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The Living Soil

The world beneath our feet

Prepared by

Pat Patterson, OSU Lane Co. Extension

Master Gardener™

Soil: Animal, Vegetable or

Mineral? Traditionally classified soil by its

chemistry & texture

Ecological Soil Science goes a step further

Soil is now considered a partnership of many living and non-living factors

Can you name one living part in soil and one non-living?

Soil Is

A kind of placenta

that enables living things

to feed upon the earth.

Ethic of caring for the earth

Interacting with environment

in mutually beneficial ways

Sustainable Human Environment

Dynamic System

Seasonal and event-oriented changes

–Moisture, aeration, temperature (internal), nutrient availability, biological activity

Inputs of organic matter (OM) & rainfall

Losses to leaching, volatilization (off-gassing), and erosion

Long-term changes

–Mineral composition & soil texture

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The Traditional View of Soil

Soil is classified by texture

–Clay, silt and sand

Clay has the smallest particle size

Silt has midsize particle size

Sand has the largest particle size

White House

Limousine

Orange

Clay

Clay feels sticky. It has the greatest water and nutrient holding capacity of all soil textures. It is the bank account of the soil.

Unfortunately, clay is a miser, not wanting to let go of its wealth, so we add OM to loosen its purse strings and avoid compaction.

Wet clay forms a ribbon -or a pot

Silty clay texture. This soil has 2% sand, 54% silt and 44% clay. It forms a ribbon nearly 3” long!

Silt

Silt feels like flour, smooth & slick.

Silt may form a partial ribbon. It tends to crust, but holds a medium amount of water & nutrients.

Silt is rarely found alone.

Silty clay loam texture. This soil has 3% sand, 68% silt, and 29% clay.

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Sand

Sand feels gritty. It will form no ribbon.

Sand has little capacity to hold water or nutrients, almost no nutrient exchange capacity (CEC.)

Adding OM allows the well-draining sand to also maintain its bank account.

Feel the Soil

Break into mentor groups and work through the soil bags.

Please do not proceed to a new part until indicated.

There are few soils of only one texture. Some soils do seem that way, however.

Feeling Texture & Texture

Interaction

Each of your groups has bags of some soil texture, one wet and one dry. You need to feel them (in the bag) and determine which is which

Take out the 3 dry bags & feel.

Put each of the wet samples separately on a plate. Mix all 3 together. Make a snake?

Loam is not topsoil!

Texture refers to the amounts of sand, silt and clay in a soil.

Loam is a mixture of clay, silt and sand. Thus we can have sandy loam, clay loam or silty loam.

The clay percentage should not exceed 30%, 25% is preferable.

Topsoil is often from the bottom of a hole.

Sandy loam texture. This soil has 73% sand, 23% silt and 4% clay.

Altering soil textural properties

This is virtually impossible!

Texture operates on the geologic scale of millennia as a rule.

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What is soil structure?

Soil structure is how the individual soil bits are bound together. It is what the gardener can change.

If left alone, the structure will revert.

Good soil structure is called good tilth.

Soil life stimulated by OM glues soil particles into “peds” which then have good air and water pore space and thus, tilth.

Altering Soil Structure

Many clays, when combined with sand, form a low-grade concrete!

One acre of soil just 1 mm thick can weigh as much as five tons! This does complicate change.

OM is the closest thing to a cure-all you’ll ever find! It may be added or grown on site.

Let’s Talk Water Porosity & Permeability

Porosity refers to the amount of space (pore space) between particles in a soil.

Permeability is how well water can move through that pore space.

Good structure is associated with large pores.

Soil life is essential to the formation and maintenance of good soil structure (tilth).

Macropores:

Large pores.

Mostly occur between peds (crumbs).

Drain well (good permeability) but hold few nutrients (low Cation Exchange Capacity)

Micropores:

Relatively small pores.

Mostly occur within peds.

Drain poorly (low permeability) but hold the majority of a soil’s nutrients (high CEC).

Water and soil

Plants can use only cohesive water. Clay has lots of adhesive force.

Water is held by cohesion & adhesion in the pore spaces. Cohesion is water to water, adhesion is water to soil particle.

Excess water moves out by gravity

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Water Demo

Water Demo

How water moves

Water always fills like soil before moving into a new type soil, whether from clay to sand or from sand to clay when not in contact with free air.

This is why we can create a clay pot in the soil by adding a different material to the hole. The plant in the hole may die of thirst-or drown!

Unlike layers create a “perched” water

table whether in a pot or a yard.

Fine Soil over Coarse Soil Later

Breakthrough Cation Exchange Capacity

(CEC)

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Nutrient Availability

98% of the minerals used by plants are taken up from the soil solution with the aid of soil organisms.

pH has a dramatic effect on nutrient availability! See your pH scale.

Cation exchange can occur because of cations being knocked off by competing cations, but mainly by their being eaten and then released by soil life.

pH effects on nutrient

availability What about gypsum?

Not west of the Cascades to soften clays!

Gypsum only works in sodic (high in Na) soils. NaCl is table salt.

Na is Sodium and Cl is Chloride

Gypsum is Calcium sulfate

It may be added to add Ca & sulfur without changing pH.

What is the Significance of the

next slide?

Rule of nutrient availability

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Elements in Soil Suspension

Mobile elements are not attached to soil particles and are thus “cash in hand” for the plant’s use.

We need to capture any “extras” so they do not leach into the groundwater.

Mobile in soil: N, S, Cl, B, Na

Somewhat immobile: K, Ca, Mg

Immobile: P, Fe, Mn, Cu, Zn, Mo

Soil supplies at least 13 additional essential plant nutrients.

The Nitrogen Cycle

Root-nodulating rhizobia bacteria found in legumes (e.g. peas, vetch, clover) are capable of fixing atmospheric N2 in the soil. Others work with other microbes to do this (i.e. alder)

Nitrogen can also be lost to the atmosphere by changing to a gaseous form.

– Always incorporate N fertilizers!

– Remember, don’t add NH4 (ammonium) fertilizers with liming materials!

The Nitrogen Cycle

Here’s another example of N cycling in the soil.

Bacteria have a C:N of 5:1 (narrowest

known).

Protozoans have a C:N of 30:1.

Protozoans release excess N after consuming bacteria.

Adding N results in a decrease in OM due to blooming bacterial populations.

The Nitrogen Cycle in Review

The N cycle is driven largely by the activity of soil microbes.

The activity of those same soil microbes is controlled by environmental factors such as temperature and moisture.

Thus the N cycle is dependent upon the same environmental factors that control the activity of soil microbes and plants.

Problems with Nitrogen

All N problems are increased if it is rapid release.

Most organic N does not leach as readily as it is held by soil organisms, but over application of any N can result in run off, leaching and volatilization—all bad results.

Plants are luxury feeders on N, resulting in increased insect and disease problems.

Phosphorus

Phosphate rock is the primary source of all Phosphorus. Bone meal’s P comes to the animal from plants which probably got the P from some form of rock phosphate or bones.

Organic P is in manure and plant residues.

Double super P is from rock phosphate treated with sulfuric acid.

Triple super P from rock phosphate treated with phosphoric acid.

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Phosphorus

Rock phosphate is mined. Originally from fossil shells on the ocean floor. 3-7% soluble. Lasts about 5 years. Needs acid soil. Very efficient as timed to release by level of microbial activity.

Colloidal rock phosphate is from washed rock phosphate. Lower total phosphate. Also contains colloidal clay.

Potassium (K)

The original source was ashes, i.e. Pot-ash, formed by mixing ashes and hot water and filtering. The resulting slurry was then dried. It contained most of the minerals accumulated by the burned matter.

Most now is mined.

Most of our soils have adequate K naturally.

Fertilizer: What and When

Seed is independent

P 1st 15% of life

Mix some fertilizer into the bottom of planting hole for transplants.

Sidedress if not enough residual nutrients (building blocks) Best to scratch into soil.

What about a soil sample?

Soil tests are not always necessary.

Always sample at the same time of year.

Fall is a good time to sample, because slow-acting amendments (such as lime) that need to be added will have plenty of time to take effect over the winter.

Maintain good records!

Learning to Know Your Soil

Run pH test

Soil judging (feeling & jar test)

Observation of weeds and plant growth

How many of you did the jar test of your soil? Comments?

The Web of Life

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Soil Life

Moles to microbes, the soil is alive and teeming.

Plant roots influence other plants.

If any part of the soil web is disturbed, all parts

are disturbed. Till as little as possible

The Big OM

Organic Matter is the keystone of a live soil

–helps soil form peds

– improves aeration, H2O penetration, H2O & nutrient retention

–provides a bank of plant nutrients

–buffers chemical changes & detoxifies

– increases CEC

– is the energy source for soil biolife

The Web of Life

The live part of soil is

temperature driven. It functions

best at 50oF or above. If the

diverse population of microbes in

the soil were to fail in their

functions, life for higher plants

and animals would cease.

Most beneficial organisms

prefer aerated soil

BPGT AND BPGG

Bug poop grows trees and gardens!

Macro-organisms in the soil include the visible organisms from moles to mites.

Micro-organisms actually do most of the work and are dominated by bacteria and fungi, although mites and other teeny critters plus the root hairs also function.

Why Might Early Plants Turn

Yellow and Not Thrive?

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What do all these beings do?

Drive the fertilizer cycle

Aerate soil

Act as a catalyst

Add huge amounts of OM

Prevent disease

Act as a buffering agent

Form mycorrhizal associations

Fungal or Bacterial?

All living soils contain high populations of fungi and bacteria.

Whether the soil is primarily run by fungi or bacteria depends on the plant life present.

A forest is fungally dominated.

A field or garden is bacterially dominated.

Bacteria: the Horde

Bacteria do the lion’s share of work in the soil. They will be present at 1012 close to the roots of plants.

Bacteria are the heaviest users of N at 5:1

A well-balanced soil will have a preponderance of “good” bacteria, a killed soil will be recolonized by “bad” ones.

Bacteria Work Hard

Soil Bacteria Fungi-the conveyer belt

Fungi have miles of mycelial strands in a healthy soil.

Fungi enter into reciprocal agreements with the plants, as do the bacteria.

Fungi extend the usable nutrient and water area for a plant’s roots.

Plants often interact through the mycorrhizae.

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Fungal Mycelium Ectomycorrhizae

Ecto- & Endomycorrhizae Fungi Lassoing dinner

It’s a “mitey” world

200 Different Mites

Soil Arthropods

Soil fauna: Shred, burrow and mix

Graze to release nutrients,

esp. N

Disperse fungi and bacteria

Increase diversity of habitat

and so change it.

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Decomposer Mite Springtail

Psocid Symphylan

Millipede Sowbugs and Pill Bugs

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Dampwood Termite Predator & Prey

Centipede Harvester ants

Plant Partners?

About 60% of the plant’s sugars go to the roots and 1/2 or more of that is put into the soil medium to attract and feed bacteria and fungi.

The drawing in of the micro-organisms then builds the soil structure, releases nutrients and minimizes diseases. Soil toxins are also then broken down.

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How can we enhance beneficial

Organisms in the soil? Imitate nature.

Put back what you remove. Partially decomposed OM is a major food source.

Soil life needs all the nutrient elements.

Hydroponic or mineral base media will grow plants, but never be a balanced ecosystem.

Respect how little we know

How About Buying in the

Organisms?

There are many problems with substituting packaged organisms for the natural ones.

The main problem is how little we really

know about these organisms and how they interact.

As with worms, if you create the proper habitat, the rest will follow.

The soil and plants will select which ones they need/want.

Beware of miracle cures.

How Soil Dies

Erosion

Compaction is one key

(Anything that removes the oxygen from soil)

Imbalance of nutrients-excess salt

Overcropping, Overtilling, Monocropping, excess N all reduce OM and soil life diversity

Love that Tiller?

Research has clearly shown that soil ecology disturbance can cause great harm.

In line of damage from worst to least: rotary tillers, plows, shovel turning, fork turning, working a small area at a time, leaving a reservoir of active soil life to recolonize, permaculture.

As average vegetable gardeners, we just

do the best we can.

Research shows that the

nutritional quality of the plant, the

defense systems of the plant, the

immune systems of the plant

eaters and the susceptibility of

the plant to diseases and insects

may all hinge on the BALANCE in

the soil ecosystem.

…I seem to have been only like a boy playing on the sea shore, and diverting myself in now and then finding a smoother pebble or a prettier shell…, whilst the great ocean of truth lay all undiscovered before me.

--Isaac Newton

(Also the Master Gardener ™ motto)

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The End...or just the

beginning?

– we may be able to decide

Bibliography

Edaphos: Dynamics of a Natural Soil System by Paul D. Sachs

Teaming with Microbes: A Gardener’s Guide to the Soil Food Web by Jeff Lowenfels and Wayne Lewis

An Agricultural Testament by Sir Albert Howard

www.soilfoodweb.com