying ignition as pretreatment for removing organic matter was also evaluated. The hydrometer method (HM) tended to overestimate sand fraction and underestimate silt fraction, respect to the pipette method (PM). However, HM and PM were highly correlated for sand and silt fraction, but not for clay fraction: Sand_PM = 0,94 Sand_HM - 3,99 (r² =0,83); Silt_PM= 1,07 Silt_HM + 8,49 (r² =0,79); Clay_PM = 0,62 Clay_HM + 1,79 (r² =0,54) HM and laser diffraction method (LM) showed similar values for sand and silt fractions and differed in clay fraction, which showed higher values by HM. Both methods were highly correlated for sand and silt fractions, and not for clay fraction: Sand_LM = 1,32 Sand_HM - 17,72 (r² =0,78); Silt_LM = 1,30 Silt_HM - 7,20 (r² =0,77); Clay_LM = 0,83 Clay_HM - 2,32 (r² =0,27) Results were influenced not only by the technique followed for grain-size determination, but also by the pretreatment applied in each case. The removal of organic matter by ignition was not appropriate. High temperature (430 ºC) modified the different grain size fractions.

Palavras-chave : Hydrometer; Pipette; Laser diffraction; Removal of organic matter.

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