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Conceptual Aspects: Habitat Micro-organisms Bacteria, Fungi – both good and bad Viruses Macro-organisms Worms, Arthropods, Detrivores and Predators Plants.

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Presentation on theme: "Conceptual Aspects: Habitat Micro-organisms Bacteria, Fungi – both good and bad Viruses Macro-organisms Worms, Arthropods, Detrivores and Predators Plants."— Presentation transcript:

1 Conceptual Aspects: Habitat Micro-organisms Bacteria, Fungi – both good and bad Viruses Macro-organisms Worms, Arthropods, Detrivores and Predators Plants Small Mammals Birds

2 Conceptual Aspects: Provider to plant life Rooting substrate Water holding and release Nutrient supply and reserve Heat sink and release Soil gases Symbionts Bacterial and fungal Insects

3 Physical Aspects: Minerals (from rocks) Sand Silt Clay and Colloids Organic Matter Plants and Roots Detritus (decaying organic matter) Animal waste (including microbes) Pore Space Air Water

4 Carbon Sink Water filter Indicator of ecosystem health

5 We need to keep all these things in mind in our management practices How does this change how we treat the soil?

6 Habitat What happens when we disturb this habitat? At micro and macro level? What happens when we make additions to, or removals from, this habitat? Carbon:Nitrogen ratio? How do soil organisms and plants respond? Nutrient loss or gain? Providing for plant life What are the short-term and long-term results? Are we providing for the soil as well as the plants? What is the difference?

7 As a habitat we need to treat soil like a living organism, which requires: Food Water Air Shelter Cover crops Mulch Living Dead Snow Tender loving care…


9 Click me

10 Mineral Components Sand Silt Clay

11 Sand Largest soil mineral particles (.02 – 2 mm) Formed greatly from physical processes Spherical/erratic in shape Sand = little rocks Larger pore spaces Good drainage Does not hold a charge Difficult to compact

12 Silt Size between sand and clay (.002 -.02 mm) Usually physically formed out of sand Hold and releases water well Flat or round in shape Holds very little charge Feels soapy Carried in moving water

13 Clay Smallest soil mineral particle (<.002 mm) Holds water very well Holds strong negative charge for mineral adsorption Susceptible to compaction Platy-/flat-shaped particles Various lattice structures

14 Clay Understanding structure of clay is important for: Compaction Water holding Cation adsorption Soil cultivation Clays are categorized by their layer structure Relationship of Si-tetrahedral and Al-octahedral sheets 2:1; 1:1; 4:1; 5:2

15 2:1 Clay  Shrink and swell 1:1 Clay No change

16 Shrink and Swell of Clay Interlayer space expands with increasing water content in soil Space contracts as water is removed Clay can crack when it shrinks

17 Mineral ratios determine soil texture

18 Attributes of Different Soil Textures PropertySandSiltClay Water HoldingPoorMedium to highHigh Nutrient Holding PoorMedium to HighHigh AerationGoodMediumPoor

19 Why is Texture Important? Water Infiltration Water Storage Fertility Aeration Trafficability Soil texture knowledge is the key to developing an overall soil maintenance and improvement plan

20 Click me

21 Soil organic materials are made up of: Dead and decaying plants or animals Animal manures Microbial by products Materials decomposed to different stages exist simultaneously Manure and compost are common OM additions to soil

22 Organic matter’s role in soil: Holds soil particles together; stabilizes soil Reduces erosion risk Increases soil’s water holding and transmitting ability Stores and supplies nutrients to plants and microbes Minimizes soil compaction Carbon sink Ameliorates the effect of environmental pollutants Immobilizes them; reduces leaching Usually 5-8% of soil; 30% or more in org. soils

23 Soil Organic Matter Characteristics High Cation Exchange Capacity (CEC) High in Carbon (C) C:N ratio- indicator of Nitrogen (N) availability to plants Nutrient concentration and ratios variable Particle density: 900-1300 kg/m 3 Bulk density: 180-200 kg/m 3 (peat) or 130 kg/m 3 (forest) Holds water better than mineral soils

24 Two Types of Organic Matter Non-humic Primary components from fresh animal and plant waste Easily decomposed by microbes (when present) Comprise 20-30% of Soil OM Decompose to: Carbohydrates (several types) Amino Acids Lipids Lignin Very resistant to decay Other compounds

25 Two Types of Organic Matter Humic Biochemical decomposition of non-humic materials Resistant to further decomposition Accumulate in soil Dark in colour – give soil dark characteristic 60-80% of soil OM 3 types: Humins: larger particles; low number of carboxyl groups; inactive. Humic acids: smaller than humins (approximately colloid- sized); more carboxyl groups than humins. Fulvic acids: smallest humic substances; large number of carboxyl groups; most active among humic substances.


27 Carboxyl and Hydroxyl Groups

28 Living MaterialDies onto soilHumicNon-Humic This process is driven by biological decomposition – mostly from soil bacteria and fungi

29 What role does OM play in texture?

30 Click me, damnit

31 Soil Colloids Microscopic soil particles (w/electron microscope) Made up mostly of clays and organic materials Very large surface area Carry many exchange sites/charges Mostly negative except in acid soils Hold soil cations (positively charged) Holds water to cations Major contributor to soil nutrient holding capacity

32 There might be a diagram here someday…

33 Click Me

34 Where does the mineral component come from? From the weathering of rocks. Rocks are made up of minerals

35 Primary Minerals  Sand and Silt Primary Minerals Formed at high T and P (at depth); anaerobic conditions Formed at high T and P Physically and chemically formed Secondary Minerals  Clay Secondary Minerals Come from primary minerals Formed at low T and P (at surface) with Oxygen present Mostly chemically formed

36 Weathering of Rocks Physical Chemical 1 Chemical 2 (note: base-forming cations) Chemical 3 Biological

37 Parent Material Climate Biota Topography Time

38 Tiny little Video here

39 You know what to do

40 Parent Material Residual In situ; long periods of weathering Cumulose Due to plant life and anaerobic conditions High water table Peat and muck soils Transported Gravity - ColluviumColluvium Wind - EolianEolian Water - AlluviumAlluvium Ice - Glacial

41 Climate Temperature and rainfall are major factors Affect intensity of weathering Increased T and precipitation accelerate weathering Biota Plants influence organic matter Arthropods and worms mix soil; add to OM Small mammals also mix soil

42 Topography Slope influences soil development Water infiltration rate Surface runoff Vegetation Aspect North and South slopes develop differently Elevation Climate changes with altitude

43 Time Often noted as most important soil formation factor Our soils in Lower Mainland are relatively young Since last ice age 10,000 years ago

44 Great Soil Formation Videos Here

45 Additions Losses Transformations Translocations

46 Video here


48 Organic (O) Horizon High in organic residue from plant drop A Horizon Mineral component mixed with OM Most fertile part of soil; location of much root activity Exhibits Eluviation in soil solution B Horizon Subsoil Exhibits Illuviation of clay, OM, oxides C Horizon Little influence by soil-forming processes

49 Water (W) Horizon Due to high water table Found in Gleysols Bedrock Underlying consolidated material (solid rock) LFH Horizons Usually found in forest soils with high surface residue

50 Click Me

51 Soil Structure: How the soil fits together Primary particles are arranged into secondary particles called aggregates (or peds)

52 Why is Structure Important? Pore space Air and water movement Rooting space Nutrient storage and release Contributes to soil resilience Cultivation Erosion resistance

53 How does aggregate formation occur? Flocculation + Cementation = Aggregation Flocculation: Primary pulled close together (into flocs) by attractive forces (electrostatic forces, H bonding) Cementation Primary particles held together by cementing agents Carbonates; clays; OM; Oxides


55 Soil Aggregates are classified by their shape

56 Spheroidal Typical in A Horizon Rounded; loose Granular (porous) or Crumb (very porous) Greatly affected by soil management/mismanagement Improved with OM additions

57 Soil structure is particularly important in providing adequate pore space for: Root growth Water movement Gas exchange Microbial activity Macrobial activity

58 Related to texture Very important when considering soil cultivation Dependant on Texture/clay content Clay type Soil water content


60 Cultivating soil when too dry Breaks aggregates into small pieces De-aggregates Can result in dust Very damaging to soil structure The drier the soil – the more it acts like powder

61 Cultivating soil when too wet Where to start?! Compaction Risk and depth of compaction increases in wet soil

62 Cultivating soil when too wet The wetter the soil - the more it acts like water


64 Particle density: Density of individual particles Density = Mass/Volume (M/V) ρ particle = M solids /V solids Some particle densities: Water: 1000 kg/m 3 Organic Matter: 900-1300 kg/m 3 Minerals: 2650 kg/m 3

65 Bulk density: Density of particles and pore space ρ bulk = M solids /V soil Some bulk densities: Mineral or organic soil: 1300 kg/m 3 Clay Soil: 1100 - 1300 kg/m 3 Sandy Soil: 1500 – 1700 kg/m 3

66 Measuring Particle Density: Weight out a dry sample of particle type (e.g., sand) This is your M ass value Fill graduated cylinder with water Record exact water level Drop particles into cylinder of water Record new water level New Reading – Old Reading = Volume Mass/Volume = Particle Density

67 Measuring Bulk Density: Collect known sample (Volume) size of soil Use soil core; Volume = πr 2 h Weigh sample then dry in oven Removes water from sample Weigh dried sample This is your soil Mass Mass/Volume = Bulk Density

68 Why is density important? Particle density: not as important as bulk density Bulk density is indicator of pore space Changes in bulk density = changes in pore space


70 Soil Water

71 For future lecture…

72 Agricultural Capability Classes Class 1 Class 1 land is capable of producing the very widest range of crops. Soil and climate conditions are optimum, resulting in easy management. Class 2 Class 2 land is capable of producing a wide range of crops. Minor restrictions of soil or climate may reduce capability but pose no major difficulties in management. Class 3 Class 3 land is capable of producing a fairly wide range of crops under good management practices. Soil and/or climate limitations are somewhat restrictive. Class 4 Class 4 land is capable of a restricted range of crops. Soil and climate conditions require special management considerations. Class 5 Class 5 land is capable of production of cultivated perennial forage crops and specially adapted crops. Soil and/or climate conditions severely limit capability. Class 6 Class 6 land is important in its natural state as grazing land. These lands cannot be cultivated due to soil and/or climate limitations. Class 7 Class 7 land has no capability for soil bound agriculture.

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