Caracterização por espectroscopia de reflectância de horizontes com e sem caráter coeso de solos do nordeste brasileiro

Abstract

Proximal sensing has been widely applied over the years in relation to soil studies. This technique allows characterizing the spectral behavior of soils, contributing to the generation of a spectral database, also known as a spectral library. Thus, this study aimed to develop visNIR spectral libraries of horizons with and without the cohesive character of soils collected from different states of Brazil, descriptively evaluating the variations in their spectral data. Soil samples from the states of Maranhão, Ceará, Pernambuco, Alagoas, Sergipe and Bahia were collected, with two horizons for each soil, one with and one without the cohesive character. Chemical analyzes to determine pH (H2O and KCl), phosphorus, sodium, potassium, aluminum, potential acidity, calculation of CEC and base saturation, organic carbon, calcium and magnesium content, and physical analyzes for granulometry and sand fractionation, which were carried out for the characterization of the horizons; as well as the collection of spectral data from the samples, using the FieldSpec Pro FR 3 spectroradiometer (Analytical Spectral Devices, Boulder, Colorado, USA), and the analysis of the soil line. From the bidirectional reflectance factor, the spectra were obtained, through the performance of three spectral readings for each sample and with their average values, later, calculated. In order to carry out the descriptive evaluation of the spectral curves, both the generated shapes of each sample along the electromagnetic spectrum were observed, as well as their reflectance intensities, paying attention to the existing absorption features in both soil horizons. In addition, the data were also evaluated using the soil line, which used bands present in the spectral curves so that it was also possible to identify differences between soils that have the cohesive character and those that do not. Therefore, with the use of physical and chemical analyses, together with the analysis of the spectral data and soil line, it was possible to find differences in the reflectance intensities present in the soil samples with and without the presence of the cohesive character, which varied according to the their textures and amounts of organic matter.