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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