ABSTRACT
Soil bulk density (pb), the weight per unit volume, is an important soil physical property that influences biomass productivity and environment quality. The biomass productivity effects of soil bulk density influence root growth and proliferation, which influence uptake of plant nutrients and water. The environmental effects of soil bulk density are due to its effects on aeration, soil-water regime, runoff and erosion. Anaerobiosis can lead to emissions of CH4 and N20 , whereas accelerated runoff and erosion can cause pollution of natural waters. Runoff and erosion are the principal causes of non-point source pollution. Soil bulk density is influenced by natural and anthropogenic factors (Figure 1). Important among natural factors are soil properties, particle size distribution, degree of aggregation, soil organic carbon content, cation exchange capacity (CEC), exchangeable cations, flora and fauna including soil biotic activity, and climatic factors. The clay content and nature of clay strongly interact with soil organic carbon (SOC) and other cations to form aggregates. Degree of aggregation and stability of aggregates strongly influence soil bulk density. High activity clays (HACs, 2:1 minerals) tend to have higher bulk densities than soils low in clay and SOC contents. Low activity clays (LACs, 1:1 minerals) tend to have lower bulk densities and behave like low clay soils. Soils dominated by amorphous materials (e.g., Andisols) have very low bulk densities, as do organic soils (e.g., Histosols, Mollisols).
