New methods and models for characterising structural heterogeneity of soil

The dual cause of quantifying and modelling soil structure is a regular irr itant to most soil scientists, whatever their discipline. All know of the i mportance of placing soil processes in the context of the physical framewor k of the soil. It is the habitat for all soil biota, and plant roots; it ac ts as a reservoir for solutes, and is composed of the main conduits that tr ansfer gases to the atmosphere, and potential pollutants to the waterways. Unfortunately, an explicit account of the heterogeneity inherent in the soi l physical architecture has, until recently, been beyond experimental and t heoretical insight. This discussion aims to draw together some current meth ods and models for characterising the soil structural heterogeneity. We que stion the use of aggregates as indicators of structure, assess possible alt ernatives, and discuss several theoretical approaches that promise to captu re the ubiquitous heterogeneity in soil structures. The key question that i s examined is, can we functionally quantify soil structure and causally rel ate that quantification to specific processes? (C) 2001 Elsevier Science B. V. All rights reserved.