Applications of S-THEORY in the study of soil physical degradation and its consequences

The S-theory for soil physical quality is introduced. It is shown how values of S can be determined from the water retention characteristic curve. It is also explained how, when experimental data are not available, pedotransfer functions can be used to obtain estimates of S. Although S was first introduced as an index of soil physical quality, it is being increasingly found that it is a useful numerical quantity that can be used in equations for prediction of a range of soil physical properties. Its use is illustrated with examples for hydraulic conductivity, friability, tillage, compaction, penetrometer resistance, plant-available water, root growth and readily dispersible clay. The main merit of S derives from the fact that given values of S have the same meaning and consequences in different soils. It is described how S can be used to identify areas of land where physical degradation or amelioration are taking place, and to evaluate management practices that will give sustainable land use. Copyright (C) 2007 John Wiley & Sons, Ltd.