Pore Size, Particle Size, Aggregate Size, and Water Retention

Abstract Measurements of water retention and pore‐size distribution for a soil are time consuming and affected by changes in aggregate‐size distribution. A method of compared distribution curves was used to relate distributions of pore size (PO), particle size (PA), aggregate size (AG), and pore size from water retention (WR). Seven surface soils varying in texture and aggregation were tested. After normalization to 100% volume, the pore‐, particle‐, and aggregate‐size distribution, as well as water‐retention (converted to pore diameter) curves were each fitted to a linearly transformed logistic function to evaluate their interrelations using R ( m/n ), a coefficient for the ratio of the diameters of component m to component n . Identical distribution curves have an R ( m/n ) value of 1. The R (PO/PA) and R (WR/PA) for the seven soils ranged from 0.25 to 2.26 and from 0.18 to 1.34, respectively, indicating that the theoretical packing parameters of 0.225 to 0.414 do not hold for PA distribution. The R (PO/AG) ranged from 0.06 to 0.23 and R (WR/AG) from 0.04 to 0.16. Both ranges of R values smaller than the theoretical packing parameters suggests interactions may occur between large and small aggregates. However, R (PO/AG) and R (WR/AG) values were more consistent and were significantly related to aggregation level and bulk density, suggesting that AG distribution should be used as a parameter to predict PO distribution and water retention. Comparisons between water retention curves and PO distributions from Hg intrusion gave R (PO/WR) ranging from 0.78 to 2.59, showing that equivalent PO for a given soil is not the same when different measuring methods are used.