FIGURE 6.4. Arenas of activity in soil systems. These "hot spots" of activity may be less than 10% of the total soil volume, but represent more than 90% of the total biological activity in most soils worldwide (from Beare et al., 1995, reprinted with permission).

(Elliott, 1986; Elliott and Coleman, 1988; Beare et al., 1995; Six et al., 1999). This zone of influence is less well studied and is a major source of some of the dynamic yet highly patchy behavior found in soils. Foster (1985) and Foster and Dormaar (1991) have demonstrated, using electron microscopy (Fig. 3.3), amoebal pseudopodia extending into very small pore-necks and pores (only a few tenths of micrometers in diameter) in well-structured soil, attacking bacterial colonies which seemed to be inaccessible to the smallest nematodes and amoebae or other protozoa. A study using a combined approach to rhizosphere and soil cracks for locations of "hot spots" of labile organic matter was used by van Noordwijk et al. (1993) to good effect.

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