ABSTRACT Soil chemical and physical analyses are the major sources of data for agriculture. However, traditional soil analyses are time-consuming, not cost-efficient, and not environmentally friendly. An alternative to traditional soil analyses is soil spectroscopy. This technique is a low-cost and quick analytical method, which can be implemented in a laboratory and/or in-situ. Nevertheless, some spectrometers are expensive and do not contemplate the entire spectrum. Despite this limitation, the main objective of the study was to create a soil spectral library of the Piauí State using only the 1000–2500 nm range. In this sense, it was evaluated and standardized the soil spectral library by accessing the combination of smoothing, standard normal variate, continuum removal, and Savitzky-Golay derivative spectral preprocessing procedures with partial least squares, random forest, and cubist machine learning algorithms. It was collected 262 geo-referenced soil samples at the layer of 0.00–0.20 m across the entire Piauí State, representing most of its soil variability. The soil properties evaluated were pH(H2O), sand, clay, and soil organic carbon (SOC) contents. This study demonstrated that the Standard Normal Variate was one of the most promising preprocessing procedures to improve model predictions for pH(H2O), sand, and clay. For SOC and pH, the best overall results were without preprocessing the soil spectra. Moreover, the cubist model was the most accurate in predicting soil properties. Finally, our study showed evidence of the potential and feasibility of using this soil spectral library to estimate soil properties such as pH(H2O), sand, clay, and SOC.

ABSTRACT: Environmental impacts caused by the addition of rare earth elements (REEs) to agricultural soils are a growing concern. The sedimentary basin of the Gurguéia River is located in one of the last agricultural frontiers in Brazil; nevertheless, data regarding quality reference values (QRVs) for REEs in soils are still scarce. The objective of this study was therefore to determine the natural concentration and establish the QRVs of REEs in soils of Gurguéia watershed, Brazil. Fifty-five composite soil samples were collected at sites under no or minimal anthropic interference. The average REE natural concentrations in soils from the Gurguéia watershed were lower than those found in other regions of Brazil and worldwide, following the order (mg kg−1): Ce (14.01) > Nd (6.19) > La (5.52) > Pr (2.51) > Sm (1.45) > Gd (0.93) > Dy (0.63) > Er (0.42) > Yb (0.39) > Tb (0.28) > Eu (0.26) > Lu (0.20). The parent material was the main factor that controlled the distribution of REEs in soils. The QRVs in soils followed the order (mg kg−1): Ce (18.8) > Nd (7.92) > La (6.32) > Pr (3.3) > Sm (1.97) > Gd (1.35) > Dy (0.85) > Er (0.55) > Yb (0.47) > Tb (0.37) > Lu (0.25). These values serve as a basis to assist the development of legislation, including REE thresholds for Brazilian soils.

ABSTRACT. Metal concentrations in suspended sediments of one of the most polluted rivers in Brazil were measured. Concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were determined by inductively coupled plasma while Hg and As were analyzed with hydride generation flow injection atomic absorption spectroscopy. Contamination of As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn was assessed using pollution indices, ecological risk assessment, statistical multivariate techniques and comparison with sediment quality guidelines. Suspended sediments of the upstream portion of the Ipojuca River are moderately contaminated, especially with Mn and As. On the other hand, sediments of the downstream section are highly contaminated, mainly with Zn, Pb, and As. Furthermore, the mean Ei (potential ecological risk) values of Pb and As showed considerable ecological risk in the downstream cross section. The comparison of our data with sediment guideline values indicated that the concentrations of Mn and Pb in the upstream section of the Ipojuca River pose a risk to sediment-dwelling organisms, while Pb and Zn are the metals of concern in the downstream section.

Resumo Objetivou-se com este trabalho caracterizar atributos morfológicos, físicos e químicos de solos formados a partir de arenitos no Cerrado Piauiense, na tentativa de encontrar padrões evolutivos. O estudo foi realizado em cinco perfis de solos representativos identificados como P1-RY (Neossolo Flúvico Psamítico típico - Aquents), P2-PA (Argissolo Amarelo Distrófico típico - Alfisol), P3-RL (Neossolo Litólico Distrófico fragmentário - Psamments), P4-RQ (Neossolo Quartzarênico Órtico típico - Orthents) e P5-PV (Argissolo Vermelho Distrófico Típico - Ultisol). As amostras dos solos foram submetidas à descrição morfológica e análises laboratoriais. Em geral, os solos desta região apresentaram altos teores da fração areia, baixo pH, baixo conteúdo de bases trocáveis e baixa capacidade de troca catiônica (CTC). A matéria orgânica governou a CTC na maioria dos horizontes, sugerindo uma dependência da matéria orgânica no fornecimento de cargas. Estes solos mostraram baixo grau de intemperismo, mas com ferro de alta cristalinidade. Assim, é possível afirmar que o relevo e o material de origem são os fatores de formação do solo que possuem maior influência nos atributos dos solos do Cerrado Piauiense, Brasil. Além disso, estes solos são jovens, sendo os mais evoluídos aqueles originados da Formação Piauí. Contudo, os arenitos do grupo Canindé aparentemente estão fornecendo minerais secundários diretamente da rocha ao solo.

Abstract This study characterized the morphological, physical and chemical attributes of sandstone-derived soils at the Cerrado of the Piauí State, Brazil, in order to identify evolutionary standards. The study was carried out with five representative soil profiles identified as P1-RY (Typical Flavic Psychotic Neosol - Aquents), P2-PA (Typical Dystrophic Yellow Argisol - Alfisol), P3-RL (Fragmentary Litholic Distrophic Neosol - Psammenit), P4-RQ (Typical Ortic Quartzenetic Neosol - Orthents) and P5-PV (Typical Dystrophic Red Argisol - Ultisol). Soil samples were submitted laboratory analysis described morphologically. In general, the soils presented high sand content, low pH, low content of exchangeable bases and low cation exchange capacity (CEC). Organic matter governed the CEC in most cases, suggesting dependence of organic matter in the supply of charges. These soils showed a low degree of weathering, but with iron of high crystallinity. Thus, the relief and the parent material are the major important soil-forming factors at the Cerrado of the Piauí State. Moreover, these soils are young, with the soils from the Piauí Formation being more evolved. However, the sandstones from the Canindé Group apparently are providing lithological secondary minerals for the soil.

ABSTRACT Growth in the agricultural and industrial sectors has increased the demand for rare earth elements (REEs) in the production of technological devices and fertilizers. Thus, the accumulation of these elements in the soil has become an environmental concern. Here, we aim to determine the natural contents of REEs in soils derived from different parent materials and under climatic conditions ranging from humid to semi-arid. We then evaluate the influence of major elements and soil properties on the geochemistry of REEs. The contents of REEs were determined using inductively coupled plasma optical emission spectroscopy. Major elements were determined by X-ray fluorescence spectrometry. The mean content of REEs in soils from Rio Grande do Norte (RN), Brazil, were in the followed order (mg kg-1): Ce (40.4) > La (18.9) > Nd (15.8) > Pr (7.3) > Sm (3.0) > Gd (2.6) > Dy (1.0) > Er (0.7) > Yb (0.6) > Eu (0.5) = Tb (0.5) > Ho (0.3) > Lu (0.2). The parent material was the main factor that governed the geochemistry of the REEs in soils of RN. Higher levels of REEs were observed in soils derived from igneous and metamorphic rocks. In contrast, sedimentary rocks - except for the region formed from limestone - generated soils with lower contents of REEs in the state. In addition, soils developed from the same parent material and under different climatic conditions showed the same geochemical signatures for REEs in soils. These results confirm the small effect of climate on REE geochemistry in soils of RN and lead to the conclusion that the geochemical signature of REEs in these soils reflects the composition of the underlying parent material. The lack of significant correlation between (La/Yb)N ratio and the Chemical Alteration Index also confirms the low influence of climate on soil REE geochemistry. Among the major elements, Fe and Si had a greater influence on soil REE geochemistry. Higher REEs were seen in areas with more Fe and less Si. These REE levels were clearly controlled by the type of parent material. The Nd, Sm, Tb, Dy, Ho, Yb, and Er levels showed strong spatial dependence; this dependence was moderate for the Pr, La, Ce, Eu, Gd, and Lu levels. Spatial variability maps of REEs are particularly important to identify areas under environmental impact. Our results represent the most detailed study of the surface geochemistry of REEs in Brazilian soils and contribute to the scarce data available on these elements in Brazil.

ABSTRACT: Studies regarding background concentrations of rare earth elements (REEs) are scarce and have mainly focused on a limited number of soil types from the northern hemisphere. The aim of this study was to determine REE concentrations in thirty-five benchmark soils of Brazil. Composite soil samples were taken from areas under native vegetation or with minimal anthropogenic influence. Concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, Lu, Dy, Er, Ho, Tb, Tm, Y, Sc, and Fe were determined by ICP-OES using a cyclonic spray chamber/nebulizer system after microwave acid digestion. Results were assessed by descriptive statistics, Pearson correlation, and principal component analysis (PCA). Regression analyses among Fe, organic carbon, and REEs were performed to provide a tool for estimating REE concentrations in soils. The REE concentrations in the Brazilian benchmark soils were in the following order: Ce > La > Nd > Pr > Y > Sm > Gd > Sc > Dy > Yb > Eu > Er > Tb > Ho > Lu > Tm. The clear decoupling between light and heavy rare earth elements in soils, indicated by multivariate analysis, is mainly related to differences in parent material. The lowest REE concentrations were found in sandy sediments, whereas the highest REE concentrations were observed in basalt, biotite gneiss, and clayey sediments. The organic carbon and Fe concentrations can properly predict REE concentrations in soils; such a finding can assist in estimating REE concentrations in soils not only in Brazil but also in similar soils developed under tropical conditions.

Os solos dos tabuleiros costeiros cultivados com cana-de-açúcar, durante longo período de tempo, sob sistemas de manejo com diferentes aportes de matéria orgânica podem apresentar alterações nas propriedades físicas e químicas. O objetivo deste trabalho foi avaliar o efeito do aporte de matéria orgânica pelos diferentes sistemas de manejo da cana-de-açúcar sobre as propriedades físicas e químicas de um Latossolo Amarelo distrocoeso dos tabuleiros costeiros de Alagoas. Foram selecionadas áreas em talhões de produção com a cultura da cana-de-açúcar, sendo objeto de pesquisa experimental três áreas, representativas de três sistemas de manejo adotados pela unidade sucroalcooleira: uma área cultivada sob sistema de manejo irrigado (SMI), uma área sob sistema de manejo de fertirrigação com vinhaça (SMV) e uma área sob sistema de manejo com aplicação de vinhaça + torta de filtro (SMVT). Esses sistemas de manejo foram comparados entre si e em relação a uma testemunha-padrão, representada por um fragmento de Mata Atlântica nativa (MN). Para avaliar as propriedades físicas e químicas, amostras de solo foram coletadas ao acaso, nas áreas submetidas aos diferentes sistemas de manejo, nas profundidades de 0-0,20, 0,20-0,40 e 0,40-0,60 m, sendo retiradas num ponto situado nas entrelinhas da cana-de-açúcar. Os resultados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey a 5 %. Estudos de correlações simples foram realizados entre algumas variáveis medidas. Os resultados permitiram concluir que os diferentes sistemas de manejo investigados promoveram alterações nas propriedades físicas e químicas do solo. As medidas de consistência do solo apresentaram tendência de aumento em seus valores com o incremento do carbono orgânico total (COT) do solo, promovido pela adição de resíduos da cana-de-açúcar. Os sistemas de manejo que receberam adição de resíduos da cana-de-açúcar denotaram menor degradação nas propriedades físicas e químicas do solo.

The physical and chemical properties of coastal plain soils cultivated with sugarcane for a long period under different management systems may undergo changes. The objective of this study was to evaluate the effects of different sugarcane management systems on the chemical and physical properties of a dystrophic cohesive Yellow Latosol of coastal tablelands in the state of Alagoas. Three experimental plots were selected in sugarcane growing areas, representing the three management systems used for ethanol production, namely: a cultivated area under irrigation management, an area under fertirrigation with vinasse and an area with application of vinasse + filter cake. The management systems were compared with each other and with a control area of native forest. To assess physical and chemical properties, soil samples were randomly collected in the areas under different management systems at depths of 0-0.20; 0.20-0.40 and 0.40-0.60 m, from the sugarcane interrows. The results were subjected to analysis of variance and the means compared by the Tukey test at 5 %. Simple correlation analysis was performed between some variables. Results showed changes in the soil physical and chemical properties due to the different management systems. The soil consistency parameters tended to increase with the increase of total organic carbon, resulting from the application of sugar cane waste. In the management systems with application of sugar cane waste the deterioration in soil physical and chemical properties was reduced.