Teaching Organic Farming and Gardening

Soil Biology and Ecology

Unit 2.3 | 5
Instructor’s Lecture Outline

Lecture Outline: Soil Biology and Ecology

for the instructor

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

1. Soil components

a) Mineral fraction

b) Organic matter fraction

c) Water and air

d) Biota

2. Soil structure vs. soil texture (definitions, examples)

a) Soil texture, a native characteristic

b) Soil structure, a manageable characteristic influenced by soil biology and soil health

C. What Is a Healthy/Quality Soil?

1. Is soil merely a solid medium that holds nutrients for plant growth?


2. Soil health and soil quality generally synonymous


3. Definition: “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.” (For a more detailed definition, see Unit 1.1, Managing
   
   Soil Fertility.)


4. Assessment of soil quality/soil health


5. Protection of soil quality as a national priority

D. Nutrient Cycling and Decomposition

1. Mineralize/immobilize


2. Organic matter: Includes all organic substances in or on the soil

a) Living organisms: Includes plant roots and all soil biota (<5%)

b) Fresh and decomposing organic residues (40–60%)

c) Resistant (recalcitrant) organic matter fraction: Humus, stable organic matter

resistant to further decomposition (33–50%)