hammemermeister origin of soil & its properties.acorn

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The Origin of Soil and Its Properties

Andrew Hammermeister

Organic Agriculture Centre of Canada

Dalhousie University, Faculty of Agriculture

How can I live my life stepping on this

stuff and not wonder at all? William Bryant

“Probably more harm has been done to soil science by the almost universal attempts to look

upon the soil merely as a producer of crops rather than as a natural body worth in and for itself of all the study that can be devoted to it,

than most men realize.”

--- C. F. Marbut, 1920

A Rainbow of SoilA rainbow of soil is under our feet; Red as a barn and black as a peat.

It’s yellow as lemon and white as the snow;

Bluish gray. So many colors below. Hidden in darkness as thick as the

night; The only rainbow that can form

without light. Dig you a pit, or bore you a hole,

you’ll find enough colors to well rest your soul.

F.D. Hole, 1985

Soil is any naturally-occurring, unconsolidated (loose) material on the surface of the earth, which will support plant growth.

• Basic resource sustaining all terrestrial ecosystems.

• Soils are not a renewable resource in the scale of human lifetimes.

• Most soil profiles are thousand of years in the making

• In some regions of the world, human activities are destroying some soils faster than nature can rebuild/restore them

Soil

1. Provide a medium for plant growth

2. Regulate and partition water flow through the

environment

3. Serve as an environmental buffer

a. Can hold nutrients and release them as required by plants

b. Can also breakdown harmful compounds into substances that

are not toxic to plants and animals (limited ability).

Soil performs 3 main functions:

Soil is a product of:

Parent materialClimate

TopographyBiology

Time

Humans!

Glacial deposition

(Photo K.Murray)

Soil formed on Glacial "Till"

(Photo Dr.J.A.Robertson)

Influence of Parent (geological) Material

Glacial Action

(Photo J.C.Miller)

Fluvial materials – sorted by water

Aeolian materials – sorted by wind

Bedrock

(Photo A.R.Aandahl)

Fluvial sediment

(river deposits)

(Photo A.R.Aandahl)

Loess (wind deposits)

(Photo A.R.Aandahl

Influence of Parent (geological) Material

Influence of Parent (geological) Material

Tidal deposits

(Photo J.C.Miller)

Tidal landscape (Stewiacke River)

(Photo J.C.Miller)

Influence of Climate (precipitation)

“Essentially, all life depends upon the soil ... There can be no life without soil and no soil without life; they have evolved together.”

--- Charles E. Kellogg, USDA Yearbook of Agriculture, 1938

Soil Ecology

The soil biological community can weigh from 1100 to 14000 kg/ha; a similar weight as 2 to 28 yearling steers!

Over 1 billion microbes in 1 tsp of a fertile soil

Soil biology (soils.usda.gov/sqi/concepts/soil_biology/arthropods.html)

Earthworm burrows

Topographic (land shape) effects

Slope effects on soilserc.carleton.edu/details/images/12506.html

Ecosystems and biology

Ecosystem and biologyEastern Acid Forest Soil &

Landscape (Podzol)

(Photos - Agriculture Canada)

Prairie Black Soil

(Chernozem)

(Photos - Agriculture Canada)

Poorly drained soil

(Gleysol)

“The nation that destroys its soil, destroys itself.” ---

Franklin Delano Roosevelt “Plowed ground smells of earthworms and empires.” ---

Justin Isherwood

Soil colour is related to organic matter content, iron oxides, and drainage.

Munsell soil color charts

• www.organicagriculture.co/

Soil organic matterComponent Rate of

decayPrimary Function

Light fraction Weeks to months

• Serves as food for soil organisms

• Stores and provides plant nutrients

Physically protected

Decades • Enhances soil structure, porosity and water holding capacity

Chemically stable

Hundreds to thousands of years

• Holds nutrients (CationExchange Capacity)

• Stabilizes microaggregates

Organic matter builds structure

Sticky byproducts of decay Soil aggregation - organic "glue" binds

mineral particles together

Soil organisms shape the soil

Soil aggregation - burrowing

organisms (S.S.S.A.) Worm castes (S.S.S.A.)

The stability of soil structure

Soil MineralsClay Mineral (Koalinite)

Clay Mineral Clay minerals - shrinkage & swelling

Soil Particle Size Classes

Most Important Aspect of Soil Texture = SPECIFIC SURFACE.

(Specific Surface = Total area on particle surfaces / total mass of particles)

Separate Class Size (mm)# of particles per

gramSpecific Surface

Coarse Sand 1 mm 400 22.5 cm2/gram

Fine Sand 0.1 mm 400,000 225 cm2/gram

Medium Silt 0.01 mm 400,000,000 2250 cm2/gram

"Illite" Clay 0.0001-0.001 mm 7 x 1013 1,200,000 cm2/gram

"Montmorillonit

e" Clay0.0001-0.002 mm 4 x 1014

8,000,000 cm2/gram

= 1/5 Acre

= ave. house lot (per gram)

Influence of soil separates on other soil properties (T.J. Rice, 2002)

Property Sand Silt Clay

Water holding Low Med-high High

Aeration when moist Good Med Med-poor

Soil organic matter Low Med-High High - Med

Organic matter decomp Rapid Med Slow

Warmup in spring Rapid Med Slow

Shrink-swell Very low Low Mod-High

Compactability Low Med High

Water erosion risk Low High Low if aggreg.

Cation exchange cap. Low Med High

Resistance pH change Low Med High

Soil Structure (aggregation)

Factors influencing soil structureSoil aggregation -

wetting/drying & clay content Soil aggregation - Tillage

Andy’s favorite: SolodizedSolonetic

Soil

(Found in the prairies)

Cation Exchange Capacity (CEC)

Black – colloid of clays & humus with a negative charge, attract cations (+ ions).

Molecules including nutrients in the soil come in the form of ‘ions’, molecules with a ‘+’ or ‘-’ charge:Cations (+): NH4

+, Ca++, Mg2++, K+, Fe2

++, H+, Al+++

Anions (-): HPO4-, SO4

-, Cl-, HCO3-, HPO3

--, OH-

CEC: The capacity of the soil to hold cations(positively charged molecules)

Cation Exchange Capacity (CEC)

Black – colloid of clays & humus with a negative charge, attract cations (+ ions).Dark blue - inner zone around the colloid has more cations (+) than anions (-). Cationswithin this zone are said to be "adsorbed", or "exchangeable".Light blue - The outer soil solution (lighter blue) has a balance of anions & cations. The cations within this zone are "free" to move with & within soil water.

Soil pH• pH: measure of the concentration of H+ in soil

solution:pH = - log [H+]

• Therefore, low pH value, means high H+ concentration, and more acidic

• Higher concentration:– Acidic or sour

– Corrodes metals

– Bumps desirable cations off of soil exchange

– Nutrient imbalance

“... only rarely have we

stood back and celebrated our soils as something beautiful,

and perhaps even mysterious. For what other natural body,

worldwide in its distribution, has so

many interesting secrets to reveal to the patient observer? ” --- Les Molloy, Soils

in the New Zealand Landscape: the Living Mantle, 1988

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Visit OACC.INFO for

• Production, research and market information

• Upcoming workshops & symposiums

• Virtual farm tours

• Organic award winners

• Organic policy toolbox

• Monthly e-zine