Modeling the relationship between soil bulk density and the water retention curve

Increases in the soil bulk density during compaction may influence many aspects of the soil-water-plant-atmosphere system. An empirical approach is suggested that could model the effect of an increase in soil bulk density on the water retention curve (WRC). Two expressions of the WRC are considered. Relationships between their parameters and the bulk density of a compacted soil were calibrated and validated against experimental WRC data of soils at various levels of compaction. These relationships enable a relatively good prediction of the effect of bulk density on the WRC. The relationship between the pore size distribution index and the coefficient of variation of the WRC, previously found for a wide range of soil types, is appropriate also when soils at different bulk densities are considered. The silt/clay content ratio was found to be an important factor in a quantitative expression of soil strength.