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Advanced Methods for Soil Organic Matter Decomposition Analysis

Explore the intricate process of organic material breakdown with techniques like Litterbags and Decomposition Analysis. Understand the sensitivity of methods for temporal comparisons and delve into different aspects of soil ecology.

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Advanced Methods for Soil Organic Matter Decomposition Analysis

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  1. Global Carbon Model petagrams Pg = 1x1015g 1

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  3. Soil Ecology • the process whereby organic material is broken down into its smaller molecules • biological, physical, and chemical breakdown of organic matter resulting in humus formation, release of CO2, H2O, and nutrients Decomposition Methods ?? 3

  4. Soil Organic Matter (SOM) Methods • LOI– loss on ignition • Wet Oxidation–eg, Walkley-Black (determining C by titration of unreduced dichromate) • Dry Combustion– eg, LECO (Infrared & OC&Inorg C) • Fractionation 4

  5. SOM Fractionation 5

  6. But are these methods sensitive enough for temporal comparisons????? 6

  7. Decomposition Methods • Litterbags --- weight loss (g) • Density change (g/cm3) • Calculation of k values (year-1) (input/accumulation) • CO2 evolution (g m-2) 7

  8. Decomposition • Litterbags http://www.geog.uu.nl/fg/gapsize/thesis-ovd/Deel10%20Hfd07.pdf 8

  9. Decomposition • Litterbags • Different mesh sizes • Different times • Different substrates (pure/mix) • Standards? http://www.geog.uu.nl/fg/gapsize/thesis-ovd/Deel10%20Hfd07.pdf 9

  10. Needle/Leaf Litterbags 10

  11. Grass Litterbags 11

  12. Log Decomposition (HJ Andrews) Litterbags??? 12

  13. Root decomposition Litterbags 13

  14. Wood Decomposition density changes g/cm3 14

  15. Decay Constant (k) X = X0 e-kt 100 50 0 % mass remaining Time 15 Olsen 1963

  16. Decay Constant (k) • k = (-ln(wt remaining fraction))/yrs decomp k yr-1 = (-ln(Xt/X0 )) / t yr 16

  17. Examples involving Negative Exponential Decay Curves (Jenny et al 1949, Olson 1963) 17

  18. Decomposition Time • Mean Residence Time (MRT) steady state Forest Floor Biomass/Annual Litterfall = ? Year • Half-Life (50% remaining) k = (-ln(Xt/X0 )) / t years t(1/2) = -ln 0.5/k = 0.693/k • 1% remaining (~MRT) t(.01 ) = -ln 0.01/k = 4.605/k kg / kg year-1 = year 18

  19. Examples involving Negative Exponential Decay Curves (Jenny et al 1949, Olson 1963) 19

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  21. (C g/m2 yr) 21

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  23. So multiple 1st order decay curves may present different k values thru time!! 23

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  26. Net Ecosystem Carbon Exchange Gross Photosynthesis Dark and Photo Respiration CO2 Storage bole respiration litter respiration microbial respiration root respiration The Carbon Balance http://www.vaisala.com/DynaGen_Attachments/Att32668/GMP343%20Introduction.pps#6 26

  27. Decomposition usingCO2 Evolution Gilson respirometer Warburg Apparatus 27 http://history.nih.gov/exhibits/stadtman/lab.htm

  28. Decomposition usingCO2 Evolution • Soda lime - Ca(OH)2 (about 75%)   • Weight change • KOH traps • Titration 28

  29. Soil Respiration System (PP System) http://www.ppsystems.com/soil.html 29 Infra-Red Gas Analysis Systems (PP Systems)

  30. Century Model - variables predicting SOM accumulation • Amount above- & belowground plant material to decay • Chemical quality of material added to detritus (e.g. lignin, N) • Soil texture • Climate 30

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