Density and Porosity Relationships of Aggregates of Alluvial Soils

Aggregate density decreased asymptotically with increase in aggregate size to a minimum constant value, which was characteristic of a given soil. This constant value decreased with the fineness of soil texture in general. Density of aggregates, especially of bigger size fraction, depended more on organic carbon (r=−0.88) and clay contents (r=−0.85) than on silt (r=−0.35). A high correlation (r=0.92) was observed between the aggregate density of neighbouring size fractions, which diminished as the sizes departed from each other. In a given size range, the aggregate density was highly correlated (r=0.99) with the bulk-density. The inter-aggregate porosity was independent of the size of fraction of aggregates and its average value was 42.3 per cent and it lay between the limits set by theoretical models of cubic and cubic-tetrahedral packing of spheres. Intra-aggregate and total porosity, however increased with increase in size of aggregates. Maximum intra-aggregate porosity was recorded in the aggregate size range of about 1.5 mm, which signifies the importance of these aggregates in providing soil physical conditions most conducive to better soil-air-water relationships in alluvial soils of Punjab.