Each field, forest, or pasture has a unique soil food web with a particular proportion of bacteria, fungi, and other groups, and a particular level of complexity within each group of organisms. These differences are the result of soil, vegetation, and climate factors, as well as land management practices. The structure of a food web is the composition and relative numbers of organisms in each group within the soil system. Grasslands and agricultural soils usually have bacterial-dominated food webs that is, most biomass is in the form of bacteria. Forests tend to have fungal-dominated food webs.
Organisms reflect their food source .
For example, protozoa are abundant where bacteria are plentiful. Where bacteria dominate over fungi, nematodes that eat bacteria are more numerous than nematodes that eat fungi. Management practices change food webs . For example, in reduced tillage agricultural systems, the ratio of fungi to bacteria increases over time, and earthworms and arthropods become more plentiful. Direct counts counting individual organisms with the naked eye or with a microscope.