Soil science has a myriad of methods to measure soil structural stability.  Conventional methods range from, for example wet and dry sieving, soil strength,  various types of dispersion tests, and more engineering type tests.  Most of these tests apply energy to break up soil structure and then use crisp empirical data sets to assess the change in aggregation as a consequence of energy input.  Sieving methods are limited by how many sieves are used and the crisp set always result in a very limited number of aggregate size fractions; the crisp data set of dispersion is almost binary data.  The same applies to particle size distribution where particle distribution is simplified to a small number of size classes. In most cases only the three main classes; i.e. sand silt and clay.  A relatively new method to measure a continuous particle size distribution is by laser refraction.  This method can potentially also be used to measure the stability of aggregate size distribution rather then a limited number of size classes by sieving to different mesh sizes.  Only limited data exists where laser refraction has been used to assess soil structural stability.

The first part of this project aims to develop a robust methodology to assess aggregate size distribution stability using laser refraction, the 2nd part of the project is to assess the method’s ability to quantify aggregate size distribution stability on Ferrosols with different organic carbon contents.  The project will use the laser refraction machine Malvern Mastersizer 2000  located at the St Lucia soil laboratories.

Project members

Dr Gunnar Kirchhof

Principal Research Fellow & Senior Lecturer
School of Agriculture and Food Sciences