Spectral reflectance of soils developed on a toposequence of diabase and shale in Piracicaba, SP, Brazil

Abstract

The objective of the present research was to study the spectral reflectance of soils developed on a toposequence composed by diabase and shale, in Piracicaba region, São Paulo State, Brazil. Soil samples were collected at three depths along a transection, as they were, Typic Haplorthox (TH), Rhodic Paleudult (RP), Lithic Distrochrept (L) and Typic Fluvent (TF). Bidirectional spectral reflectance factors of the soil samples were obtained by using a spectroradiometer from 350 to 2,500 nm in laboratory conditions. Spectral alterations observed between the surface and sub-surface layers were related to their organic matter and clay content differences; and these soil parameters were important on the spectral characterization of the soils. Along the toposequence, alterations on the soil characteristics occurred, mainly on iron, silt and mineralogy, that influenced variations of the spectral data. Soils developed by diabase presented higher content of iron, that influenced the spectral curve, with a deeper concavity shape at 850 nm, and lower reflectance intensity, differently of the soils developed by shale. The spectral curves of RP presented higher reflectance intensities from TH. The less weathered soils, L and TF, presented higher reflectance intensity than the more weathered soil, TH.