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Introduction to Soils and Soil Resources

Introduction to Soils and Soil Resources. 2001 Lecture 7 Soil Air and Soil Organic Matter. Table 9.1. Relative concentrations of atmospheric gases on Earth, Mars and Venus. Credit: after Margulis and Hinkle, 1991. Oxidation.

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Introduction to Soils and Soil Resources

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  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, hydrogenhas 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 (CFC’s) parts per trillion • Refer to Table 9.3 (Section 9.3)

  12. Fig. 9.3. Active sites, mineral particles and water films

  13. Atmospheric Air vs Soil Air (% volume)

  14. 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)

  15. Aerobic Respiration C6H12O6 + O2 6 CO2 + 6 H2O + energy

  16. Anaerobic Respiration NO3- NO2- NO  N2O  N2 5 3 2 1 0 Nitrate is terminal electron acceptor when oxygen is limiting

  17. Gas Conc. (% vol.): Corn field Elliott and McCalla 1972. Soil Sci. Soc. Am. Proc. 36:68

  18. Gas Conc. (% vol.): Feedlot Elliott and McCalla 1972. Soil Sci. Soc. Am. Proc. 36:68

  19. Gas Dynamics • Normally O2 decreases and CO2 increases with depth • Normally, CO2<0.5% in soil atmosphere while O2 >10%

  20. Soil Organic Matter

  21. Air 25% Mineral Mineral 45% Organic Water Air Water 25% Organic 5% Soil: Major Components

  22. Soil Organic Matter • All organic substances, by definition, contain carbon • The element carbon is the foundation of all life

  23. 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

  24. Credit: U of A Extension & Pedosphere.com

  25. Physical Properties • The physical properties of soil horizons vary tremendously within a pedon • Example is given in Table 11.2 in Section 11.2

  26. 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

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

  28. Fig. 1.9. Pores and particles in soil (Pawluk) Credit: Pedosphere.com

  29. Porosity/Structure

  30. Fig. 6.12. Structure of a model humic acid (Schulten & Schnitzer, 1997)

  31. Fig. 6.10. Impact of soil pH on net charge oforganic acids

  32. Charge Characteristics * cmolc/kg

  33. 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

  34. Soils & the Global C cycle

  35. How much organic C is present in this landscape?

  36. How much organic C is present in the Prairies?

  37. How Much C is present in Canadian Soils? Credit: Acton and Gregorich (1995)

  38. Credit: Ecological Monitoring & Assessment Network

  39. Fig. 5.14. A Catena Credit: Rennie and Ellis (1995)

  40. 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 tons1 ton = 1 x 106 g1 Gt = 1 x 1015 g = 1Pg (petagrams)

  41. Fig. 11.2. The Global Carbon Cycle

  42. 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 Rocks1 x 106 Pg

  43. Fig. 11.2. The Global Carbon Cycle

  44. 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

  45. Fig. 11.2. The Global Carbon Cycle

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