RESUMO

Spade methods to visually evaluate soil structural quality (Sq) are simple, quick, cheap and can be used by farmers, gardeners, consultants and the scientific community. However, European and Brazilian users of one such method, viz. visual evaluation of soil structure (VESS) which is a development of the Peerlkamp test, have been concerned about its subjectivity. The method of soil slice break‐up and operator influence on scores have been questioned. Thus, our aim was to make soil scoring by the VESS technique more objective and thus to revise the scoring guide. We compared scoring with normal breaking up of the soil slice by hand with scoring after breaking up the slice by dropping (drop shatter) to make the soil break‐up more operator independent. After slice break‐up, aggregates were split by hand and their internal porosity was evaluated to develop the use of visible porosity as an aid to scoring. This proved inconclusive on its own, so a method of reducing larger aggregates to 1.5–2.0 cm core fragments and describing their shape and porosity was developed to score soil Sq. Breaking up a spadeful of soil by hand or by dropping resulted in the same Sq score. The method of reducing aggregates and evaluation of their shape improved VESS, particularly in the middle range of soil quality and the revised chart is shown. VESS was sensitive to changes in Sq in layers within the profile and its use for diagnosing Sq in different layers allows targeted soil improvement by tillage.

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APPLICATIONS OF THE RESISTANCE CURVE IN THE CONTROL OF THE PHYSICAL QUALITY OF SOILS UNDER GRASSABSTRACT -The degradation of the physical quality of soils has been associated with the soil compaction caused by animal trampling. The soil resistance to penetration (SRP) is a soil physical parameter used to assess the soil compaction degree. However, SRP varies with soil moisture (q) and bulk density (D b ). The objective of this research was to quantify the soil resistance curve and use it to evaluate the physical quality of a soil under short duration grazing system of elephant grass. The soil resistance curve was measured using forty-eight undisturbed cores taken at the 0-10 cm depth of a Kandiudalfic Eutrudox used with elephant grass in intensive system of exploration. The results indicated a negative correlation among SRP and q as well as a positive correlation between SRP and D b . Predictions indicated that at soil matric potential equal to -0.01 MPa the SRP did not reach critical values to root growth. Nevertheless, at the soil matric potential equal to -0.3 MPa, the SRP reached limiting values in the whole area. For the management system and the studied species, the results suggest that soil resistance curve may be used to guide soil management practices for maintaining a good soil physical quality for grass growth.

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(1) Recebido para publicação em abril de 2006 e aprovado em janeiro de 2007.(2) Professor do

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RESUMONo sistema de plantio direto, a ausência de revolvimento do solo, aliada ao tráfego de máquinas, promove a compactação excessiva do solo em superfície. Com o objetivo de estudar alguns fatores que interferem na compactação do solo em plantio direto, foi realizado um experimento no município de Ponta Grossa (PR), nos anos agrícolas de 1989/1990 e 1990/1991. Comparou-se o efeito de três métodos de preparo inicial do solo -com arado de discos, aivecas e rotativo -e dois níveis de calagem sobre algumas propriedades físicas de um Latossolo Vermelho-Escuro argiloso no sistema de plantio direto com tráfego controlado. Utilizou-se a seqüência de culturas em rotação: ervilhaca, milho, aveia-preta e soja. Avaliaram-se a densidade, a porosidade do solo e o teor de água retido entre os potenciais de -0,006 e -0,5 MPa. Não houve efeito significativo da calagem sobre as propriedades físicas estudadas. Os resultados demonstraram efeitos significativos do tráfego, aumentando a densidade do solo e reduzindo a sua porosidade e o conteúdo de água retido entre aqueles potenciais. A distribuição, em profundidade, das cargas aplicadas pelo tráfego de máquinas, principalmente de colheitadeiras, foi, provavelmente, influenciada pelo volume de solo revolvido pelos diferentes sistemas de preparo inicial. Nas parcelas em que a estrutura do solo foi submetida a pressões por meio do tráfego, obteve-se redução na produtividade da soja, em comparação às áreas com ausência de tráfego, no período em que o estudo foi realizado.Termos de indexação: rotação de culturas, estrutura do solo, compactação, densidade do solo, porosidade.