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Soil Biology & Ecology

Unit 2.3 | Part 2 – 87
Lecture 1: Soil Biology & Ecology

Lecture 1: Soil Biology & Ecology

Pre-Assessment Questions

1. What is soil?


2. What forms of life exist in soil ecosystems?


3. How would you define a “healthy” agricultural soil?


4. What is a food web?


5. Can you describe a decomposer food web that may exist in the soil?


6. What might be some negative effects of the long-term practice of monoculture cropping
   and the use of synthetic chemical fertilizers and pest control agents on the soil ecosystem?

A. What Is Soil? (should be a review in part; see also Unit 2.1, Soils and Soil Physical Properties)

1. Soil components

a) Mineral

i. Derived from parent material

b) Soil organic matter

c) Water and air

i. 1/2 soil volume = pore space

ii. Importance of gas diffusion: When diffusion is slow, as with water-saturated soil,
respiration byproducts (such as CO 2 ) accumulate and inhibit aerobic processes (such
as respiration itself )

iii. CO 2 is about 1% in dry soil, up to 10% in saturated soil

d) Biota: The smallest life forms are inseparable from soil organic matter

2. Soil structure vs. soil texture

a) Soil texture, a native characteristic

i. Soil texture: The relative percentage of sand, silt, and clay particles

ii. The bricks, boards, and mortar (the physical materials) that make up soil

iii. The particle sizes have surface area:volume effects. This influences properties such as
cation exchange capacity (CEC), pore space, water holding capacity, and aggregate
formation.

b) Soil structure, a manageable characteristic

i. Soil structure: The arrangement of soil particles. The “architecture” of soil—what
shapes you build with the “bricks, boards and mortar.”

ii. Determines movement of gases and water in soil

iii. Creates small habitat spaces

iv. Water stability: Aggregates that retain shape when wetted maintain a more stable
soil structure

v. Influences soil tilth/soil health

B. What Is a Healthy Soil? (see also Unit 1.1, Managing Soil Health)

1. Question: Is soil merely a solid medium that holds nutrients for plant growth or does soil
   serve other functions?


2. Soil health and soil quality are generally synonymous


3. Definition of soil health: “Capacity of a soil to function, within land use and ecosystem
   boundaries, to sustain biological productivity, maintain environmental quality, and
   promote plant, animal, and human health.”