Microstructural strength of four subtropical soils evaluated by rheometry: properties, difficulties and opportunities

The structural strength of soils has been extensively described by physical and mechanical properties evaluated on the mesoscale for different soils and management conditions. However, changes in the organization of the soil matrix at the microstructural level, which can be obtained by rheometry, are still seldom used in soil mechanics. Our aim was to use the amplitude sweep test, a rheometry technique, to investigate the microstructural strength of four subtropical soils (two Oxisols, an Ultisol and a Vertisol) and to discuss difficulties with respect to the samples, water content, soil density and vertical force. The various rheological properties which reveal the soil microstructural strength were determined: deformation at the end of the linear viscoelastic range, LVE range (LVE), shear stress at the end of the LVE range (LVE), deformation at yield point, YP (YP), storage and loss moduli at YP (GGYP), maximum shear stress (max), and integral z. In general, soil elasticity (LVE and YP) and microstructural strength (LVE and max) were greater in the Oxisols and the Vertisol, which both possess high clay content, while the latter also contains expansive clay minerals. The lowest structural strength was observed in the Ultisol which had a high sand content. As rheological properties are related to soil properties such as particle size distribution and carbon content, they can be applied in the evaluation of the microstructural strength of clayey and sandy soils and allows for inferences regarding inter-particle shear strength. However, the test is not applicable to very dry soil samples and sample preparations can affect the results. We suggest a number of approaches to find solutions for these difficulties/problems.(AU)

Microstructural strength of four subtropical soils evaluated by rheometry: properties, difficulties and opportunities

The structural strength of soils has been extensively described by physical and mechanical properties evaluated on the mesoscale for different soils and management conditions. However, changes in the organization of the soil matrix at the microstructural level, which can be obtained by rheometry, are still seldom used in soil mechanics. Our aim was to use the amplitude sweep test, a rheometry technique, to investigate the microstructural strength of four subtropical soils (two Oxisols, an Ultisol and a Vertisol) and to discuss difficulties with respect to the samples, water content, soil density and vertical force. The various rheological properties which reveal the soil microstructural strength were determined: deformation at the end of the linear viscoelastic range, LVE range (LVE), shear stress at the end of the LVE range (LVE), deformation at yield point, YP (YP), storage and loss moduli at YP (GGYP), maximum shear stress (max), and integral z. In general, soil elasticity (LVE and YP) and microstructural strength (LVE and max) were greater in the Oxisols and the Vertisol, which both possess high clay content, while the latter also contains expansive clay minerals. The lowest structural strength was observed in the Ultisol which had a high sand content. As rheological properties are related to soil properties such as particle size distribution and carbon content, they can be applied in the evaluation of the microstructural strength of clayey and sandy soils and allows for inferences regarding inter-particle shear strength. However, the test is not applicable to very dry soil samples and sample preparations can affect the results. We suggest a number of approaches to find solutions for these difficulties/problems.

Physical soil properties in crop-livestock integration system in Humic Cambisol / Propriedades físicas do solo em sistema de integração lavoura-pecuária em Cambissolo Húmico

In integrated crop-livestock systems under a no-tillage system, the action of animal trampling can influence the physical properties of the soil, depending on the intensity of grazing and stocking rate. This study aimed to evaluate the physical properties of a Humic Cambisol, under an integrated crop-livestock system submitted to different grazing intensities of lactating cows in the city of Lages, SC. The treatments constituted three forage masses of winter pasture (low, medium and high), and a control area, with no grazing (no grazing), oat and ryegrass consortium was used, then the density, hydraulic properties of the soil, organic matter content, aggregation and soil penetration resistance were evaluated. Generally the animal trampling had no significant influence on physical properties, the dynamics of water and the contents of soil organic matter. The macroporosity conditions, as well as high resistance to penetration, principally in conditions of low moisture, prove that the Humic Cambisol of the franc silty clay texture provides a constraint physical problem.(AU)

Em sistema de integração lavoura-pecuária associado ao sistema de semeadura direta, a ação do pisoteio animal pode influenciar as propriedades físicas do solo, dependendo da intensidade de pastejo e da carga animal. O presente trabalho objetivou avaliar as propriedades físicas de um Cambissolo Húmico, sob sistema de integração lavoura-pecuária submetido a diferentes intensidades de pastejo de gado leiteiro, no município de Lages, SC. Os tratamentos foram constituídos por pastejo direto de gado em três disponibilidades de forragem do consórcio de aveia e azevém (baixa, média e alta) e uma testemunha, sem pastejo. Foram avaliados densidade, propriedades hidráulicas, teor de matéria orgânica, agregação e resistência à penetração do solo. De maneira geral, o pisoteio animal não influenciou significativamente as propriedades físicas, a dinâmica da água e os teores de matéria orgânica do solo. As condições de macroporosidade, bem como a resistência à penetração, principalmente em condição de baixa umidade, demonstram que o Cambissolo Húmico de textura franco argilo siltosa possui restrições físicas ao desenvolvimento das plantas.(AU)

Physical soil properties in crop-livestock integration system in Humic Cambisol / Propriedades físicas do solo em sistema de integração lavoura-pecuária em Cambissolo Húmico

In integrated crop-livestock systems under a no-tillage system, the action of animal trampling can influence the physical properties of the soil, depending on the intensity of grazing and stocking rate. This study aimed to evaluate the physical properties of a Humic Cambisol, under an integrated crop-livestock system submitted to different grazing intensities of lactating cows in the city of Lages, SC. The treatments constituted three forage masses of winter pasture (low, medium and high), and a control area, with no grazing (no grazing), oat and ryegrass consortium was used, then the density, hydraulic properties of the soil, organic matter content, aggregation and soil penetration resistance were evaluated. Generally the animal trampling had no significant influence on physical properties, the dynamics of water and the contents of soil organic matter. The macroporosity conditions, as well as high resistance to penetration, principally in conditions of low moisture, prove that the Humic Cambisol of the franc silty clay texture provides a constraint physical problem.

Em sistema de integração lavoura-pecuária associado ao sistema de semeadura direta, a ação do pisoteio animal pode influenciar as propriedades físicas do solo, dependendo da intensidade de pastejo e da carga animal. O presente trabalho objetivou avaliar as propriedades físicas de um Cambissolo Húmico, sob sistema de integração lavoura-pecuária submetido a diferentes intensidades de pastejo de gado leiteiro, no município de Lages, SC. Os tratamentos foram constituídos por pastejo direto de gado em três disponibilidades de forragem do consórcio de aveia e azevém (baixa, média e alta) e uma testemunha, sem pastejo. Foram avaliados densidade, propriedades hidráulicas, teor de matéria orgânica, agregação e resistência à penetração do solo. De maneira geral, o pisoteio animal não influenciou significativamente as propriedades físicas, a dinâmica da água e os teores de matéria orgânica do solo. As condições de macroporosidade, bem como a resistência à penetração, principalmente em condição de baixa umidade, demonstram que o Cambissolo Húmico de textura franco argilo siltosa possui restrições físicas ao desenvolvimento das plantas.