Soil Structure: Science or Fantasy.

Arrangement of soil physical components often identified as soil structure, controls internal movement and storage of heat and fluids, impacts plant root growth, affects the soil environment critical to soil biology, and interacts with precipitation affecting water runoff, infiltration, and water quality.  Soil structure, one of the most studied and important soil science phenomena, remains arguably the most elusive soil property to quantify.  The objective of the paper is to review selected influences of soil structure on soil processes and discuss an alternative for advancing the science of soil structure characterization. Heat conduction depends on continuous pathways through which heat flows in response to temperature gradient, and the thermal conductivity of material comprising the pathway. Critical to heat conduction is frequency and distribution of particle to particle contact points as these form the heat conduction bridge between soil solids. Movement of water in the unsaturated state occurs on particle surfaces and also is highly dependent on frequency and distribution of the bridge for water flow from particle to particle in response to a water potential gradient. Through managing particle contact points and size and continuity of voids between particles, which determines saturated water movement and gas exchange, we manage soil water, temperature and gas conditions.  Soil structure effects on mass and energy flow are modified by water dynamics on particle surfaces and at particle contact points as it affects the mass and energy flow network. An alternative method for characterizing soil structure, the Generalized Soil Structure Index, involving the three phases of solids, liquid and gas will be proposed for characterizing soil structural conditions as they impact soil productivity.