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)

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. 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. Cropping doesn’t always lead to C losses

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. Soil Organic Matter is only a small component of the soil

6. But it Contains Lots of Carbon (billions tonnes C)

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. 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. 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

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. 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. 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. 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. 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. 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. Microbial biomass C:N

18. Microbial biomass C:S

19. Microbial biomass C:P C:N:P:S of soil microbial biomass is constant

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. Total soil C:N Equation predicts 10t C requires 833kg N Graphs suggests 838kg

22. Total soil C:S Equation predicts 10t C requires 143kg S Graphs suggests 145kg

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

25. Adding NPS with stubble created more humus

26. Active Pool – Plant Remains

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. Never Farmed Long Term Long Term or fertilised Pasture Cropping 118 t/ha 116 t/ha 9 t/ha

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. Pools and min-till Lots of active pool C built up under min till It disappeared quickly following cultivation

31. Thanks for listening

33. Pastures do generally increase soil C But it soon disappears

34. Changes in C and N

35. Maize Grain Yield

36. Engine load ripping the beds

37. Water Stable Aggregates

38. We Did Much The Same Thing In The Field

39. Measuring GHG’s

40. CO 2 emitted

41. N 2 O emitted

42. Adding nutrients to a low nutrient soil increased the decomposition rate

44. Organic amendments (+ +)

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. 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