Humin Fraction Research Articles

N2O and NOx emissions by reactions of nitrite with soil organic matter of a Norway spruce forest

Nitrite (NO2 −) as an important intermediate of the biological nitrogen cycle is particularly reactive in acidic soils and acts as a source of N2O and NOx (NO and NO2). However, abiotic and biotic pathways of NO2 −-driven N2O and NOx production in forest soil and the role of soil organic matter (SOM) in these processes are still unclear. In this study, NO2 − was applied to both unsterile and sterilized soil samples as well as to different SOM fractions from a Norway spruce forest. Biotic and abiotic N2O emission was measured with an infrared absorption analyzer and gas chromatography, while NOx emission was quantified with a chemiluminescence analyzer. Isotopic signatures of N2O (δ15Nbulk, δ18O, and 15N-N2O site preference) were analyzed with an isotope ratio mass spectrometer. After NO2 − addition, a large amount of NOx was emitted immediately, while N2O emission occurred 15–60 min later and was much lower compared to NOx. Sterilization of soil decreased N2O emission significantly, but not NOx emission. The 15N site preference of N2O ranged from 7.98 to 11.58‰ for abiotic and 4.69–7.42‰ for biotic sources. The fulvic acid fraction contributed the most to abiotic N2O emission, while the fastest NO and N2O emission occurred after NO2 −application to the humin fraction, followed by the humic acid fraction. These results are important for the future understanding of NOx and N2O sources, as well as the use of isotopic signatures for source-partitioning N2O emission from soil.

Contrasting effects of NH4+ and NO3− amendments on amount and chemical characteristics of different density organic matter fractions in a boreal forest soil

Elevated nitrogen (N) deposition variously affects the soil carbon (C) cycle. It is not clear how deposited NH4+ and NO3− divergently affect the amount and stability of soil organic C (SOC) in the N-limiting forests. A multi-form N addition experiment was conducted in a boreal forest in the Great Khingan mountain in 2010. Three fertilizers, NH4Cl, KNO3 and NH4NO3, were applied at four rates of 0, 10, 20, and 40kgNha−1yr−1. Solid-state 13C nuclear magnetic resonance spectroscopy and elemental analysis were used to determine the chemical structure and C contents in bulk soils and/or two density fractions (<1.70gcm−3 light fraction and >1.70gcm−3 heavy fraction). NH4Cl addition significantly decreased the SOC contents in the organic layer by 28.35% to 54.23%, but KNO3 addition significantly increased the SOC contents in the organic layer and mineral layer by 26.53% and 87.44%, respectively. Nitrogen addition rates significantly influenced the degradability (alkyl-C/O-alkyl-C) and hydrophobicity ((alkyl C+aromatic C)/(O-alkyl C+carboxyl C)) of light and heavy fractions, whereas N addition forms only impacted their aromaticity (aromatic C/(aromatic C+alkyl C+O-alkyl C)). The movement between residue-C and stable humin fraction, as well as the chemical stability of SOM could profoundly affect the storage of SOC under N enrichment. Overall, added NH4+ and NO3− differently affect C sequestration in the N-limiting forest soils. This should be differentiated in the biogeochemical models of CN cycle coupling.

Towards the photophysical studies of humin by-products.

Biomass conversion into chemicals, materials and fuels emerged in the past decade as the most promising alternative to the current petroleum-based industry. However, the chemocatalytic conversion of biomass and bio-derived sugars often leads to numerous side-products, such as humins. The limited characterization of humin materials restricts their study for possible future applications. Thus, herein photophysical studies on humins and separated humin fractions were carried out using steady-state and time-resolved fluorescence techniques. This paper aims to add to the literature important information for scientists involved in the photophysical studies.

Phosphorus fractions and correlation with soil attributes in a chronosequence of agricultural under no-tillage

In no-tillage (NT) soils, changes in the quantity and quality of soil organic matter (SOM) have been observed over time. These changes can interfere with the dynamics of P in surface soil layers. Thus, the objectives of this study were: to evaluate the organic and inorganic fractions of P and their degree of lability (labile, moderately labile, and moderately recalcitrant) in an Oxisol under NT for 6 years (NT6), 14 years (NT14), and 22 years (NT22) and cultivated with a succession of soybean and corn/wheat. The fractions were evaluated for 16 years of NT, with the last four years under integrated corn second crop and Brachiaria (NT16+B). We also analyzed an area of native forest, as well as analyzing the correlations between the results of the P fractions of these areas with other attributes such as total carbon content, vegetable waste deposited on the ground, phosphorus and humic fractions remaining in SOM. From each of the areas, samples were collected at 0.00-0.05 m and 0.05-0.10 m. A completely randomized design with 5 replicates was used. Management of phosphorus fertilization and SOM following adoption of the SPD of time (6 to 22 years) increased the levels of all fractions of inorganic P (0.0 to 0.10 m), as well as the fractions of labile (0.05-0.10 m), moderately labile (0.0-0.10 m), and moderately recalcitrant (0.05-0.10 m) organic phosphorus. The correlation matrix shows interactions between the evaluated soil attributes, especially between inorganic phosphorus fractions and fulvic and humic acids and between the moderately recalcitrant organic phosphorus and humin fraction.

Molecular composition of several soil organic matter fractions from anthropogenic black soils (Terra Preta de Índio) in Amazonia — A pyrolysis-GC/MS study

The stability of soil organic matter (OM) in Amazonian anthropogenic soils, Terra Preta de Índio (TPI), is still not completely understood. The large contribution from black carbon (BC) and minerals to these soils is well-known; OM stability is therefore frequently explained by these properties, providing intrinsic recalcitrance (BC) and chemical protection against decomposition (OM-mineral associations), but the relative importance of both mechanisms that underlie the stability are not yet understood. In order to better understand the sources and decay processes of soil OM in these soils, we studied the molecular composition using pyrolysis gas-chromatography/mass-spectrometry. To this end, several soil OM fractions of samples from two TPI soils and an adjacent Xanthic Acrisol that served as a reference soil (REF) were studied (0–2m depth). A sequential fractionation was applied in order to better understand the composition of soil OM pools with different association to the soil matrix. The studied soil OM fractions included the free light fraction (FLF; i.e., charcoal and litter), the occluded light fraction (OLF; charcoal and litter within aggregates), 0.1M NaOH extractable OM (EX; comparable with the combined humic acid and fulvic acid fractions), and the remaining residue (RES; treated with HF/HCl; comparable with the humin fraction). The largest contribution to the total soil OM was found for EX and/or RES, the sum of which varied between 79% and 98% (Ave. 90.8%, n=18). The minor contribution from the OLF (Ave. 4.4%) indicates that stabilisation within aggregates was not a major factor that contributed to OM stability in the studied profiles. Differences in molecular composition between the fractions were larger than those between profiles or with depth. The EX fraction showed the lowest contribution from plant (lignin phenols) and BC (PAHs, indenes, aromatics) derived products. The RES fraction showed a significantly larger contribution from BC related pyrolysis products compared to the EX. This non-extractable BC that is present in the RES after removal of the light fractions may reflect preferential binding of PAHs to minerals or, alternatively, the presence of highly condensed macromolecular polyaromatic structures. Changes with depth within the EX and RES fractions showed a larger contribution from products derived from BC in the anthropogenic horizons. Furthermore, the OM composition in EX and RES indicated that the degree of degradation of OM in anthropogenic horizons was relatively low. Apart from these similarities for anthropogenic horizons, the chemical composition of soil OM also showed large differences between both TPI soils. TPI-1 showed large variation between horizons while TPI-2 showed only minor changes with depth; this may be related to different phases of human occupation with time and/or a different soil usage.

Chemical nature of humic substances in two typical Chinese soils (upland vs paddy soil): A comparative advanced solid state NMR study

Knowledge of the structural features of humic substances (HSs) is essential for elucidating the mechanisms of humification in different soil environments and realizing their profound roles in environmental issues. The aim of this work was to investigate the chemical structures of fulvic acid (FA), humic acid (HA) and humin (HM) fractions isolated from an upland soil (Fluvisol) and a paddy soil (Anthrosol) typical in China using advanced solid-state 13C nuclear magnetic resonance (NMR) techniques. The results revealed that there were great structural differences of HSs between the two soils. The two FAs showed distinct quantitative differences in aliphatics with more polysaccharides in the FA from the upland soil than from the paddy soil. The HM from the upland soil differed from the paddy soil HM in having more proteins/peptides (23% vs 20%), total aromatics (21% vs 12%) as well as fewer lipids (24% vs 35%) and polysaccharides (27% vs 31%). The HM fractions represented the most different components of organic matter between the two soils. The degree of difference between the two HAs fell in between that of FAs and HM fractions. In particular, the HA from the upland soil had relatively greater degree of aromaticity. Our study indicated that the upland soil exhibited a higher degree of humification compared with the paddy soil. Among the three humic fractions, the FAs featured COO/N-CO groups, and the HAs were more enriched in protonated aromatic C for both soils. In contrast, the two HM fractions contained more O-alkyl C and fewer aromatics than did the other humic fractions, being closer to the original organic materials in soils. We speculate that the evolutionary route of HSs is likely to be the transformation of original organic materials into HM, followed by increased degradation, further oxidization and conversion into HA, and then into FA.

Frações químicas e oxidáveis da matéria orgânica do solo sob diferentes sistemas de manejo, em Latossolo Vermelho

Resumo O objetivo deste trabalho foi avaliar a qualidade do solo a partir das frações químicas e oxidáveis da matéria orgânica (MOS) em áreas com diferentes sistemas de manejo. O trabalho foi realizado no Município de Guaíra, no Oeste do Paraná, em áreas com diferentes tempos de adoção do sistema plantio direto (SPD, 6, 14 e 22 anos), com sucessão das culturas soja (verão) e milho/trigo (inverno), além de áreas com 12 anos de SPD - no mesmo arranjo de sucessão - mais quatro anos de cultivo de braquiária (Urochloa ruziziensis) consorciada com milho (M+B) e com pastagem e mata nativa. As frações químicas de ácido fúlvico (AF), ácido húmico (AH) e humina (HUM) foram avaliadas, bem como as frações oxidáveis da MOS (F1, F2, F3 e F4), o carbono total (CT) e o estoque de carbono (C) nas frações húmicas. Os teores de CT aumentaram com o tempo de adoção do SPD, principalmente entre SPD6 e SPD22. Verificou-se predomínio da fração HUM e movimentação de AH e AF na camada de 0,0-0,4 m de profundidade. As frações oxidáveis apresentaram equilíbrio na distribuição do conteúdo de C, com maiores teores nas frações mais lábeis, em superfície. O cultivo com sucessão de culturas contribui para o aumento das frações mais lábeis, mas não para o aumento das frações mais recalcitrantes do C.

Spatial distribution of organic carbon and humic substances in irrigated soils under different management systems in a semi-arid zone in Ceará, Brazil

Spatial distribution of organic carbon and humic substances in irrigated soils under different management systems in a semi-arid zone in Ceará, Brazil Knowledge of the spatial variability in soil properties can contribute to effective use and management. This study was conducted to evaluate the spatial distribution of the levels of total organic carbon (TOC) and humic substances (humic acid (C-FAH), fulvic acid fraction (C-FAF), and humin fraction (C-HUM)) in an Ultisol under different land uses, located in the irrigated perimeter of Baixo Acaraú-CE, transition to semiarid Ceará. The distribution and spatial dependence of the humic fractions were evaluated using descriptive statistics, including semivariogram analysis and data interpolation (kriging). The TOC showed a pure nugget effect, whereas the other fractions showed moderate spatial dependence. Forested and banana cultivation areas showed similar distributions of C-FAH and C-FAF, due to the high input of organic matter (leaves and pseudostems) in the area of banana cultivation and the absence of soil disturbance in the forested area. Data interpolation (kriging) and mapping were useful tools to assess the distribution and spatial dependence of soil attributes.

Characterization of carbofuran bound residues and the effect of ageing on their distribution and bioavailability in the soil of a sugar beet field in north-western Morocco

This study was undertaken to investigate distribution, fractionation, bioavailability and remobilization characteristics of bound soil-aged carbofuran and the effect of ageing in clay soil in a typical field of sugar beet at Loukkos in northwest Morocco. Results indicate that initially there were high levels of bound residues (BR) in the humin fraction, which decreased with incubation time and ageing of the BR. While in the fulvic and humic acid fractions, the amount of BR increased with the ageing of the BR and occurred predominantly (60%) in the fulvic acid fraction. The possibility of the mineralization and release of BR with ageing was studied using fresh soil and an incubation period of 90 days. The results indicate that the ageing of the residues have a great influence on the remobilization and mineralization rates of carbofuran BR; 9.45 to 14.90% of the total BR was released as extractable residues, and 1.95 to 4.15% was mineralized depending on the age of the residues in soil and the soil-aged carbofuran BR. The incorporation of the residues in the humin fraction is considered to be a threat to the environment. On the other hand, the clear prevalence of residues in the fulvic and humic acid fractions, may have an important effect on their bioavailability and movement in soil. Moreover, the re-extractability of BR could pose a potential environmental risk. Consequently, the BR remobilized must be taken into account when assessing for registration processes the environmental risk of pesticides persisting in soils.

Assessment of carbon storage under rainforests in Humic Hapludox along a climosequence extending from the Atlantic coast to the highlands of northeastern Brazil

An understanding of the stock of soil organic carbon (SOC) in the umbric epipedon of Oxisols located in the tropical forests surrounded by a semi-arid region is limited but essential because of their importance in the global cycle of carbon (C). The purpose of this study was to assess the effects of climatic (temperature and rainfall), soil organic matter (SOM) composition and litter on the stability of C in surfaces and subsurfaces in five Humic Oxisols along a 475-km climosequence from 143 to 963ma.s.l. in a tropical environment in northeastern Brazil. We assessed vertical changes in SOC; soil total nitrogen (N); C from the microbial biomass; δ13C, δ15N and the humified composition of SOM; the composition of the humin (HUM) fraction by Fourier Transform Infrared (FTIR); and Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) at depth. The elemental and isotopic composition of the litter samples were analyzed in all areas studied. The results indicated that the current climate and recalcitrant organic compounds are not preponderant factors in the formation of the umbric epipedon, as suggested by the partial influence of temperature and rainfall on SOM. In addition, SOM was dominated by easily decomposable compounds, as indicated by the predominance of aliphatic C–H groups in the HUM fraction in the FTIR spectra; by the thermal oxidation through DSC-TG, which revealed that approximately 50% of the HUM was composed easily decomposable compounds; and by the high proportion of organic C present in the microbial biomass. Values of δ13C showed a predominance of C3 plant-C in SOM whereas δ15N patterns indicated that N dynamics differ among the profiles and drive the accumulation of C. These findings can help to characterize the susceptibility of these soils to changes in climate and land use and the implications for the sequestration of soil C.

Insights into the composition of recalcitrant organic matter from estuarine sediments using NMR spectroscopy

Sediment cores (ca. 6m) from an estuarine environment gave insights into the composition and preservation of recalcitrant organic carbon (OC) in the environment. The coring locations provided organic matter (OM) of terrestrial origin and of marine origin. Our study specifically focused on the humin (HU), the OM fraction that is most difficult to isolate and to characterize. HU fractions were compared with the total OM recovered after removal of the associated mineral colloids. Solid state and multiphase (nuclear magnetic resonance) NMR experiments were carried out on dried and swollen samples to obtain comparative information about the whole samples and the fractionated samples. The total OM associated with the clay-size fraction provided a standard that allowed differences between the fractions to be observed.The NMR data provided new insights into the molecular structures that become part of the long term C sink in sediments. The recalcitrant OC in the sediments is composed mainly of aliphatic hydrocarbon material that may be protected from, or otherwise unavailable for, degradation. Microbial peptides and carbohydrates were also shown to be important contributors to the C sink and these biomolecules may be from living biomass or preserved necromass. Lignin residues formed only a small part of the OM in the surface sediments but made a greater contribution at depth. Highly ordered components in HU (that resists swelling by dimethylsulfoxide, DMSO) play a major role in C sequestration.

ORGANIC MATTER AND HUMIC FRACTIONS OF A HAPLIC ACRISOL AS AFFECTED BY COMPOSTED PIG SLURRY

The goal of this study was to investigate the effect of composted pig slurry (PS) on the organic matter concentration and distribution of humic acid (HA), fulvic acid (FA) and humin (HU) fractions. The fractions were quantified following the addition of composted PS to the soil, which was produced with no acidification (T2) or with acidification with H3PO4 (T3); and in soil without compost addition (T1). The HA chemical composition was analyzed by FTIR spectroscopy. The addition of the two composts did not change the soil carbon concentration but affected the distribution of the humic fractions. For the three treatments, the carbon concentration of humic substances increased until 52 days following compost addition, with more pronounced increases with the addition of non-acidified PS compost (14.5 g kg-1) and acidified PS compost (15.1 g kg-1). This increase was reflected in both the FA and HA concentrations. The addition of compost with PS acidification resulted in the formation of larger humic micelles (HA) with higher aromatic content and fewer functional groups than the non-acidified PS compost. These findings, together with a lower proportion of carbohydrate-type structures, indicated the presence of more stable humic micelles in the soil treated with acidified PS compost.

Comparison of different methods for the determination of total organic carbon and humic substances in Brazilian soils

ABSTRACTAiming to compare three different methods for the determination of organic carbon (OC) in the soil and fractions of humic substances, seventeen Brazilian soil samples of different classes and textures were evaluated. Amounts of OC in the soil samples and the humic fractions were measured by the dichromate-oxidation method, with and without external heating in a digestion block at 130 °C for 30 min; by the loss-on-ignition method at 450 °C during 5 h and at 600 °C during 6 h; and by the dry combustion method. Dry combustion was used as reference in order to measure the efficiency of the other methods. Soil OC measured by the dichromate-oxidation method with external heating had the highest efficiency and the best results comparing to the reference method. When external heating was not used, the mean recovery efficiency dropped to 71%. The amount of OC was overestimated by the loss-on-ignition methods. Regression equations obtained between total OC contents of the reference method and those of the other methods showed relatively good adjustment, but all intercepts were different from zero (p &lt; 0.01), which suggests that more accuracy can be obtained using not one single correction factor, but considering also the intercept. The Walkley-Black method underestimated the OC contents of the humic fractions, which was associated with the partial oxidation of the humin fraction. Better results were obtained when external heating was used. For the organic matter fractions, the OC in the humic and fulvic acid fractions can be determined without external heating if the reference method is not available, but the humin fraction requires the external heating.

FERTILIDADE DO SOLO E SUBSTÂNCIAS HÚMICAS EM ÁREA DE CAVA DE EXTRAÇÃO DE ARGILA REVEGETADA COM EUCALIPTO E LEGUMINOSAS NO NORTE FLUMINENSE

http://dx.doi.org/10.5902/1980509819606A revegetação de áreas de extração de argila com eucalipto e leguminosas pode favorecer a melhoria dos atributos químicos do solo. O objetivo do trabalho foi avaliar a influência de plantios puros e consorciados de leguminosas e eucalipto na fertilidade do solo e nos teores de carbono orgânico total e das substâncias húmicas, em uma cava de extração de argila no Norte Fluminense. O solo original da área da cava em estudo é um Cambissolo Háplico Sódico gleico, no qual a camada superficial (espessura de 20 cm, aproximadamente), com maiores teores de matéria orgânica, foi retirada e devolvida ao fundo da cava após a extração da argila. A cava foi nivelada mecanicamente e mantida sob pousio durante dois anos. A revegetação foi realizada com as espécies Eucalyptus camaldulensis (Euc), Acacia mangium (Ac) e Sesbania virgata (Sesb), em plantios puros e consorciados. O delineamento experimental utilizado foi o de blocos casualizados com sete tratamentos (plantios puros de Euc, Ac e Sesb; plantios consorciados de Euc + Ac, Euc + Sesb, Ac + Sesb; e área degradada com vegetação espontânea (ADVE)) e três repetições. Aos 48 meses após implantação dos sistemas foram coletadas amostras de solo na camada de 0,00 a 0,05 m, em que se avaliaram algumas variáveis da fertilidade do solo (pH em água, P, K+; Ca+2, Mg+2, Na+, Al+3, H+Al), carbono orgânico total (COT), nitrogênio (N) e quantificado o carbono das substâncias húmicas em carbono da humina (C-HUM), carbono da fração ácido húmico (C-FAH) e ácido fúlvico (C-FAF). Observou-se que todos os plantios promoveram aumentos nos teores Ca, Mg, P, K, N, COT, C-HUM, C-FAH e C-FAF em relação à ADVE. A revegetação de áreas de cava de extração de argila no Norte Fluminense com plantios puros ou consorciados de eucalipto e leguminosas, acarreta em melhorias da fertilidade do solo e dos teores de carbono e nitrogênio totais do solo e do carbono das substâncias húmicas. Aos quatro anos após a revegetação, os sistemas mais indicados, de uma forma geral, para acarretar em aumentos dos teores de COT, N total, Mg, soma de bases e capacidade de troca catiônica, destaca-se o plantio de acácia, dentre os plantios puros, e o plantio de eucalipto + sesbânia, dentre os plantios consorciados. Além disso, o consórcio eucalipto + sesbânia, apresentou um dos maiores teores C da fração humina.

The importance of humin in soil characterisation: A study on Amazonian soils using different fluorescence techniques

Soil organic matter (SOM) is a complex mixture of molecules with different physicochemical properties, with humic substances (HS) being the main component as it represents around 20–50% of SOM structure. Soil of the Amazon region is considered one of the larger carbon pools of the world; thus, studies of the humic fractions are important for understanding the dynamics of organic matter (OM) in these soils. The aim of this study was to use laser-induced fluorescence spectroscopy (LIFS) and a combination of excitation–emission matrix (EEM) fluorescence with Parallel Factor Analysis (CP/PARAFAC) to assess the characteristics of humin (HU) extracted from Amazonian soils. The results obtained using LIFS showed that there was an increasing gradient of humification degree with depth, the deeper horizon presenting a higher amount of aromatic groups in the structure of HU. From the EEM, the contribution of two fluorophores with similar behaviour in the structures of HU and whole soil was assessed. Additionally, the results showed that the HU fraction might represent a larger fraction of SOM than previously thought: about 80–93% of some Amazon soils. Therefore, HU is an important humic fraction, thus indicating its role in environmental analysis, mainly in soil analysis.

ORGANIC MATTER FRACTIONS IN A QUARTZIPSAMMENT UNDER CULTIVATION OF IRRIGATED MANGO IN THE LOWER SÃO FRANCISCO VALLEY REGION, BRAZIL

Improper land use has lead to deterioration and depletion of natural resources, as well as a significant decline in agricultural production, due to decreased soil quality. Removal of native vegetation to make way for agricultural crops, often managed inadequately, results in soil disruption, decreased nutrient availability, and decomposition of soil organic matter, making sustainable agricultural production unviable. Thus, the aim of the present study was to evaluate the impact of growing irrigated mango (over a 20 year period) on the organic carbon (OC) stocks and on the fractions of soil organic matter (SOM) in relation to the native caatinga (xeric shrubland) vegetation in the Lower São Francisco Valley region, Brazil. The study was carried out on the Boa Esperança Farm located in Petrolina, Pernambuco, Brazil. In areas under irrigated mango and native caatinga, soil samples were collected at the 0-10 and 10-20 cm depths. After preparing the soil samples, we determined the OC stocks, carbon of humic substances (fulvic acid fractions, humic acid fractions, and humin fractions), and the light and heavy SOM fractions. Growing irrigated mango resulted in higher OC stocks; higher C stocks in the fulvic acid, humic acid, and humin fractions; and higher C stocks in the heavy and light SOM fraction in comparison to nativecaatinga, especially in the uppermost soil layer.

Degradation of Plant Cuticles in Soils: Impact on Formation and Sorptive Ability of Humin-Mineral Matrices

Plant cuticles are important precursors for soil organic matter, in particular for soil humin, which is considered an efficient sorbent for organic pollutants. In this study, we examined degradation and transformation of cuticles isolated from fruit and leaves in loamy sand and sandy clay loessial arid brown soils. We then studied sorption of phenanthrene and carbamazepine to humin-mineral matrices isolated from the incubated soils. Low degradation (22%) was observed for agave cuticle in a sandy clay soil system, whereas high degradation (68-78%) was obtained for agave cuticle in a loamy sand soil system and for loamy sand and sandy clay soils amended with tomato cuticle. During incubation, most of the residual organic matter was accumulated in the humin fraction. Sorption of phenanthrene was significantly higher for humin-mineral matrices obtained from soils incubated with plant cuticles as compared with soils without cuticle application. Sorption of carbamazepine to humin-mineral matrices was not affected by cuticle residues. Cooperative sorption of carbamazepine on humin-mineral matrices isolated from sandy clay soil is suggested. Sorption-desorption hysteresis of both phenanthrene and carbamazepine was lower for humin-mineral matrices obtained from soils incubated with plant cuticles as compared with nonamended soils. Our results show that cuticle composition significantly affects the rate and extent of cuticle degradation in soils and that plant cuticle application influences sorption and desorption of polar and nonpolar pollutants by humin-mineral matrices.

Variabilidade espacial das frações da matéria orgânica do solo em área degradada sob recuperação

Objetivou-se, neste estudo, avaliar a variabilidade espacial das frações da matéria orgânica do solo em uma área degradada em recuperação com pinhão-manso; para isto se estabeleceu, em um Argissolo Vermelho-Amarelo, uma malha de 30 por 30 m para amostragem, totalizando 55 pontos. Em cada ponto foram coletadas amostras de solo nas camadas de 0-0,05; 0,05-0,10 e 0,10-0,20 m e determinados carbono orgânico total (COT), carbono lábil (CL) e o carbono das frações ácido fúlvico (C-FAF), ácido húmico (C-FAH) e humina (C-HUM). Os maiores teores de COT foram observados na camada de 0-0,05m e variaram de 2,0 a 15,5 g kg-1. O C-FAF nas camadas de 0-0,05 e 0,10-0,20 m e o C-FAH na camada de 0,10-0,20 m apresentaram altos coeficientes de variação (CV) de 66, 74 e 77%, respectivamente. As demais variáveis apresentaram CV médio, variando de 32 a 58%. Com exceção do C-FAF e C-HUM (0,0-0,05 m) os demais atributos apresentaram dependência espacial classificada como moderada ou forte, com alcances variando de 39,60 a 410,90 m. Os baixos valores observados para o carbono orgânico total e suas frações realçam o estado de degradação do solo indicando a necessidade de aumento na entrada de carbono por meio da inclusão de espécies com elevado aporte de resíduos.

CHROMIUM IN SOIL ORGANIC MATTER AND COWPEA AFTER FOUR CONSECUTIVE ANNUAL APPLICATIONS OF COMPOSTED TANNERY SLUDGE

Tannery sludge contains high concentrations of inorganic elements, such as chromium (Cr), which may lead to environmental pollution and affect human health The behavior of Cr in organic matter fractions and in the growth of cowpea (Vigna unguiculata L.) was studied in a sandy soil after four consecutive annual applications of composted tannery sludge (CTS). Over a four-year period, CTS was applied on permanent plots (2 × 5 m) and incorporated in the soil (0-20 cm) at the rates of 0, 2.5, 5.0, 10.0, and 20.0 Mg ha-1 (dry weight basis). These treatments were replicated four times in a randomized block design. In the fourth year, cowpea was planted and grown for 50 days, at which time we analyzed the Cr concentrations in the soil, in the fulvic acid, humic acid, and humin fractions, and in the leaves, pods, and grains of cowpea. Composted tannery sludge led to an increase in Cr concentration in the soil. Among the humic substances, the highest Cr concentration was found in humin. The application rates of CTS significantly increased Cr concentration in leaves and grains.

SOIL ORGANIC MATTER FRACTIONS IN PRESERVED AND DISTURBED WETLANDS OF THE CERRADO BIOME

Veredas are humid tropical ecosystems, generally associated to hydromorphic soils and a shallow water table. The soils of these ecosystems are affected by the use of the areas around these veredas. The objective of this study was to determine soil organic matter (SOM) fractions in veredas adjacent to preserved (native savanna) and disturbed environments (agricultural areas and pastures) in the Cerrado biome. Soil samples were collected from the 0-10 and 10-20 cm layers along reference lines drawn along the relief following the upper, middle and lower positions of one of the slopes, in the direction of the draining line of the vereda. The soil analysis determined: total soil OC, total nitrogen and C:N ratio; C and N contents and C:N ratio in particulate and mineral-associated fractions (of SOM); fulvic acids, humic acids and humin fractions and ratio between humic and fulvic acids. The agricultural use around the veredas induced changes in the SOM fractions, more pronounced in the lower part of the slope. In the soil surface of this part, the OC levels in the humic substances and the particulate fraction of SOM, as well as total soil OC were reduced in the vereda next to crop fields.