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  1. Understanding C sequestration Joel Gruver NCSU Soil Science jgruv@hotmail.com www.soil.ncsu.edu/lockers/Gruver_J/Carbon

  2. Global C cycle Gt = 109 t = Pg = 1015 g http://www.grida.no/climate/vital/graphics/large/12.jpg

  3. C fluxes

  4. Relative contributions of major greenhouse gases: H20 vapor - 36-70% CO2 – 9-26% CH4 – 4-9%

  5. ~ 1600 Gt globally < 5 % of the mass of most soils C Mineral particles

  6. SOM is a complex mixture Living organisms Biologically active SOM Recent residues Recalcitrant SOM Adapted from Magdoff and Weil (2003)

  7. POM IOM DOM ed Are these materials components of humus ? http://www.grdc.com.au/growers/res_summ/pdfs/cso00029.pdf

  8. What is humus ???? • Humus is organic matter that has been transformed such that its original source is no longer apparent… The diverse products of “humification” have many common characteristics: • Extreme chemical complexity • Resistance to further decomposition • High specific surface and negative charge • Dark color

  9. Organic fractions obtained using classical alkali extraction methods Most evidence indicates that these fractions are poorly related to soil function Humic acid Fulvic acid Humin

  10. There is growing evidence that humic substances are aggregated mixtures rather than macromolecules Does humus have a macromolecular structure ? hydrophilic hydrophobic hydrophilic hydrophilic hydrophilic Piccolo (2002)

  11. Location within the soil matrix affects SOM dynamics ↑ Free POM Sensitivity to management Intra-aggregate POM ↑ Mineral associated OM Adapted from Carter (2002)

  12. SOM pools < 1 year decades What is the mean residence time of SOM ?? centuries Janzen (2006)

  13. Many studies have shown that physical fractions of OM are related to soil function Sand sized Silt and clay sized Particulate OM Humus http://www.grdc.com.au/growers/res_summ/pdfs/cso00029.pdf

  14. Functional impact of SOM fractions http://www.grdc.com.au/growers/res_summ/pdfs/cso00029.pdf

  15. Humus adsorbs ions and molecules Adapted from Brady and Weil (2002)

  16. Humus gives soil a darker color

  17. Humus increases plant available H20 Adapted from Brady and Weil (2002)

  18. Aggregates form around particulate organic matter (POM) Processes that disrupt aggregates accelerate loss of POM

  19. Some very interesting data… Ladd et al. (1993)

  20. SOM reduces bulk density Magdoff and Weil (2004)

  21. Do not till or traffic on wet soils !!! Structural damage Soils with high C are more resistant to structural damage ! (Watts and Dexter, 1997)

  22. Active OM energizes biologically mediated processes

  23. The Soil Stomach Bacteria Fungi Algae Protozoa Nematodes Microarthropods Enchytraeids Earthworms Ants, termites, spiders Mollusks Others: rodents, snakes, voles, amphibians, etc. Body size increasing Microflora Microfauna Mesofauna Macrofauna Megafauna

  24. The metabolic potential of soil microbial communities greatly exceeds organic inputs to soils

  25. Why does organic matter accumulate in soils ?

  26. Blechh !!! Tastes Bad !!!! Biochemical recalcitrance How do you expect to live off this stuff ??? Mineral protection I can’t get if off, you try !! Fe Al We already are !!!!!! Yuck !!!!! Sure is gritty ! Physical protection There’s gotta to be a way inside !!! Hey !! There’s good stuff in there !!!! Adapted from Jastrow and Miller (1997)

  27. Understanding organic resource quality (Giller, 2000)

  28. Relationship between fine mineral fraction and SOM Magdoff and Weil (2004)

  29. Relationship between clay content and SOC for 1261 agricultural soils in England and Wales Webb et al.(2003)

  30. Microorganisms behave very differently in a petri dish than they do in soils http://picturethis.pnl.gov/im2/8208417-5cn0/8208417-5cn.jpg

  31. Most of the pores where soil microorganisms reside are either environmentally suppressive or lacking in suitable substrates.

  32. Microorganisms have very limited ability to move within the soil matrix.

  33. As a result, most soil microorganisms are in a dormant state For their prince charmings to arrive ! waiting…

  34. Roots Rain There are many types of prince charmings ! Tillage Organic Amendments

  35. Impact of earthworms on SOM dynamics Ingested soil Fresh casts Aging casts Soil profile ? Assimilation Comminution Nutrient release Physical protection (Lavelle and Spain, 2001)

  36. The priming effect of plant roots AggregateDisruption Exposition of organic matter GrowingRoot Priming Effect Exudation Activation of microorganisms (Lavelle and Spain, 2001)

  37. Crop related changes in mineralizable N No Till Plow/Disk Sorghum Wheat Soybean Adapted from Magdoff and Weil (2004)

  38. Climate affects SOM dynamics Organic matter accumulation Brady and Weil (2002) 70 F

  39. Landscape position affects SOM dynamics Poorly drained Interstream divide Somewhat poorly drained Moderately well drained LANDSCAPE POSITIONS Well drained Poorly drained Interfluve Shoulder Valley floor SOIL DRAINAGE CLASSES Backslope

  40. Blackland soils of North Carolina Lily (1981)

  41. Geographic distribution of SOM

  42. How much is enough ??

  43. Attempting to hoard as much organic matter as possible in the soil, like a miner hoarding gold, is not the correct answer. Organic matter functions mainly as it is decayed and destroyed. Its value lies in its dynamic nature. W. Albrecht, 1938

  44. Janzen (2006)

  45. There are many ways to “measure” SOM Total organic matter mass loss by ignition OM ~ 1.72 x C Total C by several methods Humic matter alkali extraction Adapted from Strek and Weber (1985)

  46. Soil from a long term experiment in Beltsville, MD 20 yrs sod, 5 yrs CT corn 25 yrs CT corn