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Introduction to Soils and Soil Resources

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Introduction to Soils and Soil Resources 2001 Lecture 7 Soil Air and Soil Organic Matter Oxidation Oxidation: A reaction in which atoms or molecules gain oxygen, or ... – PowerPoint PPT presentation

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Title: Introduction to Soils and Soil Resources


1
Introduction to Soils and Soil Resources
  • 2001
  • Lecture 7
  • Soil Air and Soil Organic Matter

2
Table 9.1. Relative concentrations of
atmospheric gases on Earth, Mars and Venus
Credit after Margulis and Hinkle, 1991
3
Oxidation
  • Oxidation A reaction in which atoms or
    molecules gain oxygen, or lose hydrogen or
    electrons Fe 2 Fe 3 e-

4
Reduction
  • Reduction A reaction in which atoms or
    molecules lose oxygen, or gain hydrogen or
    electrons N2 H2 NH3

5
Oxidation State
  • In a free state, oxidation state is zero. For
    example elemental sulfur (S0)
  • Monoatomic ions have oxidation state equal to the
    ionic charge. For example, Ca2 has oxidation of
    2

6
Oxidation State
  • In a combined state, hydrogen has oxidation
    state of 1 oxygen has oxidation state of -2
  • For example H2O
  • For example H2SO4 (S 6)

7
Examples
  • Oxidation and reduction reactions occur in
    nature
  • Responsible for energy transformations
  • Examples are given in Table 9.2

8
The atmosphere
  • The atmosphere is a large, layer system
  • Troposphere (80 air mass)
  • Stratosphere (Ozone region)
  • Mesosphere
  • Thermosphere

9
Fig. 9.1. The profile of the atmosphere
10
Fig. 9.2. Radiation Budget
11
Greenhouse gases
  • Water vapor (H2O)
  • Carbon dioxide (CO2) parts per million
  • Methane (CH4) parts per million
  • Ozone (O3) parts per million
  • Nitrous oxide (N2O) parts per billion
  • Halocarbons (CFCs) parts per trillion
  • Refer to Table 9.3 (Section 9.3)

12
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13
Fig. 9.3. Active sites, mineral particles and
water films
14
Atmospheric Air vs Soil Air ( volume)
15
Soil Atmosphere
  • The soil atmosphere is different from the
    atmosphere (Table 9.4 in Section 9.4)
  • Soil is a biologically, porous medium
  • Activities of plant roots and soil biota change
    soil atmosphere
  • Metabolic pathways change if oxygen is limiting
    (Fig. 9.3 in Section 9.4)

16
Aerobic Respiration
  • C6H12O6 O2 ? 6 CO2 6 H2O energy

17
Anaerobic Respiration
  • NO3- ? NO2- ? NO ? N2O ? N2
  • 5 3 2 1
    0
  • Nitrate is terminal electron acceptor when oxygen
    is limiting

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22
Gas Conc. ( vol.) Corn field
Elliott and McCalla 1972. Soil Sci. Soc. Am.
Proc. 3668
23
Gas Conc. ( vol.) Feedlot
Elliott and McCalla 1972. Soil Sci. Soc. Am.
Proc. 3668
24
Gas Dynamics
  • Normally O2 decreases and CO2 increases with
    depth
  • Normally, CO2 lt0.5 in soil atmosphere while O2
    gt10

25
Soil Organic Matter
26
Soil Major Components
27
Soil Organic Matter
  • All organic substances, by definition, contain
    carbon
  • The element carbon is the foundation of all life

28
Soil Organic Matter
  • SOM consists of living or dead plant material,
    living organisms, microbial and faunal products,
    and stabilized complex organic matter called
    humus
  • Organic matter has a profound impact on soil
    physical, chemical and biological properties

29
Credit U of A Extension Pedosphere.com
30
Physical Properties
  • The physical properties of soil horizons vary
    tremendously within a pedon
  • Example is given in Table 11.2 in Section 11.2

31
Soil C
  • Present as organic matter
  • Present as inorganic carbon in form of carbonates
    in some soils
  • Example is given in Table 11.3 in Section 11.2

32
OM Impacts
  • Formation of organo-mineral complexes
  • Aggregation
  • Cation and anion exchange capacity
  • Movement of pollutants
  • Decomposition and nutrient cycling (next lecture)

33
Fig. 1.9. Pores and particles in soil (Pawluk)
Credit Pedosphere.com
34
Porosity/Structure
35
Fig. 6.12. Structure of a model humic acid
(Schulten Schnitzer, 1997)
36
Fig. 6.10. Impact of soil pH on net charge
of organic acids
37
Charge Characteristics
cmolc/kg
38
Application
  • Given a soil with 5 OM and 20 montmorillonite
    clay. Calculate total negative charge.
  • Charge 0.05(200) 0.20(100) 10
    20 30 cmolc/kg

39
Soils the Global C cycle

40
How much organic C is present in this landscape?
41
How much organic C is present in the Prairies?
42
How Much C is present in Canadian Soils?
Credit Acton and Gregorich (1995)
43
Credit Ecological Monitoring Assessment Network
44
Fig. 5.14. A Catena
Credit Rennie and Ellis (1995)
45
Global Carbon Cycle Units
  • Units 1 ton 1 x 103 Kg 1 x 106 g
  • 1 gigaton (Gt) 1 billion tons 1 x 109 tons 1
    Gt 1 x 109 tons 1 ton 1 x 106 g 1 Gt 1 x
    1015 g 1Pg (petagrams)

46
Fig. 11.2. The Global Carbon Cycle
47
Global Carbon Cycle Pools
  • Atmosphere 750 Pg
  • Vegetation 610 Pg
  • Soil 1,580 Pg
  • Fossil Fuels 5,000 Pg
  • Oceans (organic) 1,020 Pg
  • Oceans (inorganic) 38,100 Pg
  • Carbonate Rocks 1 x 106 Pg

48
Fig. 11.2. The Global Carbon Cycle
49
Global Carbon Cycle Fluxes (Pg/yr)
  • Atmosphere to vegetation 61.4
  • Vegetation to atmosphere 60
  • Deforestation (loss) 1.6
  • Change in land use (gain) 0.5
  • Fossil Fuel combustion 5.5

50
Fig. 11.2. The Global Carbon Cycle
51
Fig. 11.1. Atmospheric CO2 concentration trend
at Mauna Loa Station (1958-1996)
Credit Environment Canada
52
Crops at the Breton Plots, University of Alberta
53
Wheat Residue Composition (g/kg)
  • Soluble components 288
  • Cellulose 361
  • Hemicellulose 184
  • Lignin 141
  • N-compounds (proteins) 9
  • Ash 84

Credit Broder and Wagner, 1988
54
Decomposition Rates
  • Soluble Components Rapid
  • Crude Proteins
  • Cellulose
  • Hemicellulose
  • Fats, Waxes
  • Lignins Slow

55
Controls on Decomposition Rates
  • Biochemical composition
  • Chemical structure
  • Amount present
  • Microbial and faunal activity

56
Processes
  • Enzymatic solubilization of substrates through
    microbial activity
  • Transformation of organic compounds
  • Biophysical stabilization (reaction of organic
    compounds with mineral materials)
  • Formation of organo-clay complexes

57
Credit U of A Extension Pedosphere.com
58
Decomposition Sequence
59
Decomposition Kinetics
  • First Order kinetics
  • Amount decomposed rate constant
    pool size
  • dc/dt kC

60
Amount of Decomposition
61
Simulation Models
  • This model illustrates that substrates are
    decomposed at different rates
  • Soil organisms grow and die
  • Organic matter is recycled
  • Part of carbon decomposed is used for energy
    production and is respired
  • Model by Verberne et al. (1993)

62
Linking the C Cycle to Nutrient Cycling

63
Needs of Organisms
  • Heterotrophic organisms need organic carbon for
    biosynthesis and energy production
  • Need N for proteins, DNA, RNA
  • Need P for DNA, RNA
  • Need S for proteins
  • Need trace elements and water

64
Decomposition Mineralization of N
decomposition
mineralization
Nitrogen is excreted by microbes because
organisms have excess N
65
Decomposition Immobilization of N
decomposition
immobilization
Nitrogen is taken up by microbes because
organisms need N for growth
66
Carbon and Nutrient Cycling
Decomposition
Respiration (oxidation)
immobilization
Recycling
mineralization
Humification
67
Tramin Model Demonstration
  • N is mineralized in non-amended soil
  • N is immobilized in glucose-amended soil
  • N dynamics under field conditions is more complex
  • The Tramin Model (Juma Paul, 1981)

68
Ecosystem Processes
Photosynthesis
Respiration
Decomposition
Respiration (oxidation)
immobilization
Recycling
mineralization
Humification
69
Humic Substances
  • The less resistant, identifiable biomolecules are
    produced by microbial action are called nonhumic
    substances
  • The ill-defined, complex, resistant, polymeric
    compounds are called humic substances

70
Properties of Humic Substances
  • Molecular weight range 2,000 to 300,000 daltons
    (mass of H atom is one dalton)
  • Resistant to decomposition
  • Form complexes with silicate clays
  • Have pH dependent charge

71
Fate of 100 g of Crop Residues
decomposition
synthesis
Humic Compounds
3 - 8
3 - 8
10 - 30
polymerization
60 - 80
72
Factors Affecting SOM
  • SOM increases as moisture content increases
    Example Brown vs. Black Chernozems

73
Factors Affecting SOM
  • Grasslands generally dominate in subhumid and
    semiarid areas (Chernozems)
  • Forests dominate in humid regions (Luvisols)

74
Factors Affecting SOM
  • Texture All else being equal, soils high in
    clay and silt are generally higher in organic
    matter than are sandy soils

75
Factors Affecting SOM
  • In poorly drained soils, high moisture promotes
    plant dry matter production and relatively poor
    aeration inhibits organic matter decomposition.
    SOM accumulates.

76
Cropping, Tillage Fertilization
  • First cultivation results in a rapid loss of SOM
  • In contrast, soils with low organic matter can be
    improved with crop rotations and increase in soil
    fertility.
  • The University of Alberta Breton Plots

77
Next Week
  • Soil Ecology
  • Review module 2
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