ABSTRACT Soil mapping is a permanent demand, but the traditional method does not allow fast execution and low cost. Digital soil mapping (DSM) aims to improve the process by working with models that treat soil spatial variability quantitatively. In this perspective, the objective of the study is to perform DSM of the Parnaíba River Delta, Northeastern Brazil, through the decision tree (DT) integration technique using a set of attributes derived from the digital elevation model (DEM) and satellite images as input parameters. Data matrices were created considering different soil groups. The performance of the J48 machine learning algorithm (DT) was assessed for a set of two data matrices: one elaborated for the mapping units of the pre-existing conventional pedological map and the other for a set of associations determined based on the characteristics of the landscape of the study area with close correlation with the existing soils, mainly due to the source material. From the data processing, digital soil maps were created and validated by means of error matrices, whose reference points were classified in the field and validated using a pre-existing traditional soil map of the area. The results revealed that the attributes derived from satellite images stood out from those derived from DEM in predicting soil groups. Based on the validation coefficients applied (overall accuracy, Kappa index, user’s accuracy and producer’s accuracy), the classification quality was satisfactory, despite the complexity of the environment.

Resumo A presente pesquisa busca fazer o levantamento das mudanças acontecidas na evolução da cobertura do solo no município de Cajueiro da Praia, Piauí, no período de 2000 e 2015, utilizando-se de técnicas de Sensoriamento Remoto e Geoprocessamento. Foi feita a classificação supervisionada de imagens LANDSAT 8 e LANDSAT 5, instrumentos imageadores OLI/TIRS e TM respectivamente, anos de 2015 e 2000, através do método Maxver, processadas no software Arcgis 10.2, possibilitaram a produção dos mapas de uso e cobertura e a dinâmica da cobertura das terras. A análise identificou nove classes de uso e cobertura das terras, que demonstraram alterações observadas a partir da dinâmica entre as duas datas. A análise destes dados, juntamente com dados socioeconômicos dos censos e pesquisas realizadas pelo Instituto Brasileiro de Geografia e Estatística - IBGE mostrou um contexto de mudanças do uso e cobertura das terras, com um crescimento da área urbana, a diminuição da área de mangue e o aumento dos corpos hídricos do município. A mudança no quantitativo da população do município ocorre perceptivelmente em sua área litorânea, o aumento dos corpos hídricos se dá especialmente devido ao crescimento de tanques de carcinicultura. As questões da legislação ambiental são fatores que podem explicar a recuperação de algumas áreas de vegetação, assim como seu descumprimento explica a perda de outras, como a vegetação de mangue, o qual foi observado ao longo do trabalho.

Abstract The Brazilian northeast coast has tourism potential, and in the last decades its landscapes have been impacted by the expansion of tourism activity. The present research aimed to survey the change s that occurred in the evolution of soil cover in the municipality of Cajueiro da Praia, Piauí, in 2000 and 2015, using Remote Sensing and Geoprocessing techniques. The supervised classification of images LANDSAT 8 and LANDSAT 5, OLI/TIRS and TM imager instruments, respectively, in 2015 and 2000, using the Maxver method, processed in the Arcgis 10.2 software, made possible the production of the maps of use and coverage and the dynamics of land cover. The analysis identified nine classes of land use and land cover, which showed changes observed from the dynamics between the two dates. The analysis of these data, together with socioeconomic data from the census and surveys carried out by the Brazilian Institute of Geography and Statistics, showed a context of land use and land cover changes, with growth of urban areas, the increase of water bodies of the municipality. The change in the quantitative population of the municipality occurs perceptibly in its coastal area, the increase of water bodies is especially due to the growth of shrimp tanks. The issues of environmental legislation are factors that may explain the recovery of some vegetation areas, as their non-compliance explains the loss of others, such as mangrove vegetation, which was observed throughout the work.

ABSTRACT Soils in alluvial plains of the lower course of the Acaraú River, Ceará State, Brazil, are weakly developed and have a complex distribution in the landscape. This study reports the pedogenic characterization of such soils in an effort to understand their formation. Soil pits were opened in four representative sites, profile morphology was described, and soil samples were collected for chemical, physical, mineralogical, and micromorphological analyses. All profiles had weak pedogenic development, as inferred from their morphological characteristics, lack of B horizon, and high silt/clay ratio. Organic carbon and particle size distributions were heterogeneous in Fluvisol, Planosol, and Solonchak, in agreement with their sedimentary nature. Intrinsic characteristics of each profile indicated variations in pedogenic processes related to depositional conditions, which, in turn, were determined by the alluvial nature of sediments and water table dynamics. Consequently, Fluvisols at higher elevations showed reduced pedogenic development. In adjacent areas, Planosols showed pores filled with clay minerals and a texture gradient, indicative of past lessivage. Vertisol was identified in small depressions and exhibited intense pedoturbation and high sodium concentration in deep layers. Solonchak had a high degree of hydromorphism, high sodium concentration, and high electrical conductivity. The distinct pedogenesis of alluvial plain soils in Northeastern Brazil is evidenced by their morphological, chemical, and physical properties.

RESUMO O presente trabalho teve por objetivos: (i) determinar e mapear os teores dos micronutrientes (cobre - Cu, ferro - Fe, manganês - Mn e zinco - Zn) em solos do Estado do Ceará; (ii) avaliar atributos do solo relacionados à disponibilidade dos micronutrientes; (iii) avaliar, por krigagem ordinária, a dependência espacial dos teores dos micronutrientes. A área estudada está localizada na região central do Ceará, na bacia do Rio Banabuiú. Amostras de solo foram coletadas, nas camadas superficiais e subsuperficiais, para determinação dos atributos químicos, granulometria, e dos teores de micronutrientes, extraídos com solução de Mehlich-1. Os pontos dos principais tipos de solos da região foram espacializados. Os resultados foram submetidos a análises descritivas e análises de correlação de Pearson. Foram testados os semivariogramas que tiveram os melhores ajustes, utilizando o método de krigagem ordinária, e elaborados os mapas de variabilidade espacial. Os maiores teores de média, máximo e mínimo para Cu e Fe se encontram nas camadas subsuperficiais, e para Mn e Zn nas camadas superficiais. Nas camadas superficiais, a maioria dos solos apresentam Fe, Mn e Zn em teores adequados à produção agrícola, e Cu apresenta teores nas classes médio a baixo. Os micronutrientes apresentaram correlações significativas positivas, principalmente, com os atributos dos solos e entre si. Cu, Fe, Mn e Zn apresentam dependência espacial classificada como média a forte, nas camadas superficiais e subsuperficiais.

ABSTRACT The aim of the present work was to: (i) determine and map the micronutrient content (copper - Cu, iron - Fe, manganese - Mn and zinc - Zn) in soils of the State of Ceará; (ii) evaluate soil attributes related to micronutrient availability; and (iii) evaluate, by ordinary kriging, the spatial dependence of the micronutrient content. The study area is located in the central region of Ceará, in the basin of the River Banabuiú. Soil samples were collected in the surface and subsurface layers to determine the chemical attributes, granulometry, and micronutrient content, extracted with Mehlich-1 solution. The sites of the principal types of soil in the region were spatialised and the results submitted to descriptive analysis and Pearson correlation analysis. The semivariograms with the best fit were tested using the ordinary kriging method, and the maps of spatial variability were prepared. The highest values for the mean, maximum and minimum levels of Cu and Fe are found in the subsurface layers, while for Mn and Zn, they are found in the surface layers. In the surface layers, the majority of soils present Fe, Mn and Zn in levels suitable for agricultural production, while the levels of Cu are classified as medium to low. The micronutrients showed a significant positive correlation, especially with the soil attributes and with each other. Cu, Fe, Mn and Zn are classified as having medium to strong spatial dependence in the surface and subsurface layers.

ABSTRACT Lithological and geomorphological variations determine formation of soils with different mineralogical constitutions and can influence the distribution of potentially toxic elements (PTE). The aim of this study was to determine the contents of PTE and mineralogical assemblages along soil profiles of different classes and parent materials and to investigate the association among these factors in the São Francisco sedimentary basin in the northern part of the state of Minas Gerais (Brazil). Eight soil pedons of different classes that developed from different parent materials (limestone, siltstone, phyllite, alluvial-colluvial sediments, detrital cover, and rhythmite) were studied in two lithotoposequences. Soil morphological, particle-size, and chemical analyses were carried out for soil characterization and classification. A mineralogical investigation was carried out by X-ray diffraction on soil sand, silt, and clay fractions. Potentially toxic elements were extracted by microwave-assisted acid digestion (EPA 3015A method) and determined in an ICP-OES. Soil mineralogy showed relevant interactions between pedogenesis and morphogenesis. Quartz is the main mineral in the sand and silt fractions, with varying amounts of weatherable primary minerals, whereas kaolinite is the main mineral in the clay fraction, followed by 2:1 clay minerals and oxides. The main soil properties associated with PTE variability were pH, redox environment, mineral and organic reactive surfaces, and clay content. The unique patterns of PTE distribution per pedon and differences in PTE contents in soils from the same parent material, but with different pedogenic evolution, showed that pedogenic processes influence PTE distribution. Mainly Mn, Ni, Pb, and Ba were influenced by parent material, especially limestone, siltstone, and detrital cover, but Cd, As, and Cu were also influenced. To a lesser extent, Mo was influenced by phyllite and Cr by detrital cover and phyllite. Rhodic Ferralsol (Latossolo Vermelho Distrófico típico) was the only taxonomic class to show class association with PTE. The association of Ferralsols (Latossolos) with Cd, Mn, Ni, Pb, Ba, As, and Cu and the low contents of these elements in soils of this class suggest that pedogenic processes common to Ferralsol (Latossolo) evolution are responsible for decreasing levels of these PTE.

ABSTRACT Bulk density (Bd) can easily be predicted from other data using pedotransfer functions (PTF). The present study developed two PTFs (PTF1 and PTF2) for Bd prediction in Brazilian organic soils and horizons and compared their performance with nine previously published equations. Samples of 280 organic soil horizons used to develop PTFs and containing at least 80 g kg-1 total carbon content (TOC) were obtained from different regions of Brazil. The multiple linear stepwise regression technique was applied to validate all the equations using an independent data set. Data were transformed using Box-Cox to meet the assumptions of the regression models. For validation of PTF1 and PTF2, the coefficient of determination (R2) was 0.47 and 0.37, mean error -0.04 and 0.10, and root mean square error 0.22 and 0.26, respectively. The best performance was obtained for the PTF1, PTF2, Hollis, and Honeysett equations. The PTF1 equation is recommended when clay content data are available, but considering that they are scarce for organic soils, the PTF2, Hollis, and Honeysett equations are the most suitable because they use TOC as a predictor variable. Considering the particular characteristics of organic soils and the environmental context in which they are formed, the equations developed showed good accuracy in predicting Bd compared with already existing equations.

Resumo O objetivo deste trabalho foi avaliar diferentes estratégias para a predição da distribuição de classes de solo em mapas pedológicos digitais de áreas sem dados de referência, na bacia sedimentar do São Francisco, no Norte de Minas Gerais. As estratégias incluíram: o detalhamento da legenda, o treinamento por observações em campo, a ampliação do conjunto de treinamento e o uso de diferentes algoritmos de mineração de dados. Foram elaboradas quatro matrizes, diferenciadas pelo volume de dados, para o aprendizado dos algoritmos, e pelo nível taxonômico das classes de solo a serem preditas. Avaliou-se o desempenho dos algoritmos de aprendizado de máquina - Random Forest, J48 e MLP -, associados a procedimentos de discretização, balanceamento de classes, seleção de variáveis e expansão do conjunto de treinamento. O balanceamento de classes, a discretização de variáveis por frequências iguais e o algoritmo Random Forest apresentaram os melhores desempenhos. A extensão da representatividade das observações em campo, que presume uma área de treinamento mais ampla, não trouxe ganho preditivo. A generalização taxonômica para subordem diminui a fragmentação dos polígonos mapeados e aumenta a acurácia dos mapas pedológicos digitais. Quando são produzidos após treinamento por observações de solo in situ, na área de mapeamento, os mapas pedológicos digitais têm valores de acurácia equivalentes aos dos treinados em mapas preexistentes.

Abstract The objective of this work was to evaluate different strategies for the prediction of soil class distribution on digital soil maps of areas without reference data, in the sedimentary basin of San Francisco, in the north of the state of Minas Gerais, Brazil. The strategies included: taxonomic generalization, training by field observations, training set expansion, and the use of different data mining algorithms. Four matrices were developed, differentiated by the volume of data for machine learning and by soil taxonomic levels to be predicted. The performance of the machine learning algorithms - Random Forest, J48, and MLP -, associated with discretization, class balancing, variable selection, and expansion of the training set was evaluated. Class balancing, variable discretization by equal frequencies, and the Random Forest algorithm showed the best performances. The representativeness extension of field observations, that assumes a larger training area, brought no predictive gain. Soil taxonomic generalization to the suborder level reduces the fragmentation of mapped polygons and improves the accuracy of digital soil maps. When generated by training on in situ soil observations at the mapping area, digital soil maps are as accurate as those trained on preexistent maps.

ABSTRACT Information is scarce on the genesis and classification of soils derived from calcareous rocks in the Northeastern region of Brazil. This study describes the morphological, physical, chemical, mineralogical, and micromorphological properties of four soil profiles (P1-P4) located in the Apodi Plateau. A pedogenesis hypothesis and soil classification, according to the Brazilian System of Soil Classification (SiBCS), are proposed for these profiles. The interactions between parent material, surface topography and climate affected the pedogenesis processes and soil properties, although the calcareous nature of the parent material most affected the soil morphology and chemical properties. The sand fraction contained mainly quartz and calcite, and a smaller amount of mica. Smectite and interstratified illite-smectite occurred in the clay fraction of profile P1 and in some horizons of P2 (Ccmќ and Ccrќ) and P3 (2Ccrќ). Kaolinite predominated in profiles P2, P3, and P4; where as illite and vermiculite were present in the Bicќ, Bcќ, Bcmќ horizons of P2, in Bt2c of P3, and in C of P4. The mineralogy showed illite, hematite, and goethite, and anatase in a number of horizons. Micromorphological analysis of P2 indicated a strong cementation of Bcmќ and Ccmќ by calcium carbonate, and other properties indicate the formation of a petrocalcic horizon, but this horizon lacked lateral continuity in the profile. Therefore, the parapetrocalcic term is proposed for classifying P2 in the fourth level of the SiBCS. The 3Biќ-P1 horizon exhibited calcite coating and iron coating or quasi-coating, indicating distinct pedogenesis processes occurring under different environmental conditions. Likewise, the occurrence of petroplinthite in P2 indicates that climatic conditions during its formation differed from present conditions, and both situations are interpreted as evidence that the soils were formed by polygenetic processes. In the SiBCS classification, the soils are classified as Cambissolo Háplico Carbonático vertissólico (P1), Cambissolo Háplico Carbonático concrecionário (P2), Luvissolo Crômico Pálico petroplíntico (P3), and Neossolo Litólico Carbonatico típico (P4); and a new class (parapetrocálcico concrecionário) is proposed for P2 in the fourth level.

ABSTRACT Despite limited geographic expression of Organosols in Brazil, their high carbon storage capacity and natural environmental vulnerability justifies further studies on C and N stocks in these soils and their relationship to the nature of organic matter. Evaluation of physical and chemical properties of organic soils and their ability to store C is important so as to develop sustainable management practices for their preservation. The objectives of the study were to measure the total organic carbon stock (OCst), total nitrogen stock (Nst), and humic fractions in Organosols from different environments and regions of Brazil, and to correlate the data with soil chemical (pH, P, K, Ca2+, Mg2+, Al3+, H+Al, CEC, V) and physical properties (soil bulk density, Bd; organic matter density, OMd; total pore space, TPS; minimum residue, MinR; and proportion of mineral matter, MM), and degree of organic matter decomposition (rubbed fiber content; pyrophosphate index, PyI; and von Post index). For that purpose, 18 Organosol profiles, in a total of 49 horizons, were sampled under different land usage and plant coverage conditions. The profiles were located in the following Brazilian states - Alagoas, Bahia, Distrito Federal, Espírito Santo, Mato Grosso do Sul, Minas Gerais, Paraná, Rio de Janeiro, Rio Grande do Sul, Santa Catarina, and São Paulo. The OCst and Nst varied significantly among horizons and profiles. The Organosols exhibited, on average, 203.59 Mg ha-1 OCst and 8.30 Mg ha-1 Nst, and the highest values were found in profiles with pasture usage. The content of the humic fraction (humin, HUM; fulvic acid, FAF; and humic acid, HAF) and C storage varied in the soil horizons and profiles according to the degree of decomposition and other factors of soil formation. The OCst, Nst, OMd and the C stocks in the humic fractions were positively correlated. The values of acidity were lower in the soils with higher contents of mineral material, and low pH values were related to a high C/N ratio. The OCst and Nst were correlated with different soil properties, the most important being the degree of soil organic matter decomposition, which was inversely correlated.

Os Organossolos são geralmente associados às regiões Sudeste e Sul do Brasil, e são poucos os estudos sobre a ocorrência e os efeitos do uso e manejo agrícola desses solos na região Nordeste. Os objetivos deste trabalho foram caracterizar física, química e morfologicamente seis perfis de Organossolos de várzeas dos Estados do Ceará, Rio Grande do Norte e da Paraíba e correlacionar seus atributos ao ambiente de formação, além de quantificar seus estoques de carbono e suas capacidades de armazenamento de água. Foram utilizados os métodos recomendados no Sistema Brasileiro de Classificação de Solos (SiBCS) para caracterizar química e fisicamente o solo, bem como a umidade e o volume residual dele. O aumento dos valores da Ds nos horizontes foi em decorrência da maior decomposição das fibras esfregadas (FE) e da redução dos teores de matéria orgânica. O volume residual apresentou correlações positiva e significativa a 5 % com o valor de resíduo mínimo (r = 0,64) e Ds (r = 0,74) e negativa com a porcentagem de FE (r = -0,75), podendo ser usado para avaliar a subsidência desses solos. As propriedades químicas foram influenciadas pelo material orgânico e pelos sedimentos fluviomarinhos. A variação da drenagem influenciada pela posição no relevo e pelo uso agrícola dos solos conduziu a classes de diferentes graus de decomposição da matéria orgânica e com isto às classes dos Organossolos Fíbrico, Hêmico e Sáprico. Um dos perfis CE1, com maior influência de sedimentos marinhos, foi classificado como Organossolo Tiomórfico com caráter solódico.

The Histosols are generally associated with Southeastern and Southern regions of Brazil, and there are few studies on the occurrence and effects of the use and agricultural management of these soils in the Northeast. The aim of this paper is to physically, chemically and morphologically characterize six profiles of Histosols from flood plains in the states of Ceara, Rio Grande do Norte and Paraiba, Brazil and correlate their soil properties to the training environment, as well as quantify their carbon stores and water storage capacities. We used the methods recommended in the Brazilian System of Soil Classification (SiBCS) for chemical and physical characterization, moisture content and residual volume soil. The increase in the values of bulk density (BD) in the horizons was due to greater decomposition of rubbed fibers (RF) and decrease in soil organic matter. Residual volume was positively and significantly (5 %) correlated with the minimum residual value (r = 0.64) and BD (r = 0.74) and negatively correlated with the percentage of RF (r = -0.75), and it can be used to assess the subsidence of these soils. Chemical properties were affected by the material of organic origin and fluvial-marine sediments. Drainage variation, influenced by position in the landscape and crop use of the soils, led to classes with different degrees of decomposition of organic matter and, thus, Fibric, Hemic and Sapric classes of 'Organossolos'. One of the CE1 profiles, with greater influence from marine sediments, was classified as an 'Organossolo Tiomórfico' of a solodic nature.

A matéria orgânica do solo é parte de um sistema dinâmico influenciado por vários fatores, incluindo clima, conteúdo e natureza das argilas, uso da terra, sistemas de manejo e drenagem, os quais afetam as taxas de adição e os processos de transformações e evolução dos compostos orgânicos. O objetivo deste trabalho foi quantificar e avaliar a distribuição das frações húmicas em Organossolos de diferentes ambientes e regiões do Brasil, relacionando-os com os processos de subsidência. O teor de carbono (C) nas substâncias húmicas indicou predomínio do C da fração ácido húmico (C-FAH de 22,1 g kg-1 a 153,7 g kg-1) nos solos de regiões altimontanas e ambientes de planalto. Possivelmente, o clima mais frio, aliado a uma melhor fertilidade, favoreceu a formação desta fração em detrimento das frações ácido fúlvico e humina. Por outro lado, o maior teor de ácidos húmicos torna os Organossolos nesses ambientes mais susceptíveis aos processos de subsidência, principalmente quando manejados para agricultura. Já nos ambientes de várzeas e de planícies litorâneas, houve maior formação do C da fração humina (C-HUM de 79,2 a 267,2 g kg-1), que é a fração das substâncias húmicas mais resistente à decomposição. O somatório das frações húmicas representou 89% do carbono total, estando essas duas variáveis altamente correlacionadas. A relação Extrato alcalino humina (EA/HUM) agrupou classes de Organossolos pelo ambiente de formação, sendo sugerida como atributo diagnóstico nos níveis inferiores do Sistema Brasileiro de Classificação de Solos (SiBCS), possibilitando diferenciar os Organossolos quanto ao potencial de subsidência.

ABSTRACT The organic matter of soil is part of a dynamic system influenced by several factors, including climate, the content and nature of clays, land use, management and drainage systems, all of which affect the addition rates, and the processes of transformation and evolution of organic compounds. The objective of this study was to quantify and assess the distribution of humic fractions in histosols in different environments and regions of Brazil, relating them to the processes of subsidence. The carbon (C) content in humic substances indicated a predominance of C from the humic-acid fraction (HAF-C of 22.1g kg-1 to 153.7g kg-1) in soils from high altitude mountainous regions and upland areas. Possibly the colder climate, coupled with improved fertility, favored the formation of this fraction at the expense of the fulvic acid and humin fractions. On the other hand, the higher humic-acid content makes organosols in these environments more susceptible to the processes of subsidence, especially when under agricultural management. Whereas in flood and coastal-plain environments, there was a greater formation of C from the humin fraction (HUM-C from 79.2 to 267.2g kg-1), being the fraction of humic substances most resistant to decomposition. The sum of the humic fractions represented 89% of the total carbon, these two variables being highly correlated. The relationship between alkaline extract and humin (AE / HUM) groups classes of histosols by their formation environment, and is suggested as a diagnostic attribute at the lower levels of the Brazilian System for Soil Classification (SiBCS), allowing differentiation of the histosols as to their potential for subsidence.

O objetivo deste trabalho foi avaliar a geração de um mapa de suscetibilidade à erosão, em área rural, no Município de Guararapes, SP, por meio de modelo multicritério aditivo. Foram utilizados mapas digitais dos temas: relevo (declividade e comprimento das rampas); pedologia (obtida em campo); uso e cobertura das terras da região; e interpretação do modelo digital de elevação. Os mapas digitais foram tratados em ambiente de sistema de informação geográfica, por meio do método multicritério aditivo, e validados pelo modelo da equação universal de perda de solo (USLE). Foram geradas cinco classes de suscetibilidade à erosão: baixa, moderada, alta, muito alta e altíssima. O mapa de risco obtido por multicritério aditivo teve boa correspondência com o modelo USLE. O mapa de suscetibilidade à erosão pode ser aplicado ao planejamento agrícola e ambiental da área rural do Município de Guararapes.

The objective of this work was to evaluate the construction of an erosion susceptibility map for a rural area of the municipality of Guararapes, SP, Brazil, using a multicriteria additive model. Digital maps on the themes relief (declivity and length of the slopes), pedology (obtained at the field), land use and land cover of the region, and interpretation of the digital elevation model were used. The digital maps were treated in a geographic information system environment using the additive multicriteria method and were validated by the universal soil loss equation (USLE) model. Five erosion susceptibility classes were generated: low, moderate, high, very high, and extremely high. The risk map obtained by additive multicriteria had good correspondence with the USLE model. The erosion susceptibility map can be used for the agricultural and environmental planning of the rural area of the municipality of Guararapes.

Em determinadas condições de relevo, do clima e de uso, com certa frequência pode acontecer acúmulo de sais nos solos, dando lugar à formação dos solos salinos e sódicos - também denominados de solos afetados por sais. A fim de orientar as práticas de manejo e uso das terras da região do Baixo Acaraú, CE, objetivou-se com o presente trabalho gerar um mapa de risco de salinização. Para obtenção das classes de vulnerabilidade, foram avaliados os temas pedologia, geologia, geomorfologia e uso e cobertura das terras e informações de declividade e altimetria, tratados em ambiente SIG com o método multicritério aditivo. Foram definidas quatro classes de risco de salinização: baixo, moderado, alto e altíssimo ou solos naturalmente salinos/sódicos. Foi constatado que 35,47 % da área corresponde à classe de baixo risco de salinização; 26,22 %, à de risco moderado; 8,23 %, à de risco alto; e 19,65 %, à de risco altíssimo.

Certain conditions of relief, climate and use can lead to the formation of saline and sodic soils, also called salt-affected soils. With a view to establish guidelines for management practices and land use in the region of Baixo Acaraú, Ceará, the purpose of this work was to generate a map of salinization risk. To classify levels of vulnerability, the pedology, geology, geomorphology and land use/cover were evaluated as well as slope altimetry information, treated in a GIS environment with an additive multi-criteria method. Four classes of salinization risk were defined: soils with naturally low, moderate, high, or very high salinity/sodicity. It was found that the risk of salinization was low in 35.47 % of the area, moderate in 26.22 %, high in 8.23 % and very high in 19.65 %.

Este trabalho objetivou elaborar um mapa de vulnerabilidade à degradação dos solos da bacia do rio Acaraú, CE, através de Sistema de Informações Geográficas e de metodologia multicritério aditivo. Para a obtenção das classes de vulnerabilidade, foram avaliados os temas geologia, geomorfologia, pedologia, vegetação e clima, definindo-se cinco classes: estável, moderadamente estável, medianamente estável/vulnerável, moderadamente vulnerável e vulnerável. A classe medianamente estável/vulnerável foi a mais representativa, ocupando 9.776 km² de extensão (67,8% da bacia), seguida da classe moderadamente estável que ocupou 4.180 km² de extensão (mais de 28% da bacia). Os resultados obtidos mostraram a viabilidade da aplicação do método para a elaboração do mapa de vulnerabilidade ambiental que pode ser utilizado na gestão territorial da bacia do Rio Acaraú.

This work aimed to prepare a map of soil degradation vulnerability in the Acaraú basin, Ceará, through the Geographic Information System and multicriterium additive methodology. For the obtaining of classes of vulnerability, we evaluated information related to geology, geomorphology, pedology, vegetation and climate, resulting in five classes: stable, moderately stable, medium stable/vulnerable, moderately vulnerable and vulnerable. The class medium stable/vulnerable was the most representative, occupying 9,776 km² of extension (67.8 % of the basin), followed by the class moderately stable, which occupied 4,180 km² of extension (more than 28% of the basin). The results showed the viability of the method for preparing the map of environmental vulnerability, which can be applied in the territorial management of the Acaraú basin.

Este trabalho teve como objetivo caracterizar a distribuição das substâncias húmicas (ácidos fúlvicos livres, ácidos húmicos, ácidos fúlvicos e humina) e atributos edáficos em perfis de solos de diferentes regiões do Brasil, que foram objeto de estudos de reuniões de correlação e levantamentos de solos realizados pela Embrapa e outras instituições. As amostras foram selecionadas e fracionadas seguindo conceitos da IHSS. A fração humina apresentou os maiores valores de C em todos os perfis, seguida pelos ácidos fúlvicos livres. Nos perfis em ambientes com altitudes elevadas o clima (Cwa, Cfb, Cwb) favoreceu a formação dos ácidos fúlvicos livres. Quanto às propriedades químicas, em ambos os horizontes foram verificados coeficientes de correlação positiva entre o hidrogênio e o conteúdo de carbono orgânico, r=0,58* e r=0,83**, para os horizontes A e B, respectivamente. Dentre as substâncias húmicas a de melhor correlação com o conteúdo de carbono orgânico foi a fração humina, com r=0,89** e r=0,91** para os horizontes A e B, respectivamente. Foi observada correlação positiva (p<0,05) entre a areia grossa e os C-FAF, C-FAH, C-HUM e a relação C-EA:C-HUM, nos horizontes A, indicando que a textura mais arenosa de alguns horizontes superficiais favorece a formação destas substâncias húmicas. O teor de C nos horizontes superficiais e subsuperficiais e a distribuição das substâncias húmicas variaram com a pedogênese e a altitude.

This study had as objective to characterize the distribution of humic substances (free fulvic acids, humic acids, fulvic acids, and humin) in soil profiles from different regions of Brazil, that had been object of studies of correlation meetings and soils surveys carried through by Embrapa and other institutions. The soil samples were selected and fractionated following concepts recognized by the IHSSS. The humin fraction presented the highest values of C in all the profiles, followed by the free fulvic acid fraction. In the profiles located on high altitude the climate (Cwa, Cfb, Cwb) favored the formation of free fulvic acid. As for the chemical properties, both horizons showed positive correlation coefficients between hydrogen and organic carbon content, with r=0.58* and r=0.83** for A and B horizons, respectively. Amongst the humic substances the humin showed the best correlation with the organic carbon content, with r=0.89** and r=0.91**) for A and B horizons, respectively. A positive correlation was observed between the coarse sand fraction and the C-FAF, C-HAF, C-HUM and the relation C-EA:C-HUM in the A horizons, indicating that the coarse texture of some surface horizons favors the formation of these humic substances. The organic C content in the surface and subsurface horizons and the distribution of humic substances varied with pedogenesis and altitude conditions.