Characterization of seasonal freeze-thaw and potential impacts on soil erosion in northeast China

Zhao, Y., Wang, E., Cruse, R. M. and Chen, X. 2012. Characterization of seasonal freeze-thaw and potential impacts on soil erosion in northeast China. Can. J. Soil Sci. 92: 567–571. Freeze-thaw cycles are regarded as a critical factor inducing and accelerating gully erosion in the Black soil region (Chernozem) of northeast China. The major objective of this study was to identify the effect of seasonal freeze-thaw processes on soil structure relevant to soil erosion. Perched water due to an argillic horizon brings about higher water potential in the top soil, which lowers the soil shear strength and increases the risk of soil erosion by rainfall and surface flow; and the argillic horizon, with a higher clay content, is more vulnerable to freeze-thaw processes, which break or weaken the structure of the argillic horizon, increasing its vulnerability to gully erosion.

Predicting Spatial Distribution of Argilic Horizon Using Auxilary Information in Regional Scale

For supporting better soil management, the spatial distribution of soils having argilic hori=on (argilic soils) must berecognized and it can be delineate in soil survey mapping activity, but this activity consumes much time and money. This study aimed to build a decision tree model for predicting the spatial distribution of argillic hori=on based on auxiliary information using 3 predicting environmental variables; namely, geomorphic sUrface or substrate, landsurjace unit, and ecoregion beh.Three-based modeling technique was used to generate classification tree model from 318 pedon of Lampung Province,Indonesia. Argillic horizon is predicted to present in hot belt (elevation of 0-200 m above sea level) on interfluve-seepageslope with probability 84% for acid igneous rock, 83% for basic igneous rock, and 90% for acid sedimentary rock. Argillichorizon is also predicted to present in hot belt on transportational midslope with the probability 65% for transported acid sedimentary rock. Argillic horizon is predicted absent with the probability to occur ranging from 0% to 32% on otlrer combinations of landsurface unit, ecoregion belt, and substrate.

UTILIZAÇÃO DO MICROSCÓPIO ELETRÔNICO DE VARREDURA (MEV) PARA O RECONHECIMENTO DE REVESTIMENTOS ARGILOSOS

Diversos autores têm ressaltado, nos seus trabalhos de pesquisa, uma certa dificuldade na identificação de revestimentos argilosos em observações de campo e de laboratório. O presente trabalho tem por objetivo avaliar a importância da utilização do Microscópio Eletrônico de Varredura (MEV) na identificação e na caracterização destas feições pedológicas encontradas em Argissolos nas proximidades de Bauru-SP. A área de estudo situa-se no oeste do estado de São Paulo, onde o quadro geológico regional é dominado por rochas sedimentares da Formação Marília, Grupo Bauru (Cretáceo da Bacia do Paraná), associadas aos Latossolos e aos Argissolos. Os estudos foram desenvolvidos no laboratório de Ciência do Solo do INRA/ Rennes (França). Um MEV possibilitou a observação e a caracterização química pontual das amostras. Foram utilizadas lâminas delgadas de solo de pequenas dimensões (4,5 X 7 cm) e pequenos torrões de solo (1 cm 3 ) com estrutura preservada. O MEV mostrou-se uma ferramenta eficaz nos estudos de gênese dos solos. Os resultados revelaram ainda que os revestimentos argilosos encontrados no topo no horizonte Bt dos Argissolos apresentam limite nítido com o fundo matricial, forte birrefringência, microlaminação, além da orientação das argilas paralela à parede dos poros, essas características indicam um processo de iluviação mecânica das argilas. As microanálises efetuadas nos revestimentos argilosos forneceram infor-mações adicionais àquelas obtidas com o estudo micromorfológico, principalmente por mostrar a existência de forte variação dos elementos ao longo das microestratificações. THE USE SCANNING ELECTRON MICROSCOPY (SEM) TO RECOGNITION OF CLAY COATINGS Abstract Many authors have been pointing out the difficulties of identification of clay coatings in field and laboratory observations. This work aims at estimating the importance of the Scanning Electron Microscopy (SEM) at the characterization and identification of these pedologicals features found in Alfisols in Bauru (SP) region. The studied region is located in the western part of São Paulo State, where the regional geology is dominated by sedimentary rocks from Marília Formation of Bauru Group (Cretaceous period), associated with soils of Alfisol and Oxisol type (figure 1). The studies were developed at the INRA/Rennes Soil Science laboratory. A Phillips XL20 scanning electron microscopy connected to an EDS spectrometer make the observation and punctual chemistry characterization of the samples possible. Soil thin blades of small dimensions (4,5 X 7,0 cm) and small soil lumps (1,0 cm³) with preserved structure were used. The SEM showed to be an effective tool in soils genesis studies. The results showed that the clay coatings found in the chambers porosity from the superior portion of argillic horizon in Alfisols present a clear boundary with the immediately underlying soil materials, strong birrefringence, micro lamination, besides the orientation of the clays parallel to the pores wall, indicating a mechanic illuviation process of the clay (figures 2 to 6). The microanalyses done in clay coatings found in the argillic horizon, gave additional information to those acquired from the micromorphological studies, especially for showing the existence of a strong variation of the oxides elements through the micro laminations (figure 9 and table 1).