ABSTRACT Vast areas of the Brazilian Amazon have been deforested for the expansion of livestock and the agricultural frontier, which has resulted in soil exhaustion. It is therefore urgent to reduce deforestation and encourage sustainable land use to promote social and economic development in the region. The aim of this study was to evaluate the impact of different land use systems (an agroforestry system, cassava cultivation, non-degraded pasture, native forest) on the chemical properties of the soil (0-40 cm) in the mesoregion of the Juruá Valley, in the state of Acre, Brazil. Principal component analysis showed the soil in the forested area (reference) has greater values for P, Ca2+, Mg2+, K+, Na+, sum of bases, and cation exchange capacity; while hierarchical cluster analysis suggested little dissimilarity to the soil in the agroforestry system, and high dissimilarity to the soil in the areas of cassava cultivation and pasture. The results therefore support agroforestry as the most sustainable land use system, compared to cassava cultivation or pasture.

ABSTRACT There is a need for greater knowledge about the medium- and long-term effects of prescribed fire management on soil in ecosystems prone to wildfires and more vulnerable to climate change. This study examined the short- and medium-term effects of prescribed fire on soil chemical properties and chemical fractions of soil organic matter (SOM) in two positions of the landscape in a high-elevation grassland environment. The ecosystem is located in the mountain peaks of southeastern Brazil associated with the Atlantic Forest biome. Prescribed fire was conducted in 2017 to reduce understory vegetation and thus prevent potential severe wildfires. Soil samples were collected at the layers of 0.00-0.10, 0.10-0.20, and 0.20-0.40 m, at eight composite sampling. The composite samples were collected on five different occasions: before the prescribed fire, and 10, 30, 90, and 240 days after the prescribed fire. Soil chemical properties, total organic carbon, labile C, and chemical fractionation of SOM were analyzed. All soil properties investigated were affected by the prescribed fire, with variations in landscape position, duration of effect, and soil layer. In the backslope area, the medium-term effect of fire was negative and induced soil degradation and induced soil degradation. In the footslope area, the system showed greater resilience to the effects of fire, as indicated by the recovery of the soil’s chemical properties. These results can help assess the suitability of controlled burning of vegetation for managing risks of fire in mountainous regions, such as high-elevation grasslands.

RESUMO Na região da Serra da Mantiqueira os estudos pedogenéticos podem contribuir tanto para o entendimento de eventos pretéritos como para auxiliar na conservação dos recursos naturais. Este estudo objetivou caracterizar solos de região altomontana de Minas Gerais para avaliar a influência das condições paleoambientais na pedogênese. Cinco perfis foram selecionados e caracterizados quanto aos atributos morfológicos, físicos e químicos. Análises isotópicas de 13C foram realizadas em amostras de solo coletadas nas profundidades de 10, 20, 30, 40, 50, 60, 80 e 100 cm; exceto em P2, que foi coletado até 60 cm de profundidade. A distribuição errática das frações granulométricas e de C evidenciam a natureza sedimentar dos solos, resultado da ação erosiva condicionada pelo relevo. Nos perfis P2, P4 e P5 (Cambissolos/Cambisols) a coloração brunada indica o processo de xantização, enquanto no perfil P1 (Argissolo/Lixisol) é evidenciado o processo de eluviação e iluviação, resultando no incremento de argila em profundidade e pela presença de cerosidade. Em P3 (Latossolo/Ferralsol) os pequenos valores de soma de bases, remoção de sílica e valores da razão SiO2/Al2O3 (índice ki) inferiores a 1,0 evidenciam o intemperismo avançado e o processo de alitização. Nos perfis verifica-se elevados teores de C orgânico em profundidade e acúmulo superficial, o que sugere a ocorrência do processo de melanização. A variação na assinatura isotópica do δ 13C indica uma condição pretérita mais seca, com vegetação mista, com mudança gradual de vegetação com via fotossintética predominante C3. Em P1 e P4, a diminuição dos teores de δ 13C em superfície é resultado da ação antrópica.

ABSTRACT In the Serra da Mantiqueira region the pedogenetic studies contribute to both the understanding of past events and supporting the conservation of natural resources. This study aimed to characterize the soils from the Minas Gerais high-mountains region to evaluate the influence of paleoenvironmental conditions on pedogenesis. Five profiles were selected and characterized for morphological, physical and chemical properties. Isotopic analyses of 13C were performed in soil samples collected at depths of 10, 20, 30, 40, 50, 60, 80 and 100 cm; except in P2, which was collected up to 60 cm deep. Erratic distribution of the particle-size fractions and C contents highlight the sedimentary nature of the profiles, resulting from the erosive action favored by the relief. High organic C content in subsurface and its accumulation in the surface were observed in the profiles, which suggests the occurrence of the melanization process. In the profiles P2, P4 and P5 (Cambissolos/ Cambisols) the brownish color indicates the xanthization process, while in P1 (Argissolo/ Lixisol), is highlighted the process of eluviation and illuviation resulting in the increase of clay in subsurface and presence of clay films. In P3 (Latossolo/ Ferralsol), the low values of sum of bases, silica removal and SiO2/Al2O3 ratio (ki index) values below 1.0 point to the advanced weathering and the allitization process. The variation in the isotopic signature of δ13C indicates a drier past condition, with mixed vegetation, with gradual change of vegetation with predominant C3 photosynthetic pathway. In P1 and P4, the decrease in the contents of δ13C in surface results from anthropic action.

ABSTRACT: The soil particles can be gathered through physical and/or chemical processes in association with the biological activity, leading to the formation of aggregates. Soil aggregates has several functions in the soil, increasing macroporosity and water circulation - consequently reducing soil erosion and mechanical resistance to root growth, contributing to greater fixation of plants to the soil and absorption of water and nutrients, and protection of intra-aggregate organic matter. The aggregates were initially classified morphologically and in terms of their stability. In recent years, another way of evaluating aggregates, regarding their formation or origin pathway, has gained prominence in the studies conducted in Brazil. As for their origin, the aggregates can be classified morphologically as physicogenic, biogenic, or intermediate. This manuscript presents the techniques used to sample aggregates, the morphological patterns for their distinction observed in different soil classes and management types, and the chemical and physical properties. Additionally, we present analyses that are not commonly used to evaluate aggregates but which have the potential to be used as tools for a better understanding of their origin and to evaluate their modifications when subject to different types of management. In practical terms, identifying the aggregate origin and determining the related attributes allows recognizing the effect of vegetation/soil/management on soil aggregate forming agents, mainly roots and soil fauna, which reflects soil quality. For future studies, and especially to determine the importance of biogenic aggregation in improving edaphic properties, we suggest the use of micromorphology, near-infrared spectroscopy, X-ray computed tomography, clay dispersion analyses in addition with chemical, physical, and biological analysis. This approach can contribute to the identification of other patterns related to pedogenesis and the pathways of aggregate formation.

RESUMO Avaliou-se a eficiência da aveia preta na recuperação da agregação do solo e quantificou-se os teores dos nutrientes nos agregados biogênicos e fisiogênicos em áreas de cultivo de Nova Friburgo, RJ. A paisagem foi estratificada nas secções: superior - com o emprego de aveia preta, adubada e outra não adubada; e inferior: com aveia preta adubada, outra com consórcio de aveia preta, nabo forrageiro e ervilhaca com adubação. Ambas as secções tinham área adjacente de floresta. Os agregados foram separados quanto às vias de formação quantificando-se a porcentagem de massa em cada via de formação. Foram analisados: estabilidade dos agregados, teores de nutrientes e conteúdo de carbono orgânico. Na parte superior, na área adubada verificou-se a maior porcentagem de agregados biogênicos associada a maiores valores de carbono orgânico total, e fertilidade. Nessa área também foram observados maiores valores de diâmetro médio ponderado e o diâmetro médio geométrico dos agregados. Na parte inferior, na área de consórcio foi quantificada a maior porcentagem de agregados biogênicos e quantificados os menores teores de P, Ca+2, Mg+2 e K+. Os sistemas de manejo influenciaram nas vias de formação dos agregados. A classificação morfológica representa uma importante ferramenta para o monitoramento do manejo do solo. A aveia preta promoveu o aumento da formação dos agregados biogênicos, os quais se comportaram como compartimentos de reservas de nutrientes.

ABSTRACT The objective of this study was to evaluate the efficiency of black oat (Avena strigosa Schreb) crops in recovering soil aggregation, and quantify the nutrient contents in aggregates considering their formation pathways (biogenic and physicogenic) in crop areas in a mountains environment in the municipality of Nova Friburgo, RJ, Brazil. The landscape was stratified into two sections for the study: upper, two areas with black oat crops, one fertilized and one not fertilized one not fertilized, and one adjacent forest area representing the original soil conditions; and lower: one fertilized area with black oat, and one fertilized area with black oat intercrops with oilseed radish (Raphanus sativus L.) and vetch (Vicia sativa L.), and one adjacent forest area representing the original soil conditions. The aggregates were separated according to their formation pathways, quantifying the weight percentage of each formation pathway. The aggregate stability and nutrient and organic carbon contents were evaluated. The fertilized area in the upper section had the highest biogenic aggregate percentage, which was associated with the highest total organic carbon contents, and soil fertility. This area also had the highest weighted mean diameter (WMD) and geometric mean diameter (GMD) of aggregates. The intercrop area in the lower section had the highest biogenic aggregate percentage and the lowest P, Ca+2, Mg+2, and K+ contents in the aggregates. The management systems affected the aggregate formation pathways. Morphological classification is an important tool for the monitoring of soil management. The black oat crops increased the biogenic aggregate formation, which become reservoir of nutrients.

ABSTRACT Histosols provide several ecosystem services, related mainly to their reserves of carbon and nitrogen. Management practices in these soils can increase the mineralization of organic matter and contribute to the emission of greenhouse gases. This study aimed to investigate the effect of tillage with plowing and drainage on Histosol properties in three land use systems located in the municipality of Rio de Janeiro, Brazil. Three areas subjected to different land use systems over the last twenty years were chosen: Area 1, secondary forest with natural regeneration; Area 2, conventional tillage of cassava with plowing; and Area 3, intercropped coconut + cassava with an artificial drainage system. The chemical characterization, von Post scale of organic matter decomposition, percentage of rubbed fiber, organic matter, percentage of mineral material, bulk density, electrical conductivity, soluble phosphate, total organic carbon (TOC) and nitrogen (NT), organic carbon fractions, and C and N stocks were analyzed. Our results showed the critical, nearly irreversible effects of agricultural practices comprising drainage and plowing of the soil. Over twenty years, in Area 2, the TOC and NT values decreased by 33 and 20 %, respectively in the histic horizon, and by about 17 and 8 %, respectively in the gley horizon. In Area 3, the TOC and NT values decreased by 31 and 18 %, respectively, in the histic horizon, and by 27 and 21 % in the gley horizon. Our findings also showed that the loss of C is related to the labile organic carbon, which is more sensitive to environmental changes, even at deeper depths. The plowing of the soil decreases the organic matter content due to the accelerated oxidation of organic matter, increasing the bulk density. Drainage, besides the loss of organic matter by subsidence, promotes the sulfidization of the soil with a high content of SO42-, due to the oxidation of soil materials containing sulfides.

Resumo O fósforo (P) é um elemento essencial para a produtividade dos vinhedos. Este estudo avaliou a influência do material de origem nas frações orgânicas de P em solos de vinhedos formados e áreas de solos origem basáltica e riodacítica. O estudo foi conduzido em quatro municípios localizados nas regiões montanhosas de Santa Catarina, Brasil: Urubici, São Joaquim, Campos Novos e Água Doce. Amostras de solo foram coletadas nas entrelinhas das videiras nas profundidades de 0,00-0,05, 0,05-0,10, 0,10-0,20 e 0,20-0,40 m. Foram avaliados os atributos químicos do solo (pH em H2O, Ca2+, Mg2+, Al3+, P, K + e H+Al), carbono orgânico total (COT), P disponível e residual, P lábil (extraído com bicarbonato de sódio), moderadamente lábil (extraído com ácido sulfúrico) e P moderadamente resistente (extraído com hidróxido de sódio). Nas áreas de solos formados a partir de material de origem de natureza basáltica foram verificados os maiores teores de COT, P disponível e residual, e P moderadamente lábil e moderadamente resistente, enquanto naqueles formados a partir de rochas como riodacitos observaram-se valores de P lábil mais elevados. Os altos níveis das frações P moderadamente lábeis e moderadamente resistentes nos solos formados a partir de basalto foram atribuídos ao seu alto COT, P disponível e conteúdo residual de P. Verificou-se que o material de origem dos solos influencia as frações orgânicas de P nos solos dos vinhedos.

Abstract Phosphorus (P) is an essential element for vineyard productivity. This study assessed the influence of parent material on organic P fractions in vineyard soils of basaltic and rhyodacitic origin. The experiment was conducted in four municipalities located in mountainous regions in Santa Catarina, Brazil: Urubici, São Joaquim, Campos Novos, and Água Doce. Disturbed soil samples were collected between grapevine rows at depths of 0.00-0.05, 0.05-0.10, 0.10-0.20, and 0.20-0.40 m. Soil chemical attributes (pH in H2O, Ca2+, Mg2+, Al3+, P, K+, and H + Al), total organic carbon (TOC), available and residual P, labile P (extracted with sodium bicarbonate), moderately labile P (extracted with sulfuric acid), and moderately resistant P (extracted with sodium hydroxide) were determined. Soil parent material influenced the dynamics of phosphorus in vineyard soils. Both P forms (available and solution equilibrium P) and P organic fractions (labile, moderately labile, and moderately resistant P), are affected by the parent material. Basaltic soils had higher TOC, available and residual P, and moderately labile and moderately resistant P, whereas rhyodacitic soils showed higher labile P. The high levels of moderately labile and moderately resistant P fractions in basaltic soil were attributed to its high TOC, available P, and residual P contents. Parent material was found to influence organic P fractions in vineyard soils.

ABSTRACT. In Amazonia, the main causes of deforestation are systems based on slash-and-burn agriculture. The objective of this work was to evaluate temporal changes in the soil chemical attributes after the vegetation has been slashed and burned in an area of native forest in the Western Amazon. For this study, four hectares of forest in Cruzeiro do Sul, State of Acre, Brazil, was slashed and burned. The soil in the study area was classified as Ultisol (Argissolo Amarelo Distrófico típico). Soil samples were collected over the course of one year, the first one being collected 16 hours after the burn and the others at 30, 60, 90, 150, 210, 270, and 360 days after the burn. The soil surface layers were more sensitive to fire action. Ashes from vegetation burn increased pH values, basic cations, and C values only in the first months, resulting in higher basal saturation values (V%). The practice of slash-and-burn after 12 months resulted in lower values of pH, Ca, Mg, K, and P and higher values of Al and H, as well as saturation by aluminum in the soil, indicating this practice contributes to the reduction of soil fertility.

ABSTRACT: Records of changes in the phytosociological structure of vegetation can be observed more clearly in soils that have more significant accumulation of organic matter, like those occurring in high-mountain environments. The aim of this study was to characterize soils formed in high-mountain environments in the Itatiaia National Park (INP), state of Rio de Janeiro, southeastern Brazil, and to discuss the potential of preserved phytoliths as markers of vegetative history and environmental factors. Four profiles were selected, which were morphologically described and evaluated for their physical and chemical properties. For phytolith analysis and high-resolution determination of the stable carbon isotopes, samples were collected at 0.10 m intervals. The profiles showed highly similar morphological characteristics, with peat deposits and colluvial sediments as source material, produced in the highest parts of the landscape. High-mountain soils in the INP have properties related to high contents of organic matter, like high acidity, low base saturation, and high CEC values due to high H+ contents. The soils are formed by the addition of plant residues, which accumulate due to the cold and humid climate during most of the year in these environments. The phytolith assemblage had a high frequency of morphotypes characteristic of temperate, cold, and high elevation intertropical regions, especially of Pooideae plants. The phytolith indexes indicated open vegetation environments with a predominance of C3 grasses, suggesting cold climate conditions, and corroborating the δ13C isotopic values. The results of phytolith analysis of the profiles reflected characteristics related to soil genesis. Organism is the main soil formation factor, conditioned by the factors relief (elevation) and climate, which resulted in low temperatures and lead organic matter accumulation.

RESUMO A formação e estabilidade de agregados estão intimamente relacionadas à qualidade do solo, contribuindo de maneira significativa na capacidade de estocar carbono e manutenção de nutrientes no solo. Os agregados do solo são formados por duas vias distintas: a fisiogênica, relacionada a ciclos de umedecimento e/ou secagem e adição de matéria orgânica e a biogênica associada à ação dos organismos da macrofauna e de raízes. Neste estudo, objetivou-se separar os agregados conforme a via de formação e, posteriormente, quantificar e comparar os teores de carbono orgânico das substâncias húmicas e a estabilidade de agregados formados por diferentes vias e coberturas vegetais, na região do Médio Vale do Paraiba Fluminense, Pinheiral (RJ). Foram coletadas amostras indeformadas de solo na profundidade de 0-10 cm, em um Cambissolo Háplico Tb Distrófico, sob quatro coberturas vegetais: floresta secundária em diferentes estádios sucessionais - avançado (FSEA); médio (FSEM); inicial (FSEI) e uma área de pasto misto manejado (PMM). Os agregados foram separados e identificados em três classes morfológicas (fisiogênica, biogênica e intermediária). Posteriormente, foram determinados o diâmetro médio ponderado (DMP) e geométrico (DMG) dos agregados, fracionamento químico da matéria orgânica e quantificação dos teores de carbono orgânico total (COT) e das substâncias húmicas: humina (C-HUM), ácido húmico (C-FAH) e ácido fúlvico (C-FAF). Os agregados biogênicos foram encontrados em menor quantidade e apresentaram maiores teores de COT, C-HUM, C-FAH em comparação aos agregados intermediários e fisiogênicos. Dessa forma, os agregados biogênicos têm potencial para serem enquadrados como indicadores de qualidade do solo, associados a ambientes mais estruturados, capazes de manter os processos intrínsecos a sua formação.

ABSTRACT Aggregate formation and stability are related to soil quality, contributing significantly to the carbon storage and nutrient maintenance capacities of the soil. Soil aggregates are formed by two different process: physicogenic, related to moistening and drying cycles and input of organic matter; and biogenic, related to the action of macrofauna organisms and roots. The objective this work was to classify aggregates according to their formation process, quantify and compare organic carbon contents in humic substances and assess the stability of aggregates formed by different processes, in areas with different coverage in the Mid Paraiba Valley, Pinheiral, State of Rio de Janeiro, Brazil. Aggregated soil samples were collected at a depth of 0-10 cm, in a Cambisol (Cambissolo Háplico Tb Distrófico) under four plant covers: secondary forest in advanced (SFAS), medium (SFMS) and initial (SFIS) successional stages and managed mixed pasture (MMP). Aggregates were classified and identified into three morphological classes (physicogenic, biogenic and intermediate). The variables evaluated were mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates, chemical fractions of organic matter, total organic carbon (TOC) and humic substances: humin (C-HUM) humic acid (C-FAH) and fulvic acid (C-FAF). Biogenic aggregates were found in smaller quantities and showed higher TOC, C-HUM and C-FAH, compared to intermediate and physicogenic aggregates. Thus, biogenic aggregates have potential to be used as soil quality indicators for structured environments, which are able to maintain its intrinsic formation processes.