title: Spectral reflectance characteristics of soils in northeastern Brazil as influenced by salinity levels.
abstract: In northeastern Brazil, large swaths of once-productive soils have been severely degraded by soil salinization, but the true extent of the damage has not been assessed. Emerging remote sensing technology based on hyperspectral analysis offers one possibility for large-scale assessment, but it has been unclear to what extent the spectral properties of soils are related to salinity characteristics. The purpose of this study was to characterize the spectral properties of degraded (saline) and non-degraded agricultural soils in northeastern Brazil and determine the extent to which these properties correspond to soil salinity. We took soil samples from 78 locations within a 45,000-km2site in Pernambuco State. We used cluster analysis to group the soil samples on the basis of similarities in salinity and sodicity levels, and then obtained spectral data for each group. The physical properties analysis indicated a predominance of the coarse sand fraction in almost all the soil groups, and total porosity was similar for all the groups. The chemical analysis revealed different levels of degradation among the groups, ranging from non-degraded to strongly degraded conditions, as defined by the degree of salinity and sodicity. The soil properties showing the highest correlation with spectral reflectance were the exchangeable sodium percentage followed by fine sand. Differences in the reflectance curves for the various soil groups were relatively small and were not significant. These results suggest that, where soil crusts are not present, significant challenges remain for using hyperspectral remote sensing to assess soil salinity in northeastern Brazil.
authors.affiliation: Department of Agronomy, Universidade Federal Rural de Pernambuco, Recife, PE, Brazil. pessoa.lgm@gmail.com.
authors.forename: Luiz Guilherme Medeiros
authors.identifier: http://orcid.org/0000-0003-1937-526X
authors.initials: LG
authors.lastname: Pessoa
authors.affiliation: Department of Agronomy, Universidade Federal Rural de Pernambuco, Recife, PE, Brazil.
authors.forename: Maria Betânia Galvão Dos Santos
authors.initials: MB
authors.lastname: Freire
authors.affiliation: Department of Ecosystem Science and Management, Texas A&M University, College Station, TX, USA.
authors.forename: Bradford Paul
authors.initials: BP
authors.lastname: Wilcox
authors.affiliation: U. S. Department of the Interior, Bureau of Land Management, National Operations Center, Salt Lake City, UT, USA.
authors.forename: Colleen Heather Machado
authors.initials: CH
authors.lastname: Green
authors.affiliation: Department of Agronomy, Universidade Federal Rural de Pernambuco, Recife, PE, Brazil.
authors.forename: Rômulo José Tolêdo
authors.initials: RJ
authors.lastname: De Araújo
authors.affiliation: Brazilian Agricultural Research Corporation, EMBRAPA, Recife, PE, Brazil.
authors.forename: José Coelho
authors.initials: JC
authors.lastname: De Araújo Filho
mesh_terms: D001938:Brazil; D004784:Environmental Monitoring; D054712:Salinity; D012965:Sodium Chloride / Q000032:analysis; D012987:Soil / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D012987:Soil; D012965:Sodium Chloride
keywords: Salinity monitoring; Semiarid; Soil salinity; Soil sodicity