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
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