Degree of compactness, soil physical properties and yield of soybean in six soils under no-tillage

The 'degree of compactness' is a useful parameter to study soil compaction and represents the current bulk density in relation to the bulk density of the same soil in a reference state. The objectives of this study were to: (i) determine the best compression stress to establish the reference bulk density in the uniaxial compression test using undisturbed samples; (a) quantify the effect of texture on degree of compactness, and (Hi) evaluate the influence of degree of compactness on selected soil physical properties and crop yield. Six soils under no-tillage from southern Brazil were used and the reference bulk density was evaluated on soil samples equilibrated to the matric suction of 33 kPa and subjected to uniaxial compression test. Soil macroporosity, mechanical penetration resistance, root growth, and yield of soybean were also evaluated. For undisturbed soil samples, stresses ≥ 800kPa (particularly the stress of 1600kPa) arc appropriate to determine the reference bulk density. Degree of compactness is independent of clay content and is associated with changes in soil physical properties. A degree of compactness ~100% restricted root growth of soybean, whereas the highest soybean yield was obtained with a DC of 82% for Alfisols and Ultisol, and 85% for Oxisols. Additional keywords: reference bulk density, relative compaction, soil compaction, uniaxial compression.
Introduction Soil compaction is defined as the process of decreasing total porosity (especially air-filled porosity), with a consequent increase in bulk density and soil penetration resistance and decrease in water [...]