Deborah Pinheiro Dick

Chemical characterization and infrared spectroscopy of soil organic matter from two southern brazilian soils

SUMMARY Soil organic matter from the surface horizon of two Brazilian soils (a Latosoland a Chernosol), in bulk samples ( in situ SOM) and in HF-treated samples (SOM),was characterized by elemental analyses, diffuse reflectance (DRIFT) andtransmission Fourier transform infrared spectroscopy (T-FTIR). Humic acids(HA), fulvic acids (FA) and humin (HU) isolated from the SOM were characterizedadditionally by ultraviolet-visible spectroscopy (UV-VIS). After sample oxidationand alkaline treatment, the DRIFT technique proved to be more informative forthe detection of “ in situ SOM” and of residual organic matter than T-FTIR. Thehigher hydrophobicity index (HI) and H/C ratio obtained in the Chernosol samplesindicate a stronger aliphatic character of the organic matter in this soil thanthe Latosol. In the latter, a pronounced HI decrease was observed after theremoval of humic substances (HS). The weaker aliphatic character, the higherO/C ratio, and the T-FTIR spectrum obtained for the HU fraction in the Latosolsuggest the occurrence of surface coordination of carboxylate ions. TheChernosol HU fraction was also oxygenated to a relatively high extent, butpresented a stronger hydrophobic character in comparison with the LatosolHU. These differences in the chemical and functional group composition suggesta higher organic matter protection in the Latosol. After the HF treatment,decreases in the FA proportion and the A

Relação entre os constituintes do solo e seu comportamento espectral

The spectral soil reflectance is an expression that characterizes the electromagnetic radiation reflected by soil surface. Most of the soil constituents can be identified and sometimes quantified by the spectral behavior. The main soil constituents that influence its spectral behavior are the organic matter, iron oxides, mineralogy and clay content and moisture. The use of soil reflectance allows to obtain information to quickly identify and quantify the soil characteristics, both in laboratory and orbital levels, but it has been tested and used mainly in developed countries. In Brazil, the research interest for the study of the soil spectral reflectance started in the 1980’s, being a recent research area which needs research support to achieve a better understanding of the spectral interaction among the different components of the soil.

Carbon stocks in organic matter fractions as affected by land use and soil management, with emphasis on no-tillage effect

Land use and soil management may affect both labile and humified soil organic matter (SOM) fractions, but the magnitude of these changes is poorly known in subtropical environments. This study investigated effects of four land use and soil management systems (forest, native pasture, and conventional tillage and no-tillage in a wheat/soybean succession) on (i) total soil organic carbon (SOC) stocks (0 to 250mm depth) and on (ii) carbon (C) stocks in labile (coarse, light) and humified (mineral-associated, humic substances) SOM fractions (0 to 25mm depth), in a Hapludox soil from southern Brazil. In comparison to the adjacent forest site, conventionally tilled soil presented 36% (46.2Mg ha-1) less SOC in the 0 to 250mm depth and a widespread decrease in C stocks in all SOM fractions in the 0 to 25mm depth. The coarse (>53 mm) and light (<1kg dm-3) SOM fractions were the most affected under no-tillage, showing 393% (1.22Mg C ha-1) and 289% (0.55Mg C ha-1) increases, respectively, in relation to conventional tillage. Similar results were observed for mineral-associated SOM and humic substance C pools (34% and 38% increases, respectively) under no-tillage. Compared with labile SOM fraction results, the percentual increments on C stocks in humified fractions were smaller; but in absolute terms this C pool yielded the highest increases (3.06 and 2.95Mg C ha-1, respectively). These results showed that both labile and humified organic matter are better protected under the no-tillage system, and consequently less vulnerable to mineralization. Humified SOM stabilization process involving interactions with variable charge minerals is probably important in maintaining and restoring soil and environmental quality in tropical and subtropical regions.

Caracterização de substâncias húmicas extraídas de solos e de lodo orgânico

The extraction of humic substances (HS) from A-horizons of two soils from Rio Grande do Sul (Oxisol, LR, and Mollisol, BZ) and from an organic sludge (LO) was investigated, employing two methods: (1) the HS were extracted with 0.5 mol L-1 NaOH, after treating the sample with 0.5 mol L-1 HCl; (2) the extraction with 0.15 mol L-1 sodium pyrophosphate solution (pH 7) was introduced before the alkaline and after the acid treatments. In each step, the contents of HS, fulvic acids (FA) and humic acids (HA) were determined by spectroscopic and gravimetric methods, and the contents of co-extracted Fe, Al, Si and Ca in the extracts of method 2 were measured by atomic absorption. The elemental composition of HA was determined and their chemical structure and characteristics were evaluated from the C/N, H/C and O/C ratios and from UV/Vis spectroscopy data. In the Oxisol, method 1 extracted a greater amount of HS, and in method 2 the pyrophosphate step extracted only AF. On the other hand, method 2 was more efficient in the Mollisol, and the greatest yield was obtained in the pyrophosphate step. These results suggest that in the Oxisol, the HS interact mainly through ligand exchange reactions and hydrogen bonding, while in the Mollisol, cation bridges are also an important mechanism. The NaOH-extracted HA showed higher H/C and lower O/C ratios than the pyrophosphate-extracted ones, indicating that the neutral solution solubilized HS with higher aromatic character and oxygenation grade.

Comparison of carbon and nitrogen determination methods for samples of a Paleudult subjected to no-till cropping systems

Organic carbon (C) concentration evaluated by the Walkley-Black method, and total nitrogen (N) concentration determined by Kjeldahl method, were compared with corresponding results of C and N concentrations obtained through the dry combustion method (Elementar Vario EL analyzer), using samples of ten soil layers down to the depth of 107.5 cm of a kaolinitic Typic Paleudult (220-418 g clay kg -1 along the profile) subjected to no-till cropping systems (fallow bare soil, pigeon pea (Cajanus cajan L. Millsp.) plus maize, and lablab (Lablab purpureum L. Sweet) plus maize). A close correlation (R 2 ≥ 0.96) was observed between the C results of the Walkley-Black and dry combustion methods, but a correction was suggested to be applied to C results of Walkley-Black (C = 1.05C W.Black + 0.47). A close correlation (R 2 ≥ 0.96) was also found between results of Kjeldahl-N and dry combustion-N, but no correction was necessary to be applied. The relationships between results of Walkley-Black and dry combustion and between results of Kjeldahl and dry combustion did not change among soil samples from different management systems, in disagreement to findings of a previous study where results of analytical C recovery were influenced by samples from different managements, supposedly because changes in lability or recalcitrance of organic matter might have affected the wet combustion reactions. A poor correlation (R 2 = 0.42) was found between the C:N ratios based on Walkley-Black and Kjeldahl analysis and the C:N ratios based on dry combustion analysis. The methods for C and N determination

Solos subtropicais de altitude: atributos químicos, teor de matéria orgânica e resistência à oxidação química

In this research, texture, soil pH, CEC at pH 7, exchangeable Al, and content of Fe-oxides (Fed and Feo) were determined in A horizons samples of eight representative soils under native pasture from Campos de Cima da Serra, Rio Grande do Sul State, Brazil. The samples were treated with hydrogen peroxide and, before and after the treatment, C and N contents were determined and Fourier Transformed Infrared (FTIR) spectroscopy was performed. The content of soil C was high (4 to 23%) and its variation correlated with the altitude and exchangeable Al indicating that lower temperatures and complexation with ionic Al contribute to soil organic matter (SOM) stabilization. The proportion of oxidation-resistant carbon varied between 1 and 16% and correlated with the ratio Feo/Fed. The stabilization of this SOM fraction was assigned to the interaction of carboxylic groups bound to aromatic and aliphatic structures with Fe-oxides of low crystallinity degree.

Matéria orgânica em Neossolo de altitude: influência do manejo da pastagem na sua composição e teor

Burning pastures after the winter is a traditional practice in highland soils, whose main purpose is the regrowth of vegetation. However, the impact of fire, as well as the influence of grazing on the organic matter of Leptosols is still unknown. The purpose of this study was to investigate the composition and content of organic matter in soil profiles from Sao Jose dos Ausentes, state of Rio Grande do Sul, and to relate the results with the occurrence of burning and grazing, in comparison with a soil under native forest. The following environments were studied: grazed native pasture (2 animals ha-1) without burning for 22 years; grazed native pasture (0.5 animals ha-1) burned every two years; and native forest adjacent to the pasture area. Composed soil samples were collected from four layers (0-5, 5-10, 10-15 and 15-30 cm) in which contents of C, of N, and of iron oxides (Fed and Feo) were determined and infrared spectroscopy and thermogravimetry analyses performed. The subsurface layers of the fire-affected environment contained greater organic matter contents, and in general, a composition with higher proportion of chemically labile structures, in comparison with the unburned pasture. In the latter environment, the lower C content than in the burned pasture was ascribed to more intensive grazing. The C distribution in the native forest environment was similar to that of the unburned pasture. Nevertheless, in the samples under forest, the proportion of organic matter of low molecular weight, extractable with 0.1 mol L-1 HCl and related mainly to microbial activity, exceeded that of the pasture environment.

Estudo comparativo da matéria orgânica de diferentes classes de solos de altitude do sul do Brasil por técnicas convencionais e espectroscópicas

Soils in the region of Campos de Cima da Serra, RS, have high organic matter contents (SOM) and high levels of exchangeable Al. This study aimed to investigate the SOM quality of surface samples (0-10 cm) of eight representative soils from the region (two Neossols, two Gleissols, three Cambissols, one Latosol) under native pasture. The objectives were to evaluate the sample behaviour under demineralization with HF solution, to determine the chemical composition and the influence of exchangeable Al and iron oxides on it. The SOM was concentrated with 10 % (v/v) HF solution and then submitted to elemental analysis, FTIR and 13C NMR CP/MAS spectroscopy. The recovered mass after HF treatment (5.8 to 10 %) was correlated with the soil C content, while the recovered C (47 to 86 %) was inversely correlated with the Fe oxide content. This result indicates that part of the SOM in these soils is associated to these minerals. The proportion of total C O-alkyl groups was high (52 to 59 %) and the values for the I1630/I2920 index (FTIR) were low, evidencing a low humification and decomposition degree of SOM in these soils.

Sorção de atrazina em cambissolo húmico do Rio Grande do Sul sob vegetação nativa

A acumulacao de herbicidas no ambiente em virtude de sua larga utilizacao em sistemas agricolas, associada a alta persistencia, e extremamente preocupante, considerando os efeitos maleficos que alguns destes compostos causam a flora e a fauna. A atrazina (2-cloro-4-etilamino-6-isopropilamino-s-triazina) e um dos herbicidas mais utilizados na atualidade e tem sido detectada em teores consideraveis em mananciais e solos. O objetivo deste estudo foi avaliar o comportamento sortivo da atrazina comercial em Cambissolo Humico em condicoes naturais e em ausencia de materia orgânica. Foram determinadas isotermas de sorcao de atrazina comercial em amostras do horizonte A na sua forma natural e na forma oxidada. A quantidade maxima de herbicida sorvido variou de 8 % (amostra oxidada) a 49 % (amostra natural) da quantidade adicionada. A aplicacao do modelo de Freundlich na forma linear aos dados experimentais forneceu altos coeficientes de correlacao para a sorcao em amostra natural (r = 0,960, P < 0,01) e na amostra oxidada (r = 0,937, P < 0,01). O coeficiente nf (modelo de Freundlich) obtido na amostra natural (1,40) indica que a afinidade do sorbato pelo sorvente aumentou com o progresso da sorcao, enquanto, na amostra oxidada, o comportamento foi inverso (nf = 0,78). O valor do coeficiente Kf foi de 1,10 L kg-1 na amostra natural e de 0,84 L kg-1 na amostra oxidada, enquanto o coeficiente de distribuicao da atrazina (Kd) foi de 4,64 e 0,33 L kg-1, respectivamente. Estes resultados mostram que a materia orgânica foi o sorvente determinante na retencao de atrazina no Cambissolo humico. Adicionalmente, o valor de Koc de 103 L kg-1 obtido classifica a atrazina comercial como de alta mobilidade para o sistema atrazina-solo estudado.

Distribuição e caracterização de substâncias húmicas em vermicompostos de origem animal e vegetal

The use of organic residues as fertilizers and soil conditioners requires their maturation and the quality monitoring of the final product. Vermicomposting is a technique which, along with the composting process, eliminates the potential harmful effect of manure residues to human health and soil. The stability and maturity degrees of a given vermicompost are usually inferred from the quantity and quality of the humic substances in the resulting compost. This study aimed to evaluate the quality and maturity of vermicomposts from six different residues: cattle manure (CM), sheep manure (SM), pig manure (PM), quail manure (QM), coffee dregs (CD) and mate-tee dregs (MD), by determining the content of humic substances (humic, HA, and fulvic acids (FA) and their chemical composition, after 70 days of composting. The humic substances were chemically fractionated according to their solubility in basic and acidic medium. The distribution of total C in the different humic fractions was determined, and the humification indices HA percentage and HA/FA ratio were calculated. The elemental composition (CHNO) and chemical composition by infrared spectroscopy (IRSP) were determined in the purified HA and FA. An aromaticity index (I1630/I2920) was calculated based on the IRSP spectra. The vermicomposts differed in humic substance content (FA+HA), which decreased in the order CD > SM ≈ MD ≈ CM > PM > QM. The maturity degree was greater in the vermicomposts of vegetal residues (coffee and mate-tee dregs). The HA showed that the proportion of O containing functional groups and the aromatic degree were lowest in these two vermicomposts.