Color in subtropical brazilian soils as determined with a Munsell chart and by diffuse reflectance spectroscopy

Abstract

The color of soils provides useful information about their origin and allows their classification. Soil color has traditionally been determined with a Munsell chart; lately, however, alternative techniques such as diffuse reflectance spectroscopy (DRS) have enabled more accurate quantification. In this work, we determined the color parameters hue, value, chroma and reddening index using a Munsell chart and a DRS instrument for comparison. The data obtained from the DRS measurements were used to develop an accurate soil color map for the Rio Grande do Sul state in Brazil (RS). DRS data were also used for removable continuum calculations to determine the [hematite/(hematite + goethite)] ratio [Hm/(Hm + Gt)] of Brazilian soils. Based on suchratio, the soils were classified as goethitic [Hm/(Hm + Gt) ≤ 25%], goethitic–hematitic [25 < Hm/(Hm + Gt) ≤ 50%], hematitic–goethitic [50 < Hm/(Hm + Gt) ≤ 75%] or hematitic [Hm/(Hm + Gt) ≥ 25%]. Color parameters differed between the two measurement methods, with the Munsell chart often overestimating or underestimating the DRS results. Based on the [Hm/(Hm + Gt)] ratio, the target soils were mainly goethitic.