Environmental Engineering Reference
In-Depth Information
O
2
Microbial respiration
CO
2
Fig. 3.10. Oxygen, carbon dioxide and toxic gases must be exchanged between the
air in the soil and the above-ground atmosphere. (Drawing by R. Castro.)
The Soil Organisms
A fertile soil may contain many organisms, such as microscopic bacteria,
fungi, actinomycetes, algae, protozoa and nematodes, as well as rela-
tively large earthworms. The soil organisms perform various activities,
mostly beneficial but sometimes detrimental to turf-grass growth and
development. They decompose organic matter, fix nitrogen, transform
essential elements from one form to another, help in soil aggregation, and
sometimes improve soil aeration and drainage. Bacteria are the smallest
and most abundant in the soil. Together with fungi and actinomycetes,
they contribute substantially to organic-matter decomposition and are
mostly beneficial. Particular fungi, nematodes or insects are sometimes
pathogenic and unwanted. Some of them infect or feed on roots, shoots or
leaves, causing harm to turf-grass plants.