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Tree species and fertilization sources may affect the soil organic carbon (SOC) and fertility in agroforestry (AF) systems in temperate regions, but this remains unexplored. This study assesses the longitudinal trends in the SOC and major nutrients in a 17-year AF site established on an Ultisol in Fayetteville, AR. We evaluated how management and fertilization (mineral vs. organic) affect the soil’s physical and chemical properties using the tree species: red oak (Quercus rubra L.) and pecan Carya illinoinensis (Wangenh.) K. Koch. Long-term applications of poultry litter increased the soil pH, whereas the Mg and S concentrations decreased compared to the baseline levels (1999). Poultry litter increased the soil P concentration in 53% compared to the baseline levels and reduced the soil C:N ratio. After 17 years, increased Ca, SOC, and N concentrations were observed in the soils under the pecan stands that received poultry litter. Positive correlations occurred between the SOC and N (r = 0.96) as well as the Ca (r = 0.71) and P (r = 0.61) at a soil depth of 0–15 cm. Our findings demonstrated that the changes in SOC and fertility in the AF soils vary according to tree species and fertilization, mostly due to distinctive leaf litter and nutrient inputs. Organic matter accumulation increased the SOC retention and nutrient availability in the temperate AF systems.

A global, unified dataset on Soil Organic Carbon (SOC) changes under perennial crops has not existed till now. We present a global, harmonised database on SOC change resulting from perennial crop cultivation. It contains information about 1605 paired-comparison empirical values (some of which are aggregated data) from 180 different peer-reviewed studies, 709 sites, on 58 different perennial crop types, from 32 countries in temperate, tropical and boreal areas; including species used for food, bioenergy and bio-products. The database also contains information on climate, soil characteristics, management and topography. This is the first such global compilation and will act as a baseline for SOC changes in perennial crops. It will be key to supporting global modelling of land use and carbon cycle feedbacks, and supporting agricultural policy development., Design Type(s)data integration objective • data collection and processing objective • factorial designMeasurement Type(s)amount of carbon atom in soilTechnology Type(s)digital curationFactor Type(s)climate • Species • experimental condition • ageSample Characteristic(s)Brazil • cultivated environment • Canada • United States of America • New Zealand • Italy • Germany • Cameroon • India • Sri Lanka • Venezuela • Kingdom of Denmark • Republic of Ireland • French Republic • United Kingdom • Kingdom of Spain • Costa Rica • Ethiopia • Ghana • Indonesia • Mexico • Nigeria • Republic of South Africa • Portuguese Republic • China • Malaysia • Turkey • Israel • Sweden • italy • Georgia • Puerto Rico • Tanzania • Australia Machine-accessible metadata file describing the reported data (ISA-Tab format)

The genesis of Planosols is a complex process since it can involve multiple cycles of soil formation, deposition of allochthonous materials and also past climate changes. Furthermore, this subject is still poorly studied in the humid tropics, thus hindering a proper appraisal of the potentials and limitations of Planosols. The objective of this research was to study pedogenetic processes and properties of Planosols formed from different parent materials in southern Brazil. Four soils were sampled: (P1) Hypereutric Luvic Albic Planosol, developed on lagoon plain sediments; (P2) Orthoeutric Luvic Albic Planosol, on Holocene alluvial deposits; (P3) Hypereutric Luvic Albic Planosol, on granite; and (P4) Orthoeutric Luvic Albic Planosol, on gneiss. All Planosols presented sandy horizons A and E, with low pH (

The Soil Management Assessment Framework (SMAF) is a quantitative soil quality (SQ) evaluation tool that is widely applied to assess soil response to specific agricultural management practices over time. Considering the reported SQ benefits of agroforestry (AF) systems and the potential usefulness of SMAF, the objective of this study was to evaluate the effects of tree species (pecan [Carya illinoinensis (Wangenh.) K. Koch] and northern red oak [Quercus rubra L.]), soil fertility source (poultry litter [PL] and inorganic N fertilizer [control]), and soil depth (0–15 and 15–30 cm) on SMAF‐derived SQ indices after 17 yr of management at an AF site in northwest Arkansas. Averaged across soil depth, soil organic C scores under red oak with PL application had a lower score (0.48) than red oak fertilized with inorganic N (0.60) and pecan receiving long‐term PL applications (0.60), which did not differ from pecan with inorganic N fertilizer application (0.51). Averaged across soil depth, the soil quality index (SQI) for pecan receiving PL applications was 1.1 times greater than that under red oak receiving PL and soils under pecan receiving inorganic N fertilizer. Soil quality assessments use in AF are novel, as SMAF has not been used to identify soil health in these systems, although specific tree crop codes need to be developed in SMAF. Results of this study demonstrate that soils planted under various tree species respond dissimilarly to fertilizer sources and that management may improve overall SQ.

Nosso objetivo foi avaliar a morfologia dos poros de um Latossolo gibbsítico submetido ao sistema multi-práticas de manejo cafeeiro com diferentes doses de gesso via análises de imagens 2 e 3 D. O delineamento foi em blocos ao acaso com três tratamentos: G0-ausência de gesso adicional; G7 e G28, com 7 e 28 Mg ha–1 de gesso adicional, respectivamente, aplicados na superfície do solo na linha de plantio, em três camadas: 0,20-0,34 m; 0,80-0,94m e 1,50-1,64 m. Amostras de solo com estrutura preservada em tubos de acrílico foram coletadas na linha de plantio, em três repetições. Utilizou-se análises de imagem obtidas via tomografia computada de raios-X e micromorfologia via secções delgadas. Os dados foram submetidos a análise estatística descritiva. A microestrutura típica do Latossolo permaneceu granular, coerente à predominância da gibbsita na fração argila. Na micromorfologia qualificou-se uma grande quantidade de poros tipo empacotamento (70%) e cavidades (10%); mudança na trama de porfírica para enáulica, conforme o incremento em gesso. Nas imagens tomográficas de raios-X detectou-se maior diversificação morfológica dos poros, especialmente no G28, com predomínio de poros laminares (12%), bioporos tubulares (12%) e de empacotamento/empilhamento (64%), bem como, contabilizou-se maior número (n>30.000) e categorias de poros devido ao maior detalhamento da técnica, a exemplo dos bioporos tubulares (G28>G7=G0) e poros laminares (G28>G7=G0). As técnicas se complementam, ou seja, a micromorfologia permitiu avaliar a organização estrutural com qualidade e a tomografia de raio-X com quantidade de poros devido à maior resolução espacial e aos algoritmos de cálculo.

This study evaluates the dynamics of soil organic carbon (SOC) underperennial crops across the globe. It quantifies the effect of change fromannual to perennial crops and the subsequent temporal changes in SOCstocks during the perennial crop cycle. It also presents an empiricalmodel to estimate changes in the SOC content under crops as a functionof time, land use, and site characteristics. We used a harmonised globaldataset containing paired-comparison empirical values of SOC andincluding different types of perennial crops (perennial grasses, palms,and woody plants) with different end-uses: bioenergy, food, other bioproducts, and short rotation coppice crops. Salient outcomes include: a20-year period encompassing a change from annual to perennial cropsled to an average 20% increase in SOC at 0-30 cm (6.0 ± 4.6 Mg ha-1gain) and a total of 10% increase over the 0-100 cm soil profile (5.7 ±10.9 Mg ha-1). A change from natural pasture to perennial cropdecreased SOC stocks by 1% over 0-30 cm (-2.5 ± 4.2 Mg ha-1) and10% over 0-100 cm (-13.6 ± 8.9 Mg ha-1). The effect of a land usechange from forest to perennial crops did not have significant impacts,probably due to the limited number of plots; but the data indicated thatwhile a 2% increase in SOC was observed at 0-30 cm (16.81 ± 55.1 Mgha-1), a decrease of 24% was observed at 30-100 cm (-40.1 ± 16.8 Mgha-1); perennial crops generally accumulate SOC through time,especially woody crops; and temperature was the main driver explainingdifferences in SOC dynamics, followed by crop age, soil bulk density, claycontent and depth. We present empirical evidence showing that the FAOperennialization strategy is reasonable, underscoring the role ofperennial crops as a useful component of climate change mitigationstrategies.

Converting abundant agricultural residues to valuable products, such as biochar, is a pressing challenge for society. Here, our objective has been to produce biochar-based fertilizers (BBFs) with high carbon stability, high yield, and characteristics favorable for their use in soils. Thus, H3PO4 with and without MgO was co-pyrolyzed with coffee husk and poultry litter. Proximate analysis, total phosphorus and magnesium, biochar yield, carbon retention, and thermal and chemical carbon stability were assessed. The BBFs were slightly acidic (pH ∼6.0) and showed high contents of total P (146–206 g kg–1) and total Mg (96–98 g kg–1), similar to commercial fertilizers. Biochar yield increased up to 65% when treated with H3PO4 and H3PO4–MgO, resulting in up to 78% greater carbon retention. BBFs showed higher thermal stability, by thermogravimetric analysis and muffle oxidation, when compared to corresponding pristine biochars. Conversely, the addition of H3PO4–MgO decreased the chemical stability (higher H2O2 and...

The C:N ratio is the most widely used indicator of the quality of organic residues and soil organic matter, but little is known about how average soil C:N ratios change when pristine lands are converted to agriculture in the humid tropics. This work aimed to compile the literature on Brazilian soils and calculate percent changes in soil organic carbon (SOC), total N and C:N ratios, after conversion of native vegetation to different land use systems. The hypotheses tested were that land use change affects mean soil C:N ratios across a range of experiments, and that different land use types would affect C:N ratios differently. Overall, average changes for SOC and total N for the 0–20 cm standard depth interval were respectively −14.4 and −13.1% (p

T errestrial ecosystems, comprising vegetation and soil in uplands and wetlands, significantly impact the global carbon (C) cycle and, under natural conditions, are a sink of atmospheric carbon dioxide (CO2) and methane (CH4). However, conversion of natural to managed ecosystems (i.e., agroecosystems, urban lands, and mined lands) depletes ecosystem C stocks, aggravates gaseous emissions, and exacerbates radiative forcing. Thus, the onset of agriculture around 8000 BC presumably transformed these sinks into a source of greenhouse gases (GHGs) (Ruddiman 2003), mostly CO2, CH4, and nitrous oxide (N2O), and depleted the terrestrial (soil, vegetation, and peatlands) C stocks. Ruddiman (2005) estimated the depletion of the terrestrial C stock (soil and vegetation) by 456 Pg (502.65 × 109 tn) since the onset of agriculture. Of this, the historic depletion of soil organic carbon (SOC) stock is estimated at 130 to 135 Pg (143.3 × 109 to 148.8 × 109 tn) (Sanderman et al. 2017; Lal 2018). Therefore, recarbonization of some of the terrestrial biosphere (soil and vegetation) is an important strategy to mitigate the anthropogenic climate change (ACC) and enhance other ecosystem services because of the link between SOC stock and atmospheric concentration of CO2 (Trenberth and Smith 2005). Recarbonizing the terrestrial biosphere involves…

Despite a multitude of studies on fertility and physics of tropical soils, the effect of soil parent material on their genesis, chemical and mineralogical composition is not yet fully understood. Here, we studied a toposequence of four deep, well-developed soils along a basalt-sandstone transition, comprising two Ferralsols and one Luvisol on the summit and midslopes of a basalt plateau, and one Cambisol at a lower sandstone plateau. Basalt soils had high (42–77%) clay contents, and were mostly comprised by gibbsite, Fe oxides, and poorly crystalline kaolinite, whereas the sandstone soil had

In tropical humid conditions, soil organic carbon (SOC) concentrations have been reported to be proportional to clay, clay + silt and Fe/Al oxide contents. Typically, soil texture and mineralogy are strongly dependent on soil parent materials, but it is not known if SOC retention would also be affected by soil parent material. Such relationship, if established, could be useful to estimate regional SOC stocks, since geological maps are more numerous and often more accurate than soil maps. The objective of this study was to assess the effect of parent material, texture,and oxide content on SOC contents in tropical highlands. Thus, samples to 1-m depth were obetained for seven soils derived from quartzite, sericite-schist, itabirite, serpentinite, limestone, gneiss and phyllite. All soils formed under similar climate and native forest, and were located on the midslope position. Despite wide variations in soil texture and mineralogy, there were no valid correlations between SOC and clay, clay + silt or Fe/Al oxide concentrations. Similarly, SOC stocks did not differ significantly when computed for 0–20, 0–40 and 0–100 cm layers, and in all soils most SOC was associated with the clay fraction. We propose that such absence of effects of soil parent material, texture and oxide contents on SOC retention can be due to the overriding effect of altitudes of 900–1100 m a.s.l., which resulted in higher SOC stocks because of lower mean annual temperatures. These trends are in contrast to those reported for tropical lowlands where the textural and mineralogical controls of SOC retention were first described. Therefore, soils on tropical highlands (> 900 m) are likely to present similarly high SOC stocks, whereas soil parent material, by means of soil texture, mineralogy and oxide contents would affect SOC retention only at lower altitudes.

The identification of paleosols is difficult when no buried horizons or lithification occur. Here, we described the identification of a possible paleosol, its characterization, and which features supported its positive diagnosis. In a construction site, a vertical cut exposed an unusual red–yellow mottling with massive structure and channels (probably faunal), in contrast with the overlying homogeneous red Oxisol with fine granular structure. A similar but more deferrified section with white–yellow mottling also occurred nearby, and both were sampled as large clods. In thin sections, many oriented clay coatings occur along channel voids, suggesting illuviation, as well as dissolving Fe nodules and Mn coatings along planar and channel voids. X-ray diffraction showed a clay dominated by kaolinite, traces of illite, and absence of gibbsite, again contrasting with the gibsitic-kaolinitic clay of the Oxisol. We confirmed the diagnosis of a Paleoultisol due to the following incompatibilities with the overlying Oxisol: (1) massive, apedal structure, and higher bulk density, (2) clay coatings indicative of illuviation as key soil-forming process, (3) low clay contents in particle-size analysis due to cementation, (4) very low organic carbon consistent with long-term inhumation, and (5) kaolinitic–illitic clay. The unusual granular microstructure of the B horizon of the Oxisol is partly derived from disintegration and desilication of the Paleoultisol.

Despite the ancillary knowledge that soil N is chiefly retained as soil organic matter, little is known about how it is affected by other soil and environmental factors, especially in the tropics. In this study, we performed a comprehensive survey of soils under native vegetation in Minas Gerais, Brazil, aiming to (a) measure soil Kjeldahl-N concentrations to a 1-m depth, (b) identify the main affecting factors of soil N retention, and (c) predict N through soil profile based on organic C (SOC) and its main conditioning factors. Soils under 36 fragments of native forest and savanna were sampled at five depths (0–10, 10–20, 20–40, 40–60, and 60–100 cm) and characterized by physical and chemical analyses, including total N determined by the micro-Kjeldahl method. Single and multivariate regressions were used to predict N concentrations based on soil properties and climatic factors. The average N concentrations ranged between 0.12 and 7.54 g kg−1, decreasing with depth, and can be predicted using SOC concentrations (R 2 = 0.86). Multivariate regressions using more input data, namely texture, cation exchange capacity (CEC), and altitude increased slightly R 2 values (0.68–0.90) for separate soil depths, but not for the whole dataset (R 2 = 0.85). We demonstrated that N can be adequately predicted based on SOC concentrations, for any depth and forest type. The implications of the stable SOC/N relation and their coupled cycles and the environmental factors affecting N retention in Brazilian weathered soils are further discussed.

Soil internal drainage plays a major role in soil genesis, and it is mostly dependent on topography. However, the existence of sedimentary and meta-sedimentary rock strata with variable dip angle allows for strong differences in internal drainage for identical topographies, which result in a marked differentiation in the properties of overlain soils. This work aimed to investigate the micromorphology of soils formed from different dip angles of rock strata and their relationships to internal drainage, in Minas Gerais, Brazil. Over horizontal strata, a Xanthic Acrudox lacking hematite and with blocky structure has developed. Over strata with 45° dip angle, strong drainage has resulted in intense desilication, forming a Rhodic Acrudox having hematite and with strong fine granular structure. Micromorphological analyses showed that both soils contain relict nodules which are probably being dissolved in the current environment, whereas only the Xanthic Acrudox has nodules in current processes of formation due to slower drainage. The Cr horizon of both soils, but mainly the Xanthic Acrudox, presented a much slower saturated hydraulic conductivity than the respective overlying horizons, which was associated with a pattern of poorly connected fissural pores as seen in thin sections. The Cr horizon of the Rhodic Acrudox showed a matrix impregnated by Mn and Fe oxides in an unusual pattern of microlamination and hypocoatings that appear to be unstable, dissolving in the current, strongly drained environment. The soil color is a reliable indicator of such differential pedogenesis in these conditions. RESUMO A drenagem interna desempenha um importante papel na gênese de solos e é principalmente dependente da topografia. Contudo, a existência de estratos de rochas sedimentares e meta-sedimentares com ângulo de inclinação variável permite forte diferença na drenagem interna em locais de topografia semelhante, o que resulta em marcante diferenciação de propriedades dos solos acima. Este trabalho teve como objetivo investigar a micromorfologia do solo com estratos de rochas com diferentes ângulos de inclinação e suas relações com a drenagem interna dos solos, em Minas Gerais, Brasil. Sobre estratos horizontalizados, formou-se um Latossolo Amarelo ácrico típico sem hematita e de fraca estrutura média em blocos subangulares. Sobre estratos com ângulo de inclinação de 45°, a drenagem forte resultou em intensa dessilicatização, formando um Latossolo Vermelho ácrico contendo hematita e de estrutura forte muito pequena granular. As análises micromorfológicas mostraram que ambos os solos contêm nódulos reliquiais que estão provavelmente sendo dissolvidos no ambiente atual, enquanto somente o Latossolo Amarelo possui nódulos em processo de formação, devido à drenagem mais lenta. Os horizontes Cr de ambos os solos, mas principalmente do Latossolo Amarelo, apresentaram condutividade hidráulica saturada muito menor do que os horizontes sobrejacentes, em associação ao padrão de poros fissurais pouco conectados. O horizonte Cr do Latossolo Vermelho apresentou uma matriz impregnada por óxidos de Mn e Fe em padrão microlaminado incomum e hipocoberturas, aparentemente instáveis, dissolvendo-se no ambiente atual excessivamente drenado. A cor do solo é um indicador confiável destes diferentes sistemas pedológicos.

Metamorphic ultrabasic rocks are typically enriched in heavy trace elements, mostly contained within easily-weatherable silicate minerals such as talc and serpentine. In the humid tropics, such rocks can decompose rapidly, thus releasing trace elements (TE) at rates likely to create extreme soil environments that hamper plant development, but few studies are available on this issue in Brazil and most South America. We sampled eight soils formed on a 3.1 km2 steatite (a type of talc-schist) hill and its piedmont, with slopes ranging from 4 to 90%. The soils varied from shallow Entisols and Inceptisols to deep (>2 m) Oxisols, along a weathering continuum well described by increasing residual concentration of Fe oxides, which ranged from 15 to 69% total Fe2O3 (determined by X-ray fluorescence). Total Co, Cr, Ni, Ti and V were high in comparison to world soils´ ranges and averages, whereas Ba, Cu and Zr were relatively low or near average. Total concentrations of these TE except Ba were proportional to total Fe, and the same trends occurred when dithionite-extractable Fe and TE were considered. Thus, both primary (magnetite, chromite, hematite) and secondary (maghemite, hematite, goethite, amorphous phases) Fe oxides likely control soil TE contents, with much variation across TE, soils and horizons. Co, Cr and Ti were mostly comprised within the residual phases, i.e. mostly resistant primary minerals, whereas a larger part of Ba, Cu, Ni, V and Zr were included in pedogenic Fe oxides and other phases. The potentially plant-available (extracted with Mehlich-I) TE were mainly Ba, Co and Cu, and to a much lower degree, Ni. The environmental implications of the concentrations and partition of the studied TE are briefly discussed.

Despite recent efforts to assess heavy metal contents in soils in Brazil, little is known about the effect of parent material and sampling depth, both critical factors controlling soil geochemical composition, especially in areas with complex geology. We determined concentrations of Cr, Cu, Mn, Ni, Pb and Zn in soil profiles developed from eight contrasting rocks (quartzite, mica schist, gabbro, gneiss, limestone, phyllite, itabirite and ironstone after serpentinite) in a relatively small area under similar climate and native forests in Minas Gerais, Brazil. The hypotheses tested were that soil metal concentrations vary with parent material and depth. Soil samplings were done in triplicate at the 0–5, 30–40 and 90–100 cm depths, and metal concentrations assessed after nitric acid digestion and atomic absorption spectrometry determination. Generally, metal concentrations varied little with depth, and Pb concentrations were low and very similar among soils (always 75 mg kg−1), reaching 210–258 mg kg−1 in the soils derived from mafic and ultramafic rocks. Ni was generally

Understanding soil formation processes across different landscapes is needed to predict how soil properties will respond to land use change. This study aimed to characterize mountainous Inceptisols (Cambisols) under high altitude subtropical climate in southeastern Brazil, by soil physical, chemical and micromorphological analyses, under native forest and pasture. The soil under pasture had a greater bulk density than under forest, resulting in a severe reduction of macroporosity. At two depths, coarse quartz grains are angular, suggesting absence of transportational processes, thus confirming an autochthonous pedogenesis from the underlying gneissic rock. Most feldspars were weathered beyond recognition, but mineral alteration was commonly seen across cleavage plans and edges of micas. The micromorphological results suggest an intermediate stage of mineral weathering and soil development, which is in accordance with properties expected to be found in Inceptisols. RESUMOHá a necessidade de se compreender os processos de formação do solo em diferentes paisagens para prever como as propriedades do solo irão responder às mudanças no uso do solo. Neste estudo, objetivou-se caracterizar Cambissolos em uma região montanhosa sob clima subtropical de altitude no Sudeste do Brasil, por meio de análises físicas, químicas e micromorfológicas do solo, sob mata nativa e pastagem. O solo sob pastagem apresentou maior densidade do solo do que sob mata, expressa pela intensa redução de macroporosidade na primeira condição. Em ambas as profundidades, os grãos de quartzo grosseiros são angulares, sugerindo ausência de quaisquer processos de transporte, confirmando, assim, uma pedogênese autóctone, a partir da rocha gnáissica subjacente. A maioria dos feldspatos se encontra intemperizada e não mais identificável, mas a alteração mineral é comumente vista ao longo de planos de clivagem e bordas de micas. Os resultados micromorfólogicos sugerem um estágio intermediário de intemperismo mineral e desenvolvimento do solo, o que está de acordo com as propriedades esperadas em Cambissolos.

A densidade do solo (Ds) é um importante indicador da qualidade física do solo, mas há pouca disponibilidade de informações sobre seus valores a maiores profundidades em razão da dificuldade amostral envolvida. Portanto, funções de pedotransferência têm sido utilizadas para estimar a Ds com relativo êxito, mas ainda sem especificidade aos diferentes biomas brasileiros. O objetivo deste trabalho foi desenvolver funções matemáticas capazes de descrever a Ds até 1 m de profundidade em áreas de vegetação nativa das regiões central e sul de Minas Gerais. A Ds foi amostrada pelo método do anel volumétrico em 53 perfis de solo de diferentes ordens, em seis profundidades (0-5, 5-10, 10-20, 30-40, 50-60 e 90-100 cm). A Ds variou entre 0,66 e 1,74 kg dm-3, com média de 1,25 kg dm-3, e foi geralmente menor nas camadas de 0-5 e 5-10 cm. Por meio de regressão linear múltipla (stepwise), foram gerados modelos com base nas propriedades químicas de rotina e granulometria, que permitiram estimar a Ds até 1 m de profundidade. Os teores de C orgânico do solo, areia, silte e argila e a capacidade de troca catiônica potencial (T) foram as variáveis de maior relevância nos modelos, que alcançaram maior acurácia para a ordem Latossolos (R2ajust = 0,85), seguida por Cambissolos (R2ajust = 0,69), Nitossolos (R2ajust = 0,67) e Argissolos (R2ajust = 0,51). Uma vez que a modelagem para a base de dados completa atingiu R2ajust de 0,50, pode-se concluir que a estratificação por ordem taxonômica foi útil para melhorar os ajustes obtidos, com exceção da ordem Argissolo. Bulk density (ρb) is an important indicator of soil physical quality, but it is seldom assessed at greater depths due to sampling difficulties. Pedotransfer functions have been relatively successful in estimating ρb, but specific functions for most Brazilian biomes are not available. The aim of this study was to develop mathematical functions to describe ρb to a depth of 1 m in areas of native vegetation in central and southern Minas Gerais, Brazil. For determination of ρb, soil core samples were taken of 53 profiles of different soil orders at six depth intervals (0-5, 5-10, 10-20, 30-40, 50-60 and 90-100 cm). The soil ρb ranged from 0.66 to 1.74 kg dm-3, with a mean of 1.25 kg dm-3, and was generally lower in the 0-5 and 5-10 cm layers. Models based on particle size analysis and standard chemical properties were created by multiple stepwise linear regression and were able to describe ρb to a depth of 1 m. Soil organic carbon and clay, silt, and sand contents, as well as cation exchange capacity at pH 7.0, were the most relevant variables in the models, which achieved higher accuracy for Oxisols (R2ajust = 0.85), followed by Inceptisols (R2ajust = 0.69), nitic Alfisols (R2ajust = 0.67), and Ultisols (R2ajust = 0.51). Since modeling for the whole database resulted in R2ajust = 0.50, we conclude that stratification by soil order was useful for improving the equations, with the exception of the Ultisol order.

Ferralsols are chemically poor soils, with management challenges associated with soil fertility heterogeneity and nitrogen limitations. Proper assessment of soil organic matter fractions can be instrumental in understanding the causes of limited nitrogen supply, and thus addressing soil fertility heterogeneity. A study was conducted in cultivated and uncultivated Ferralsols, in order to assay soil organic carbon (SOC), its particle-size fractions and their influence on soil fertility heterogeneity across small farms in central Uganda. Soil samples were taken from the 0–15 and 15–30 cm depths from 30 cultivated fields classified as of low fertility, medium fertility and high fertility, and from two nearby sites in a native shrubland as references. Soil samples were physically fractionated into sand (2000–63 μm), silt (63–2 μm) and clay ( silt > sand. The SOC pool and N in the clay-sized fraction were correlated to soil fertility indicators. More N was stored in the silt + clay size fractions, a generally more stable pool, than in the more labile sand-sized pool. The SOC pool in sand size fractions was far below in low and medium fertility soils than in a reference uncultivated soil. Thus, the sand-sized pool emerged as the most likely cause of limited N supply in cultivated low-input Ferralsols in Uganda.

Reforestation with Pinus sp. trees is often associated with changes in soil physical and chemical soil properties, including depletion of soil organic carbon (SOC). In some cases, leaching of Fe compounds complexed by organic compounds can also occur, bleaching soil colors and perhaps further affecting SOC dynamics. This work aimed to compare SOC concentrations and stocks, as well as soil Fe compounds, under pine plantation and native semideciduous forests in Brazil. The hypotheses tested were that, under pine stands, SOC concentration and stocks decrease, and bleaching caused by Fe mobilization through the profile also affects SOC dynamics. Thus, paired plots consisting of neighboring pine plantations and native forests were sampled in triplicate to a 1-m depth in four different clayey soils (1 Oxisol and 3 Ultisols). Soils were characterized by mineralogical, chemical and physical analyses, SOC content by dry combustion, extraction of Fe compounds (total and amorphous oxides, and organically-bound) and also micromorphology. Soil order influenced how pine plantation affected soil structure, as bulk density increased in the Oxisol but generally decreased in the Ultisols. SOC concentrations and stocks reached 8.5% in the 0–5 cm layer and 309 Mg ha−1 to a 1-m depth, respectively), which are high values compared with the Brazilian literature. Although SOC concentrations were significantly lower in subsurface layers of two soils under pines, after correction for changes in bulk density, only one Ultisol in the midslope position showed SOC stocks significantly lower (by ca. 56 Mg ha−1) to a 0–40 cm depth, but not to a 1-m depth. Changes in Munsell colors indicative of bleaching or Fe mobilization were noted in all soils, and could be ascribed to consistent and simultaneous changes in amorphous Fe oxides and SOC in a midslope Ultisol, demonstrating podzolization in that site. In addition, soil thin sections suggested that Fe compounds were removed from the general matrix of peds in the Ultisols under pines, and concentrated in other areas of the same peds, which can explain changes in color dissociated from vertical changes in concentration of Fe forms. In summary, pine plantations in the studied area seem more prone to conserve SOC than in other cooler or drier regions in Brazil, although changes associated with Fe mobilization can occur in some Ultisols in midslopes, as reported elsewhere in sandier soils under cooler climates.

Dissolved organic carbon (DOC) transported from the soil surface is stabilized in deeper soil profiles by physico-chemical sorption processes. However, it is unclear how different forms of organic carbon (OC) compounds common in soil organic matter interact with soil minerals in the surface (A) and subsurface (B) horizons. We added four compounds (glucose, starch, cinnamic acid and stearic acid) to the silt- and clay-sized fraction (fine fraction) of A and B horizons of eight soils from varying climates (3 temperate, 3 tropical, 1 arctic and 1 sub-arctic). Equilibrium batch experiments were conducted using 0 to 100 mg C L− 1 of 14C-labeled compounds for 8 h. Sorption parameters (maximum sorption capacity, Qmax and binding coefficient, k) calculated by fitting sorption data to the Langmuir equation showed that Qmax of A and B horizons was very similar for all compounds. Both Qmax and k values were related to sorbate properties, with Qmax being lowest for glucose (20–500 mg kg− 1), highest for stearic acid (20,000–200,000 mg kg− 1), and intermediate for both cinnamic acid (200–4000 mg kg− 1) and starch (400–6000 mg kg− 1). Simple linear regression analysis revealed that physico-chemical properties of the sorbents influenced the Qmax of cinnamic acid and stearic acid, but not glucose and starch. The sorbent properties did not show predictive ability for binding coefficient k. By using the fine fraction as sorbent, we found that the mineral fractions of A horizons are equally reactive as the B horizons irrespective of soil organic carbon content.

Steatite is a metamorphic, ultramafic rock composed by talc, serpentine, magnetite and other unique minerals. Soils developed from this rock is typically unproductive due to high Mg and low P contents, high concentrations of heavy metals, and the extent of such limitations in the humid tropics is still poorly known. Here, we aimed to study pedogenesis, morphology and composition of eight soils formed from steatite in Minas Gerais, Brazil. These soils were a) Lithic Udorthents (3 pedons); b) Oxic Dystrudepts (2 pedons); and c) Acrudoxes (3 pedons). All soils presented high particle density but low bulk density due to high packing void porosity associated to granular structure. Soil pH and exchangeable Mg+2 were relatively high, whereas Mehlich-I P and exchangeable Al+3 were very low. X-ray fluorescence data showed that Entisols and Inceptisols have high (94 a 200 g kg−1) MgO contents, whereas Oxisols are highly enriched in Fe2O3, although still bearing MgO contents as high as 30 g kg−1. The Entisols and Inceptisols were mostly composed by talc, but also had Fe oxides and small amounts of kaolinite, whereas the dusky red Oxisols contained mostly hematite. Although present in the parent material, serpentine was not detected in soils. The considerable amounts of MgO in Oxisols can be explained by rock fragments preserved by a dark Fe oxide coating, visible in thin sections. Magnetic susceptibility was high and increased strongly with increasing weathering stage. Local topography strongly controlled soil formation and composition, which allowed for the existence of three climax vegetations: canyon cloud forest, semi-deciduous forest and savanna, suggesting that soil limitations to native plants are lower than expected.

Soil organic carbon (COS) is an important indicator of soil quality, as its levels and stocks can change by soil preparation. This study aimed to evaluate COS stocks on a clayey Oxisol cultivated with coffee and subject to different weed control systems in southern Minas Gerais, Brazil. The experimental design was in randomized blocks, and weed control systems were: no weeding, manual weeding, pre-emergence herbicide, post-emergence herbicide, rotary tiller, rotary mowers and disk harrow. Undisturbed soil samples were collected at two positions in the coffee plantation (tire tracks and planting line), at depths of 0-3, 10-13, and 25-28 cm. A nearby native forest was sampled as a reference. A higher bulk density of soils under coffee plantations occurred compared to soil under the forest. There was little difference between COS concentrations in the plating line in relation to the native forest, but for the tire track position, the amount of COS was generally lower. After correction for soil compaction, it was estimated a loss of ca. 20% in SOC stock for te 0-30 cm depth for herbicide post-emergence, rotary tiller, manual weeding and disk barrow, and a 35% loss when using herbicide pre-emergence. SOC stocks under no weeding and rotary mowers did not differ from native forest (37 M-1g ha COS), indicating that the rotary mower, which allows temporary growth of weeds and does not disrupt soil structure, is the most appropriate weed control for the preservation of COS in coffee plantations.O carbono orgânico no solo (COS) é um importante indicador da qualidade do solo, pois seus teores e estoques podem ser alterados conforme o sistema de preparo do solo. Objetivou-se neste trabalho avaliar os estoques de COS em um Latossolo Vermelho distroférrico argiloso cultivado com cafeeiros (Coffea arabica L) e submetido a diferentes manejos de plantas invasoras no sul de Minas Gerais. O delineamento experimental foi em blocos ao acaso, sendo os tratamentos os seguintes métodos de controle de plantas invasoras: sem capina, capina manual, herbicida de pré-emergência, herbicida de pós-emergência, enxada rotativa, roçadora e grade. Amostras de solo com estrutura indeformada foram coletadas em duas posições (entrelinha e linha do tráfego), nas profundidades de 0–3, 10–13 e 25– 28 cm. Uma mata nativa adjacente foi amostrada como referência. Verificou-se maior densidade do solo na área sob cafezal em comparação ao solo sob a mata. Houve pouca diferença entre o teor de COS foi sempre da posição entrelinha dos cafeeiros em relação àquele sob mata, mas para a posição linha de tráfego, o teor de COS foi menor. Após correção para a compactação do solo, verificou-se perda de aproximadamente 20% nos estoque de COS a 0-30 cm quando se utilizou herbicida de pósemergência, enxada rotativa, capina manual e grade, e perdas de 35%, quando se utilizou herbicida de pré-emergência. Os manejos sem capina e roçadora não diferiram da mata nativa (37 Mg COS ha-1), indicando que a roçadora, por permitir crescimento temporário das invasoras e não revolver o solo, é o controle mais apropriado à conservação do COS em cafezais.

Proper assessment of environmental quality or degradation requires knowledge of how terrestrial C pools respond to land use change. Forest plantations offer a considerable potential to sequester C in aboveground biomass. However, their impact on initial levels of soil organic carbon (SOC) varies from strong losses to gains, possibly affecting C balances in afforestation or reforestation initiatives. We compiled paired-plot studies on how SOC stocks under native vegetation change after planting fast-growth Eucalyptus species in Brazil, where these plantations are becoming increasingly important. SOC changes for the 0–20 and 0–40 cm depths varied between −25 and 42 Mg ha−1, following a normal distribution centered near zero. After replacing native vegetation by Eucalyptus plantations, mean SOC changes were −1·5 and 0·3 Mg ha−1 for the 0–20 and 0–40 cm depths, respectively. These are very low figures in comparison to C stocks usually sequestered in aboveground biomass and were statistically nonsignificant as demonstrated by a t-test at p

Little is known about how soil organic carbon (SOC) under tropical forests is affected by altitude. We investigated the effects of soil texture and altitude on SOC retention under native forests in Brazil, by sampling two pairs of soils of coarser and finer texture, developed respectively from quartzite and mica-schist. One soil pair was sited at altitude 1060 m, and the other at 1230 m, along a mountain range. For 1060 m, the soil with ~36% clay contained 227 Mg SOC ha–1 (0–1 m depth), the double of the soil with ~16% clay. Such effect of texture was negligible at 1230 m, where SOC stocks were 205 Mg ha–1 for the soil with ~12% clay, and 217 Mg ha–1 for the soil with ~21% clay. Furthermore, there were positive correlations between SOC concentrations with clay + silt contents and specific surface area for 1060 m but not 1230 m altitude, suggesting that SOC retention was affected by texture only for altitudes near 1000 m or lower. At 1230 m, lower temperatures were predominant in SOC stabilisation through slower decomposition. In addition, 65–80% of total SOC was associated with clays, indicating a high degree of organic alteration. Interestingly, at 1235 m, SOC concentration in clay fractions reached 17%, much higher than at 1060 m, strongly suggesting SOC saturation. Thus, at 1235 m the interaction of SOC with soil minerals was probably weaker than at 1060 m or lower, and so SOC stocks are more susceptible to decay.

Soil organic carbon (SOC) retention is a function of climate, vegetation, drainage, and management interactions, but also of intrinsic soil properties such as texture, mineralogy, and structure. To assess these edaphic controls, three soils of the Brazilian savanna (Cerrado) under similar climate, vegetation, and slope but of contrasting texture were sampled to 1-m depth and characterized for textural, chemical, and mineralogical properties, and SOC concentration (in bulk samples and clay, silt, and sand fractions). The basic assumption was that SOC particle size determines its retention mechanism: colloidal forms are retained by sorption, while particulate organic matter (>20 μm) can occur outside or inside aggregates. It was hypothesized that SOC retention is controlled simultaneously by soil texture, mineralogy, and depth. The three soils are clayey, loamy, and sandy Haplustox, all kaolinitic with minor contents ofFe and Al oxides, vermiculite, and illite. The SOC concentrations in particle size fractions were inversely related to the content of the respective fraction in soil (SOC dilution effect), thus SOC partition is better assessed by determination of SOC pools in each particle size on a total soil mass basis rather than on a size-fraction concentration basis. The positive linear relations between SOC and clay + silt concentrations in bulk soil were explained mostly by greater clay-sized SOC pools, which could be modeled as a function of clay content (related to specific surface area) and depth. Quantitative clay mineralogy showed that bulk SOC and clay-sized SOC pools were well correlated with Fe oxides in topsoil and amorphous Al oxides in subsoil, but this mineralogical control is secondary to the textural control, since it depends on clay content.

Soil structure can be an important factor affecting soil organic carbon (SOC), but it is also a dynamic property affected by texture, mineralogy, land use, soil fauna, and also SOC. Assuming that structure affects SOC mostly by occlusion of particulate organic matter (POM) within aggregates, it was hypothesized that structure exerts a major control on SOC retention in soils of the Brazilian Cerrado region. Water-stable aggregates (WSA) were obtained from the 1-m depth of three different-textured, uncultivated soils. The mean weight diameter (MWD) of WSA was used as a structural indicator, and SOC concentrations were determined in intact WSA and their respective sand fractions (estimating occluded POM). Clay + silt content in bulk soils was correlated with MWD in all depths but more strongly in the top 10 cm. Although equally correlated with clay + silt contents, SOC concentrations were well correlated with MWD only in the 0- to 5-cm layer. Sand-free SOC concentrations in WSA fractions were proportional to sand content, indicating that the SOC dilution effect reported in particle size fractionations occurs naturally in the soil fabric. Occlusion of POM within aggregates was proportional to clay + silt contents, but this did not result in larger total POM pools, and the weak correlations obtained did not warrant predictive models. Aggregates produced by macrofauna comprised a minor but significant part of the soil and were mostly SOC enriched. We concluded that the structural control on SOC retention is less significant than the textural and mineralogical controls, since aggregation depends on those properties and is not as strongly correlated with SOC concentration and POM occlusion.

Land use conversion from natural to agricultural ecosystems affects concentration and storage of soil organic carbon (SOC) depending on tillage frequency and depth, soil type, climate and other factors. Despite its importance, little is known about the magnitude and consistency of changes in SOC stocks (Mg ha−1) due to management of highly weathered soils in Brazil. From 37 uncultivated/cultivated paired sites in Brazil (most on Oxisols), SOC stocks were calculated for the depths of 0–20 and 0–40 cm. Changes in SOC stocks were calculated for intensive (with annual tillage) and non-intensive (pastures, conservation tillage and perennial crops) land use systems. Intensive systems caused significant (t-test, P

Little is known about the interdependence between soil organic carbon (SOC) and texture within the soil profile. In order to describe mathematically this relation, three highly weathered soils (sandy, loamy and clayey) in the Brazilian Cerrado under similar climate, vegetation and topography were sampled in triplicate to 1-m depth and analyzed for texture and total SOC concentration. The SOC concentration was directly and linearly correlated with the combined clay + silt (but not to clay) content for all depths. The intercept and slope of these linear relations decreased with depth following exponential and logarithmic functions ( P R 2 = 0.97 and 0.95, respectively). These mathematical functions permitted the adjustment of the intercept and slope parameters of a SOC = a + b(clay + silt) function for any depth in the 0-1 m interval. This profile pedotransfer function precisely estimated SOC concentration ( P R 2 = 0.92) up to 1.0 m of the studied soils. Using data from different Cerrado soils, estimated vs. measured SOC relations with similarly high R 2 values were obtained, despite slopes and intercepts were different than 1 and 0. This indicates that for the Cerrado region the textural control of SOC varies predictably with depth, and the proposed model can be calibrated to estimate SOC in subsurface layers of highly weathered soils.

In the Brazilian tropical savanna (Cerrado), soil organic carbon (SOC) is an important factor for crop productivity of the highly weathered, low-fertility soils, and can be easily depleted by soil management or disturbance, affecting sustainability of land use. In order to assess the impact of the first cycle of fast-growing exotic tree afforestation on SOC contents and quality, one site under Pinus caribaea var. hondurensis and two sites under Eucalyptus camaldulensis were studied. The soil under Pinus is a clayey Oxisol with no significant slope. Eucalyptus forests were planted along a toposequence of a sandy Entisol to a loamy Oxisol, which permitted to compare the afforestation effects on SOC contents and properties in two different soils under the same climatic conditions and submitted to the same management practices. Site preparation consisted of mechanical clearing of native vegetation followed by use of heavy disk plow. Litter and soil up to 60 cm were sampled, and the same soil under native Cerrado-type vegetation was sampled as control for each forest site. Analysis of total organic C, soil particle-size fractionation by physical procedures, cellulosic (CPS) and non-cellulosic (NCPS) carbohydrates, lignin phenolic derivatives and 13 C nuclear magnetic resonance (NMR) were run to characterize SOC. The results indicate different patterns of SOC dynamics in each site. Pinus forest accumulated a large amount of litter (37.7 Mg ha−1), while litter under Eucalypt was less (7.6 Mg ha−1) than under Cerrado control (10.9 Mg ha−1) in the loamy Oxisol. On the sandy Entisol there was no significant difference in litter quantities (13.9 and 13.5 Mg ha−1 for Eucalyptus and Cerrado, respectively). Organic C in the surface layer (0–5 cm) was significantly lower under planted forests than under the controls. The SOC losses in topsoil were found to be more significant in the soils with the lower clay content, varying from 19% in the clayey Oxisol to 48% in the sandy Entisol, and in the coarser particle-size fractions, considered more labile. When the total carbon in the 0–60 cm profile is considered, the C losses were 11 Mg ha−1 (−9%) under Pinus and 9 Mg ha−1 (−17%) in the sandy Entisol under Eucalyptus, and no net losses occurred in the Oxisol under Eucalyptus. Chemical properties of SOC were affected by afforestation, but not in the sandy Entisol; analyses of carbohydrates and lignin derivatives showed a more advanced decomposition status in the Oxisols, while 13 C NMR spectra of humic substances showed a reduction of O-alkyl, and an increase of paraffinic C in the Oxisols. This absence of chemical alterations in the organic carbon of the sandy Entisol, despite the high C loss in topsoil, may indicate a weak adsorption of compounds issued during decomposition, once the clay content is low. On the toposequence, NMR analyses showed the influence of soil type in humic substances, which contained more paraffinic groups and less aromaticity in the sandy soil. In general, although forest plantations in the tropics are expected to conserve SOC, significant losses occurred in the surface layer, which may be reduced through less intensive practices of soil preparation such as reduced tillage, especially in coarse-textured soils.

Estudos sistemáticos sobre os fatores de formação do solo são relativamente escassos no Brasil, em razão da dificuldade de amostrar vários níveis de um fator, mantendo os demais constantes. A região de Lavras, MG, possui grande diversidade geológica em uma área pequena, o que possibilita avaliar o controle exercido por diferentes litologias na mineralogia e nas demais características do solo. Foram selecionados oito solos embasados sobre quartzito, mica-xisto, gabro, itabirito, serpentinito, metacalcário, gnaisse e filito, em condições semelhantes de vegetação (floresta tropical semidecidual), relevo (terço médio de encosta) e clima. Após a descrição dos perfis, coletaram-se amostras dos horizontes e das rochas, e realizaram-se análises físicas e químicas de rotina, composição química total e mineralogia da rocha, da areia e da argila do solo. Todos os solos são pobres em bases trocáveis (exceto o Argissolo sobre itabirito), e notou-se grande variação na composição granulométrica, mineralógica e química. Os teores de Al2O3, SiO2 e Fe2O3 presentes nas rochas não evidenciaram correlação com os respectivos teores nos solos derivados, enquanto o teor de Fe2O3 foi fortemente correlacionado à densidade de partículas e suscetibilidade magnética. Apesar de evidências de material parcialmente alóctone em alguns casos, pôde-se notar forte influência da litologia subjacente na paragênese mineralógica. Os solos foram genericamente agrupados em: cauliníticos com minerais 2:1 (Argissolos sobre mica-xisto e itabirito; e Cambissolo sobre quartzito), cauliníticos (Argissolos sobre gnaisse e filito) e oxídicos (Latossolos sobre metacalcário e gabro; e Plintossolo sobre serpentinito). Os processos de monossialitização e alitização predominam na região, sendo respectivamente associados a rochas com valores intermediários e baixos em sílica, enquanto a presença de minerais 2:1 é acessória à caulinita e parece depender da presença de mica e altos teores de sílica na rocha de origem. Systematic studies on of soil formation factors are relatively scarce in Brazil since comprehensive samplings of a variable factor while keeping others constant are difficult to perform. Near Lavras, Minas Gerais, there is wide geological diversity over a small area, which offers a chance to assess the control exerted by different lithologies on mineral suites and other soil properties. Thus, eight soils overlying quartzite, mica-schist, gabbro, itabirite, serpentinite, meta-limestone, gneiss and phyllite, under similar climate and tropical, semideciduous forest conditions were selected, all located on midslopes. After description of soil profiles, soil horizon and fresh rock samples were collected for standard physical, fertility, and chemical composition and mineralogical analyses. All soils were poor in bases (except for an Ultisol over itabirite) and showed wide textural, mineralogical and chemical variation. Despite evidence of partially allochthonous material in some cases, a strong influence of underlying lithology was noted on soil mineral suites. There were no significant correlations among Al2O3, SiO2 and Fe2O3 contents in rocks and soils, whereas Fe2O3 content was strongly correlated with particle density and magnetic susceptibility. The soils were grouped as: 1) kaolinitic with 2:1 minerals (Ultisols over mica-schist and itabirite, Inceptisol over quartzite); 2) kaolinitic (Ultisols over gneiss and phyllite), and 3) oxidic (Oxisols over meta-limestone and gabbro, plinthic Oxisol over serpentinite). Monosialitization and alitization processes predominate in the region, associated with rocks with moderate and low silica contents, respectively, whereas 2:1 minerals are accessory to kaolinite and their occurrence seems to depend on rocks rich in mica and silica.

As substâncias húmicas (SH) representam o principal reservatório de carbono orgânico total do solo (COT) e sua partição entre diferentes frações de solubilidade em meio alcalino ou ácido pode guardar relação com o tipo de solo e manejo adotado. O objetivo deste trabalho foi comparar a partição das SHs, de acordo com profundidade, tipo de solo, bioma e uso do solo no Brasil. Revisou-se a literatura, incluindo teses, dissertações, artigos e resumos em anais de eventos, em busca de dados sobre o teor de COT, sua porcentagem como ácidos húmicos (AH), ácidos fúlvicos (AF) e humina (HU) e a razão AH/AF. Os dados foram estratificados por intervalos comparáveis de profundidades (0-5, 5-10, 0-20, 20-50, 50-100 e >100 cm), biomas (Mata Atlântica, Cerrado, Amazônia, Pampa e Caatinga), ordem de solo (Argissolo, Latossolo, Cambissolo, Planossolo, Neossolo, Gleissolo e Organossolo) e principais usos do solo (florestas nativas, pastagem natural, pastagem plantada, eucalipto, culturas perenes e anuais). Os dados foram analisados por estatística descritiva, correlações de Spearman e análise de componentes principais (ACP). Nos Argissolos, Latossolos e Organossolos, a fração HU contribuiu com metade do COT, tendendo a diminuir em profundidade. Para Latossolos e Organossolos, a fração AF tendeu a aumentar em profundidade. Em Neossolos, a fração AH aumentou em profundidade, embora tenha diminuído em Gleissolos e Planossolos. A razão AH/AF geralmente diminui em profundidade. Pela ACP, não foi possível identificar um padrão de agrupamento das amostras em razão do tipo de bioma e uso do solo, sugerindo que a partição das SHs tem baixo potencial como indicador de efeitos do manejo ou condições ambientais, embora seja útil para discriminar processos de humificação em algumas ordens de solo.

O carbono orgânico no solo (COS) e um importante indicador da qualidade do solo, pois seus teores e estoques podem ser alterados conforme o sistema de preparo do solo. Objetivou-se neste trabalho avaliar os estoques de COS em um Latossolo Vermelho distroferrico argiloso cultivado com cafeeiros (Coffea arabica L) e submetido a diferentes manejos de plantas invasoras no sul de Minas Gerais. O delineamento experimental foi em blocos ao acaso, sendo os tratamentos os seguintes metodos de controle de plantas invasoras: sem capina, capina manual, herbicida de pre-emergencia, herbicida de pos-emergencia, enxada rotativa, rocadora e grade. Amostras de solo com estrutura indeformada foram coletadas em duas posicoes (entrelinha e linha do trafego), nas profundidades de 0–3, 10–13 e 25–28 cm. Uma mata nativa adjacente foi amostrada como referencia. Verificou-se maior densidade do solo na area sob cafezal em comparacao ao solo sob a mata. Houve pouca diferenca entre o teor de COS da posicao entrelinha dos cafeeiros em relacao aquele sob mata, mas para a posicao linha de trafego, o teor de COS foi menor. Apos correcao para a compactacao do solo, verificou-se perda de aproximadamente 20% nos estoque de COS a 0-30 cm quando se utilizou herbicida de pos-emergencia, enxada rotativa,capina manual e grade, e perdas de 35%, quando se utilizou herbicida de pre-emergencia. Os manejos sem capina e rocadora nao diferiram da mata nativa (37 Mg COS ha-1), indicando que a rocadora, por permitir crescimento temporario das invasoras e nao revolver o solo, e o controle mais apropriado a conservacao do COS em cafezais.

Although particles >2 mm are not considered soil material, gravels composed of resistant secondary minerals can be useful records of past soil environments. We investigated gravels (2–8 mm) from a Plinthic Haplustox in central Brazil in order to assess their composition, fabric and genesis. Gravels were initially grouped into six macromorphological types, and investigated by mineralogical, micromorphological and microprobe analyses. The results suggest that gravels can be classified as pedogenic or lithopedogenic. Pedogenic gravels comprise indurated soil materials and include black magnetic gravels, black non-magnetic gravels and red earthy gravels. Magnetic gravels contained mostly quartz, hematite and magnetite–maghemite and were poor in kaolinite, gibbsite and goethite, whereas non-magnetic and red earthy gravels had the same minerals as in the surrounding soil. Lithopedogenic gravels are fragments of resistant rocks impregnated by iron (Fe), aluminium (Al) and manganese (Mn) oxides, including platy shales, quartzites and coarse quartz. The latter two showed oxide impregnations around internal pores, whereas the shale fragments included considerable mica, which contributed illite and potassium to the soil clays and, thus, the pedogenic gravels. These results point to multiple cycles of formation and incorporation of cemented materials into the soil, as well as their later impregnation by Fe, Mn and Al oxides. Thus, the conventional classification of all such gravels as ‘ironstone’ is questionable, and their potential role as indicators of past and present soil environments is demonstrated, which deserves further investigation.

Apesar de o interesse no comportamento espacial de atributos-chave do solo, só recentemente a variação em profundidade passou a receber mais atenção na literatura. O carbono orgânico do solo (COS) é talvez o atributo que mais varie em profundidade, o que dificulta seu estudo. A partir de dados de levantamentos de solos de duas regiões de Minas Gerais (Sul e Serra do Espinhaço Meridional), foram modelados os teores de COS em profundidade, buscando identificar quais fatores mais os influenciam. Os perfis de COS foram mais bem descritos por funções logarítmicas neperianas em ambas as regiões. Houve efeito da classe de solo, uma vez que Latossolos apresentaram menores teores superficiais, mas menor decréscimo no perfil, do que Argissolos, Neossolos, Cambissolos e Nitossolos. Essas tendências podem ser devidas à maior profundidade, permeabilidade e teor de argila+silte dos Latossolos. A variação regular dos parâmetros intercepto (teor médio na superfície) e fator logarítmico (taxa de decréscimo) das equações obtidas para diferentes faixas de teor de argila+silte permitiu ainda obter funções de pedotransferência em perfil para descrever teores de COS em profundidade em qualquer classe de solo, confirmando a hipótese de que a textura é um controle importante dos teores de COS nessas duas regiões. Na região Sul de MG, os perfis de COS puderam também ser descritos em função de teores de Fe2O3 (ataque sulfúrico), evidenciando controle mineralógico do COS. Ainda na região Sul, solos entre 1.000 e 1.200 m de altitude apresentaram maiores teores de COS do que os de altitudes menores. Latossolos e Nitossolos das duas regiões mostraram perfis muito semelhantes de COS - similaridade atribuída ao efeito positivo de maiores teores de argila na região Sul e maior altitude na Serra do Espinhaço Meridional. Despite the interest in the spatial variability of key soil properties, depth-related variations have only recently received more attention in the literature. Of all soil properties, soil organic carbon (SOC) is perhaps the most depth-related and difficult to understand. Soil data from two regions in the State of Minas Gerais, Brazil, were used to model SOC profiles and identify factors of influence. In both the South and Southern Espinhaço regions, SOC profiles were best described by log functions. Oxisols had higher SOC levels in the surface, which decreased less with depth than in Ultisols, Inceptisols and Entisols. This could be ascribed to the greater depth, permeability and clay+silt content of Oxisols. Based on the regular increase of intercepts and log factors of the equations obtained for increasing clay+silt contents, profile pedotransfer functions were estimated to describe SOC concentrations based on texture and depth of any given soil, confirming the hypothesis that soil texture strongly controls SOC retention in both regions. In addition, SOC profiles could also be described according to Fe2O3 contents (by sulfuric digestion) in soils of the Southern region, suggesting a mineralogical control of SOC retention. Also in the Southern region, the SOC contents of soils located between 1,000-1,200 m a.s.l. were higher than those of soils at lower altitudes. However, the SOC profiles of the Oxisols and nitic Ultisols of both regions were very similar, which may be an effect of higher clay contents in the South region, and of higher altitudes in the Southern Espinhaço mountain region.