A Revolutionary Theory Of Humus

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Clive Kirkby (CSIRO) explained his theory of humus and soil carbon at the Third Annual Carbon Farming Conference & Expo 2009 in Orange NSW Australia - the only soil carbon farming conference of its type in the world. (4-5 November 2009)

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  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • Statistically significant increase in soil C and N but much of it below root zone – we are getting leaching of some of reteined decomposition products – suggest some went even lower than what we measured
  • Stubble incorporated outyielded burnt 4 out of 6 years with overall increase of 0.5t/ha/yr.We will discuss the 2 years in a minute
  • There have been lots of trials around the world showing an improvement in soil condition with stubble retention These figures show differences after 6 years of stubble incorporation Evidence from the literature suggests that yield suppression is often biological in origin
  • This soil has massive structure with very few large aggregates and generally has very small pores running through the soil resulting in poor drainage but high strength it dries into a solid block. Increased aggregation, especially large aggregates, gives produces an increase in the size of the pores within the soil and should give better drainage and reduced soil strength. Stubble incorporation resulted in an increase in the percentage of large aggregates and importantly they are stable even when wet.
  • There have been lots of trials around the world showing an improvement in soil condition with stubble retention These figures show differences after 6 years of stubble incorporation Evidence from the literature suggests that yield suppression is often biological in origin
  • There have been lots of trials around the world showing an improvement in soil condition with stubble retention These figures show differences after 6 years of stubble incorporation Evidence from the literature suggests that yield suppression is often biological in origin
  • There have been lots of trials around the world showing an improvement in soil condition with stubble retention These figures show differences after 6 years of stubble incorporation Evidence from the literature suggests that yield suppression is often biological in origin
  • There have been lots of trials around the world showing an improvement in soil condition with stubble retention These figures show differences after 6 years of stubble incorporation Evidence from the literature suggests that yield suppression is often biological in origin
  • A Revolutionary Theory Of Humus

    1. 1. Humus ecological stoichiometry, Redfield ratios and other stuff Clive Kirkby CSIRO Plant Industry Charles Sturt University EH Graham Centre for Agricultural Innovation Hamilton Branch – Southern Farming Systems John Kirkegaard Alan Richardson Graeme Batten Chris Blanchard Len Wade
    2. 2. Retention doesn’t always lead to C gains or burning to C losses Chan & Heenan (2005) found no difference in soil C when comparing retention & burning over 5 yrs at Temora Hamilton et al (1996) had a 7 yr trial in W.A. – found no difference between burning or retaining residues Rumpel (2008) compared residue retention & burning over 31 yrs in France – found no difference in soil C levels
    3. 3. Cropping doesn’t always lead to C losses
    4. 4. If Sampled <30cm 82% no-till had higher C BUT >30cm 69% no-till had lower C But there can be other good reasons for min-till Min-till doesn’t always lead to C increases
    5. 5. Soil Organic Matter is only a small component of the soil
    6. 6. But it Contains Lots of Carbon (billions tonnes C)
    7. 7. Some think sequestration refers to getting C into the passive pool ? While total soil C refers to C in both pools There are at least 2 pools
    8. 8. What’s stoichiometry ? H 2 O H 4 O 2 strict chemical formula AND stoichiometric formula stoichiometric formula only BUT still useful GIVES US THE RATIO OF COMPONENTS NEEDED TO BUILD SOMETHING WITHOUT WASTE
    9. 9. Biological Stoichiometry this OM is ? H 375,000,000 O 132,000,000 C 85,700,000 N 6,430,000 Ca 1,500,000 P 1,020,000 S 206,000 Na 183,000 K 177,000 Cl 127,000 Mg 40,000 Si 38,600 Fe 2,680 Zn 2,110 Cu 76 I 14 Mn 13 F 13 Cr 7 Se 4 Mo 3 Co 1 Proportion of elements in humans
    10. 10. Ecological Stoichiometry And Redfield Ratio Am. Sci. 1958 <ul><li>Ratios of dissolved C:N:P same in many oceans areas </li></ul><ul><li>Ratio the same as planktonic biomass ( equal stoichiometry ) </li></ul><ul><li>Biochemistry of organisms determines chemistry of oceans </li></ul><ul><li>Chemistry of oceans determines population of organisms </li></ul><ul><li>The elegant simplicity of this stoichiometric relationship belies its incredible utility </li></ul><ul><li>* ocean-atmosphere CO2 exchange * insight into nutrient limitation on primary production and carbon storage * contributes to knowledge on biogeochemical cycling of C, N and P </li></ul>As good as this is - he missed something C N P 106 16 1
    11. 11. CHNOPS – Main OM Building Blocks Element Human Alfalfa Insect Bacteria   C arbon 19.37 11.34 6.1 12.14 N itrogen 5.14 0.83 1.5 3.04 P hosphorus 0.63 0.11 0.13 0.60 S ulphur 0.64 0.10 0.14 0.32 H ydrogen 9.31 8.72 10.21 9.94 O xygen 62.81 77.90 79.99 73.68 Total 97.90 99.60 98.16 99.72
    12. 12. Like building a brick house OM Element House element   C arbon bricks N itrogen cement P hosphorus sand S ulphur lime H ydrogen / O xygen water
    13. 13. If We Assume We Have Water we can ignore the H and O Element Human bacteria stubble fungi Humus   C arbon 10,000 10,000 10,000 10,000 10,000 N itrogen 2654 2504 261 1091 833 P hosphorus 325 494 44 109 200 S ulphur 330 264 48 87 143
    14. 14. Which Means Insufficient N, P or S (and not just limited C inputs) Can limit humus sequestration in the soil To Emphasise Humus has constant proportions of C N P & S C N P S humus 10,000 833 200 143
    15. 15. I’m Suggesting a Redfield Like System Could Operate in the Soil CNP(S) in soil humus equivalent to Dissolved CNP in oceans CNP(S) of soil microbial biomass equivalent to CNP of planktonic biomass
    16. 16. 1st the microbes If the CNP(S) of soil microbial biomass equivalent to CNP of planktonic biomass C:N:P:S of soil microbial biomass should be constant then
    17. 17. Microbial biomass C:N
    18. 18. Microbial biomass C:S
    19. 19. Microbial biomass C:P C:N:P:S of soil microbial biomass is constant
    20. 20. Now For the Soil If CNP(S) in soil humus equivalent to Dissolved CNP in oceans then C:N:P:S of humus should be constant
    21. 21. Total soil C:N Equation predicts 10t C requires 833kg N Graphs suggests 838kg
    22. 22. Total soil C:S Equation predicts 10t C requires 143kg S Graphs suggests 145kg
    23. 23. Total soil C: organic P   Equation predicts 10t C requires 200kg P Graphs suggests 223kg Evidence supports humus has const C:N:P:S Very robust: same in soils around world
    24. 24. Looks Like Soil Does Have Redfield Ratio Like System <ul><li>Biochemistry of organisms determines chemistry of soil humus </li></ul><ul><li>Availability of N, P, S (and not just C) determines population of </li></ul><ul><li>microbes and humus potential of the system </li></ul>C N P S 10,000 833 200 143
    25. 25. Adding NPS with stubble created more humus  
    26. 26. Active Pool – Plant Remains
    27. 27. POM analysis   C N P S C:N Hamilton POM 12.8 0.72 0.056 0.115 18 Harden POM 16.2 0.87 0.073 0.081 19 Buntine POM 15.8 0.81 0.053 0.076 20 wheat straw 45.2 0.49 0.024 0.054 92 C N P S Hamilton POM 10000 563 44 90 Harden POM 10000 680 57 64 Buntine POM 10000 633 42 59 wheat straw 10000 108 5 12 humus 10000 833 200 143
    28. 28. Never Farmed Long Term Long Term or fertilised Pasture Cropping 118 t/ha 116 t/ha 9 t/ha
    29. 29. Carbon levels in virgin, pasture or long term crop soil (“cleaned” sample) The main increase in soil C under any sort of min-till is probably partially decomposed plant material (= active pool) It can disappear quickly under favourable conditions IS IT good for C trading ? C Virgin 2.0 Pasture 2.8 Cropping 2.0 C Virgin 3.6 Pasture 4.2 Cropping 2.1
    30. 30. Pools and min-till Lots of active pool C built up under min till It disappeared quickly following cultivation
    31. 31. Thanks for listening
    32. 32. Cost <ul><li>But it’s essentially a one of payment </li></ul><ul><li>Get the OM into the humus pool & it will stay there </li></ul><ul><li>BUT you mustn’t mine the nutrients or you will lose the carbon as well </li></ul>Cost of equivalent fertiliser N, P & S = $288 Payment if CO2 is worth $40/t = $150
    33. 33. Pastures do generally increase soil C But it soon disappears
    34. 34. Changes in C and N
    35. 35. Maize Grain Yield  
    36. 36. Engine load ripping the beds  
    37. 37. Water Stable Aggregates
    38. 38. We Did Much The Same Thing In The Field  
    39. 39. Measuring GHG’s  
    40. 40. CO 2 emitted  
    41. 41. N 2 O emitted  
    42. 42. Adding nutrients to a low nutrient soil increased the decomposition rate
    43. 43. Active & Passive <ul><li>● Compost </li></ul><ul><li>● Nutrient rich </li></ul><ul><li>● Energy poor </li></ul><ul><li>As far as microbes are concerned </li></ul><ul><li>Compost isn’t good tucker </li></ul>Passive pool Compost stage % C N P K S C:N Calorific value Initial material 37 1.3 0.19 0.22 0.22 32 13,300 Mature compost  17 1.3 0.39 0.71 0.43 13 6,300
    44. 44. Organic amendments (+ +)
    45. 45. <ul><li>Do limited soil nutrients retard decomposition </li></ul><ul><li>Do limited soil nutrients retard humus formation </li></ul><ul><li>Do limited soil nutrients encourage humus decomposition </li></ul><ul><li>How do we assess correct levels </li></ul><ul><li>Does the form of the nutrient matter </li></ul><ul><li>Will it be economic </li></ul>
    46. 46. Humus Formation without extra nutrients Stubble DW (kg/ha) C N P S wheat 10,000 4600 71 7 7 Max humus formed without extra nutrients 350 29 7 5 Excess nutrients 4250 42 0 2 Humification efficiency 8% humus  10000 833 200 143
    47. 47. Humus Formation using ALL stubble nitrogen Stubble DW (kg/ha) C N P S wheat 10,000 4600 71 7 7 Max humus formed if ALL nitrogen used 852 71 17 12 Excess/ deficient nutrients 3748 0 -10 -5 Humification efficiency 19% Need to add 10kg P and 5kg S per 10t stubble
    48. 48. <ul><li>Adding FOM to low nutrient soil induces very positive priming effect </li></ul><ul><li>Possible cause: </li></ul><ul><li>Microbes can get lots of energy from FOM but not lots nutrients </li></ul><ul><li>Microbes can get lots nutrients from humus but not energy </li></ul><ul><li>To get maximum microbial proliferation in low nutrient soils </li></ul><ul><li>microbes decompose FOM for energy and humus for nutrients </li></ul><ul><li>Final effect: little or possible decrease in overall SOM levels </li></ul>

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