ABSTRACT
Macropores are large, continuous voids in soil and include structural, shrink-swell, and tillage fractures, old root channels, and soil fauna burrows (Fig. 1). They are important because they can increase infiltration and may result in bypass flow where water and solutes move rapidly through the profile and do not interact with the soil matrix. This is one type of preferential flow. Other types of preferential flow include finger flow[1] and funnel flow.[2] Reviews of macropores were published by Beven and Germann,[3] White,[4] Germann,[5]
Brusseau and Rao,[6] Beven,[7] and Bouma.[8]
MACROPORE FLOW OF WATER
One of the earliest documentations of macropore flow was by Lawes, Gilbert, and Warington:[9]
Suggested lower limits for macropore diameters and widths are in the 0.03-3.00 mm range.[10,3,4] The lower limit would include some pores that would fill by capillarity and the upper limit would exclude all capillary pores. Consequently, the dominant driving force in macropore flow is gravity, whereas matrix flow is driven primarily by capillarity. Continuity is also an important feature of macropores.
