Observations on the Biological Development of Macropores in Soils of Romney Marsh

Abstract

Many of the soils developed on Recent alluvium in Romney Marsh have abundant interconnecting pores, holes, and cavities in their subsurface horizons formed by the activity of roots, ants, and earthworms. Ants are considered to be the dominant agents in forming highly developed underground systems of galleries and chambers. These features are apparently continuous over large areas and are not restricted to any particular soil, but occur on differing soils with a considerable range of pH, salinity, texture, and fluctuations of water-tables. Consequently, many of the soils have drainage and other characteristics that cannot be deduced from a consideration of texture or structure (pedality) alone. The characteristics of these macropores, as revealed by the infiltration into the soil of cast-forming materials such as plaster of Paris, are described, and their origin, distribution, and significance in relation to land use are discussed.

A Century of Denial: Preferential and Nonequilibrium Water Flow in Soils, 1864‐1984

“…Hoover (1962) noted that abundant plant and animal channels in surface soil layers increases their lateral permeability so that water movement may take place downslope before the underlying soils are completely wet. Green and Askew (1965) studied the macropore networks produced by ants down to depths of 1 m; whereas Williams and Allman (1969) found cylindrical macropores to depths of at least 10 m in a loess soil, they were unsure what had produced them. Ehlers (1975) found that the macropores produced by earthworms increased in frequency down to a depth of 0.6 m in both tilled and untilled soils at his site, although frequencies were generally less in the tilled soil.…”

Macropores and water flow in soils

“…Several observations and estimates of the age of macropore networks are reported. Green and Askew [1965] for example considered the age of ant-developed macropore systems to be one of several hundreds of years. Mellanby [1971] suggested that where food is readily available mole runs may be hundreds of years old and may not be apparent from the soil surface.…”

“…The additional temporal variability of the macropore network gives rise to problems about which there is very little information (see section on experimental determination of macroporosity). Some types of macropores will change size and shape on a time scale of minutes or hours, there will certainly be important seasonal effects in many soils; while some biotic channels may be relatively stable for many years [e.g., Green and Askew, 1965;Mellanby, 1971].…”

Quantification of macropores and their impact on preferential solute transport

“…Use of plaster of Paris in studying macropores dates back to Green and Askew (1965) , who used plaster of Paris to study macropores in the soils of Romney Marsh. FitzPatrick et al (1985) used plaster of Paris (dental grade) to study pore continuity in the soil and also to preserve seedbeds for undisturbed sampling.…”

“…Macropores are formed in various ways: by shrinkage of natural planes of weakness on drying (Brewer, 1964), freezethaw cycles, mole draining and subsoiling (Beven and Germann, Beven and Germann (1981) Bullock and Thomasson (1979) Edwards et al (1988) FitzPatrick et al 1985Luxmoore 1981Tippkotter (1983) 1982), plant roots (Aubertin, 1971); and soil fauna (Green and Askew, 1965;Ehlers, 1975). Beven and Germann (1982) concluded that most soils contain some macropores, the nature and volume of which depend on a dynamic balance between constructive and destructive processes.…”