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RESUMO O objetivo deste trabalho foi avaliar os teores de carbono orgânico total e alguns atributos físicos (densidade do solo, macroporosidade, microporosidade, diâmetro médio ponderado e geométrico de agregados) de um Cambissolo Háplico sob fragmentos florestais de Mata Atlântica em estágio inicial; intermediário e avançado, e compará-los à áreas de pastagem e agricultura (anual e perene). A regeneração de florestas secundárias em função do estágio de recuperação contribuiu para o aumento de carbono orgânico total e da macroporosidade, reduzindo os valores de densidade do solo, diâmetro médio ponderado e geométrico de agregados. Na área de pastagem foram verificados valores de carbono orgânico total, densidade do solo, macroporosidade, microporosidade e diâmetro médio ponderado e geométrico de agregados similares aos observados nas áreas de floresta. Na área de agricultura anual observou-se redução dos teores de carbono orgânico total, macroporosidade, diâmetro médio ponderado e geométrico de agregados e aumento da densidade do solo em função do manejo adotado.

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This study aimed to spatialize fractions of organic matter of soil in an agroforestry system (AFS) located in the Atlantic Forest in Brazil. Thirty-one soil samples were collected at depths of 0-10, 10-20 and 20-40 cm from georeferenced collection points. We determined total organic carbon (TOC), particulate carbon (COp), carbon associated with clay and silt (COam), carbon content in the fulvic acid fraction (C-FAF), humic acid fraction (C-HAF) and humin fraction (C-HUM). Semivariogram analysis and model adjustment were carried out using ArcGIS 10.2 software. Subsequently, spatial interpolation was performed using Ordinary Kriging. We observed spatial dependence for all variables except for TOC and COp at the 0-10 cm depth, which presented a pure nugget effect. It was possible to observe modifications in the distribution of humic substances in the study area. The results from this study are similar to those of other studies conducted in naive areas in the Atlantic Forest, demonstrating the benefits of using the agroforestry system. ESPACIALIZAÇÃO DAS FRAÇÕES DA MATÉRIA ORGÂNICA DO SOLO SOB UM SISTEMA AGROFLORESTAL, NA MATA ATLÂNTICA, BRASIL RESUMO: Este estudo teve como objetivo espacializar as frações da matéria orgânica do solo em um sistema agroflorestal (SAF) localizado na Mata Atlântica. Foram coletadas trinta e uma amostras de terra nas profundidades de 0-10, 10-20 e 20-40 cm, sendo cada ponto georeferenciado. Foram determinados os teores de carbono orgânico total (COT), carbono particulado (COp), carbono associado a argila e silte (COam), teor de carbono na fração de ácido fúlvico (C-FAF), fração de ácido húmico (C-FAH) e fração de humina (C-HUM). A análise dos semivariogramas e o ajuste do modelo foram realizados utilizando o software ArcGIS 10.2. Posteriormente foi realizada a interpolação espacial através de Krigagem Ordinária. Foi observada dependência espacial para todas as variáveis, com exceção do COT e COp na profundidade de 0-10 cm, visto que apresentaram efeito pepita puro. Foram verificadas modificações na distribuição das substâncias húmicas na área de estudo. Os resultados deste estudo são semelhantes aos de outros realizados em áreas de Mata Atlântica, demonstrando os benefícios do uso do sistema agroflorestal.

Sandy soils in tropical climates with low organic matter (OM) content result in degradation and fertility loss. It is important to note that humified OM accumulation and stabilization increases soil fertility. This study aimed to characterize humic acids (HAs) in sandy soils on an agroecological farm operating for more than 20 years. The structures of the HA of two Planosols under a grazing (G) and crop rotation (R) management system and of an Acrisol under an agroforestry management system (AFS) were characterized using HA extracted from a local Organosol under cassava monoculture (M) as a structural reference. Lower C HA /C FA ratio in sandy soil reveals a slightly humified OM and higher E 4 /E 6 ratio value in HA confirming lower aromatic structure condensation. The HA in Planosols (R and G) and Acrisols (AFS) are predominantly formed by C Alq-O,N -, C Alq-O -, and C Alq-di-O structures closely related to the soil physical properties and preserved by interaction with the mineral fraction confirmed by νO-H, νSi-O stretching of kaolinite and hematite bands in FTIR spectroscopy. Management and vegetal carbon type (−20.65‰ AFS -C 3 ) or (−15.55‰ (G) and −17.82‰ (R) -C 4 ) had no effect on HA formation. Evolution of structural change in HA modeled by chemometric analyses showed that more recalcitrant structure characteristic in HA can enhance OM preservation in these sandy soils. This study elucidated the OM stabilization mechanisms of sandy soil HA, their relationship with soil properties and models structural changes for humified OM recovery and preservation, which contribute to increased fertility and agricultural production.

RESUMOO objetivo deste trabalho foi avaliar alterações nos teores de C e N e abundância natural de δ 13 C e δ 15 N de um Cambissolo Háplico Tb distrófico em uma área com sistema agroflorestal (SAF). Em cada área de estudo foram coletadas amostras de solo, em 8 profundidades de 0,0-1,0 m. O delineamento experimental utilizado foi o inteiramente casualizado, em esquema de parcelas subdivididas 2 × 8 (2 áreas florestais e 8 profundidades), com três repetições. Com exceção da camada superficial do solo (0,0-0,10), a área de SAF está preservando os teores de C e aumentando os teores de N (0,2-1,0) em relação à mata nativa. Ambas as áreas avaliadas apresentaram sinais de abundância natural de δ 13 C referente a plantas do ciclo fotossintético C3, e a área de mata nativa apresentou nas camadas superficiais (0,0-0,20) maiores valores de δ 15 N, demonstrando maior decomposição da matéria orgânica.Palavras-chave: reflorestamento, matéria orgânica do solo, Cambissolo.Carbon, Nitrogen, and Natural Abundance Of Δ 13 C and Δ 15 N of Soils Under Agroforestry Systems ABSTRACTThe aim of this study was to evaluate changes in C and N levels and in the natural abundance of δ 15 N and δ 13 C of a Inceptisol in an agroforestry system (AFS). Soil samples were collected from eight depth levels from 0.0-1.0 m in each studied area. The experiment was carried out in a completely randomized 2 × 8 (2 forest areas and 8 depths) split-plot design with three replications. Except for the topsoil (0.0-0.10), the area of this AFS has preserved content of C and increased level of N (0.2-1.0) compared to the Forest. Both areas showed signs of natural abundance of δ 13 C in plants with C3 photosynthetic pathway, and the forest area presented higher values of δ 15 N in the superficial layers (0.0-0.20), indicating greater decomposition of organic matter.

The gradual change in management practices in sugarcane (Saccharum spp.) production from burning straw to a green harvesting system, as well as the use of minimum soil tillage during field renovation, may affect soil fertility and soil organic matter (SOM) contents. The objectives of this work were to investigate the influence of sugar cane production systems on: (1) soil fertility parameters; (2) on physical carbon fractions; (3) and on humic substance fractions, in a long-term experiment, comparing two soil tillage and two residue management systems an Xanthic Udult, in the coastal tableland region of Espírito Santo State, Brazil. The treatments consisted of plots (conventional tillage (CT) or minimum tillage (MT)) and subplots (residue burned or unburned at harvesting), with five replicates The highest values of Ca 2+ + Mg 2+ and total organic carbon (TOC) were observed in the MT system in all soil layers, while high values of K + were observed in the 0.1-0.2 m layer. The CT associated with the burned residue management negatively influenced the TOC values, especially in the 0.1-0.2 and 0.2-0.4 m layers. The carbon in the humin fraction and organic matter associated with minerals were significantly different among the tillage systems; the MT showed higher values than the CT. However, there were no significant differences between the sugarcane residue management treatments. Overall, fractioning the SOM allowed for a better understanding of tillage and residue management systems effects on the soil properties. Key words: Saccharum spp. Soil tillage systems. Residue retention. ResumoA mudança gradual nas práticas de manejo da cana de açúcar (Saccharum spp.) de colheita com queima de palha para o sistema de colheita sem queima, bem como o uso de preparo mínimo do solo durante a renovação do canavial, podem afetar a fertilidade do solo e o conteúdo de matéria orgânica do solo (MOS). Os objetivos específicos foram investigar a influência de sistemas de produção de cana-deaçúcar sobre: (1) os parâmetros de fertilidade do solo; (2) sobre as frações físicas do carbono; (3) e em frações de substâncias húmicas, em um experimento de longa duração, comparando dois tipos de preparo do solo e dois sistemas de manejo da palhada em Argissolo Amarelo, na região tabuleiros costeiros do Espírito Santo, Brasil. Os tratamentos consistiram de parcelas (preparo convencional (PC)

Were quantified the plant residues on the soil, total soil organic carbon (TOC) and nitrogen (TN) contents and the different soil organic matte (SOM) fractions and to determine 13C and 15N isotopic soil composition and plant residues in the crop–livestock integration system (CLIS), pasture and Cerrado areas, in Goias, Brazil. TOC and TN, C and N light organic matter content (C-LOM/N-LOM); C and N of particulate organic matter (C-POM/N-POM); and mineral organic matter (C-MOM/N-MOM) were evaluated. δ13C and δ15N of soil and LOM, POM, and MOM fractions, as well as the δ13C of plant residues, were also determined. Plant residues from pasture were more enriched with nutrients and C, and CLIS which are richer in N. δ13C of pasture and CLIS soils indicated that the C from the Cerrado vegetation (typically C3) was replaced by vegetation with C4 photosynthetic mechanisms. CLIS accumulated more TOC than the pasture, and provided higher C-MOM and N-MOM values than pasture, and higher N-LOM levels than pasture and Cerrado. δ13C of LOM is associated with more recent origins of carbon. δ15N of POM and soil of the CLIS and pasture indicate greater mineralization of SOM.