New methods and models for characterising structural heterogeneity of soil

The dual cause of quantifying and modelling soil structure is a regular irritant to most soil scientists, whatever their discipline. All know of the importance of placing soil processes in the context of the physical framework of the soil. It is the habitat for all soil biota, and plant roots; it acts as a reservoir for solutes, and is composed of the main conduits that transfer gases to the atmosphere, and potential pollutants to the waterways. Unfortunately, an explicit account of the heterogeneityinherent in the soil physical architecture has, until recently, been beyond experimental and theoretical insight. This discussion aims to draw together some current methods and models for characterising the soil structural heterogeneity. We question the use of aggregates as indicators of structure, assess possible alternatives, and discuss several theoretical approaches that promise to capture the ubiquitous heterogeneity in soil structures. The key question that is examined is, can we functionally quantify soil structure and causally relate that quantification to specific processes?