Teaching Organic Farming and Gardening

Soil Biology and Ecology

Unit 2.3 | 9
Students’ Lecture Outline

Detailed Lecture Outline: Soil Biology and Ecology

for students

a. 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?

b. what is soil?

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 saturated soil, respiration
byproducts accumulate and inhibit aerobic processes

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

d) Biota: 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 and silt and clay particles

ii. Surface area/volume effects (e.g., influences CEC, pore space, water holding capacity,
aggregate formation)

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

b) Soil structure, a manageable characteristic

i. Soil structure: The arrangement of soil particles. The “architecture” of soil.

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

c. what is a Healthy soil?

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 generally synonymous