One of the critical design parameters used in evaluating soil structure is the friction angle, derived from Mohr's Circle failure criterion. The soil friction angle is an engineering parameter estimated in the laboratory to quantify the soil shear strength in geotechnical applications. This paper indicates an experimental study investigating the impact of particle size on different sandy soils shear strength behavior. The direct shear test equipment is useful for simulating various stress regimes to determine the soil strength by employing a slow moving lateral force to a consolidated sample along a shear plane. A series of direct shear tests were conducted to investigate the interface behavior of soil. Soil samples were selected from different locations in New Mexico, United States. The influence of soil particle size on the soil's shear strength behavior is discussed by performing a series of symmetric direct shear tests according to ASTM D3080 and analyzing the results. To minimize errors, electronic transducers were used to measure vertical and horizontal displacements. DS7 is geotechnical testing software controlling the test by utilizing a data logger. The investigation indicates that the maximum vertical deformation for all different kinds of sandy soils accrued simultaneously. It was concluded that a soil's friction angle is affected by coarse-grained material. Accordingly, sandy soils with bigger particle size record a higher friction angle than soils containing small particles. Furthermore, a non-linear regression analysis was performed to determine the direct relationship between soil's friction angle and soil particle characteristics.

Stem borers (Lepidoptera) are common cereal pests. In many parts of the world, the species Ostrinia nubilalis and Sesamia nonagrioides stand out as important insect pests of economically important crops such as maize. Their management relied mainly on transgenic host plant resistance over the last 25 years. Technologies based on the insecticidal properties of Bacillus thuringiensis-derived proteins allowed widespread pest population suppression, especially for O. nubilalis. However, the recent discovery of Bt resistance, which has revitalized interest in both pests' biology and management, may jeopardize the effectiveness of such transgenic technologies. Historical information on O. nubilalis bionomy may need to be reassessed in light of changing climate conditions and changing agricultural practices, as well as increased production of alternate host crops across its distribution range. The current paper examines the bioecology and historical research that has been conducted to manage these two important maize-boring pests.

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A B S T R A C TThe aims of this study were to evaluate the effects of the soil structural physical attributes on the water retention and to develop pedotransfer functions (PTFs) for the estimation of the soil water content (θ) at different matric potentials of a Dystrophic Red Latosol (Hapludox) under conventional tillage (CT) and no-tillage (NT) soil management systems. The effects of long-term CT and NT (over 25 years) management on the soil bulk density (BD), total porosity (TP), macroporosity (Ma), microporosity (Mi) and water retention were investigated. The PTFs were developed to predict θ and used to evaluate the soil water retention curve only for the NT system. The NT system was characterized by smaller values of the soil BD and higher values of the soil TP and Mi than the CT system. The NT system exhibited a higher θ retained than the CT system for the pore-size interval of 0.2-30 µm. However, the CT system exhibited a large amount of water retention for pores smaller than 0.2 µm. The PTFs were utilized to estimate θ at matric potentials of -1, -3, -6, -10, -33, -100, -400, -800, and -1,500 kPa with adequate accuracy. The soil BD, Ma, Mi and sand content were the main variables considered to estimate θ for the different matric potentials evaluated.Atributos físicos e funções de pedotransferência para estimativa da retenção de água em sistemas de manejo R E S U M OOs objetivos deste estudo foram avaliar os efeitos de atributos físicos estruturais do solo sobre a retenção de água e desenvolver funções de pedotransferência (FPT) para a estimativa de conteúdos de água (θ) em diferentes potenciais mátricos de um Latossolo Vermelho distrófico em sistema convencional (SC) e sistema plantio direto (SPD). Os efeitos de longo prazo dos manejos SC e SPD (mais de 25 anos) sobre a densidade do solo (DS), porosidade total (PT), macroporosidade (Ma), microporosidade (Mi) e retenção de água foram investigados. As FPT foram desenvolvidas para predizer os θs utilizados na determinação da curva de retenção de água apenas para o SPD. O SPD apresentou menor DS e maior PT e Mi que o SC. O SPD aumentou o conteúdo de água retido em poros de tamanho entre 0,2 e 30 µm, em relação ao SC. No entanto, o SC apresentou maior conteúdo de água retido em poros com raio menor que 0,2 µm. As FPTs utilizadas para estimar θ para os potenciais mátricos de -1, -3, -6, -10, -33, -100, -400, -800 e -1500 kPa tiveram acurácia adequada. A DS, Ma, Mi e teor de areia foram as principais variáveis consideradas para estimar o conteúdo de água nesses potenciais mátricos. Key words:no-tillage conventional tillage soil porosity Palavras-chave: sistema plantio direto sistema plantio convencional porosidade do solo

Susceptibility to landslides in mountain areas results from the interaction of various factors related to relief formation and soil development. The assessment of landslide susceptibility has generally taken into account individual events, or it has been aimed at establishing relationships between landslide-inventory maps and maps of environmental factors, without considering that such relationships can change in space and time. In this work, temporal and space changes in landslides were analysed in six different combinations of date and geomorphological conditions, including two different geological units, in a mountainous area in the north-centre of Venezuela, in northern South America. Landslide inventories from different years were compared with a number of environmental factors by means of logistic regression analysis. The resulting equations predicted landslide susceptibility from a range of geomorphometric parameters and a vegetation index, with diverse accuracy, in the study area. The variation of the obtained models and their prediction accuracy between geological units and dates suggests that the complexity of the landslide processes and their explanatory factors changed over space and time in the studied area. This calls into question the use of a single model to evaluate landslide susceptibility over large regions.