1. Genesis of the use of RothC to model soil organic carbon

2. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Outline Composition of soil organic carbon – isolating biologically important fractions Methodology for quantifying C allocation to fractions Why attempt to understand allocation to fractions? Modelling soil carbon with RothC Substitution of conceptual with measureable C pools in RothC MIR prediction of soil carbon fractions

3. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Composition of soil organic matter Extent of decomposition increases Rate of decomposition decreases C/N/P ratio decreases (become nutrient rich) Dominated by charcoal with variable properties Crop residues on the soil surface (SPR) Buried crop residues (>2 mm) (BPR) Particulate organic matter (2 mm – 0.05 mm) (POC) Humus (<0.05 mm) (HumC) Resistant organic matter (ROC)

4. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Biologically significant soil organic fractions Humus (HumC) Particulate material (POC) Charcoal (ROC)

5. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Quantifying SOC allocation of SOC to fractions Recalcitrant Charcoal C Humus + recalcitrant HF treatment, UV-PO, & NMR <53 µm fraction>53 µm fraction Na saturate, disperse, sieve <53 µm Total soil organic carbon Density fractionation Buried plant residue carbon Soil sieved to <2mmSoil sieved to >2mm Surface plant residue carbon Quadrat collection Particulate organic carbon Density fractionation Humus = <53µm - Recalcitrant

6. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Variation in amount of C associated with soil organic fractions 0 5 10 15 20 25 Average for Hamilton (long term pasture) Organic carbon in 0-10 cm layer (Mg C/ha) Surface plant residue C (SPR) Buried plant residue C (BPR) Particulate organic carbon (POC) Humus C (HumC) Recalcitrant C (ROC - charcoal)

7. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Variation in amount of C associated with soil organic fractions Pasture CroppedMix 0 5 10 15 20 25 30 1P8P 32P NoTill (MedN) NoTill (HighN) Strat (MedN) Strat (HighN) 0P 11P22P Arboretum Perm Pasture W2PF Canola/wheat Pulse/wheat Pasture/wheat HamiltonHartYassUrrbraeWaikerie Organic C in 0-10 cm layer (Mg C/ha) SPR BPR POC HumC ROC

8. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Years Soil organic carbon (g C kg -1 soil) 0 5 10 15 20 25 30 0 102030 40 50 60 70 Total soil organic C Conversion to permanent pasture 33 Changes in total soil organic carbon with time 1543 Initiate wheat/fallow 18 y 10 y

9. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Years Soil organic carbon (g C kg -1 soil) 0 5 10 15 20 25 30 0 102030 40 50 60 70 TOC Conversion to permanent pasture 33 Importance of allocating C to soil organic fractions 1543 Humus C ROC POC Initiate wheat/fallow 18 y 10 y ~30% less humus C ~800% more POC

10. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Vulnerability of soil carbon content to variations in management practices Years Soil organic carbon (g C kg -1 soil) 0 5 10 15 20 25 30 0 102030 40 50 60 70 TOC Humus ROC POC Conversion to wheat/fallow 18 y Conversion to pasture 10 y 15 43 33 9 y 52 Initiate wheat/fallow

11. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Importance of quantifying allocation of C to soil organic fractions Soil Organic Carbon (g C kg -1 soil) Time 0 5 10 25 15 20 Soil 1 20 g SOC kg -1 soil Soil 2 20 g SOC kg -1 soil Time 0 5 10 25 15 20 Active C Soil Organic Carbon (g C kg -1 soil) Inert C 10 g Char-C kg -1 soil Inert C 2.5 g Char-C kg -1 soil

12. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Summary SOC fractions Recalcitrant Charcoal C Humus + recalcitrant HF treatment, UV-PO, & NMR <53 µm fraction>53 µm fraction Na saturate, disperse, sieve <53 µm Total soil organic carbon Density fractionation Buried plant residue carbon Soil sieved to <2mmSoil sieved to >2mm Surface plant residue carbon Quadrat collection Particulate organic carbon Density fractionation Humus = <53µm - Recalcitrant

13. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC Model (Version 26.3) DPM RPM Plant Inputs BIO HUM CO 2 Decomposition BIO HUM CO 2 IOM Fire Decomposition Original configuration – monthly time step

14. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Roth C data requirements Monthly climate data: rainfall (mm), open pan evaporation (mm), average monthly air temperature (°C) Soil clay content (% soil OD mass) Soil cover (vegetated or bare) Monthly plant residue additions (t C ha -1 ) Decomposability of plant residue additions Monthly manure additions (t C ha -1 ) Soil depth (cm) Initial amount of C contained in each pool

15. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – partitioning residue inputs into decomposable and resistant material All plant material entering the soil is partitioned into DPM and RPM via DPM/RPM ratio ManagementDPM/RPM Grassland and most agricultural crops1.44 Unimproved grassland and scrub (savannas)0.67 Deciduous and tropical woodlands0.25

16. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – amount of each type of carbon decomposed The amount of carbon associated with each pool that decomposes follows an exponential decay a = the rate modifying factor for temperature b = the plant retainment rate modifying factor c = the rate modifying factor for soil water k = the annual decomposition rate constant for a type of carbon t = 0.0833, since k is based on a yearly decomposition rate. Values of k for each SOC fraction (y -1 ) BioFBioSDPMRPMHum 0.660.66100.150.02

17. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – calculation of rate constant modifying factors Temperature modifying factor (a) Plant retainment modifying factor (b) b = 0.6 if soil is vegetated b = 1.0 if soil is bare tm= average monthly temperature

18. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – calculation of rate constant modifying factors Soil water modifying factor – calculated based on top soil moisture deficit (TSMD) Water present in the soil (mm) Saturation Dry Lower Limit Upper Limit TSMD Total porosity

19. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – calculation of rate constant modifying factors Calculation of maximum TSMD Calculation of accumulated TSMD over each time step under the constraint that the accumulated TSMD can only vary between 0 and MaxTSMD

20. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – calculation of rate constant modifying factors Calculation of the rate modifying factor (c) if TSMD acc < 0.444 MaxTSMD then c=1.0 otherwise, 1.0 0.2 c 0.444 MaxTSMD MaxTSMD

21. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – amount of each type of carbon decomposed The amount of carbon associated with each pool that decomposes follows an exponential decay a = the rate modifying factor for temperature b = the plant retainment rate modifying factor c = the rate modifying factor for soil water k = the annual decomposition rate constant for a type of carbon t = 0.0833, since k is based on a yearly decomposition rate. Values of k for each SOC fraction (y -1 ) BioFBioSDPMRPMHum 0.660.66100.150.02

22. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC Model (Version 26.3) DPM RPM Plant Inputs BIO HUM CO 2 Decomposition BIO HUM CO 2 IOM Fire Decomposition

23. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC model structure – partitioning of decomposition products Fraction decomposing organic matter that goes to CO 2, humus and biomass Partitioning to CO 2 is defined by clay content Biomass + Humus partitioning 46% Bio 54% Hum

24. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 RothC output under constant inputs and climate – to define equilibrium SOC

25. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Modelling the measurable DPM RPM Plant Inputs BIO HUM CO 2 Decomposition BIO HUM CO 2 IOM Fire Decomposition RPM=POC IOM=ROC (Charcoal C) HUM=TOC – (POC + ROC)

26. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Requirements for calibration Soil samplesRepresentative composite soil samples collected at the beginning and end of a period >10 years to a soil depth of 30 cm. Bulk densityMeasured at time of sampling using soil core weight/volume. Crop yieldsYield of grain and pasture over each year to be modelled and estimates of harvest index and root/shoot ratios ManagementDetails of individual crops, rotations, fallow periods, stubble burning and incorporation. If grazing occurred, estimates of consumption and return from animals. ClimateDetails of average monthly air temperature, rainfall and pan evaporation

27. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Model calibration and verification sites 0350 Kilometres 700 Verification Sites Brigalow Tarlee Calibration Sites

28. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Brigalow calibration site: influence of modifying RPM decomposition constant (k)

29. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Tamworth – wheat/fallow 0 10 20 30 40 50 1970198019902000 Year Soil C (t/ha) Wagga – wheat/pasture 0 20 40 60 198819901992199419961998 Year Soil C (t/ha) Salmon Gums – wheat/wheat 0 10 20 30 40 50 1979198319871991 Year Soil C (t/ha) Salmon Gums - wheat/ 3 pasture Year Soil C (t/ha) 0 10 20 30 40 50 1979198319871991 DPM RPM HUM IOM BIO Soil Modeled POC HUM CHAR TOC Measured Model Verification: (sites with archived soil samples)

30. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Model verification: (paired sites) Is this result due poor model performance or poor pairing of the sites? Did the sites start off similar or were there significant initial differences in soil/plant/environmental properties? Kindon - pasture 15 y 0 10 20 30 40 50 Year Soil C (t/ha) 1986199119962001 Dunkerry South - crop 0 10 20 30 1967197719871997 Year Soil C (t/ha) DPM RPM HUM IOM BIO Soil Modeled POC HUM CHAR TOC Measured

31. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Quantifying SOC allocation of SOC to fractions Recalcitrant Charcoal C Humus + recalcitrant HF treatment, UV-PO, & NMR <53 µm fraction>53 µm fraction Na saturate, disperse, sieve <53 µm Total soil organic carbon Density fractionation Buried plant residue carbon Soil sieved to <2mmSoil sieved to >2mm Surface plant residue carbon Quadrat collection Particulate organic carbon Density fractionation Humus = <53µm - Recalcitrant

32. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Predicting total organic carbon and its allocation to SOC fractions using MIR 1 2 3 4 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 Intensity Frequency (cm -1 ) Fourier Transform Infrared Spectrum Dependence on soil chemical properties Prediction of allocation of carbon to fractions via calibration and PLS

33. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Prediction of total organic carbon (TOC) MIR predicted TOC (g C/kg soil) Measured TOC (g C/kg soil) Janik et al. 2007 Aust J Soil Res 45 73-81 177 Australian soils (all states) from varying depths within the 0-50 cm layer n = 177 Range: 0.8 – 62.0 g C/kg R 2 = 0.94

34. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Tasmanian soils project

35. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 MIR prediction of particulate organic carbon MIR predicted POC (g C/kg soil) Measured POC (g C/kg soil) Janik et al. 2007 Aust J Soil Res 45 73-81 141 Australian soils (all states) from varying depths within the 0-50 cm layer n = 141 Range: 0.2 – 16.8 g C/kg R 2 = 0.71 Variability in crop residue type exits

36. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 MIR prediction of charcoal C MIR predicted Char C (g/kg) Measured Char C (g/kg) Janik et al. 2007 Aust J Soil Res 45 73-81 121 Australian soils (all states) from varying depths within the 0-50 cm layer n = 121 Range: 0.0 – 11.3 g C/kg R 2 = 0.86

37. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Summary Methodologies exist to quantify biologically significant pools of carbon Understanding the dynamics of the pools allows accurate interpretation of potential changes Substitution of measureable fractions for conceptual pools in models is possible Rapid methods for predicting soil carbon allocation to pools exist

38. Thank you CSIRO Land and Water Jeff Baldock Research Scientist Phone: +61 8 8303 8537 Email: jeff.baldock@csiro.au Web: http://www.clw.csiro.au/staff/BaldockJ/http://www.clw.csiro.au/staff/BaldockJ/ Acknowledgements Jan Skjemstad, Kris Broos, Evelyn Krull, Ryan Farquharson, Steve Szarvas, Leonie Spouncer, Athina Massis Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: Enquiries@csiro.au Web: www.csiro.au

39. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Model Calibration Brigalow South ws64 (RPM 0.15) 1982198719921997 Year 0 10 20 30 40 50 60 70 0-30 cm Soil C (t/ha) DPM RPM HUM IOM BIO Soil Modeled POC HUM CHAR TOC Measured

40. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Defining soil C dynamics at Roseworthy, SA under continuous wheat production Average growing season (Apr-Oct) rainfall (mm)338 Water limited potential grain yield (Mg/ha)4.56 Grain yield used (Mg/ha) (85% water use efficiency)3.88 Harvest index (Mg grain/Mg dry matter)0.45 Total shoot dry matter production (Mg/ha)8.62 Soil clay content (%) Amount of C in 0-30cm layer (Mg C/ha) C content of 0-10 cm layer (%) 5652.32 15782.79 30933.32 Equilibrium conditions (model for 500 years)

41. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Changes in soil C for different levels of average grain yield

42. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Changes in soil C for different levels of average grain yield Shift yield from 4 to 8 T grain/ha = 1.0 %C increase over 20 years Shift yield from 4 to 6 T grain/ha = 0.4 %C increase over 20 years

43. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Composition of methodologically defined SOC fractions Particulate organic carbon (POC) Fragments of plant residues >53 µm (living and dead) Molecules sorbed to mineral particles >53 µm Large pieces of charcoal Humus (HUM-C) Fragments <53 µm Molecules sorbed to particles <53 µm Recalcitrant (ROC) Materials <53 µm that survive photo-oxidation Dominated by material with a charcoal-like chemical structure NMR to quantify char-C

44. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Spatial variation in soil charcoal and carbon contents (0-10 cm layer) 0.00 0.40 0.80 1.20 1.60 2.00 2.40 0255075100 Western Boundary (m) TOC 0 20 40 60 80 100 120 140 160 180 200 N o r t h e r n B o u n d a r y ( m ) 0 111 222 333 444 555 666 777 888 999 10 11 12 13 14 15 16 17 19 20 21 22 23 24 25 26 27 29 30 31 32 33 34 35 18 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0255075100 Western Boundary (m) Inert OC 0 20 40 60 80 100 120 140 160 180 200 N o r t h e r n B o u n d a r y ( m ) 0 111 222 333 444 555 666 777 888 999 10 11 12 13 14 15 16 17 19 20 21 22 23 24 25 26 27 29 30 31 32 33 34 35 18 35 W F P P F W Perm. Past. Contour bank W O O(g) F B Pe W W P P W W W P P P P P W O F W O(g) F W Pe Perm. Past

45. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Predicting soil organic carbon contents Clearing of Brigalow bushland

46. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Options for increasing soil carbon content Principal: increase inputs of carbon to the soil Maximise capture of CO 2 by photosynthesis and addition of carbon to soil Options Maximise water use efficiency (kg total dry matter/mm water) Maximise stubble retention Introduction of perennial vegetation Alternative crops - lower harvest index Alternative pasture species – increased below ground allocation Addition of offsite organic materials – diversion of waste streams Green manure crops – legume based for N supply

47. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Options for increasing soil carbon content Constraints Soil type – protection and storage of carbon Local environmental conditions – Dryland conditions – amount and distribution of rainfall – Irrigation – maximise water use efficiency Economic considerations – alterations to existing systems must remain profitable Social Options need to be tailored to local conditions and farm business situation

48. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Defining inputs of organic carbon to soil – dryland conditions Availability of water – amount and distribution of rainfall imposes constraints on productivity and options

49. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Evaluating potential C sequestration in soil Soil carbon sequestration situation Stable soil organic carbon (e.g. t 1/2 ³ 10 years) Attainable sequestration SOC attainable Rainfall Temperature Light Limiting factors Potential sequestration SOC potential Reactive surfaces Depth Bulk density Defining factors Actual sequestration SOC actual Soil management Plant species/crop selection Residue management Soil and nutrient losses Inefficient water and nutrient use Disrupted biology/disease Reducing factors Optimise input and reduce losses Add external sources of carbon

50. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 $$ for C sequestration – fact or fiction There is no doubt that soils could hold more carbon Challenge – increase soil C while maintaining economic viability Options Perennial vegetation Regions with summer rainfall Portions of paddocks that give negative returns Reduce stocking, rotational grazing, green manure Optimise farm management to achieve 100% of water limited potential yield External sources of carbon Under current C trading prices Difficult to justify managing for soil C on the basis of C trading alone Do it for all the other benefits enhanced soil carbon gives

51. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Climate data Crop growth Incorporation into a decision support framework MIR Analysis SOC fractionsClaySoil water limits Soil C model with N and P dynamics C sequestration in soils in response to management Soil fertility and fertiliser addition rate calculators

52. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 CO 2 Plant production Photosynthesis Death/Harvest Plant residues Mineralisation Soil animals and microbes Recalcitrant organic C (ROC) Burning Options for sequestering carbon Particulate organic C Humus organic C Increasing extent of decomposition Carbon sequestration options 1) increase C stored in plants – e.g. grow a forest 3) increase C stored in one or all soil components 2) move more carbon into the recalcitrant pool

53. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 What determines soil organic carbon content? Soil organic carbon content Inputs of organic carbon Losses of organic carbon =, f Inputs Net primary productivity Addition of waste organic materials Losses Conversion of organic C to CO 2 by decomposition

54. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Years Soil organic carbon (g C kg -1 soil) 0 5 10 15 20 25 30 0 204060 80 100 120 140 Balance between inputs and outputs Inputs > Outputs Inputs >> Outputs Inputs < Outputs Inputs << Outputs Inputs = Outputs

55. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Understanding the residue input requirements to change soil carbon content 0 10 20 30 40 50 60 70 80 90 0.911.11.21.31.41.51.61.7 Bulk density (g/cm3) Amount of carbon in the 0-10 cm layer (Mg C/ ha) 1% SOC 2% SOC 3% SOC 4% SOC 5% SOC 24 48 Amount of C required: 24 Mg C 50 Mg Dry Matter (DM) Rate per year (no losses): 10 Mg DM/y 50% allocation below ground equates to 5 Mg shoot DM/y Rate per year (with 50% loss) 20 Mg DM/y (50% loss) 50% allocation below ground 10 Mg shoot DM/y

56. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Nutrients associated with soil carbon Assumptions: C/N =10 and C/P=120)

57. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008

58. Variation in C/N ratio of different fractions of soil organic matter

59. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Minimum requirements for tracking soil organic carbon for accounting purposes 1.Collection of a representative soil sample to a minimum depth of 30 cm 2.An accurate estimate of the bulk density of the sample 3.An accurate measure of the organic carbon content of a soil sample For 0-30 cm soil with a bulk density of 1.0 Mg/m 3 and a carbon content of 1.0% = Mass of Carbon (Mg C/ha) Depth (cm) 30 Mg C/ha x Bulk density (g/cm 3 ) x Carbon content (%) =

60. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Dynamic nature of SOC and its fractions 0 8 16 24 32 1/6/986/2/9914/10/9920/6/0025/2/01 Date of sample collection Amount of organic C (Mg C ha -1 in 0-10 cm) POCHumusROCTOC Irrigated Kikuyu pasture – Waite rotation trial

61. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Dynamic nature of SOC and its fractions Date of sample collection Amount of organic C (Mg C ha -1 in 0-10 cm) 0 4 8 12 16 20 24 28 32 36 1/6/986/2/9914/10/9920/6/0025/2/01 TOCPOCHumusROC Dryland Pasture/Wheat/Wheat – Waite rotation trial

62. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 New 30 cm depth Soil bulk density (Mg/m 3 )1.11.21.31.4 Management induced compaction Correcting soil carbon for management induced changes in bulk density Original soil surface Original 30 cm depth Mass Soil 0-30 cm (Mg/ha)3300360039004200 Depth for equivalent mass (cm)30.027.525.423.6 Organic C loading (Mg/ha) 1% OC, no BD correction33363942 1% OC, with BD correction33333333

63. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Predicted equilibrium soil organic C contents for 3 regions in SA with different climate type ClareRoseworthyWaikerie Growing season rain (mm)491338170 Water limited potential grain yield (T/ha)6.24.61.8 Grain yield (T/ha) (85% WUE)5.33.91.5 Total shoot dry matter (T/ha)11.78.63.4 Equilibrium soil carbon content Modelled amount of C in 0-30 cm (t C/ha)987841 Estimated %C in 0-10 cm soil layer3.52.81.5

64. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Take home messages Organic matter (carbon + other elements) is composed of a variety of materials and improves soil productivity Different soils can hold different amounts of carbon Nature of soil minerals, depth and bulk density Balance between inputs and losses – goal is to maximise production per mm available water Measuring changes in soil carbon requires careful consideration Options to increase carbon must be tailored to the local conditions and economic considerations of the farmer Computer models exist to predict the impact of management on soil carbon

65. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Tasmanian soils project Objective: Prediction of total organic carbon Samples 154 soils collected from 0-10 cm layer of a diverse set of soil x management combinations 30 measured values used to derive the calibration All other samples predicted from this calibration Range of Walkley-black C contents 3.7 – 99.9 g C/kg soil

66. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Tasmanian soils project

67. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Functions of organic matter in soil Biological functions - energy for biological processes - reservoir of nutrients - contributes to resilience - cation exchange capacity - buffers changes in pH - complexes cations Chemical functions Physical functions - improves structural stability - influences water retention - alters soil thermal properties Functions of SOM

68. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Distribution and turnover of organic carbon in soil 0 cm 10 cm 30 cm 100 cm SOC content High Low Very low Proportion of profile SOC 30-50% 20-30% 10-30% Relative response time Rapid Intermediate to slow Slow

69. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Variation in soil organic carbon with depth for different soils 01010101230246 Grey clays Red brown earths Red earths Krasnozems Black earths 0 50 100 150 200 Soil Depth (cm) Soil organic carbon content (% by weight) 2

70. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Significance of carbon in soils Annual fluxes (10 15 g C/yr) Emissions Fossil fuel burning6 Land use change2 Responses Atmospheric increase3 Oceanic uptake2 Other3 World wide C pools (10 15 g C) Atmosphere (CO 2 ­C)780 Living Biomass (plants, animals)550 Soil 0-1 m depth1500 0-3 m depth  2300 Houghton (2005) 1330

71. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Potential for soils to sequester C 0 cm 10 cm 30 cm 100 cm Potential does exist to sequester C in soil SOC pool size: 1500 Pg Rapid cycling SOC: 500-750 Pg 1% increase in stored SOC/yr: 5 - 7.5 Pg/yr CO 2 -C emissions: 8 Pg/yr Issues Permanency of increase Native unmanaged soils Constraints on C inputs (biophysical, economic, social)

72. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Take home messages Soil organic matter provides many benefits to soil Different soils can hold different amounts of carbon Soil carbon represents the balance between additions and losses Soil carbon is composed of a variety of materials Understanding soil carbon composition allows more accurate assessment of management impacts Measuring changes in soil carbon requires careful consideration Computer models exist to predict the impact of management on soil carbon Options to improve soil carbon and productivity need to be tailored to local conditions

73. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Understanding the residue input requirements to change soil carbon content 0 10 20 30 40 50 60 70 80 90 0.911.11.21.31.41.51.61.7 Bulk density (g/cm3) Amount of carbon in the 0-10 cm layer (Mg C/ ha) 1% SOC 2% SOC 3% SOC 4% SOC 5% SOC Amount of C required: 14 Mg C 28 Mg Dry Matter (DM) Rate per year (no losses): 5.6 Mg DM/y 50% allocation below ground 2.8 Mg shoot DM/y Rate per year (with 50% loss) 11.2 Mg DM/y (50% loss) 50% allocation below ground 5.6 Mg shoot DM/y 14 28

74. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Soil organic carbon content: influence of management Defining the influence of management practices on soil organic carbon is difficult Different types of organic C respond at different rates POC - years to decades Humus – decades to centuries Charcoal – centuries to millennia Other factors may be more influential in some years than management (e.g. rainfall) Spatial variability and within year temporal variability Use of computer simulation models offers a way to estimate likely outcomes quickly example soil carbon model: RothC

75. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Changes in soil C for different climates at a constant wheat grain yield

76. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Nutrients associated with soil carbon Assumptions: C/N =10 and C/P=120)

77. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Significance of carbon in soils Annual fluxes (10 15 g C/yr) Emissions Fossil fuel burning6 Land use change2 Responses Atmospheric increase3 Oceanic uptake2 Other3 World wide C pools (10 15 g C) Atmosphere (CO 2 ­C)780 Living Biomass (plants, animals)550 Soil 0-1 m depth1500 0-3 m depth  2300 Houghton (2005) 1330

78. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Chemical function: Cation exchange capacity

79. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Questions remaining – from an organic matter perspective What is the capacity of soils to store organic matter (carbon and nutrients)? How much of the carbon and nutrients stored in soil organic matter can be made available to microbes and plants? What are the potential effects of alternative and new management options on organic matter levels? Further quantification of the role of soil organic fractions is required to extend the range of soil types and environments examined. What is the role of external sources of organic matter and do their influences persist?

80. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Significance of carbon in soils World wide C pools (10 15 g C) Soil1500 Atmosphere (CO2)720 Living Biomass (plants, animals)560 Soil in Australia30 World fluxes (10 15 g C/year) Fossil Fuel 5 Ocean Uptake 1.6 Vegetation Destruction 1.8 Atmospheric Increase 3 Missing Sink 2.2 +=++ 0.1% increase in soil organic C = 1.5

81. CSIRO. Soil carbon modelling workshop Adelaide 25-26/06/2008 Adding charcoal to soil : the Terra Preta phenomenon High soil organic carbon – significant charcoal High P contents – 200–400 mg P/kg Higher cation exchange capacity Higher pH and base saturation Terra Preta Oxisol