摘要: The relationship between hydraulic conductivity and water content for each soil horizon within a soil profile has a major control on the local soil-water regime, and is therefore of great practical significance. Hydraulic conductivity strongly depends on water content because, as a soil dries, fewer water-filled pores contribute to flow. The reduction in hydraulic conductivity with water content is dramatic due to the exponential relationship between pore size and flow. As a result, macropores (including fissures and channels) can have an overriding control on water movement in soils at or near saturation. The presence of these structural features complicates the measurement of hydraulic conductivity. Methods in this Handbook are presented for saturated and unsaturated hydraulic conductivity. The latter is restricted to conditions near saturation (ie potentials between 0 and-150 mm). More elaborate methods are required to extend the range towards more negative potentials (see Dirksen 2001). For land evaluation, it will be usually sufficient to use estimation methods for this range (Chapter 22) in conjunction with measurements near saturation. The selection of a method for hydraulic conductivity depends on a range of factors. These include the nature of the soil to be measured, purpose of measurement and resources available. A large number of methods exist, and many have variants that can return dramatically different results. In this chapter, we consider the practical and theoretical factors that determine the most suitable strategy for measurement and prediction. This chapter is a prerequisite for Chapters 7 to 11.