Chapter 6

Biological Properties of Soil

(book excerpts)

The soil environment is teeming with biological life and is one of the most abundant and diverse ecosystems on earth. These organisms interact with one another forming a web of biological activity. Soil organisms include moles, gophers, earthworms, millipedes, springtails, termites, nematodes, fungi, bacteria, and other organisms. These organisms form a food web playing an important role in maintaining fertility, structure, drainage, and aeration of soil. The smaller organisms, such as bacteria, fungi, algae and protozoa, decompose the organic matter, releasing stored nutrients and converting them into forms usable by plants and other organisms. Many of the biota can break down pesticides and pollutants. Special types of bacteria, called nitrogen fixers, infect the roots of clover and other legumes, forming visible nodules and convert nitrogen from the air into a form that the plants can use. Some fungal hyphae (mycorrhizal fungi) attach to plant roots and act like an extended root system, providing nutrients and water to the plant. The larger organisms in the soil shred dead leaves and stems. This stimulates cycling of nutrients, among the most prominent being the carbon, nitrogen, and sulfur. The food web is quick to respond when food sources are available and moisture and temperature conditions are good. And while it may seem that plants (flora) are passive observers of this activity that surrounds them, plant roots in fact release into the soil various substances that stimulate soil microbes. Farming practices, such as amending soils with organic matter, returning crop residues to the soil, and rotating plantings are practices that tend to increase the number and diversity of beneficial organisms.

Topics Within This Chapter:

  • Soil Food Web
  • Trophic Levels
  • Soil Microorganisms
  • Bacteria
  • Soil Benefits from Bacteria
  • Nitrogen-Fixing Bacteria
  • Fungi
  • Mycorrhizae
  • Actinomycetes
  • Protozoa
  • Algae
  • Conditions Affecting Soil Microorganisms
  • Organic Matter Content
  • Soil Temperature and Moisture
  • Soil pH
  • Management Practices
  • Soil Fauna
  • Earthworms
  • Benefits of Earthworms
  • Conditions Affecting Earthworm Activity
  • Nematodes
  • Arthropods
  • Large Soil Animals
  • Soil Respiration
  • Conditions Affecting Soil Respiration
  • Improving Soil Respiration