Abstract Background The use of carbonaceous materials for environmental remediation is attractive due to low expense and high sorption capacity. However, their efficiency in contaminant removal is affected by substrate composition and sorption mechanism. Objective This study investigated atrazine sorption and desorption in three carbon-rich substrates. Data were evaluated considering isotherm models and sorbent chemical composition. Methods Sorption was performed by the batch equilibrium method with three substrates obtained from pig slurry composting with different proportions (w/w) of charcoal fines (CF): CF0, CF9 (9% CF), and CF18 (18% CF). The substrates were characterized by elemental analysis, 13C NMR CP/MAS spectroscopy. The Freundlich and Dubinin-Radushkevich (DRK) models better fitted the sorption data (0.96>R2>0.81), followed by Temkin (0.95>R2>0.76). Charcoal addition to composting substrates increased carbon content and the aromaticity in the order CF0<CF9< CF18. However, the sorption affinity decreased in the opposite order as indicated by the Kf values: 675, 335 and 290 L kg-1, respectively. Values of the E parameter (DRK) varied from 8.05 to 8.29 kJ mol-1, suggesting a predominant physical sorption mechanism, whereas the Bt coefficient (Temkin) indicated an endothermic process. Desorption was only observed at higher atrazine concentrations (>10 mg L-1), and the desorption Kf values were greater than the respective sorption values. Conclusions Atrazine sorption in the tested C-rich substrates is not governed by the carbon content or aromaticity. The low sorption reversibility implies a low atrazine mobility from the tested substrates and suggests their potential for herbicide removal in the environment.

RESUMO As substâncias húmicas (SH) têm se mostrado eficazes em incrementar a produtividade de hortaliças. O objetivo deste trabalho foi avaliar o efeito de bioestimulantes comerciais ricos em ácidos húmicos (AH) e fúlvicos (AF), obtidos de leonardita, na eficiência agronômica da cultura de alface e teor de nutrientes na planta. Foi realizado um experimento em casa-de-vegetação em vasos de 2,5 L com amostras de Argissolo, aos quais foram aplicados bioestimulantes comerciais ricos em AH e em AF, isoladamente e em combinação com o fertilizante mineral NPK. A aplicação dos bioestimulantes à base de SH associada à fertilização mineral na cultura da alface apresentou os maiores valores das variáveis estudadas: altura e diâmetro de plantas, número de folhas por planta e comprimento de raiz. A combinação do bioestimulante rico em AF e o fertilizante mineral aumentou a produção da alface em relação à aplicação isolada do fertilizante inorgânico. A aplicação combinada dos bioestimulantes ricos em AF e em AH com o fertilizante NPK influenciou a absorção de K e Fe pelas plantas, e seu acúmulo na parte aérea. Nossos resultados sugerem que as SH potencializam o efeito nutricional do fertilizante mineral, quando aplicadas conjuntamente.

ABSTRACT Humic substances (HS) have proved to be effective in improving the productivity of vegetable crops. We examined the effect of commercial biostimulants rich in humic (HA) and fulvic acids (FA) obtained from leonardite on agronomic efficiency and nutrient content in the leaves of lettuce (Lactuca sativa). A greenhouse experiment was carried out employing 2.5-L pots containing Ultisol samples that were supplied with commercial biostimulants rich in HA and FA, alone and in combination with NPK mineral fertilizer. The application of HS biostimulants associated to mineral fertilization to the lettuce plants provided the greatest values of the studied variables, namely: plant height and diameter, leaf number per plant and root length. The combination of FA biostimulants and mineral fertilization increased the lettuce productivity relative to the inorganic fertilizer alone. The combined application of rich biostimulants FA and HA with NPK fertilizes influenced K and Fe uptake by the plants, and their accumulation in the aerial portion. Our results suggest that HS products potentialize the nutritional effect of the mineral fertilizer, when applied in combination.

The beneficial effects of humic substances (HS) on crop development have been evidenced in the last decade, leading to the commercialization of HS products with fertilizing properties. Currently, three methods are frequently used for HS determination: method described in the manual of the Brazilian Ministry of Agriculture, Livestock and Supply (MAPA); method employed by the United States Humic Products Trade Association (HPTA) and method used for the determination of soil HS (“HS-Soil”). This study aimed to evaluate and compare the quantification of HS in commercial liquid fertilizers, by the mentioned methods. For HA-rich fertilizers the studied methodologies presented results close to the HA and FA contents informed in the labels. For products rich in FA, the methodologies that use dichromate to oxidize organic carbon overestimated the results of FA, taking as reference the HPTA method, that determines gravimetrically the purified FA and HA. The time of analysis varied between the methodologies studied, as well as the type and volume of the produced waste. Based on the chemical principle of HS determination of the method and the environmental impact of the waste generated, we propose that the most appropriate method for determination of HS in liquid fertilizers is that of HPTA.

The aim of this study was to investigate impacts of Amazon Forest (AF) fire and conversion to pasture on carbon accumulation in particle size fractions and organic matter (OM) composition of an Acrisol. Soil samples were collected (0.00-2.00 m depth) in three sites: native AF (NAF); AF under natural regeneration for two years after burning (BAF); 23-years old Brachiaria pasture after AF burning (BRA). Assuming NAF area as reference, BAF and BRA areas showed negative carbon balance when carbon emitted to the atmosphere at AF burning is taken into account. Soil OM aromaticity and hydrophobicity, assessed via 13C nuclear magnetic resonance, in BRA and BAF were similar to that in NAF. Fire and post-fire land use altered the carbon distribution in sand, silt and clay along the soil profile and seem to have affected organo-mineral and OM self-assemblage interactions, since the relation between total soil carbon and carbon in clay was asymptotic in BAF and linear in NAF and BRA.

RESUMO O efeito de ácidos húmicos (AH) na disponibilidade de fósforo (P) ainda é contraditório. Assim, é necessário identificar as principais condições que podem influenciar esse efeito. Com o trabalho, objetivou-se investigar o efeito da aplicação de AH, combinada com doses de P, no teor desse nutriente em Latossolo com e sem correção de acidez. Foram conduzidos dois experimentos, um com AH extraído de turfa e outro com AH extraído de carvão mineral (leonardita). Doses desses ácidos (0; 1,12 e 5,62 mg C g-1 de solo) e de P (26,2 e 104,7 mg P g-1 de solo, 1 e 4 vezes maior que o recomendado, respectivamente) foram testadas, em dois valores de pH do solo (4,5 e 7,0), em esquema trifatorial. O solo foi incubado por 20 dias e os teores de P foram extraídos com os métodos Mehlich-1 e P remanescente. O efeito dos AHs na disponibilidade desse nutriente variou com as doses de P e o pH do solo. A adição desses ácidos aumenta o teor desse nutriente em latossolo somente quando a dose de correção de P for maior que a recomendada e a acidez (pH 4,5) não for corrigida. Por outro lado, os AHs não influenciam o teor desse nutriente quando a dose de correção aplicada corresponder à quantidade recomendada, independentemente do pH do solo.

ABSTRACT The effect of humic acids (HA) on phosphorus (P) availability is still contradictory; thus, it is necessary to identify the conditions that play a crucial role in this effect. The aim of this study was to investigate the effect of HA application, combined with doses of P, on the content of this nutrient in a Latosol with and without acidity correction. Two experiments were carried out, one with HA from peat and another with HA from mineral charcoal (leonardite). Doses of these acids (0; 1.12 and 5.62 mg C g-1 of soil) and P (26.2 and 104.7 mg P g-1 of soil, 1 and 4-fold higher than recommended, respectively) were tested at soil pH 4.5 and 7.0, in a three-factorial design. The soil was incubated for 20 days and the soil-P content was measured by Mehlich-1 and remaining-P tests. The effect of HAs on P availability varied with the P doses and soil acidity. Humic acids application increases P content in Latosol when P dose is higher than recommended and there is no acidity correction (pH 4.5). However, there is no effect of HAs application on soil-P content when applying the recommended amount of this nutrient, irrespective of the pH value.

In this study, changes on the chemical composition and on the humic acids yield of coal matrices promoted by 25% HNO3 treatment were investigated, by means of elemental, thermogravimetric analyses, and Fourier transform infrared spectroscopy (FTIR). The "run of mine" (ROM) matrix C-MTR (ROM coal) showed the highest C content (41%), highest C/N ratio (76) and lowest ash content (54%) of the studied samples. In contrast, coal tailings presented a higher degree of aromaticity. Treatment with HNO3 solution increased N content, but not that of C. Therefore, the C/N ratio of all samples decreased to values between 11 and 20. The insertion of N occurred in the aromatic structures, while the oxidation occurred in both the aromatic and aliphatic chains. HNO3 treatment increased the humic substances content and the largest increase being observed in the coal tailings (16 to 31% increment in comparison to the untreated sample). The generated humic acids showed in general a chemical composition similar to that of soil humic acids, but a greater aromaticity degree.

Este estudo investigou a composição química e distribuição da matéria orgânica do solo (SOM) em compartimentos de Oxissolo sob pastagem nativa sem queima há 41 anos (NP), pastagem nativa sem queima há oito anos (BP), pastagem nativa em solo com calcário e adubado, sem queima há 41 anos (AP), e mata nativa (NF). Os estoques de carbono (C) e nitrogênio (N) no solo e nos compartimentos físicos foram determinados e a composição química da SOM foi investigada por espectroscopia de infravermelho com transformada de Fourier (FTIR) e análise termogravimétrica. Entre os ambientes sob pastagem, AP apresentou maiores estoques de C e de N no solo e nas frações leves. A fração pesada de BP apresentou maior índice de aromaticidade, o que pode ser devido à presença de carbono pirogênico. O sistema AP apresenta uma alternativa sustentável para sequestrar carbono em comparação com as práticas de queima da vegetação em sistemas de pastagens nativas no sul do Brazil.

This study evaluated the chemical composition and distribution patterns of soil organic matter (SOM) of Oxisol under native pasture without burning for the last 41 years (NP), native pasture without burning for the last eight years (BP), native pasture in soil amended by liming and fertilization and without burning for the last 41 years (AP), and native forest (NF). Stocks of carbon (C) and nitrogen (N) in the whole soil and in physical pools were determined and SOM composition was investigated by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. Among the pasture environments, AP presented the greatest C and N stocks in soil and in the light fractions. The heavy fraction of BP presented the greatest aromaticity index, and this can be related to the presence of pyrogenic carbon. Concerning soil carbon accumulation, AP represents a sustainable alternative in relation to the practice of vegetation burning in the management of native pastures in southern Brazil.

Ácidos húmicos (HA) extraídos de carvões de diferentes ranks, de suas amostras regeneradas e de uma amostra nitrada, foram caracterizados por análise elementar e por espectroscopia de infra-vermelho (FTIR), de ressonância magnética nuclear de 13C no estado sólido (NMR) e de ressonância paramagnética eletrônica (EPR). O HA de carvão de baixo rank apresentou maiores valores de teor de C e razão C/N e menores valores de teor de O e razões H/C e O/C do que o de alto rank. Resultados de RMN mostraram que ambas amostras foram mais aromáticas e menos carboxílicas do que HA comuns em solos. Estas características podem limitar o uso de HA de carvão como condicionadores e fertilizantes adequados para solos. A regeneração não provocou alterações relevantes, exceto pelo decréscimo no teor de radicias livres determinados por espectroscopia de EPR. Provavelmente as condições e o tempo de regeneração não foram adequados para oxidar as amostras. Os espectros de FTIR obtidos foram semelhantes, excentuando-se aquele da amostra nitrada, onde a banda de absorção em 1533 cm-1 comprova a presença de grupos nitrogenados. A nitração aumentou o teor de N e reduziu a razão C/N a valores comparáveis aos observados em HA de solos, porém a aromaticidade permaneceu alta e o teor de carboxílicos diminuiu após o processo.

Humic acids (HA) extracted from two coals of different ranks, from their regenerated samples and from a nitrated sample, were characterized by elemental analysis and by infra-red (FTIR), solid state 13C nuclear magnetic resonance (NMR) and eletronic paramagnetic resonance (EPR) spectroscopies. The low rank coal HA presented higher C and lower O contents, higher C/N and lower H/C and O/C ratios than high rank coal HA. NMR results showed that both samples were more aromatic and less carboxylic than common soil HA. Those characteristics may limit the coal HA efficiency as an appropriate soil conditioner and fertilizer. The regeneration process did not produce major alterations in the coal HA, except a decrease of the free radical content as determined by EPR spectroscopy. Probably, the regeneration conditions and time were not adequate to oxidize the samples. The obtained FTIR spectra were much alike, except that from the nitrated sample, where the absorption band at 1533 cm-1 confirms the presence of nitrated groups. The nitration process increased the N content and reduced the C/N ratio to values comparable to those reported for soil HA, but the aromaticity still remained high and the carboxylic content was lowered after the procedure.