STABILITY OF AGGREGATES OF DIFFERENT SIZE GRADES IN ALLOPHANIC SOILS FROM VOLCANIC ASH IN NEW-ZEALAND

Samples from six ash soils were chosen with a range of Fe and C contents. Stabilities over the aggregate size‐range from < 1 †m to > 2 mm were measured by selectively removing aggregating agents from fresh soil samples. Wet‐sieving was also carried out on both field‐moist and air‐dried 3.4–2.0 mm macroaggregates. Macroaggregate stabilities were closely related to C contents and were also enhanced by high contents of allophane and/or Feox. High water contents decreased the stability of field‐moist macroaggregates. Clay‐sized material was most readily dispersed with Na resin after pretreatment with hydrogen peroxide; removing the latter alone was usually ineffective in dispersing clays. Copyright © 1987, Wiley Blackwell. All rights reserved