Fundamentals of Soil Science

1. Fundamentals of Soil Science Soil Organic Matter

2. Soil Organic Matter • Reading Assignment: Brady and Weil, Chapter 11 • Soil Organic Matter • 3 lectures • Why Worry about SOM? • Creating SOM • SOM’s Influence on Soil Properties and Plants • Lab for Chapter 10 and Chapter 11 • Blended learning materials available on web site and DVD

3. Learning Objectives • Lecture 4 – • Define and explain the importance of soil organic matter • Describe the carbon (C) cycle, including pools and fluxes • Explain basic principles of organic decomposition including chemical formulas • Lecture 5 – • Describe the factors the control litter decay • List characteristics of low quality litter • Describe the importance of C:N ratio • Distinguish between factors that control decomposition of litter vs. decomposition of soil organic matter

4. Learning Objectives (cont.) • Lecture 6 – • List values of organic matter in soil: physical, chemical, biological • Relate the names and activities of three SOM pools • Discuss changes in various pools of organic matter as a result of changes in land use and management • Describe the interaction between SOM pools over time • Explain Conundrum – selecting materials to attain balance in particular ecosystem • Articulate value of managing organic matter in soil

5. Lecture 4 Topics • Recall Previous Learning • Definition and Importance of Soil Organic Matter • Global Carbon Cycle • Balance and Imbalance

6. Lab • Description of lab and objectives of lab relating to Chapter 10 and Chapter 11

7. Lecture 5 Topics • Decomposition in Soil • By-products of decomposition • Humus and its sources • Mechanisms for SOM Stabilization • Carbon to Nitrogen Ratio • Nitrogen Fixation

8. Lecture 6 Topics • Influence of SOM: Physical, Chemical, Biological • Pools of Organic Carbon • Managing SOM • Greenhouse Gases

9. Lecture 4Why Worry about SOM?

10. Learning Objectives • Lecture 4 – • Define and explain the importance of soil organic matter • Describe the carbon (C) cycle, including terrestrial pools and fluxes • Explain basic principles of organic decomposition

11. Lecture 4 – Topics • Recall Previous Learning • Definition and Importance of Soil Organic Matter • Global Carbon Cycle • Balance and Imbalance

12. What is Soil? • Air • Water • Minerals • Organic Matter • What is soil organic matter? • Living biomass (plant tissues, animal tissues and microorganisms) • Dead roots and dead plant residues or litter • Mixture or organic substances no longer identifiable as tissues

13. Soil Function and Properties • The percentage of soil organic matter (SOM) in most soils is small. • SOM exerts a dominant influence on soil physical, chemical and biological properties: • Soil cation exchange capacity • Water-holding capacity • Formation and stabilization of soil aggregates • Storehouse of plant nutrients, especially nitrogen (next section) • Soil supplies energy and body-building constituents for microorganisms

14. Carbon (C) in soil • Soil organic matter is a complex and varied mixture of organic substances • All organic substances contain C cutin glucose cellulose protein Lignin sugars

15. Global Carbon Cycle SOM plays large role in global carbon balance. Small changes in rates of stabilization/destabilization are important for global budgets Imbalance 221.5 Pg/yr enters the atmosphere while only 215 Pg/yr of carbon is removed. Carbon dioxide levels in the atmosphere are rising. 110 7.5 550 760 50 60 2,400 Soil 62 105 102 0.5 5,000 Fossil Fuel 40,000 Oceans and Lakes Sediment 0.5 75,000,000 Carbonate Rocks

16. Plants Litter Soil organic matter Carbon inputs – outputs = storage

17. Soil C • Soil carbon represents a larger global pool than living plant and atmospheric pools combined. • Carbon comprises about ½ the mass of soil organic matter • The world’s soils contain 3x as much carbon as the worlds vegetation.

18. Global C in upper 100 cm Wetlands cover xx percent of global land cover but contain 30% of global C Andisols cover xx percent of global land cover, but contain xx% of global C Wetlands (Histosols) cover 2% of global land cover, but contain approx. 30% of soil Carbon

19. Decomposition Breakdown of large organic molecules into simpler components • Stages of decomposition: • Leaching by water removes simple soluble compounds and ions • Fragmentation (physical break down) creates surface area • Chemical alteration – Microbially mediated by-products

20. Decomposition Process • Microbially mediated reactions: • Enzymatic oxidation of organic matter to CO2, H2O, energy, and biomass • Mineralization of proteins into their inorganic constituents: e.g., NH4, NO3, P and SO4 • Formation of compounds that resist further decay • Decomposition is an oxidation process Input entire eqn 11.1 In an aerobic or anaerobic environment

21. Composition of Plant Material • Plant residues are the primary source of soil organic matter. • Plants = 75% Water, • 25% Dry Matter • Elemental analysis of dry matter? • Structural components of dry matter? • Carbohydrates • Lignins and polyphenols • Proteins

22. Plant Decomposition Rapid Decomposition Very slowdecomposition • Sugars, starches, simple proteins • Crude proteins • Hemicellulose • Cellulose • Fats and waxes • Lignins and phenolic compounds

23. Detecting organic decomposition • Soil Respiration rate (level of CO2 emission from the soil) • What happens when falling leaves replenish litter layer? • R-strategists – opportunistic species • K-strategists – slow and steady decomposers • Priming – decay of older organic matter as a result of addition of fresh inputs

24. Detecting organic decomposition • r-strategists (opportunists), microorganisms who were dormant awaken and overtake k-strategists (slow and steady decomposers) • During r-strategists reign: respiration high, microbial biomass high • r-strategists go dormant or die when food is gone, k-strategists eat them and help promote mineralization • Some carbon from decomposition process is converted to soil humus