Soilbiologyziegler201110 121108101543-phpapp02

©2009 Rodale Institute

Soil Biology: Why is it important? and

Why does it matter to me?

Becky Pfeufer, Research Technician, and Christine Ziegler, Researcher and Science Editor


"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?


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


The Soil Texture Triangle

Drains water very quicklyNot many nutrients to help plants grow

Very dense – nutrient rich, causes water to puddle and not drainNot much permeability for air or microbes

Holds water and nutrients wellCan get mucky and lose pore space

Erodes easily


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


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).


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)


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


The Nitrogen Cycle


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


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


Plants we rely on, that rely on the cycles…

wheat

soybeans

corn

What about these guys?


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


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)

Documents

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