PROPERTIES OF SUBSOILS IN RELATION TO VARIOUS MEASURES OF SURFACE-AREA AND WATER-CONTENT

Neither the specific surface area values (from N, sorption) nor the ethylene glycol monoethyl ether (EGME) retention values of 21 soil samples from New Zealand and Fiji could all be accounted for by the sum of the contributions from their component minerals. Much EGME is probably retained by internal surfaces of interlayered and interstratified clay minerals. EGME retention correlated well with cation exchange capacity (CEC) and a number of measures of water content of these soils. The water contents of air-dried soils (measured as 'moisture factors' or the ratios of air-dry and oven-dry weights) showed almost as close a relationship to CEC as EGME retention for this set of 21 subsoils. Moisture factors and CEC were closely related, within groups defined by dominant clay mineralogies, for a much wider selection of 1318 New Zealand soil horizons with low carbon contents. The relationships between surface area and a number of other soil properties including dispersibility of soils were also examined.