Atributos de solo determinantes para a estimativa do índice de estabilidade de agregados

The objective of this work was to identify the most important soil attributes to estimate the aggregate stability index. To identify these attributes, multiple stepwise regression was used on data collected from anEutrorthox cultivated under a no‑tillage system. To obtain the prediction models for the aggregate stability index (IeaE), ten independent variables were evaluated: total clay, bulk density, penetration resistance, organic matter, pH in water, effective cation exchange capacity, available water, total porosity, macroporosity, and gravimetric moisture. The attributes total clay (Arg), bulk density (Ds), penetration resistance (RP), organic matter (MO), and pH are the most important for the estimation of the IeaE, and the pedotransfer function that best describes this index is: IeaE = 27.80 + 0.04Arg + 27.97Ds + 12.35RP + 0.45MO ‑ 9.72pH (R2 = 0.89).O objetivo deste trabalho foi identificar atributos de solo importantes para a estimativa do índice de estabilidade de agregados. Para a identificação dos atributos, utilizou-se a regressão múltipla “stepwise” em dados coletados de Latossolo Vermelho eutroférrico, cultivado em sistema de plantio direto. Para a obtenção dos modelos de estimativa do índice de estabilidade de agregados (IeaE), foram analisadas dez variáveis independentes: argila total, densidade do solo, resistência à penetração, matéria orgânica, pH em água, capacidade efetiva de troca de cátions, água disponível, volume total de poros, macroporosidade e umidade gravimétrica. Os atributos argila total (Arg), densidade do solo (Ds), resistência à penetração (RP), matéria orgânica (MO) e pH são os mais importantes para a estimativa do IeaE, e a função de pedotrânsferência que melhor descreve esse índice é: IeaE = 27,80 + 0,04Arg + 27,97Ds + 12,35RP + 0,45MO ‑ 9,72pH (R2 = 0,89)

Developing a novel basal animal model for use in exploring the development of early sensory systems

Freshwater and marine sponges are members of the phylum Porifera, which split off of the animal lineage before the Cnidarian and the Bilaterian split (Peterson and Davidson, 2000). This makes sponges the most basal extant animal species and an excellent candidate for looking at the evolutionary conservation of ancient genes in animals. As basal animals, sponges do not have true developmental tissue layers although they do have 11 different cell types, some of which may function together (Simpson, 1984; Manconi and Pronzato, 2002). Sponges are filter feeders, and move water through their bodies so that they can absorb particles in the water column to eat. They have ciliated cells that function to move the water to the channels that run through their bodies. Water enters the sponge body through holes in the tissue called ostea, moves into choanocyte chambers, and then is moved through the body by the canals until it exits through a chimney-like osculum (Simpson, 1984; Manconi and Pronzato, 2002). Due to their role in moving water through the sponge, the choanocyte chambers are an important part of the structure and function of a sponge. These chambers are composed of flat, ciliated cells arranged in a ring (Elliot and Leys, 200). Groups of these chambers surround the ostea where the water enters the sponge (Elliot and Leys, 2009)

Modelling of soil penetration resistance for an oxisol under no-tillage

Soil penetration resistance is an important property that affects root growth and elongation and water movement in the soil. Since no-till systems tend to increase organic matter in the soil, the purpose of this study was to evaluate the efficiency with which soil penetration resistance is estimated using a proposed model based on moisture content, density and organic matter content in an Oxisol containing 665, 221 and 114 g kg-1 of clay, silt and sand respectively under annual no-till cropping, located in Londrina, Paraná State, Brazil. Penetration resistance was evaluated at random locations continually from May 2008 to February 2011, using an impact penetrometer to obtain a total of 960 replications. For the measurements, soil was sampled at depths of 0 to 20 cm to determine gravimetric moisture (G), bulk density (D) and organic matter content (M). The penetration resistance curve (PR) was adjusted using two non-linear models (PR = a Db Gc and PR' = a Db Gc Md), where a, b, c and d are coefficients of the adjusted model. It was found that the model that included M was the most efficient for estimating PR, explaining 91 % of PR variability, compared to 82 % of the other model

Morphostructural characterization of soil conventionally tilled with mechanized and animal traction with and without cover crop

The structural stability and restructuring ability of a soil are related to the methods of crop management and soil preparation. A recommended strategy to reduce the effects of soil preparation is to use crop rotation and cover crops that help conserve and restore the soil structure. The aim of this study was to evaluate and quantify the homogeneous morphological units in soil under conventional mechanized tillage and animal traction, as well as to assess the effect on the soil structure of intercropping with jack bean (Canavalia ensiformis L.). Profiles were analyzed in April of 2006, in five counties in the Southern-Central region of Paraná State (Brazil), on family farms producing maize (Zea mays L.), sometimes intercropped with jack bean. The current structures in the crop profile were analyzed using Geographic Information Systems (GIS) and subsequently principal component analysis (PCA) to generate statistics. Morphostructural soil analysis showed a predominance of compact units in areas of high-intensity cultivation under mechanized traction. The cover crop did not improve the structure of the soil with low porosity and compact units that hamper the root system growth. In areas exposed to animal traction, a predominance of cracked units was observed, where roots grew around the clods and along the gaps between them