Soil Biology


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Covers the basics of soil biology, what it is “in there” and why it matters. Includes details on the carbon and nitrogen cycles and the soil food web. (Excellent for high school students, good for all audiences)

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Soil Biology

  1. 1. ©2009 Rodale Institute Soil Biology: Why is it important? and Why does it matter to me?
  2. 2. ©2009 Rodale Institute "The soil is not, as many suppose, a dead, inert substance. It is very much alive and dynamic. It teems with bacteria, actinomycetes, fungi, molds, yeasts, protozoa, algae and other minute organisms." ~J.I. Rodale Pay Dirt: Farming and Gardening with Composts (1945) What is soil?
  3. 3. ©2009 Rodale Institute Four basic facts about soil • Soil is composed of three sizes of mineral particles: Sand (large), silt (medium), and clay (small) • The other important type of soil particle is called organic matter • Soil is also comprised of a lot of empty spaces, called pores, which are important for holding air or water • Soil is full of living organisms, both large and microscopic
  4. 4. ©2009 Rodale Institute The Soil Texture Triangle Drains water very quickly Not many nutrients to help plants grow Very dense – nutrient rich, causes water to puddle and not drain Not much permeability for air or microbes Holds water and nutrients well Can get mucky and lose pore space Erodes easily
  5. 5. ©2009 Rodale Institute What does soil do? … besides giving us something to walk on and build on… Soil supports plants – holds them upright, provides moisture and nutrients to the roots
  6. 6. ©2009 Rodale Institute How do plants use what the soil provides? • Uptake soil water to power photosynthesis • Use soil nutrients to build cell structures and produce complex sugars, proteins and other molecules • Soil nutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S).
  7. 7. ©2009 Rodale Institute What do plants give back to the soil? Dead plant material! What good things do dead plants add to the soil? Nutrients (plant food, NPK) Carbon (microbe food, organic matter)
  8. 8. ©2009 Rodale Institute Why carbon and nitrogen are vital for plants Soil Carbon – provides food for microbes that cycle nutrients through the soil, holds moisture in the soil Nitrogen – one of the primary nutrients (along with phosphorus and potassium) required by plants to make proteins and other important structural molecules lignin a simple protein
  9. 9. ©2009 Rodale Institute The Nitrogen Cycle
  10. 10. ©2009 Rodale Institute The Carbon Cycle How carbon gets into the soil: How carbon leaves the soil: photosynthesis plant death plant consumption by animals and microbes microbial respiration: eating larger carbon- containing molecules, like sugars, and breaking them into smaller components, such as CO2 (carbon dioxide) and CH4 (methane) wind and water erosion
  11. 11. ©2009 Rodale Institute The Soil Food Web – powering the cycles First trophic level: Photosynthesizers Second trophic level: Decomposers, Mutualists, Pathogens, Parasites, Root- feeders Third trophic level: Shredders, Predators, Grazers Fourth and higher trophic levels: Hither level predators
  12. 12. ©2009 Rodale Institute Plants we rely on, that rely on the cycles… wheat soybeans corn What about these guys?
  13. 13. ©2009 Rodale Institute Ways to increase soil carbon, in your garden or on the farm • Keep your soil covered throughout the year, as much as possible, with crops, cover crops, and mulches - retains moisture, prevents erosion, adds organic matter, reduces weeding • Grow a diversity of crops, and rotate them into different locations in your garden each year - prevents excessive loss of individual soil nutrients and build-up of plant-specific diseases and pests • Don’t dig too much! Some digging is good, but too much breaks down organic matter and soil structure • If you grow crops on a slope, plant your rows horizontally across the slope to help stop water run-off and erosion • Add compost to increase organic matter, microbial activity, and nutrient availability
  14. 14. ©2009 Rodale Institute How do you know how much you have carbon in your soil? Look for: Color (darker brown = more carbon) What’s growing (more plentiful, diverse plants = more carbon) Feel for: Texture (mid- to small-size particles = more carbon) Moisture (more wet = more carbon) Weight (fluffier, lighter = more carbon)