Development of an improved Vertisol stability test for SOILpak

The stability in water of soil from 3 contrasting Vertisols was measured using5 tests. Two end-over-end shaking procedures, the Loveday & Pyledispersion test, and the relatively rapid SOILpak procedure of Daniells & Larsen were assessed. The latter method has been modified to deal with severaldeficiencies such as its lack of score subdivisions; the new procedure isreferred to as the ‘aggregate stability in water’ (ASWAT) test. Wecorrelated data from all the tests under consideration to provide definitionsof the ‘critical’ point at which dispersion becomes a problem forland managers. Three soil management zones have been defined provisionallyusing data from the ASWAT and end-over-end ‘aggregate stability’tests. The scheme allows appropriate surface soil management strategies to bepredicted using the ASWAT test. The relationship between data from the ASWATtest and exchangeable sodium percentage indicated that factors other thanexchangeable sodium strongly influence dispersibility of the samples underconsideration.