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Foliar analysis is very important for the nutritional management of crops and as a supplemental parameter for soil fertilizer recommendation. The elemental composition of plants is traditionally obtained by laboratory-based methods after acid digestion of ground and sieved leaf samples. This analysis is time-consuming and generates toxic waste. By comparison, portable X-ray fluorescence (pXRF) spectrometry is a promising technology for rapid characterization of plants, eliminating such constraints. This worked aimed to assess the pXRF performance for elemental quantification of leaf samples from important Brazilian crops. For that, 614 samples from 28 plant species were collected across different regions of Brazil. Ground and sieved samples were analyzed after acid digestion (AD), followed by quantification via inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the concentration of macronutrients (P, K, Ca, Mg, and S) and micronutrients (Fe, Zn, Mn, and Cu). The same plant nutrients were directly analyzed on ground leaf samples via pXRF. Four certified reference materials (CRMs) for plants were used for quality assurance control. Except for Mg, a very strong correlation was observed between pXRF and AD for all plant-nutrients and crops. The relationship between methods was nutrient- and crop-dependent. In particular, eucalyptus displayed optimal correlations for all elements, except for Mg. Opposite to eucalyptus, sugarcane showed the worst correlations for all the evaluated elements, except for S, which had a very strong correlation coefficient. Results demonstrate that for many crops, pXRF can reasonably quantify the concentration of macro- and micronutrients on ground and sieved leaf samples. Undoubtedly, this will contribute to enhance crop management strategies concomitant with increasing food quality and food security.

The color of plant leaves can be assessed qualitatively by color charts or after processing of digital images. This pilot study employed a novel pocket-sized sensor to obtain the color of plant leaves. In order to assess its performance, a color-dependent parameter (SPAD index) was used as the dependent variable, since there is a strong correlation between SPAD index and greenness of plant leaves. A total of 1,872 fresh and intact leaves from 13 crops were analyzed using a SPAD-502 meter and scanned using the Nix™ Pro color sensor. The color was assessed via RGB and CIELab systems. The full dataset was divided into calibration (70% of data) and validation (30% of data). For each crop and color pattern, multiple linear regression (MLR) analysis and multivariate modeling [least absolute shrinkage and selection operator (LASSO), and elastic net (ENET) regression] were employed and compared. The obtained MLR equations and multivariate models were then tested using the validation dataset based on r, R

Portable X-ray fluorescence spectrometry (pXRF) is a well-known and accepted method for earth-materials analysis. It is also promising for analysis of plant tissues. However, some factors must be assessed in order to obtain a protocol for plants mainly for in-field measurements of intact and fresh leaves. This work defines an experimental approach for two distinct plant leaves (Spinach and Post Oak) considering water content (94% and 52% w/w, respectively) and anatomy. Using a commercial pXRF system equipped with a Rh X-ray tube, some conditions for in-situ and ex-situ analysis were assessed to obtain the concentrations of macro (P, K, Ca, Mg, and S) and micronutrients (Fe, Zn, Cu, and Mn). For in-situ applications, the penetration of X-rays through Pinus wood was evaluated. In this case, the goal was to propose a simple way to scan fresh and intact plant leaves in the field, using the wood as a background stage. Thus, the minimum wood thickness to avoid any influence of soil surface was investigated. Afterward, the following factors were assessed: i) the effect of water content; ii) the number of overlapped and pressed leaves on pXRF results; iii) the effect of adaxial or abaxial leaf surface. For ex-situ applications, the thickness of oven-dried and ground ( 1 cm is desirable. pXRF analysis of fresh and intact plant leaves in the field is possible in a qualitative manner.

Tropical forests are experiencing unprecedented high‐temperature conditions due to climate change that could limit their photosynthetic functions. We studied the high‐temperature sensitivity of photosynthesis in a rainforest site in southern Amazonia, where some of the highest temperatures and most rapid warming in the Tropics have been recorded. The quantum yield (F v /F m ) of photosystem II was measured in seven dominant tree species using leaf discs exposed to varying levels of heat stress. T 50 was calculated as the temperature at which F v /F m was half the maximum value. T 5 is defined as the breakpoint temperature, at which F v /F m decline was initiated. Leaf thermotolerance in the rapidly warming southern Amazonia was the highest recorded for forest tree species globally. T 50 and T 5 varied between species, with one mid‐storey species, Amaioua guianensis , exhibiting particularly high T 50 and T 5 values. While the T 50 values of the species sampled were several degrees above the maximum air temperatures experienced in southern Amazonia, the T 5 values of several species are now exceeded under present‐day maximum air temperatures.

The portable X-ray fluorescence spectrometry (pXRF) can be considered one of the most novelty for soil characterization. In tropical regions (e.g., Brazil), some studies have showed a consistent correlation between pXRF and laboratory-based methods. However, there is no any work dedicated exclusively for hydromorphic soils (gley or organic-rich soils). This study aims to assess the total elemental composition reported by portable X-ray fluorescence (pXRF) spectrometry and to compare it to laboratory-based wet digestion method and wavelength dispersive X-ray (WDXRF) spectrometry. A collection of 144 hydromorphic soil samples from six wetlands located in the Cerrado biome (Savannah), Brazil, was used for this investigation. Soil samples were disaggregated and passed through a 150- μ m nylon mesh and subjected to wet digestion (US EPA 3051a) followed by elemental determination via atomic absorption spectrometry (AAS). Subsamples of each ground soil were also directly analyzed via both pXRF and WDXRF. Linear regressions were performed to establish the relationship between methods. Several elements (Pb, Cu, Zn, Cr, Fe, Ti, Sr, and Y) determined via pXRF were successfully correlated to other methods (USEPA 3051a and WDXRF). Specially for Pb, a very strong correlation (R > 0.90) was observed between pXRF, WDXRF and US EPA 3051a methods. The pXRF revealed also to be a useful tool for characterization of hydromorphic soils and future studies can be conducted directly in the field to assess the elemental composition of Cerrado wetland soils.

Considering the importance of soil water retention for agricultural and environmental purposes, the objective of this study was to assess three pedotransfer functions (PTFs) used to estimate the soil moisture at field capacity (FC) based on soil attributes easily determined. A collection of 17 soils from the Cerrado and Pantanal biomes, including surface and subsurface horizons, was used. PTF-1 considers clay, organic matter, coarse sand, and microporosity; PTF-2 clay, total sand, and organic matter; and PTF-3 only microporosity. The estimated FC values were correlated to soil moisture values measured at different soil water potentials (0, 6, 10, 33, 100, 300, and 1500 kPa) to verify which potential corresponded to estimated FC. The data were subjected to regression analysis and Mann-Whitney rank-sum test to compare predicted and measured values and to principal component analysis (PCA). The analysis of the full dataset indicated that there was a strong correlation (R 0.84-0.91; R2 0.71-0.82; RMSE 0.07-0.09) between estimated FC and soil water retention measured at potentials of 10 kPa and 33 kPa. FC estimated by PTF-3 correlated better with water holding capacity at 6 kPa. When the PTFs were reapplied to homogeneous soil groups (identified by PCA analysis), the correlation between predicted and measured FC was decreased. Considerando a importância da retenção de água no solo para fins agronômicos e ambientais, objetivou-se com este trabalho avaliar três funções de pedotransferência (FP) para estimativa da capacidade de campo(CC) com base em atributos de solo facilmente determinados. Uma coleção de 17 solos dos biomas Cerrado e Pantanal, incluindo amostras superficiais e subsuperficiais, foram utilizadas. FP 1 considera o conteúdo de argila, matéria orgânica, areia grossa e microporosidade. FP 2 considera argila, areia total e matéria orgânica. A FP 3 leva em consideração apenas microporosidade. Os valores estimados de CC foram correlacionados aos valores de umidade obtidos em diferentes potenciais (0, 6, 10, 33, 100, 300, and 1500 kPa) com o intuito de verificar qual potencial corresponde à CC estimada. Os dados foram submetidos à análise de regressão, ao teste Mann-Whitney rank-sum para comparar valores medidos e estimados e realizada análise de componentes principais (PCA). Considerando todo o conjunto de dados, foi obtida umaforte correlação (R 0.84–0.91; R2 0.71–0.82; RMSE 0.07–0.09) entre CC estimada e a umidade do solo obtida nos potenciais de 10 kPa e 33 kPa. A CC estimada pela FP 3 correlacionou melhor com a retenção de água no potencial de 6 kPa. Quando as FP’s foram reaplicadas em grupos de solos homogêneos (identificados pela PCA), a correlação entre valores estimados e medidos diminuiu.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais O fósforo (P) e o cálcio (Ca) são macronutrientes de plantas e contribuem com importantes funções metabólicas. Já o silício (Si), embora não o seja assim considerado, é classificado como elemento benéfico em reconhecimento ao seu efeito condicionador do meio. Diferentemente dos demais, o flúor (F) é essencial somente para humanos, mas sua presença no solo até determinadas concentrações pode contribuir na neutralização do alumínio e na dessorção do fósforo previamente adsorvido. No processo de fabricação de ácido fosfórico, a indústria de fertilizantes emana grandes quantidades de gases contendo Si e F, os quais devem ser capturados e neutralizados para evitar a poluição atmosférica. A reação de captura e neutralização dos gases possibilita a obtenção de um subproduto contendo Ca, Si e F que apresenta potencial para reaproveitamento com foco no uso agrícola. O objetivo deste estudo é avaliar o potencial de uso deste subproduto como condicionador de solo. Para isso, foram realizados experimentos de adsorção, de dessorção e de deslocamento envolvendo Si, P e F em horizontes de um Latossolo Amarelo Ácrico plintossólico, bem como a avaliação de dois cultivos da cultura da soja neste mesmo solo após a aplicação do subproduto contendo Si, Ca e F. Inicialmente, foi realizada a caracterização do solo por meio das análises de fertilidade, balanço de cargas, textura, área superficial específica, porosidade, ataque sulfúrico, cristalinidade dos sesquióxidos de ferro e alumínio e difratometria de raios-X e do subproduto pela composição química e poder relativo de neutralização. A capacidade sortiva do P, Si e F foi realizada em solução de NaCl 30 mmol L-1, com o pH ajustado para 5,5, sendo utilizadas as seguintes concentrações de cada um dos elementos: 0; 0,05; 0,10; 0,20; 0,40; 0,80 e 1,6 mmol L-1. A dessorção foi realizada pela adição de NaCl 30 mmol L-1 a pH 5,5 sem adição dos respectivos elementos. No deslocamento, as amostras foram previamente adsorvidas com doses crescentes de P (0; 0,003; 0,008; 0,016; 0,032; 0,113; 0,226; 0,807; 2,260 e 4,520 mmol L-1) e na solução de dessorção foram adicionados 0,6 mmol L-1 de Si e F mono e multielementar para promoverem o deslocamento do P previamente adsorvidos. Os modelos Langmuir e Freundlich foram utilizados para obtenção dos parâmetros sortivos do solo e a dessorção ajustada às curvas de regressão. Para a avaliação agronômica, foram realizados dois cultivos de soja em uma área com diferentes tipos de manejo utilizando-se o subproduto nas doses de 500 e 1000 kg ha-1 e uma fonte comercial de Si, nas doses de 400 e 800 kg ha-1. O delineamento experimental foi em blocos, contendo um tratamento controle e as respectivas doses de cada um dos produtos considerando o mesmo aporte de Si. As variáveis respostas utilizadas consistiram de avaliações realizadas no solo e na cultura. Os modelos de Langmuir e Freundlich foram adequados para explicar o comportamento sortivo dos elementos e possibilitaram a obtenção dos parâmetros que indicaram maior capacidade de adsorção de F, seguido de P e Si para o horizonte superficial (Ap) e P, F e Si para os horizontes subsuperficiais (Bw e Bf). Não foi constatado deslocamento do P por Si e F, sendo a matéria orgânica e os teores dos óxidos de ferro e alumínio os parâmetros que mais influenciaram na adsorção e dessorção desses elementos no solo. Os parâmetros avaliados no solo e na cultura não possibilitaram comprovar o efeito do subproduto nos dois cultivos de soja. No entanto deve-se avaliar o possível efeito residual do subproduto nos anos posteriores. Phosphorus (P) and calcium (Ca) are macronutrients of plants and contribute to important metabolic functions. However, silicon (Si), although not considered as such, is classified as a beneficial element in recognition of its environmental conditioning effect. Different from the others fluorine (F), it is essential only for humans, but its presence in the soil up to certain concentrations may contribute to the neutralization of aluminum and desorption of previously adsorbed phosphorus. In the phosphoric acid manufacturing process, the fertilizer industry emits large quantities of gases containing Si and F, which must be captured and neutralized to avoid atmospheric pollution. The gas capture and neutralization reaction makes it possible to obtain a by-product containing Ca, Si and F that has potential for reutilization with a focus on agricultural use. The objective of this study is to evaluate the potential use of this byproduct as soil conditioner. For this, adsorption, desorption and displacement experiments involving Si, P and F were carried out in horizons of a Plintossolic Yellow Latosol, as well as the evaluation of two soybean crops in the same soil after application of the by-product containing Si , Ca and F. The soil characterization was performed through fertility, load balance, texture, specific surface area, porosity, sulfuric attack, crystallinity of iron and aluminum sesquioxides and X-ray diffraction and by-product by chemical composition and relative neutralization power. The sorptive capacity of P, Si and F was performed in NaCl solution 30 mmol L-1, with the pH adjusted to 5.5, using the following concentrations of each of the elements: 0; 0.05; 0.10; 0.20; 0.40; 0.80 and 1.6 mmol L-1. Desorption was performed by the addition of 30 mmol L-1 NaCl at pH 5.5 without addition of the respective elements. In the displacement, the samples were previously adsorbed with increasing doses of P (0, 0.003, 0.008, 0.016, 0.032, 0.113, 0.226, 0.807, 2.266 and 4.520 mmol L-1) and in the desorption solution 0.6 mmol L-1 of Si and F mono and multielement were added to promote the displacement of P previously adsorbed. The Langmuir and Freundlich models were used to obtain the soil sorption parameters and the desorption adjusted to the regression curves. For the agronomic evaluation, two soybean cultivations were carried out in an area with different types of management using the by-product at 500 and 1000 kg ha-1 and a commercial source of Si at 400 and 800 kg ha- 1. The experimental design was in blocks, containing a control treatment and the respective doses of each of the products considering the same contribution of Si. The variables responses consisted of evaluations carried out in the soil and in the culture. The Langmuir and Freundlich models were adequate to explain the sorption behavior of the elements and allowed to obtain the parameters that indicated higher adsorption capacity of F, followed by P and Si for the surface horizon (Ap) and P, F and Si for the subsurface horizons (Bw and Bf). It was not observed the P displacement by Si and F, being the organic matter and the iron and aluminum oxide content the parameters that most influenced the adsorption and desorption of these elements in the soil. The parameters evaluated in the soil and in the crop did not make it possible to prove the effect of the byproduct in the two soybean crops. However, the possible residual effect of the by-product in subsequent years should be assessed. Dissertação (Mestrado)

Agregação e o conteúdo de carbono orgânico são importantes indicadores de qualidade do solo e estão intimamente relacionados com o fluxo de CO2 na interface solo-atmosfera. Objetivou-se com este trabalho avaliar: i) a agregação do solo; ii) a distribuição do carbono orgânico total e substâncias húmicas em diferentes classes de tamanho de agregados; e iii) a emissão de CO2 em áreas sob diferentes usos na região do Triângulo Mineiro. Foram selecionadas quatro áreas na região de Uberlândia, MG: (1) área de capim Mombaça; (2) área de capim Tanzânia; (3) área de cana-de-açúcar; e (4) área de mata nativa (controle). Em cada área foram coletadas amostras de solo da camada 0-10 cm, as quais foram secas ao ar e peneiradas para obtenção de agregados de tamanho 4-2 mm. As amostras foram submetidas ao peneiramento úmido para avaliação da estabilidade e para obtenção de agregados de diferentes classes de tamanho: 4-2 mm; 1-2 mm; 1-0,5 mm; e 0,5-0,25 mm. Nesses materiais determinou-se o carbono orgânico total, substâncias húmicas (ácidos fúlvicos, ácidos húmicos e humina) e textura. A emissão de CO2 foi avaliada em condições de campo e laboratório, ambas pelo método da captura em solução NaOH. As áreas de mata e capim Tanzânia (mais argilosa) apresentaram maior agregação do solo. O manejo do solo adotado na área de cana contribuiu significativamente para destruição dos agregados do solo. Para uma mesma condição, agregados de maior tamanho apresentaram maior conteúdo de carbono orgânico e de substâncias húmicas. O conteúdo de carbono orgânico e textura do solo parecem ter sido determinantes na emissão de CO2 das áreas estudadas. Soil aggregation and carbon distribution are important indicators of soil quality. Moreover, these attributes are closely related to CO2 fluxes in the soil-atmosphere interface. We sought to evaluate soil aggregation, organic carbon distribution and CO2 evolution in different land uses of Minas Gerais Triangle. Four different land uses were selected: (1) Panicum maximum, (2) Panicum maximum Jacqvr. (Tanzânia), (3) sugarcane, and (4) native Cerrado (control). In each land-use type, soil samples from a 0-10 cm layer were collected. The samples were air-dried and sieved in order to obtain aggregates sized 4-2 mm. The samples were submitted to wet-sieving to evaluate stability and also to obtain aggregates of different sizes: 4-2 mm; 2-1 mm; 1-0.5 mm; and 0.5-0.25 mm. Total organic carbon, humic substances and texture were determined for each aggregate size fraction. The CO2 emission was measured in field and lab conditions, both by the capture in NaOH solution method. The native Cerrado and Panicum maximum Jacqvr. (Tanzânia) areas (mostly clay) showed the highest soil aggregation. The conventional soil tillage adopted in sugarcane areas contributed significantly to aggregate disruption. In all of the areas, the largest aggregates had higher organic carbon and humic substances. Organic carbon content and soil texture seem to be closely associated with CO2 emissions in the areas studied.