Navegando por Autor "Vergütz, Leonardus"

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Adsorption and desorption kinetics and phosphorus hysteresis in highly weathered soil by stirred flow chamber experiments
(Soil and Tillage Research, 2016-09) Vergütz, Leonardus; Melo, Leônidas Carrijo Azavedo; Guedes, Rafael Silva; Rodríguez-Vila, Alfonso; Covelo, Emma Fernández; Fernandes, Antonio Rodrigues
Soils with a high weathering degree present great difficulties for management of phosphorus (P) fertilization due to their high adsorption rates. The magnitude and velocity of the P retention phenomena in these soils is still poorly understood and has great importance to effective management of soil phosphorus. The objective of this study was to evaluate the adsorption and desorption kinetics and phosphorus adsorption irreversibility (hysteresis) in highly weathered soils. For this purpose, we selected four soils: Xanthic Ferralsol-1 (FR-1), Xanthic Ferralsol-2 (FR-2), Rhodic Ferralsol (FR-3) and Hortic Anthrosol “Terra Preta de Índio” (AT). Adsorption followed by desorption experiments in Stirred flow chamber were performed. From obtained data, parameters related to P kinetics were estimated, considering the presence of two types of adsorption and desorption sites (fast and slow), estimating also the hysteresis index. It was observed that FR-2 and FR-3 showed higher P adsorption and most of the adsorbed P was at first 100 min of evaluation. Furthermore, in FR-1, FR-2 and FR-3, approximately half of adsorption occurred by rapid sites (F which is the fraction of fast sites ranging from 0.45 to 0.55), while AT adsorption was lower (qmax = 48.95 mg kg^−1) and occurred slower (F = 0.33). In FR-2 and FR-3, between 71 and 72% of adsorbed P was not desorbed, while in AT, only 11% of P was irreversibly adsorbed. The P kinetics in highly weathered soils proved to be a process governed by the fast sites on adsorption and slow sites on desorption, resulting in high levels of hysteresis.
Agronomic efficiency of phosphate fertilizers produced by the re-use of a metallurgical acid residue
(Journal of Environmental Management, 2017-11-11) Barreto, Matheus Sampaio Carneiro; Mattiello, Edson Marcio; Santos, Wedisson Oliveira; Melo, Leônidas Carrijo Azevedo; Vergütz, Leonardus; Novais, Roberto Ferreira
The production of fertilizers with industrial wastes reduces the environmental impacts of waste disposal and improves environmental sustainability by generating added-value products. Our objective with this study was to evaluate the agronomic performance and potential soil/plant contamination with heavy metals of alternative phosphate (P) fertilizers, obtained from the acidulation of phosphate rocks (PR) by a metallurgical acidic waste. Seven P fertilizers were evaluated: three PR (Araxá, Patos, and Bayóvar), their respective acidulated products (PAPR), and triple superphosphate fertilizer (TSP). A greenhouse trial was carried out to test the agronomic performances of fertilizers in a sequentially cultivated maize-soybean-white oat. The reaction of PR with acid waste was effective to increase their solubility and improve plant yield and P uptake compared to their natural PR. There was a cumulative recovery by plants of 1.4 and 8.1% of added P via PR and PAPR, respectively. No increase in heavy metal (Cd, Pb, Cr, and Ni) availability in soil or accumulation in shoots was observed, indicating that the PAPR were environmentally safe. The usage of acid waste to produce P fertilizers therefore represents a strategic way to employ marginal products for the production of fertilizers.
Iron availability in tropical soils and iron uptake by plants
(Revista Brasileira de Ciência do Solo, 2015-11-12) Mielki, Guilherme Furlan; Novais, Roberto Ferreira; Ker, João Carlos; Vergütz, Leonardus; Castro, Gustavo Franco de
Given the increase in crop yields and the expansion of agriculture in low fertility soils, deficiency of micronutrients, such as iron, in plants grown in tropical soils has been observed. The aim of this study was to evaluate Fe availability and Fe uptake by corn (Zea mays L.) plants in 13 different soils, at two depths. Iron was extracted by Mehlich-1, Mehlich-3, and CaCl2 (Fe-CC) and was fractionated in forms related to low (Feo) and high (Fed) crystallinity pedogenic oxyhydroxides, and organic matter (Fep) using ammonium oxalate, dithionite-citrate, and sodium pyrophosphate, respectively. In order to relate Fe availability to soil properties and plant growth, an experiment was carried out in a semi-hydroponic system in which part of the roots developed in a nutrient solution (without Fe) and part in the soil (the only source of Fe). Forty-five days after seeding, we quantified shoot dry matter and leaf Fe concentration and content. Fed levels were high, from 5 to 132 g kg^-1, and Feo and Fe-CC levels were low, indicating the predominance of Fe as crystalline oxyhydroxides and a low content of Fe readily available to plants. The extraction solutions showed significant correlations with various soil properties, many common to both, indicating that they act similarly. The correlation between the Mehlich-1 and Mehlich-3 extraction solutions was highly significant. However, these two extraction methods were inefficient in predicting Fe availability to plants. There was a positive correlation between dry matter and Fe levels in plant shoots, even within the ranges considered adequate in the soil and in the plant. Dry matter production and leaf Fe concentration and content were positively correlated with Fep concentration, indicating that the Fe fraction related to soil organic matter most contributes to Fe availability to plants.
Layered double hydroxides: nanomaterials for applications in agriculture
(Revista Brasileira de Ciência do Solo, 2015-01-20) Benício, Luíz Paulo Figueredo; Silva, Rejane Alvarenga; Lopes, Júnia Aparecida; Eulálio, Denise; Santos, Rodrigo Morais Menezes dos; Aquino, Leonardo Angelo de; Vergütz, Leonardus; Novais, Roberto Ferreira; Costa, Liovando Marciano da; Pinto, Frederico Garcia; Tronto, Jairo
The current research aims to introduce Layered Double Hydroxides (LDH) as nanomaterials to be used in agriculture, with particular reference to its use as storage and slow release matrix of nutrients and agrochemicals for plant growing. Structural characteristics, main properties, synthesis methods and characterization of LDH were covered in this study. Moreover, some literature data have been reported to demonstrate their potential for storage and slow release of nitrate, phosphate, agrochemicals, besides as being used as adsorbent for the wastewater treatment. This research aims to expand, in near future, the investigation field on these materials, with application in agriculture, increasing the interface between chemistry and agronomy.
Lixiviação de cátions favorecida pela presença de ânions inorgânicos e ácidos orgânicos de baixa massa molecular em solos adubados com camas de aviário
(Revista Brasileira de Ciência do Solo, 2008-10) Gebrim, Fabrício de Oliveira; Silva, Ivo Ribeiro da; Novais, Roberto Ferreira; Vergütz, Leonardus; Procópio, Lorena Costa; Nunes, Tiago Novais; Jesus, Guilherme Luiz de
Com o incremento exponencial da avicultura no Brasil, a disponibilidade de dejetos de aves e de cama de aviário tem aumentado de maneira semelhante. A proibição de uso desses produtos na ração animal tem feito com que eles sejam direcionados para a produção agrícola como fertilizantes. Ainda há na literatura carência de informação sobre lixiviação de bases no perfil do solo em conseqüência do efeito de ânions inorgânicos acompanhantes, como cloreto, nitrato e sulfato, e do efeito complexante de ácidos orgânicos de baixa massa molecular. O objetivo deste trabalho foi estudar o efeito da aplicação de cama de aviário na lixiviação de Ca, Mg, K e Na em solos e sua associação com ânions inorgânicos e ácidos orgânicos de baixa molecular. Amostras de dois Latossolos Vermelho-Amarelos, um de textura média e outro de textura argilosa, foram colocadas em colunas de PVC constituídas de cinco anéis, cada um com 10 cm de altura e 5 cm de diâmetro, ligados entre si com fita adesiva. O solo colocado no anel superior recebeu, homogeneamente, cinco tipos de camas de aviário: casca de café, casca de arroz, sabugo de milho, capim-napier e maravalha, totalizando 160 t ha-1 de material seco, comparado à testemunha (sem a cama de aviário). O experimento constituiu um fatorial 5 x 2, com cinco camas e dois solos, dispostos em blocos casualizados com três repetições. As colunas foram submetidas a 10 percolações com água deionizada, duas vezes por semana, até atingirem o volume de 1.200 mm de chuvas. Nos 10 percolados, foram analisadas as concentrações de Ca, Mg, K e Na, dos ânions Cl-, NO3-e SO42- e de ácidos orgânicos de baixa massa molecular. Houve grande lixiviação de bases nas colunas, principalmente até a terceira percolação. Esse fato foi causado pela adição dessas bases, em doses elevadas, pelas camas de aviário e, aparentemente, também pelo efeito dos ânions acompanhantes Cl-, NO3-e SO42-no solo de textura média, Cl-e NO3-no solo de textura argilosa e, de maneira menos expressiva, pelo efeito acompanhante/complexante dos ácidos orgânicos de baixa massa molecular. No solo argiloso, a percolação de Ca esteve positivamente correlacionada com a concentração dos ácidos málico e oxálico. A concomitante elevada concentração de ácido acético nos percolados de solos tratados com todas as camas sugere que este pode estar favorecendo a lixiviação de bases no solo, provavelmente como ânion acompanhante.
Mobility of inorganic and organic phosphorus forms under different levels of phosphate and poultry litter fertilization in soils
(Revista Brasileira de Ciência do Solo, 2010-06) Gebrim, Fabrício de Oliveira; Novais, Roberto Ferreira; Silva, Ivo Ribeiro da; Schulthais, Fernanda; Vergütz, Leonardus; Procópio, Lorena Costa; Moreira, Frederico Fonseca; Jesus, Guilherme Luiz de
The eutrophication of aquifers is strongly linked to the mobility of P in soils. Although P mobility was considered irrelevant in a more distant past, more recent studies have shown that P, both in organic (Po) and inorganic forms (Pi), can be lost by leaching and eluviation through the soil profile, particularly in less weathered and/or sandier soils with low P adsorption capacity. The purpose of this study was to determine losses of P forms by leaching and eluviation from soil columns. Each column consisted of five PVC rings (diameter 5 cm, height 10 cm), filled with two soil types: a clayey Red-Yellow Latosol and a sandy loam Red-Yellow Latosol, which were exposed to water percolation. The soils were previously treated with four P rates (as KH2PO4 ) to reach 0, 12.5, 25.0 and 50 % of the maximum P adsorption capacity (MPAC). The P source was homogenized with the whole soil volume and incubated for 60 days. After this period the soils were placed in the columns; the soil of the top ring was mixed with five poultry litter rates of 0, 20, 40, 80, and 160 t ha-1 (dry weight basis). Treatments consisted of a 4 x 5 x 2 factorial scheme corresponding to four MPAC levels, five poultry litter rates, two soils, with three replications, arranged in a completely randomized block design. Deionized water was percolated through the columns 10 times in 35 days to simulate about 1,200 mm rainfall. In the leachate of each column the inorganic P (reactive P, Pi) and organic P forms (unreactive P, Po) were determined. At the end of the experiment, the columns were disassembled and P was extracted with the extractants Mehlich-1 (HCl 0.05 mol L-1 and H2SO4 0.0125 mol L-1) and Olsen (NaHCO3 0.5 mol L-1; pH 8.5) from the soil of each ring. The Pi and Po fractions were measured by the Olsen extractant. It was found that under higher poultry litter rates the losses of unreactive P (Po) were 6.4 times higher than of reactive P (Pi). Both the previous P fertilization and increasing poultry litter rates caused a vertical movement of P down the soil columns, as verified by P concentrations extracted by Mehlich-1 and NaHCO3 (Olsen). The environmental critical level (ECL), i.e., the P soil concentration above which P leaching increases exponentially, was 100 and 150 mg dm-3 by Mehlich-1 and 40 and 60 mg dm-3 by Olsen, for the sandy loam and clay soils, respectively. In highly weathered soils, where residual P is accumulated by successive crops, P leaching through the profile can be significant, particularly when poultry litter is applied as fertilizer.
Mudanças na matéria orgânica do solo causadas pelo tempo de adoção de um sistema agrossilvopastoril com eucalipto
(Universidade Federal de Viçosa, 2007-08-01) Vergütz, Leonardus; Silva, Ivo Ribeiro da; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4799432D0; Barros, Nairam Félix de; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4783694P8; Novais, Roberto Ferreira de; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4783732H4; http://lattes.cnpq.br/1282294478259902; Costa, Maurício Dutra; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4728228J5; Jucksch, Ivo; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4723123H4
A matéria orgânica do solo (MOS) é a principal propriedade indicadora da sustentabilidade de um sistema de cultivo, principalmente em solos sob condições tropicais. Além disso, ela é o maior compartimento de C orgânico no ciclo global deste elemento, sendo extremamente importante para a manutenção dos seus estoques no ambiente. Sistemas agrossilvopastoris (SASPs) representam práticas de manejo agroflorestal que têm como principal objetivo permitir maior diversidade e sustentabilidade do sistema. Sendo assim, espera-se que eles mantenham ou até mesmo elevem os estoques de carbono (C) do solo, quando comparados a uma área sob vegetação nativa, que neste caso é o Cerrado. Uma medida para se comparar sistemas produtivos é o índice de manejo do C (IMC) proposto por Blair et al. (1995), que compara sistemas produtivos com relação à área de referência. Para isso esse índice se baseia em medida não muito confiável de labilidade do C (C oxidável por permanganato de potássio). Os objetivos deste trabalho foram estudar o impacto dos SASPs de cultivo do eucalipto em diferentes frações de C e de N da MOS, como variável do tempo de implantação dos SASPs, tendo a área de vegetação nativa como referencial (Cerrado). Adicionalmente, propõe-se modificação no IMC proposto por Blair et al. (1995). Para isso, foi amostrada uma cronosseqüência composta por seis tempos de implantação dos SASPs, onde o tempo zero foi representado pela área de referência (Cerrado) e os demais com dois, três, quatro, sete e dez anos de implantação. Foram coletadas amostras de solo das camadas de 0-10, 10- 20, 20-40, 40-60 e 60-100 cm, na linha e na entre-linha de cultivo do eucalipto. Foi feita a caracterização física e química desses solos, assim como as determinações de C orgânico total (COT), N total (NT), C na matéria orgânica leve (MOL), N na MOL e C oxidável por permanganato de potássio, como uma medida de labilidade do C (CL). A partir desses dados foram calculados o IMCCL, proposto por Blair et al. (1995) e o IMCCMOL, que é o índice modificado. Os estoques de COT apresentaram perda inicial de C para as camadas superficiais de 0-10 e 10-20 cm na linha e 0-10 e 20-40 cm na entre-linha, com tendência de recuperação ao final do ciclo (dez anos). As camadas mais profundas (60-100 cm), tanto para a linha quanto para a entrelinha, apresentaram acúmulo inicial de C, sendo maior na linha de plantio do que na entre-linha. Porém, esse acúmulo não foi sustentável e as perdas de C nessa camada foram maiores quanto maior for o ciclo. Para o estoque total de C na camada de 0-100 cm, o manejo da linha de plantio manteve os estoques de COS, enquanto na entre-linha há tendência de perda inicial de C num primeiro momento, sem que esses níveis retornem aos originais (Cerrado) no final do décimo e último ano analisado. As principais mudanças nos estoques de NT ocorreram nas camadas mais profundas (20-40 e 60-100 cm). Nestas camadas, após perda acentuada de N, houve tendência de acúmulo desse elemento ao longo do tempo de implantação dos SASPs. Porém esse acúmulo não foi sustentável e ao final do período estudado esses valores eram menores que os originais (Cerrado). Essa mesma tendência foi observada para o estoque de N na camada de 0-100 cm, sendo que para a entre-linha de plantio essas alterações foram mais acentuadas. A fração da MOL foi a que apresentou as maiores alterações, confirmando sua sensibilidade a alterações de manejo. As perdas de C e N da MOL também foram maiores para a entre-linha de plantio de eucalipto do que para a linha. O C lábil (CL), assim como o índice calculado a partir dele (IMCCL) não possibilitaram ajustes dos seus resultados como variável do tempo de implantação dos SASPs. Entretanto o IMC modificado, calculado a partir do C da MOL (IMCCMOL), apresentou bons ajustes para todas as camadas estudadas. Além disso, apresentou correlação mais elevada com o COT, mostrando-se mais indicado para a comparação dos sistemas de manejo estudados. A partir dos resultados desse estudo pode-se perceber a importância de se estudar camadas mais profundas de solo, já que essas camadas podem apresentar perdas de C significativas e de difícil recuperação. A implantação dos SASPs acarretou diminuição dos estoques de COT das camadas superficiais, sendo que o tempo necessário para a recuperação dos estoques originais está além do período de tempo máximo estudado. A fração mais sensível ao manejo adotado foi a MOL livre.
Nitrogen release from urea with different coatings
(Journal of the Science of Food and Agriculture, 2017-09-01) Campos, Odirley R; Mattiello, Edson Marcio; Cantarutti, Reinaldo Bertola; Vergütz, Leonardus
Coatings or urease inhibitors are designed to reduce losses of ammonia [NH 3(g) ] from urea fertilizers. However, nitrogen (N) release and its effects on soil solution have not previously been evaluated under standardized conditions in soils. In this study, the urea fertilizers were incubated in chambers filled with sandy loam soil, adapted for the collection of NH 3(g) and soil solution by centrifugation. In the fast-release N fertilizers, around 93% and 100% of urea-N applied was recovered within the first hours of incubation. In contrast, in the slow-release N fertilizers, less than 40% of urea-N applied, was recovered at 19 days of incubation. The maximum N release from the fertilizers followed the order: UP1 (106%) ≈ UNBPT (102%) ≈ urea (93%) > USP2 (57%) ≈ USP3 (57%) > USP4 (31%) ≈ USP5 (18%). NH 3(g) volatilization accounted for only 3% of the applied N in the slow-release fertilizers, which corresponded to about 88% less than the NH 3(g) loss from prilled urea. This study demonstrated distinct N release patterns, which changed the N dynamics in the soil. Some coatings effectively delayed urea release from granules and reduced NH 3(g) gas losses, while other were not efficient.
Soil organic matter formation as affected by eucalypt litter biochemistry — Evidence from an incubation study
(Geoderma, 2018-02-15) Almeida, Luís F.J.; Hurtarte, Luis C. C.; Souza, Ivan F.; Soares, Emanuelle M. B.; Vergütz, Leonardus; Silva, Ivo R.
Linking plant litter biochemistry, its decomposition and soil organic matter (SOM) formation is not straightforward. In this research, we evaluated the decomposition of four biochemical fractions operationally defined as i) hot-water extractable (HWE), ii) total solvent (acetone) extractable (TSE), iii) acid-base (HNO3-KOH) unhydrolyzable cellulosic fraction (CF), and iv) acid (H2SO4) unhydrolyzable (AUR) and the transfer of C from these fractions to SOM. Each biochemical fraction was Soxhlet-extracted from isotopically labeled (13C) leaves, twigs, bark and roots of eucalypt plants (120 days old). The molecular composition of each fraction was inferred from thermochemolysis with tetramethylammonium hydroxide (TMAH), followed by gas chromatography coupled to mass spectrometry (GC-MS). For the incubation, we collected soil samples from the topsoil (0–20 cm) of a sandy-clay loam, kaolinitic Haplic Ferralsol. Four plant organs and four biochemical fractions were arranged into a (4 × 4) + 1 factorial scheme, including one control treatment (soil only). The samples were incubated at 80% of their water-holding capacity and kept under controlled temperature (25 °C). The decomposition of the biochemical fractions was monitored by determining the CO2 concentration into the headspace of the vials at 1, 2, 3, 4, 7, 13, 21, 28, 38, 46, 70, 80, 92, 112, 148, 178, and 200 days after the incubation had started. After the incubation, soil samples were submitted to density followed by particle-size fractionation. HWE and CF decomposed at faster rates than TSE and AUR throughout the incubation. The soil fraction < 53 μm retained a significantly higher proportion of the initial C input of HWE (32%) and AUR (31%) than TSE (19%) or CF (15%). Light fraction of organic matter (LFOM) with density < 1.8 g cm− 3, retained a significant proportion of AUR (37%) and TSE (32%) while CF was mostly lost as CO2 (79%). Selective preservation of organic materials (e.g., long-chain lipids) within the AUR and TSE fractions appears to be a significant pathway for the formation of SOM. SOM formation through a microbial-driven pathway cannot be ruled out for any biochemical fraction evaluated, but it seems more relevant for HWE and CF. In short-term, substrate biochemistry exerts a strong influence on the conversion of eucalypt litter fractions into either CO2 or SOM. Despite inherent challenges upfront, considering such dynamics at the ecosystem level will help to improve our current understanding on C storage and CO2 emissions from soils in long-term scales.
Soluble phosphate fertilizer production using acid effluent from metallurgical industry
(Journal of Environmental Management, 2015-10-24) Mattiello, Edson M.; Resende Filho, Itamar D.P.; Barreto, Matheus S.; Soares, Aline R.; Silva, Ivo R. da; Vergütz, Leonardus; Melo, Leônidas C.A.; Soares, Emanuelle M.B.
Preventive and effective waste management requires cleaner production strategies and technologies for recycling and reuse. Metallurgical industries produce a great amount of acid effluent that must be discarded in a responsible manner, protecting the environment. The focus of this study was to examine the use of this effluent to increase reactivity of some phosphate rocks, thus enabling soluble phosphate fertilizer production. The effluent was diluted in deionized water with the following concentrations 0; 12.5; 25; 50; 75% (v v−1), which were added to four natural phosphate rocks: Araxá, Patos, Bayovar and Catalão and then left to react for 1 h and 24 h. There was an increase in water (PW), neutral ammonium citrate (PNAC) and citric acid (PCA) soluble phosphorus fractions. Such increases were dependent of rock type while the reaction time had no significant effect (p < 0.05) on the chemical and mineralogical phosphate characteristics. Phosphate fertilizers with low toxic metal concentrations and a high level of micronutrients were produced compared to the original natural rocks. The minimum amount of total P2O5, PNAC and PW, required for national legislation for phosphate partially acidulated fertilizer, were met when using Catalão and the effluent at the concentration of 55% (v v−1). Fertilizer similar to partially acidulated phosphate was obtained when Bayovar with effluent at 37.5% (v v−1) was used. Even though fertilizers obtained from Araxá and Patos did not contain the minimum levels of total P2O5 required by legislation, they can be used as a nutrient source and for acid effluent recycling and reuse.
Studying the soil compartment of the global carbon cycle
(Universidade Federal de Viçosa, 2011-08-12) Vergütz, Leonardus; Silva, Ivo Ribeiro da; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4799432D0; Novais, Roberto Ferreira de; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4783732H4; http://lattes.cnpq.br/1282294478259902; Silva, Luis Henrique Mendes da; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4728684Y0; Barros, Nairam Félix de; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4783694P8; Cerri, Carlos Eduardo Pellegrino; http://lattes.cnpq.br/1117896124904968
Mudanças climáticas globais causadas pelo aumento da concentração de CO2 atmosférico tem estimulado uma melhor compreensão do ciclo global do C. Os solos representam um dos maiores compartimentos de C na Terra, contendo mais C que na biomassa vegetal e na atmosfera. Além disso, o C orgânico do solo (COS) também é um compartimento bastante dinâmico. Portanto, compreender o papel do COS para o ciclo global do C e como ele é afetado por diferentes condições edafoclimáticas se faz extremamente importante, especialmente para países como o Brasil, onde a maioria das emissões de gases causadores do efeito estufa são provenientes de mudanças de uso do solo e atividades agropecuárias. O objetivo geral deste trabalho foi estudar quantitativa e qualitativamente o COS, visando a melhor compreensão dos fatores que levam à sua estabilização. Para isso foram investigados três estágios que afetam a ciclagem do C nos solos, sendo eles: as concentrações e eficiências de reabsorção global do C e de nutrientes em plantas terrestres (Chapter 1), o estudo da estrutura e do comportamento dos ácidos húmicos pela técnica de titulação calorimétrica isotérmica (microcalorimetria) (Chapter 2) e a influência das argilas e de condições climáticas nos estoques de COS no Brasil (Chapter 3). Do primeiro estudo (Chapter 1) resultaram novas estimativas globais de concentrações e de eficiências de reabsorção de nutrientes. Neste trabalho foi incorporada a perda de massa que ocorre nas folhas durante a senescência, fato esse até então desconsiderado em estimativas globais e responsável pela subestimação da real reabsorção de C e nutrientes. Em geral, as folhas verdes perdem 24% de sua massa seca durante o processo de senescência. Levando essa perda em consideração as reabsorções de C, N, P, K, Ca e Mg foram de 23,2; 62,1; 64,9; 70,1; 10,9 e 28,6%, respectivamente. Esses resultados devem levar à melhoria de modelos que explicitamente representam a ciclagem de C e nutrientes, além de permitir que os pesquisadores que trabalham com modelagem associem os ciclos de outros nutrientes ao nível de grupos de plantas e ecossistemas. No segundo trabalho (Chapter 2) empregou-se uma técnica relativamente nova para o estudo da estrutura e comportamento dos ácidos húmicos. A partir desta análise foi possível demonstrar que existe uma estrutura básica (monômeros) dos ácidos húmicos e que, ao contrário do que o usual modelo supramolecular prega, essa estrutura básica não é formada por unidades simples fracamente unidas passíveis de sofrer divisões ou mudanças conformacionais durante interação. Adicionalmente, esses monômeros se mostraram similares no ambiente, não importando sua fonte, composição ou processo de estabilização. Finalmente, no último trabalho (Chapter 3) foram analizados os estoques de COS em áreas de vegetação nativa, eucalipto e pastagem de três principais biomas brasileiros. Em geral, os estoques de COS na camada de 0-100 cm para as áreas de vegetação nativa, eucalipto e pastagem de todos os biomas em conjunto foram 137,3; 127,9 e 127,1 t ha-1, respectivamente. Este tipo de trabalho em escala regional é necessário para melhorar as estimativas globais de COS. Neste trabalho foi mostrado que partículas de argila de solos argilosos, especialmente nas camadas mais profundas, ainda não se encontram saturadas com COS, indicando que existe a possibilidade de aumento do sequestro de C em solos brasileiros. Adicionalmente, o aumento da mineralização do COS após mudança de uso do solo se correlacionou positivamente com o aumento da temperatura, indicando que a oxidação do COS será ainda maior em um cenário de mudanças climáticas globais. Em geral, este trabalho contribui de diferentes maneiras para a melhor compreensão do compartimento solo no ciclo global do C.
Thermodynamic characterization of humic acid-surfactant interaction: New insights into the characteristics and structure of humic acids
(Revista Brasileira de Ciência do Solo, 2015-07-03) Vergütz, Leonardus; Silva, Luis Henrique Mendes da; Novais, Roberto Ferreira; Silva, Maria do Carmo Hespanhol da; Mageste, Aparecida Barbosa; Silva, Ivo Ribeiro
Humic acids (HA) are a component of humic substances (HS), which are found in nearly all soils, sediments, and waters. They play a key role in many, if not most, chemical and physical properties in their environment. Despite the importance of HA, their high complexity makes them a poorly understood system. Therefore, understanding the physicochemical properties and interactions of HA is crucial for determining their fundamental role and obtaining structural details. Cationic surfactants are known to interact electrostatically and hydrophobically with HA. Because they are a very well-known and characterized system, they offer a good choice as molecular probes for studying HA. The objective of this study was to evaluate the interaction between cationic surfactants and HA through isothermal titration calorimetry in a thermodynamic manner, aiming to obtain information about the basic structure of HA, the nature of this interaction, and if HA from different origins show different basic structures. Contrary to what the supramolecular model asserts, HA structure is not loosely held, though it may separate depending on the conditions the HA are subjected to in their milieu. It did not show any division or conformational change when interacting with surfactants. The basic structure of the HA remains virtually the same regardless of the different sources and compositions of these HA.
Value of copper, zinc, and oxidized charcoal for increasing forage efficiency of urea N uptake
(Agriculture, Ecosystems & Environment, 2016-05-15) Guimarãesv, Gelton G.F.; Mulvane, Richard L.; Cantarutti, Reinaldo B.; Teixeira, Breno C.; Vergütz, Leonardus
Volatilization losses reduce the efficiency of surface-applied urea for crop N uptake, and can be controlled using urease inhibitors to retard hydrolysis or by the presence of other amendments that enhance retention of NH4+ formed by urea hydrolysis. A greenhouse study was conducted to evaluate the effectiveness of oxidized charcoal (OCh; 150 g kg−1 fertilizer) applied with or without Cu and/or Zn (∼0.5–2 g kg−1 fertilizer), and of Cu and/or Zn applied without OCh, for increasing uptake of urea 15N by a common tropical pasture grass, capim-Mombaça (Panicum maximum Jacq. Cv. Mombaça), grown on a coarse-textured Oxisol. Cuttings were collected 5, 14, 28, 42, and 56 days after surface placement of amended or unamended urea pellets to estimate dry matter production, total N uptake, and 15N recovery. Soil sampling was carried out in conjunction with the first and fourth cuts to evaluate exchangeable NH4+ and NO3− concentrations. At the concentrations studied, OCh was more effective than Cu and/or Zn for prolonging NH4+-N availability in urea-treated soil; however, OCh alone or in combination with Zn and Cu had no effect on biomass production or N recovery and can safely be eliminated as a useful option for pasture improvement. The most promising amendment was Zn, which significantly increased total N uptake and the efficiency of urea N fertilization. The use of Zn in conjunction with urea has practical potential to improve forage production on tropical soils.