The Origin of Soil and Its Properties

Transcription

1 The Origin of Soil and Its Properties Andrew Hammermeister Organic Agriculture Centre of Canada Dalhousie University, Faculty of Agriculture

2 How can I live my life stepping on this stuff and not wonder at all? William Bryant

3 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

4 A Rainbow of Soil A 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

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

6 Soil is a product of: Parent material Climate Topography Biology Time Humans!

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9 Influence of Parent (geological) Material Glacial deposition (Photo K.Murray) Soil formed on Glacial "Till" (Photo Dr.J.A.Robertson) Glacial Action (Photo J.C.Miller)

10 Fluvial materials sorted by water

11 Aeolian materials sorted by wind

12 Influence of Parent (geological) Material Bedrock (Photo A.R.Aandahl) Fluvial sediment (river deposits) (Photo A.R.Aandahl) Loess (wind deposits) (Photo A.R.Aandahl

13 Influence of Parent (geological) Material Tidal deposits (Photo J.C.Miller) Tidal landscape (Stewiacke River) (Photo J.C.Miller)

14 Influence of Climate (precipitation)

15 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

16 Soil Ecology The soil biological community can weigh from 1100 to kg/ha; a similar weight as 2 to 28 yearling steers! Over 1 billion microbes in 1 tsp of a fertile soil

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

18 Earthworm burrows

19 Topographic (land shape) effects

20 Slope effects on soil serc.carleton.edu/details/images/12506.html

21 Ecosystems and biology

22 Eastern Acid Forest Soil & Landscape (Podzol) (Photos - Agriculture Canada) Ecosystem and biology Prairie Black Soil (Chernozem) (Photos - Agriculture Canada) Poorly drained soil (Gleysol)

23 The nation that destroys its soil, destroys itself. --- Franklin Delano Roosevelt Plowed ground smells of earthworms and empires. --- Justin Isherwood

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

31 Munsell soil color charts

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33 Soil organic matter Component Rate of decay Primary Function Light fraction Weeks to months Physically protected Chemically stable Decades Hundreds to thousands of years Serves as food for soil organisms Stores and provides plant nutrients Enhances soil structure, porosity and water holding capacity Holds nutrients (Cation Exchange Capacity) Stabilizes microaggregates

34 Organic matter builds structure Sticky byproducts of decay Soil aggregation - organic "glue" binds mineral particles together

35 Soil organisms shape the soil Soil aggregation - burrowing organisms (S.S.S.A.) Worm castes (S.S.S.A.)

36 The stability of soil structure

37 Soil Minerals Clay Mineral (Koalinite) Clay Mineral Clay minerals - shrinkage & swelling

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39 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 gram Specific Surface Coarse Sand 1 mm cm 2 /gram Fine Sand 0.1 mm 400, cm 2 /gram Medium Silt 0.01 mm 400,000, cm 2 /gram "Illite" Clay mm 7 x ,200,000 cm 2 /gram "Montmorillonit e" Clay mm 4 x ,000,000 cm 2 /gram = 1 /5 Acre = ave. house lot (per gram)

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41 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

42 Soil Structure (aggregation)

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44 Factors influencing soil structure Soil aggregation - wetting/drying & clay content Soil aggregation - Tillage

45 Andy s favorite: Solodized Solonetic Soil (Found in the prairies)

46 Cation Exchange Capacity (CEC) CEC: The capacity of the soil to hold cations (positively charged molecules) 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 (+): NH 4+, Ca ++, Mg 2 ++, K +, Fe 2 ++, H +, Al +++ Anions (-): HPO 4-, SO 4-, Cl -, HCO 3-, HPO 3 --, OH -

47 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 (-). Cations within 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.

48 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

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52 ... 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