Soil Structure

Soil structure refers to the organization and arrangement of soil particles and the resultant complex maze of pores. It is a composite soil quality that exerts signicant control over most physical, chemical, and biological processes that occur in both natural and anthropogenically altered soils, including transport and storage of liquids, gases, and heat; penetration and proliferation of roots; microbial life; and decomposition and storage of soil organic matter. It is an inherently complex soil property because the constituent particles are heterogeneous in size, shape, and chemical nature as well as because the mechanisms that bond the particles are diverse. It is a hierarchical organization whereby ne primary particles bond together to form secondary particles and small secondary particles merge to form bigger peds or aggregates. It is also a dynamic soil property, continuously changing in response to various internal and external drivers, including moisture and temperature ¥uctuations, biological activity, and human intervention. As such it is a concept that spans multiple spatial and temporal scales: the arrangement of colloidal clay particles in a ¥occule, the arrangement of clods on the surface of a tilled layer, an array of earthworm tunnels, and the variability of soil strength from one point to another are all aspects of soil structure (Dexter, 1988). Due to these complexities, we still lack a truly objective description for it and a universally accepted and quantiable measure of soil structure does not exist yet (Hillel, 1998).