Soil Science

Western Sustainable Agriculture Research & Education
(SARE) Farm Internship Curriculum and Handbook


Tom and Maud Powell and Michael Moss, Sustainable Farmers, Jackson County, OR.
Technical advisor: Tim Franklin, Jacksonville, OR.
Curriculum advisor: Peter O’Connell, Jacksonville, OR.
Web advisor: National Center for Appropriate Technology, Butte, MT.
Published 2007
Updated 2010


Soil Science

The understanding of basic soil science is important for many different reasons on the farm. It offers long-term farm security and viability through proper management of any farms most valuable resource, soil. It also plays a larger role in the health of a watershed or regional eco-system by combating erosion or nutrient pollution in our streams and rivers. Individuals who study and pay close attention to there soils structure and content will see far better results in cultivation and yield and will better be able to address negative issues encountered while growing on, and managing farmland.


Learning Objectives
The learner will understand the following basics through in-field study:

  • Understand how soils form
  • Understand soil characteristics and how they effect crop growth
  • Learn why and how to take soil samples, what to test for and what to do with the results
  • Learn how to manage for healthy soil ecosystems, increased fertility, and sustainable crop production


How Soils Form

  • ClORPT Concept: Climate, Organisms, Relief, Parent Material, Time
  • Soil Toposequence: Moving from the ridge top to valley bottom, soil characteristics vary greatly.


Soil Characteristics

  • Soil Components: Minerals (45%), Air and Water (25% each), and Organic Matter (usually 2 – 5%)
  • Soil Texture: Sand, silt, & clay, the soil triangle, and associated properties:
    • Sandy soils – low water and nutrient holding capacity, droughty
    • Clay soils – high water and nutrient holding capacity, but low permeability, poor tilth
  • Soil Nutrient Profile: major and minor nutrients, trace elements
  • Cation Exchange Capacity: capacity of negatively charged humus and clay particles (colloids) to hold cations (Calcium, Magnesium, Potassium – also sodium & ammonia) – importance
    • Albrecht system
  • PH (and its relation to CEC – if your bases are balanced, pH will take care of itself)


Soil Biotic Community

  • We know that an acre of soil can support or produce” 2000 lbs of beef (cow / calf pair), 5 sheep, and lots of chickens, for example, but we rarely consider the extent of the soil fauna living underground: 1 acre of topsoil contains approximately 900 pounds of earthworms, 2,400 pounds of fungi, 1,500 pounds of bacteria, 133 pounds of
  • Protozoa, 890 pounds of arthropods and algae, and small mammals
  • Earthworms – air & water penetration, high-nutrient castings, secretion of plant growth stimulant, natural soil tiller
  • Arthropods – sow bugs, centipedes, slugs, snails, springtails: primary decomposers
  • Bacteria – make plant growth hormones, make nutrients and minerals available to plants, fix atmospheric nitrogen, fight root diseases, detoxify soils
  • Fungi – break down OM and release nutrients available to plants, produce plant hormones and antibiotics; mycorrhizal associations
  • Actinomycetes – threadlike bacteria that look like fungi: decompose OM, produce root disease-fighting antibiotics, produce sweet, earthy” smell
  • Algae – upper ½ inch, fix nitrogen and enhance soil structure by producing biologic glues
  • Protozoa – free-living organisms that swim in soil water, eating bacteria and speeding up the nutrient cycle
  • Nematodes – eat decaying plant litter, bacteria, algae, protozoa, and other nematodes -; only a few species harmful to plants.


Key to managing for a healthy soil community: Build Soil Organic Matter


Soil Organic Matter

  • Carbon Cycle: role of C (CO2) and how to manage it.
  • Humus, Humic Acid (organic compounds containing displaceable hydrogen), Humate (the salt of a humic acid, where hydrogen has been displaced by cations such as potassium, calcium, and magnesium)
  • Managing SOM: cover crops, field rotations, compost and compost tea applications, etc.
  • Tillage systems
  • Nitrogen Cycle: role of N, and how to manage it.


Soil Testing and Assessment

  • What to test, how to test, when to test: texture, major nutrients, minors and trace, pH, CEC, soil biotic community,
    • Conventional
    • Emphasis on Mineral Analysis: Albrecht System
    • Soil Biotic Communities
    • USDA Soil Quality Test



  • How is soil formed?
  • What are some important soil characteristics?
  • Explain cation exchange capacity and how to improve it.
  • Describe a cropping system that improves soil organic matter and enhances the soil biotic community.


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