Data from Dindal (1990) and Lal (1991).

Data from Dindal (1990) and Lal (1991).

management, biological cycles are sometimes replaced by fossil fuel-based products, e.g., synthetic fertilizers. Intense management practices that include application of pesticides and frequent cultivation affect soil organisms, often altering community composition of soil fauna. Soil biological and physical properties (e.g., temperature, pH, and water-holding characteristics) and microhabitat are altered when native habitat is converted to agricultural production (Crossley et al., 1992). Changes in these soil properties may be reflected in the distribution and diversity of soil meso-fauna. Organisms adapted to high levels of physical disturbance become dominant within agricultural communities, thereby reducing richness and diversity of soil fauna (Paoletti et al., 1993).

Relationships between particular groups of organisms and management practices in agriculture can be studied under specific circumstances to define expected levels of diversity. The full diversity of soil communities has not been quantified for either agricultural or native ecosystems (Lee, 1991), and, in addition, the relationship between biodiversity and ecosystem function is not understood fully (Walker, 1992). Theoretically, this knowledge could be used to establish and maintain conditions that optimize beneficial effects of these organisms. Realistically, however, ideal conditions may be difficult to attain because of constraints imposed by agricultural production practices. We do not have sufficient knowledge to determine whether or not it is necessary, possible, or desirable to duplicate in agriculture the biodiversity that may be present in natural ecosystems.

This chapter examines the diversity and some of the functions of soil mesofauna in agricultural systems (Table 1). Most research on soil biota has focused on ecosystems such as forests and grasslands that are managed less intensively than agricultural or row crop systems. Ecologists have paid more attention to the role of micro- and mesofauna in ecosystem function, whereas agricultural scientists have focused on their role in nitrogen fixation and as pests and pathogens of crops. Our understanding of the role of soil organisms in agricultural systems is increasing, but more research is needed to elucidate their significance to crop production. Mesofauna occupy all trophic levels within the soil food web and affect primary production directly by root feeding and indirectly through their contribution to decomposition and nutrient mineralization (Crossley et al., 1992). Detailed reviews of the biology of soil fauna and their relationship to soil structure and ecological function are available (Wallwork, 1976; Swift et al., 1979; Freckman, 1982; Peterson and Luxton, 1982; Pimm, 1982; Seastedt, 1984; Dindal, 1990; Beare et al., 1992).

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