Yuri Lopes Zinn

Paragênese mineral de solos desenvolvidos de diferentes litologias na região sul de Minas Gerais

Estudos sistematicos sobre os fatores de formacao do solo sao relativamente escassos no Brasil, em razao da dificuldade de amostrar varios niveis de um fator, mantendo os demais constantes. A regiao de Lavras, MG, possui grande diversidade geologica em uma area pequena, o que possibilita avaliar o controle exercido por diferentes litologias na mineralogia e nas demais caracteristicas do solo. Foram selecionados oito solos embasados sobre quartzito, mica-xisto, gabro, itabirito, serpentinito, metacalcario, gnaisse e filito, em condicoes semelhantes de vegetacao (floresta tropical semidecidual), relevo (terco medio de encosta) e clima. Apos a descricao dos perfis, coletaram-se amostras dos horizontes e das rochas, e realizaram-se analises fisicas e quimicas de rotina, composicao quimica total e mineralogia da rocha, da areia e da argila do solo. Todos os solos sao pobres em bases trocaveis (exceto o Argissolo sobre itabirito), e notou-se grande variacao na composicao granulometrica, mineralogica e quimica. Os teores de Al2O3, SiO2 e Fe2O3 presentes nas rochas nao evidenciaram correlacao com os respectivos teores nos solos derivados, enquanto o teor de Fe2O3 foi fortemente correlacionado a densidade de particulas e suscetibilidade magnetica. Apesar de evidencias de material parcialmente aloctone em alguns casos, pode-se notar forte influencia da litologia subjacente na paragenese mineralogica. Os solos foram genericamente agrupados em: cauliniticos com minerais 2:1 (Argissolos sobre mica-xisto e itabirito; e Cambissolo sobre quartzito), cauliniticos (Argissolos sobre gnaisse e filito) e oxidicos (Latossolos sobre metacalcario e gabro; e Plintossolo sobre serpentinito). Os processos de monossialitizacao e alitizacao predominam na regiao, sendo respectivamente associados a rochas com valores intermediarios e baixos em silica, enquanto a presenca de minerais 2:1 e acessoria a caulinita e parece depender da presenca de mica e altos teores de silica na rocha de origem.

MICROMORPHOLOGY AND PEDOGENESIS OF MOUNTAINOUS INCEPTISOLS IN THE MANTIQUEIRA RANGE (MG)

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.

Perfis de carbono orgânico do solo nas regiões Sul e Serra do Espinhaço Meridional, Minas Gerais: modelagem em profundidade

Apesar de o interesse no comportamento espacial de atributos-chave do solo, so recentemente a variacao em profundidade passou a receber mais atencao na literatura. O carbono orgânico do solo (COS) e talvez o atributo que mais varie em profundidade, o que dificulta seu estudo. A partir de dados de levantamentos de solos de duas regioes de Minas Gerais (Sul e Serra do Espinhaco 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 funcoes logaritmicas neperianas em ambas as regioes. Houve efeito da classe de solo, uma vez que Latossolos apresentaram menores teores superficiais, mas menor decrescimo no perfil, do que Argissolos, Neossolos, Cambissolos e Nitossolos. Essas tendencias podem ser devidas a maior profundidade, permeabilidade e teor de argila+silte dos Latossolos. A variacao regular dos parâmetros intercepto (teor medio na superficie) e fator logaritmico (taxa de decrescimo) das equacoes obtidas para diferentes faixas de teor de argila+silte permitiu ainda obter funcoes de pedotransferencia em perfil para descrever teores de COS em profundidade em qualquer classe de solo, confirmando a hipotese de que a textura e um controle importante dos teores de COS nessas duas regioes. Na regiao Sul de MG, os perfis de COS puderam tambem ser descritos em funcao de teores de Fe2O3 (ataque sulfurico), evidenciando controle mineralogico do COS. Ainda na regiao 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 regioes mostraram perfis muito semelhantes de COS - similaridade atribuida ao efeito positivo de maiores teores de argila na regiao Sul e maior altitude na Serra do Espinhaco Meridional.

Impactos do cultivo por longo tempo de arroz inundado em Gleissolos

O objetivo deste trabalho foi avaliar atributos do solo em resposta a diferentes usos da terra no Sul de Minas Gerais. Foram amostrados Gleissolos sob floresta nativa e cultivos de arroz (Oryza sativa) irrigado por inundacao e de feijoeiro (Phaseolus vulgaris), bem como um Argissolo nao inundavel sob floresta nativa. O cultivo promoveu o aumento da densidade nos Gleissolos, ate a profundidade de 0,4 m, o que resultou em menores diâmetros medios geometrico e ponderado de agregados, especialmente para o arrozal sob inundacao, cultivado anualmente com enxada rotativa. A analise micromorfologica do solo evidenciou que a compactacao ocorreu em razao do menor espaco macroporoso entre agregados, bem como da menor porosidade derivada da atividade biologica. Os teores de C orgânico do solo (COS) e N total (N) nos Gleissolos cultivados foram cerca de 55 e 40% menores do que no Gleissolo sob mata, em consequencia da decomposicao orgânica acelerada pelo cultivo. Contudo, o Gleissolo sob mata nativa apresentou teores e estoques de COS e N similares aos de um Argissolo sob mata, o que indica que o efeito da anaerobiose sobre a materia orgânica do solo foi menor do que o esperado.

Soil organic carbon retention more affected by altitude than texture in a forested mountain range in Brazil

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.

Partição de substâncias húmicas em solos brasileiros

Humic substances (HS) are the main pool of total soil organic carbon (TOC). They are partitioned in different fractions according to its solubility in alkali or acid medium, which can be related to soil type and management. This work aimed to compare HS partitioning in Brazilian soils according to soil depth, soil type, biome, and land uses. In a literature review of theses, dissertations, journal articles, and abstracts in proceedings, quantitative data on TOC partitioning in humic acids (HA), fulvic acids (FA), and humin (HU), as well as the HA/FA ratio were compiled. The data were sorted according to comparable depths (0-5, 5-10, 0-20, 20-50, 50-100, and >100 cm), biomes (Atlantic rainforest, Cerrado savanna, Amazon rainforest, southern prairies, and Caatinga scrubland), soil order (Ultisols, Oxisols, Inceptisols, Entisols, Histosols and soils with aquic moisture regimes), and land use systems (native forests, prairies, pastures, eucalypt, and annual or perennial crops). Data were analyzed by descriptive statistics, Spearman correlation, and principal component analysis (PCA). In Ultisols, Oxisols, and Histosols, humin accounted for at least half of TOC and tended to decrease with depth. In Oxisols and Histosols, FA tended to increase in depth. In the Entisols, HA increased with depth, but decreased in Histosols and some Ultisols. Generally, the HA/FA decreased in the deeper layers. Results of PCA indicated no effect of biomes and land use systems on the quantitative partitioning of HS, suggesting its low potential as indicator of management effects or environmental conditions, although useful to discriminate humification processes in some soil taxa.

Similar Soils but Different Soil-Forming Factors: Converging Evolution of Inceptisols in Brazil

Abstract Soils result from the interaction of five independent formation factors. If one factor varies, while the others remain constant, different soils can be produced. Herein, we demonstrated an opposing trend, wherein two soils were similar, despite considerable differences in all factors of soil formation. We sampled two Inceptisols (Oxic Dystrudepts) formed on different parent materials (gneiss vs. mica schist), climate (tropical altimontane vs. warmer, drier plateau), topography (1 650 m, 45% slope vs. 1 000 m, 8% slope), time (rejuvenated vs. old, stable surface), and vegetation (rainforest vs. Cerrado savanna). The two soils had similar chemical properties, whereas the soil on mica schist had finer particle size distribution, lower porosity, and lower saturated hydraulic conductivity. These properties were related to a coarser blocky microstructure compared to the soil on gneiss. Both soils presented active mineral weathering and pronounced pedoplasmation, demonstrated by clay contents > 300 g kg −1 , although only the Dystrudept on gneiss possessed coarse rock fragments. The C horizons of both soils presented fragmented clay coatings suggestive of argilluviation, likely relict, because they were not observed in the B horizons. The similarities in many properties of the two Dystrudepts, despite contrasting factors of soil formation, suggest converging evolution and that soil classification at the subgroup level was efficient in grouping similar formative processes in tropical conditions. Moreover, this work revealed that similar pedogenic processes acting on different factors of soil formation can result in similar soil properties, at least for Inceptisols where further soil development is hindered by topographic limitations.

Xanthic- and Rhodic-Acrudoxes under cerrado vegetation: differential internal drainage and covarying micromorphological properties

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.