Bulk Density, Saturation Water Content and Rate of Wetting of Soil Aggregates

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Abstract
Bulk density, degree of saturation, volume increase on wetting, and rate of wetting were measured for aggregates and clods of Ormstown silty clay loam (Humaquept) of sizes from 5 cm to 0.036 cm diameter.Bulk density increased with a decrease in diameter. For 2.2‐mm to 0.36‐mm diameter aggregates this increase was due to a surface area effect, i.e., loss in porosity as a result of subdividing larger aggregates. Both surface area effects and increased porosity from root channels and fissures were required to explain the increase for clods between 5 and 1 cm diameter.An evaporation and a sorption technique are described and used to estimate the water content of aggregates at saturation, i.e., the intra‐aggregate water content. The evaporation technique gave reliable results at specific rates of evaporation, but the sorption technique was not as useful. Clods and aggregates of the soil and of pumice samples did not fully saturate; entrapped air accounted for 25 to 27% of the total pore volume.Aggregates of 1 and 2.2 mm diameter and clods of 1.0 and 5.0 cm diameter took about 1, 1.7, 45, and 1,000 seconds, respectively, to saturate. This rapid wetting would minimize differences in potential between inter‐and intra‐aggregate water during infiltration.
Funding Information
  • National Research Council Sri Lanka

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