Indirect determination of hematite content in soil from colorimetric and radiometric data

The soil color is a property that derives from some soil attributes, among them, the iron oxides content. So, the establishment of functional relationships between data related to soil color characterization and iron oxides content consists on a very useful procedure for the semiquantitative determination of the soil iron oxides contents. The present research aimed at estimating the hematite content clay fraction, in laboratory, from data related to soil color obtained by using automatic devices. Soil samples from Sao Paulo State, Brazil, had their clay fraction hematite contents semiquantitavely determined by the association of chemical and physical methods and their colors evaluated in laboratory through measurements made with a colorimeter and a spectroradiometer. The radiometric data were used to the determination of soil color in L*a*b* and Munsell systems and to the calculation of reddish indexes (RI). The RI values showed functional dependence of hematite contents and the best relation was verified with RI values derived from color determined in the L*a*b* system. Exponential models, developed from remote sensors, show themselves adequate in predicting the soil hematite contents.