ABSTRACT
The soil food web is a conceptual simplification of the soil biota, in which the microflora and
microfauna are aggregated into general trophic groups that describe major flows of energy
(organic C) and nutrients (primarily N and P) (Figure 44.1). Analyses of soil food web
structure can provide insight into how soil management practices influence microbial
immobilization, and turnover of energy and nutrients (Wardle 2002). Roots, plant residues,
agrochemicals, and animal manures are the primary inputs of energy and nutrients to cropped
soil. Bacteria and some fungi are the initial decomposers of such organic inputs, and soil
food webs can be compartmentalized into bacterial and fungal channels representing very
different storage efficiencies and turnover rates (Edwards 2000; Wardle 2002). Thus,
separation of bacterial and fungal biomass is a fundamental component of soil food web
analyses. Soil protozoa, nematodes, and microarthropods are the principal consumers of the
microbial biomass (Figure 44.1). Through their grazing, they regulate microbial community
structure and enhance mineralization of nutrients. The protozoa are primarily bacterivorous.
The soil nematode community includes bacterivores, fungivores, omnivores, predators
(which consume other microfauna), and root-grazers, in addition to the true plant parasites,
which are covered in Chapter 33 (Edwards 2000; Wardle 2002). The soil microarthropod
community is dominated by Collembola and Acarina (mites), and includes fungivore,
bacterivore, omnivore, and predator trophic groups (Edwards 2000; Wardle 2002). Methods
for extraction of microarthropods, nematodes, protozoa, and total microbial biomass are
described in Chapters 32, 33, 36, and 49, respectively.
