The benefits of using compost for mitigating climate change

Abstract

The report summarises the scientific literature reporting on research on the use of compost
and related products in mitigating climate change. Compost and related products are processed from recycled organic materials such as garden organics, food organics, crop residues, biosolids and manures. Diverting these materials from landfill reduces methane emissions. Applying the products leads to climate change benefits through carbon sequestration in soil, substitution of nitrogenous and other synthetic fertilisers and the flow-on effects of improved soil health and water holding capacity following their application.

Across Australia an estimated 3.7 million tonnes (Mt) of garden and food organics and a percentage of wood residue were diverted and recycled from landfill in 2007–08, preventing methane generation equivalent to ~ 4.28 Mt CO2-e. Methane is a potent greenhouse gas (21 to 25 times as potent as carbon dioxide) that is normally produced when organic materials break down in landfill. The drop in greenhouse gas emissions from the waste sector has largely been attributed to the rise in landfill gas capture measures (~4.5 Mt CO2-e in 2007–8); however, what goes unreported is the fact that emissions figures would be almost twice as large if the organics which are currently recycled were to be landfilled instead.
If only 50% of the 9.68 Mt (2007–8 figures) of organic residues sent to landfill was recycled, methane generation of more than 5 Mt CO2-e per annum could have been prevented. This would have brought methane generation savings through organics recycling activities to around 10 Mt CO2-e in Australia.

There are also significant opportunities for mitigating greenhouse gas (GHG) emissions through improved
agricultural management, particularly of croplands. Greenhouse gas emissions from agriculture (excluding
emissions caused by ‘Landuse, Landuse Change and Forestry’ – land clearing, soil carbon in grazing and cropland and forest management) and waste management contributed 15.2% and 2.5%, respectively, to Australia’s total GHG emissions in 2008. Of the estimated global technical agricultural mitigation potential by 2030, about 89% is from soil carbon sequestration and about 2% from mitigation of soil nitrous oxide (N2O) emissions. The soil carbon content can be raised by increasing the carbon input, decreasing the output or a combination of both.

Increases in soil carbon storage can be achieved by changes in the following areas of agricultural production,
expressed as average annual global carbon sequestration rates over a 20-year period:
􀁸 agronomy 0.29 to 0.88 t CO2-e ha-1 yr-1
􀁸 nutrient management 0.26 to 0.55 t CO2-e ha-1 yr-1
􀁸 tillage/residue management 0.15 to 0.70 t CO2-e ha-1 yr-1
􀁸 water management 1.14 t CO2-e ha-1 yr-1
􀁸 manure/biosolids use 1.54 to 2.79 t CO2-e ha-1 yr-1
􀁸 compost 1.10 to 1.80 t CO2-e ha-1 yr-1
The addition of external carbon sources (such as compost) has the highest soil carbon sequestration potential.

There are factors which limit soil carbon sequestration including nutrient supply (e.g. lack of nitrogen, phosphorus), sink saturation (optimum carbon levels reached) and reversibility (carbon sequestration is not necessarily permanent).

Although relatively small in absolute terms, nitrous oxide emissions cannot be ignored due to their high global
warming potential (nitrous oxide is 310 times more potent as a GHG than CO2), the permanency of any reductions and the potential of nitrous oxide emissions annulling carbon sequestration gains. In agriculture, nitrous oxide gas is primarily produced when there are high levels of moisture in the soils leading to anaerobic pockets and when nitrogen in excess of crop needs is applied. The primary consideration for mitigating nitrous oxide emissions from the agricultural sector is to match the supply of mineral nitrogen commensurate with the needs of crops. Nitrous oxide emissions in Australian agricultural systems were below the IPCC default (1.25% of added nitrogen) in cotton and wheat, but well above that level in high rainfall south east Queensland, and extreme in sugar cane on acid sulfate soil.

The increased input of carbon from organic soil amendments (animal manure, compost, crop residues, sewage sludge) is one of the most efficient measures for soil carbon sequestration. Organic farming systems prove this through reliance on high organic matter inputs, and on carbon and nutrient cycling to maintain soil quality and productivity. Virtually all comparative trials showed superior carbon sequestration for organic farming systems compared to conventional systems, although maintaining carbon levels on sandy soil can be difficult even for organic farms. Organic farming usually manages to reduce GHG emissions per unit land area, but not necessarily per unit of product.

It is estimated that approximately 3.2 Mt of animal manures are generated annually in Australia. Studies over a wide variety of soil textures and climates in diverse agricultural cropping systems have reported increases in soil organic matter following the addition of manure. The rate of increase in soil organic matter depends on temperature, moisture and tillage conditions, as well as the amount of manure added. For all climatic regions except for cold climates, it can be expected that between 5% and 20% of carbon applied with manure is retained and incorporated into the soil carbon pool. Composted manure retains considerably higher proportions of applied carbon in soil than does raw manure.

During the digestion of sewage sludge, much of the easily decomposable carbon is lost. The organic carbon added to soil in digested sludge is therefore more resistant to decomposition than the carbon in raw sludge. There are dramatic differences between sludges in their ability to release nitrous oxide, but there is no clear explanation of mechanisms controlling these differences.

In broad terms, there are two basic compost products:
(i) composted mulch (70% of mass >15mm, applied to soil surface)
(ii) composted soil conditioners, suitable for incorporation into the soil.
Due to a lack of data regarding the use of organic mulches, most compost information in this study relates to
compost used as a soil conditioner.

During composting, about 50% of carbon contained in the raw materials is lost as CO2, and 50% is retained, mostly in recalcitrant organic compounds. The rate and extent of mineralisation of compost products after application to soil depends on the quantity, type, maturity and particle size distribution of the applied product, as well as on soil properties, environmental conditions, and agricultural management practices. The labile organic compounds contained in compost are degraded relatively quickly, and the recalcitrant fractions remain in the soil. The consecutive use of mature garden/food organics compost for 12 years in a study has shown carbon retention rates of 45% to 50%, while the use of pasturised garden organics compost indicated about 30% carbon retention. However, the latter compost showed the highest carbon retention per dry tonne of compost applied.

No model is currently available that fully describes soil carbon dynamics following the use of compost. In the interim, a simplified compost carbon sequestration model, ‘CENTURY’, is available. The model predicts that new equilibria for soil organic carbon will not be reached before 200 and 300 years for annual compost application rates of 10 and 15 t ha-1, respectively for northern European conditions, and that soil carbon sequestration will be possible for much longer than 20 years. Using the CENTURY model, it was predicted that 117 kg C (428 kg CO2-e) is sequestered per dry tonne of applied compost over a 100-year time frame for Australian conditions, and 88 to 93 kg C (321–342 kg CO2-e) per dry tonne of applied mulch.

The IPCC framework for estimating greenhouse gas fluxes is based on a 100-year time horizon and will only
consider compost carbon as ‘sequestered’ if it remains locked in the soil for at least 100 years. It has been
suggested that 2% to 10% of carbon introduced with compost will still be in the soil after 100 years. More recent data suggest a range between 9% and 14%, depending on soil type and crop rotation.

The proportion of compost-derived carbon that becomes part of the stable soil carbon can be considered as
‘sequestered’ in the realm of the IPCC framework and for the purpose of international carbon trading. Accordingly, if Cinput (kg) is the carbon content in compost and Cbind is the fraction that is or will become ‘stable’, then the carbon sequestration, expressed as CO2 (CO2,bind, kg) can be calculated as: CO2,bind = Cinput×Cbind× 44/12. If carbon levels range between 10.0% and 28.5% (dry matter (DM)) and between 19.1 and 47.0% (DM) for garden and food organics compost respectively, and if between 2% and 14% of compost carbon are sequestered, carbon sequestration can be calculated to be in the order of 2 to 79 kg CO2-e t-1 for food organics and 3 to 73 kg CO2-e t-1 for garden organics, assuming mass losses during the composting process of 60% and 30% respectively. When compost is used regularly for four or more years, between 5% and 15% or more of nitrogen applied with compost will be utilised by crops annually, which means that between about 20% and 35% of compost-applied nitrogen will support plant growth over a three-year crop cycle. Because only a small proportion of the total nitrogen applied with compost is mineralised and used by plants, continuous compost use increases soil nitrogen levels substantially, providing significantly higher soil nitrogen supply potential.

The use of compost can supply at least some of the crop’s nitrogen, as well as most, if not all, of the phosphorous, potassium and trace elements required. Substituting the use of mineral fertiliser through compost use offers the opportunity of reducing GHG emissions generated in the manufacturing and transportation of fertilisers. If 10 t ha-1 DM of ‘typical’ garden organics compost is used continuously, resulting in 40% uptake of nitrogen and 100% of phosphorous and potassium, GHG emissions of approximately 180 kg CO2-e can be avoided.

When considering the sequestration of compost-derived carbon over both the long-term (100 years) and the
medium term (20 to 50 years) we can say carbon sequestration resulting from compost use is an important interim climate change mitigation measure, because it provides opportunities for implementing low-cost measures that are immediately available and deliver a wide range of other environmental, agronomic and societal benefits.

Studies indicate that we can assume 45% of carbon applied with compost is retained over a 20-year period, 35% over a 50-year period, and 10% over a 100-year period. Therefore the use of mature garden organics compost as agricultural soil conditioner at a rate of 10 t DM ha-1 will sequester carbon that is equivalent to reducing GHG emissions by:
􀁸 5,046 kg CO2-e over 20 years
􀁸 3,532 kg CO2-e over 50 years
􀁸 1,009 kg CO2-e over 100 years.
If GHG emission savings from fertiliser replacement are added, using 10 t DM ha-1 mature garden organics compost as agricultural soil conditioner can result in GHG emissions savings of:
􀁸 5,224 kg CO2-e within a 20-year time frame
􀁸 3,710 kg CO2-e within a 50-year time frame
􀁸 1,187 kg CO2-e within a 100-year time frame.

In summary, the literature found that using compost as an agricultural and horticultural soil amendment:
􀁸 can contribute to mitigating climate change directly and indirectly
􀁸 provides opportunities for implementing low-cost measures that are immediately available
􀁸 is one of the fastest means of improving soil carbon levels
􀁸 is ideally suited as a mitigation measure in productive agricultural soils
􀁸 fits easily into the Australian National Carbon Accounting System
􀁸 can attract carbon credits
􀁸 delivers many agronomic benefits and enhances long-term agricultural productivity and production
􀁸 offers environmental and societal benefits.

Full text

The bene ts of using compost
for mitigating climate change

Author:
Johannes Biala
The Organic Force
PO Box 74 Wynnum QLD 4178
Ph: (07) 3901 1152
Fax: (07) 3396 2511
Email: biala@optusnet.com.au
Please note:
The Organic Force, in its provision of advice, acts in good faith and takes all reasonable steps to ensure that the advice o ered is correct and
applicable to the individual circumstances being advised. However in dealing with the O ce of Environment and Heritage or any other
state or federal jurisdiction, it is suggested that the relevant department is contacted by the reader to clarify any points of law or procedure
relating to the individual situation and written answers are obtained to all queries.
Most data related to the use of organic soil amendments such as manure, biosolids and compost is sourced from Europe and North America,
and therefore does not necessarily re ect soil and environmental conditions that might be encountered in Australia. In most cases the
terminology used by authors of reviewed papers and reports has been adopted, thus terms such as ‘sewage sludge’ and ‘biosolids’, or ‘soil
carbon’ and ‘soil organic matter’ are used in parallel.
Disclaimer:
O ce of Environment and Heritage (OEH) has made all reasonable e orts to ensure that the contents of this document are factual and free
of error. However the State of NSW and the O ce of Environment and Heritage shall not be liable for any damage or loss which may occur
in relation to any person taking action or not on the basis of this document.
Published on behalf of the author by:
O ce of Environment and Heritage, Department of Premier and Cabinet
59–61 Goulburn Street
PO Box A290
Sydney South 1232
Ph: (02) 9995 5000 (switchboard)
Ph: 131 555 (environment information and publications requests)
Ph: 1300 361 967 (national parks information and publications requests)
Fax: (02) 9995 5999
TTY: (02) 9211 4723
Email: sustainability@environment.nsw.gov.au
Website: www.environment.nsw.gov.au
OEH 2011/0385
ISBN 978 1 742232 964 2
Published December 2011

The benefits of using compost for mitigating climate change
Office of Environment and Heritage NSW
III
PREFACE
The Office of Environment and Heritage (OEH) commissioned The Organic Force to provide an annotated list of research
from Australia and overseas, in which compost’s contribution to maintaining or improving soil carbon levels and reducing
nitrous oxide (N2O) emissions was investigated. Diverting organic material from landfills saves methane generation,
methane being a potent greenhouse gas. Using composted products, processed from recycled organics, results in a range of
important environmental benefits. These environmental benefits include improved soil health, water savings, improved crop
productivity, reduced need for synthetic fertiliser and biocidal products, reduced water and wind erosion, improved tilth
and, as this literature review demonstrates, enhanced capacity to mitigate climate change by sequestering carbon in soils,
reducing nitrous oxide emissions and reducing agricultural energy use.
This literature review establishes a scientific context by examining:
 the science of soil carbon and nitrogen cycles, and their relationship to climate change
 the fundamental processes associated with carbon sequestration and N2O emissions
 knowledge about climate change benefits achievable by alternative measures (and associated risks and costs)
 the possibilities for indirect climate change benefits by improving soil properties through compost use to conditions
that reduce negative climate change impacts
 the potential and limits of using compost for mitigating climate change.
The benefits of using compost for mitigating climate change need to be recognised by inclusion in Australia’s National
Carbon Accounting System. This can only be achieved if the role of compost in systems is understood, and protocols can be
created for including compost use in future Australian carbon emission inventories.
This report took a broad approach to OEH’s brief by looking at the effects of using compost on soil carbon stocks and N2O
emissions as well as providing background scientific information and context for the Government’s carbon accounting
system.
This broad approach was deemed necessary to ensure that:
 Sufficient information was collated to directly and indirectly link the benefits of using compost to mitigating climate
change and facilitate well-informed technical and policy decisions
 the organics recycling industry obtain sufficient information that directly and indirectly links to the benefits of using
compost for mitigating climate change and enables informed discussion and presentation of these facts in the
scientific, policy and public arena
 this report has tangible outcomes in both a technical and policy sense and ultimately establishes the climate change
benefits of using recycled organic products to help mitigate climate change whilst improving Australia’s farming
systems.
Note:
In Australia, the application to land of waste derived materials including biosolids and paper mill sludge, is subject to
consent of the relevant state or federal authority. For example, in New South Wales, waste is regulated under the Protection
of the Environment Operations (Waste) Regulation 2005. The Government encourages the recovery of resources from
waste where this is beneficial and does not harm the environment or human health. A provision for resource recovery
exemptions within the legislation enables the reuse of waste or waste derived materials as fill or fertiliser (land
applications) that may otherwise go to landfill.

The benefits of using compost for mitigating climate change
Office of Environment and Heritage NSW
IV
TABLE OF CONTENTS
Preface...............................................................................................................................................................................................................III
Table of contents.............................................................................................................................................................................................IV
List of figures..................................................................................................................................................................................................VII
List of tables..................................................................................................................................................................................................... IX
Abbreviations...................................................................................................................................................................................................XI
Executive summary.......................................................................................................................................................................................XIV
1 Introduction...............................................................................................................................................................................................1
2 Australia’s greenhouse gas emissions...................................................................................................................................................2
2.1 EMISSIONS FROM WASTE AND WASTEWATER ......................................................................................................................................3
2.2 EMISSIONS FROM AGRICULTURE........................................................................................................................................................4
2.2.1 Manure management............................................................................................................................................................5
2.2.2 Agricultural soils....................................................................................................................................................................6
2.2.2.1 Nitrous oxide......................................................................................................................................................................6
2.2.2.1.1 Synthetic fertiliser...........................................................................................................................................................6
2.2.2.1.2 Animal wastes applied to soils .......................................................................................................................................8
2.2.2.1.3 Nitrogen fixing crops and crop residues.........................................................................................................................9
2.2.2.1.4 Animal production ..........................................................................................................................................................9
2.3 CO2 EMISSIONS FROM LAND USE AND LAND USE CHANGE ....................................................................................................................9
2.3.1 Emissions from cropland remaining cropland.....................................................................................................................10
2.3.2 CO2 emissions from agricultural lime application ...............................................................................................................10
2.3.3 Discourse: models and data used for estimating CO2 emissions.......................................................................................10
2.3.3.1 National Carbon Accounting System...............................................................................................................................10
2.3.3.1.1 Carbon accounting methodology .................................................................................................................................11
2.3.3.2 Models used for estimating emissions from LULUCF......................................................................................................12
2.3.3.2.1 Sub-model development..............................................................................................................................................14
2.3.3.2.2 Sub-model integration..................................................................................................................................................15
2.3.3.3 Estimating changes in soil carbon...................................................................................................................................15
2.3.3.3.1 Soil mapping and inventory..........................................................................................................................................16
2.3.3.3.2 Roth-C soil carbon model calibration and validation....................................................................................................18
2.3.3.3.3 Data sources................................................................................................................................................................21
2.3.3.3.4 Emissions from forest conversion to croplands and grasslands ..................................................................................23
3 Soil carbon and climate change............................................................................................................................................................27
3.1 EFFECTS OF LAND USE CHANGE ON SOIL CARBON.............................................................................................................................29
4 Nitrogen and climate change.................................................................................................................................................................33
4.1 FACTORS CONTROLLING N2O PRODUCTION IN SOIL...........................................................................................................................36
4.1.1 Moisture and aeration.........................................................................................................................................................36
4.1.2 Temperature.......................................................................................................................................................................37
4.1.3 Soluble and readily decomposable carbon.........................................................................................................................38
4.1.4 Soil and fertiliser nitrogen...................................................................................................................................................38
4.1.5 Soil pH and salinity.............................................................................................................................................................39
4.1.6 Limitation of nutrients other than nitrogen ..........................................................................................................................39

The benefits of using compost for mitigating climate change
Office of Environment and Heritage NSW
V
5 Potential for mitigation in agriculture...................................................................................................................................................40
5.1 AVAILABLE MITIGATION MEASURES...................................................................................................................................................40
5.2 MITIGATION POTENTIAL ...................................................................................................................................................................42
5.2.1 Technical mitigation potential .............................................................................................................................................42
5.2.2 Economic mitigation potential.............................................................................................................................................44
5.3 CARBON SEQUESTRATION...............................................................................................................................................................45
5.3.1 Soil organic carbon pools ...................................................................................................................................................45
5.3.2 Effects of agricultural management practices.....................................................................................................................48
5.3.2.1 Australian data.................................................................................................................................................................51
5.3.3 Limits to carbon sequestration............................................................................................................................................52
5.3.3.1 Nutrient supply and humification .....................................................................................................................................52
5.3.3.2 Sink saturation.................................................................................................................................................................53
5.3.3.3 Non-permanence (reversibility) .......................................................................................................................................55
5.3.3.4 Availability of land and resources....................................................................................................................................56
5.4 REDUCTION OF NITROUS OXIDE EMISSIONS ......................................................................................................................................56
5.4.1 No- and reduced tillage.......................................................................................................................................................58
5.4.2 Fertiliser use.......................................................................................................................................................................59
5.4.3 Crops..................................................................................................................................................................................59
5.4.4 Australian data....................................................................................................................................................................60
5.5 OUTLOOK ......................................................................................................................................................................................62
6 Organic soil amendments......................................................................................................................................................................62
6.1 POTENTIALLY AVAILABLE ORGANIC RESOURCES................................................................................................................................63
6.2 ORGANIC FARMING SYSTEMS ..........................................................................................................................................................65
6.2.1 Carbon sequestration .........................................................................................................................................................65
6.2.2 N2O emissions....................................................................................................................................................................73
6.2.3 Multilevel assessment of using soil amendments...............................................................................................................74
6.3 MANURE........................................................................................................................................................................................75
6.3.1 Decomposition of Manure...................................................................................................................................................76
6.3.2 Soil carbon..........................................................................................................................................................................76
6.3.2.1 Increase in soil organic matter.........................................................................................................................................76
6.3.2.2 Long-term field trials........................................................................................................................................................77
6.3.2.2.1 The Broadbalk long-term experiment...........................................................................................................................78
6.3.2.2.2 The static fertilisation experiment Bad Lauchstädt.......................................................................................................79
6.3.2.2.3 The Nutrient Depletion Experiment Thyrow.................................................................................................................81
6.3.2.3 Carbon sequestration ......................................................................................................................................................82
6.3.2.3.1 Use of manure in Europe and UK................................................................................................................................84
6.3.2.3.2 Manure, nitrogen and humus.......................................................................................................................................86
6.3.2.3.3 Differences between manure types and organic amendments....................................................................................86
6.3.2.3.4 Combined use of manure and nitrogen fertiliser ..........................................................................................................87
6.3.2.3.5 Economic aspects........................................................................................................................................................88
6.3.3 Composting of manure to enhance soil carbon sequestration............................................................................................88
6.3.4 Methane and N2O emissions..............................................................................................................................................90
6.4 BIOSLIDS AND PAPER MILL SLUDGE ..................................................................................................................................................92
6.4.1 Biosolids.............................................................................................................................................................................92
6.4.1.1 N2O emissions.................................................................................................................................................................93
6.4.2 Paper mill sludge ................................................................................................................................................................93
6.5 USE OF ORGANIC AMENDMENTS AS MULCH.......................................................................................................................................94

The benefits of using compost for mitigating climate change
Office of Environment and Heritage NSW
VI
6.6 COMPOST......................................................................................................................................................................................96
6.6.1 Formation of humic substances during composting ...........................................................................................................97
6.6.2 Variability of compost products...........................................................................................................................................99
6.6.3 Fate of compost carbon after soil application ...................................................................................................................101
6.6.3.1 Degradation of carbon...................................................................................................................................................101
6.6.3.2 Storage and sequestration of carbon ............................................................................................................................105
6.6.3.2.1 Results from Europe ..................................................................................................................................................106
6.6.3.2.2 Results from North and South America......................................................................................................................114
6.6.3.2.3 Results from Australia................................................................................................................................................116
6.6.3.2.4 Simplified models for compost carbon sequestration.................................................................................................117
6.6.3.2.5 Compost carbon sequestration within the IPCCs 100-year time frame .....................................................................119
6.6.3.3 Replacement of peat .....................................................................................................................................................122
6.6.3.4 A brief, critical look at alternatives.................................................................................................................................122
6.6.4 Mineralisation and use of nitrogen....................................................................................................................................124
6.6.4.1 Nitrogen mineralisation..................................................................................................................................................125
6.6.4.1.1 Nitrogen immobilisation..............................................................................................................................................128
6.6.4.2 Nitrogen use efficiency ..................................................................................................................................................129
6.6.4.3 Effects of compost quality and application on nitrogen release.....................................................................................139
6.6.4.4 The risk of nitrate leaching from compost use...............................................................................................................139
6.6.5 GHG emission savings through fertiliser replacement......................................................................................................142
6.6.6 Gaseous emissions following compost use......................................................................................................................146
6.6.7 Other benefits...................................................................................................................................................................150
6.6.8 Combined effects of using compost on climate change mitigation...................................................................................151
6.6.8.1 Carbon sequestration ....................................................................................................................................................151
6.6.8.2 GHG emission savings by replacing mineral fertiliser use ............................................................................................152
6.6.8.3 Combined benefits of using compost for mitigating climate change..............................................................................152
6.6.8.4 Concluding remarks.......................................................................................................................................................155
7 Conclusions and recommendations for further work .......................................................................................................................159
8 References.............................................................................................................................................................................................163

The benefits of using compost for mitigating climate change
Office of Environment and Heritage NSW
VII
LIST OF FIGURES
Figure 1 Global greenhouse gas gmissions by source 2004 (Source: IPCC: Rogner et al. 2007)................................2
Figure 2 Australian greenhouse gas emissions by source, excluding land use, land use change and forestry, 2007
(Drawn from data in Dept of Climate Change 2009b)....................................................................................3
Figure 3 The FullCAM model pool structure for agricultural systems (Source: Dept of Climate Change 2009b).....13
Figure 4 Structure of the Roth-C soil carbon model as implemented in FullCAM (Source: Dept of Climate Change
2009b) ...........................................................................................................................................................15
Figure 5 The NCAS soils program (Source: Dept of Climate Change 2009b)............................................................16
Figure 6 Pre-disturbance soil carbon (Source: Dept of Climate Change 2009b).......................................................17
Figure 7 Soil clay content (Source: Dept of Climate Change 2009b)..........................................................................17
Figure 8 Examples of changes in soil carbon (

measured and

modelled) under continuous cropping and crop-
pasture rotations (Source: Dept of Climate Change 2009b).........................................................................20
Figure 9 Overview of the crop growth and plant parameters program (Source: Dept of Climate Change 2009b) ....24
Figure 10 Carbon cycle in an agricultural system (losses are indicated by dark borders) (Source: Magdoff and van Es
2000) .............................................................................................................................................................27
Figure 11 Global terrestrial carbon cycle (Source: IPCC: Watson et al. 2000)...........................................................28
Figure 12 Global carbon pools (Source: Lal 2008).......................................................................................................29
Figure 13 Comparison of models and data from North America on changes in soil carbon after deforestation (Source:
Woodbury 2006)............................................................................................................................................31
Figure 14 Long-term decline in organic carbon in top layer (0–0.1 m) of three soils in southern Queensland (Source:
Dalal 2001) ...................................................................................................................................................32
Figure 15 Nitrogen cycle in an agricultural system [losses are indicated by dark borders] (Source: Magdoff and van
Es 2000) ........................................................................................................................................................33
Figure 16 Generalised relationship between water-filled pore space (WFPS) of soils and the relative fluxes of N2O
and N2 (Source: Dalal et al. 2003)................................................................................................................37
Figure 17 Global technical mitigation potential by 2030 of each agricultural management practice on each GHG
(Source: IPCC: Smith et al. 2007) ................................................................................................................42
Figure 18 Constraints and potential for carbon sequestration in soil (Source: Baldock 2008)....................................43
Figure 19 Economic potential for global GHG agricultural mitigation by 2030 at various carbon prices (Source:
IPCC: Smith et al. 2007)...............................................................................................................................44
Figure 20 Response of soil organic carbon pools to changes in land use (Source: modified from Baldock 2008).......47
Figure 21 Dynamic interactions between carbon pools in the SOMA model (Source: Rothamsted Research).............47
Figure 22 Nitrogen and phosphorous content in humus and requirements for increasing organic carbon content by
two percent (Source: Baldock 2008).............................................................................................................53
Figure 23 Relationship between clay content and ‘optimum’ SOC content (0–30 cm) in long-term experimental sites
in Germany (Source: Körschens 2006).........................................................................................................54
Figure 24 Tendency of soil organic carbon levels toward new equilibrium after land use or management change
(Source: modified from Baldock 2008) .........................................................................................................55
Figure 25 Requirement of carbon addition for maintaining carbon levels in cropped and native soils with varying clay
content (Source: Dalal et al. 2009)...............................................................................................................56
Figure 26 Fluctuation of organic carbon levels in the topsoil (0–25 cm) of the Müncheberg Nutrient Trial over 40
years (Source: Barkusky 2009) .....................................................................................................................78
Figure 27 Mean yields of wheat at Broadbalk long-term experiment in response to use of manure, mineral fertiliser or
no fertiliser (Source: Rothamsted Research 2006)........................................................................................79
Figure 28 Soil organic carbon levels in Broadbalk continuous wheat experiment [solid lines: modelled with RothC]
(Source: Bhogal et al. 2007) .........................................................................................................................79
Figure 29 Development of soil organic carbon levels in the main treatments of the static fertilisation experiment Bad
Lauchstädt (Source: Körschens 2009) ..........................................................................................................80
Figure 30 Development of soil organic carbon levels in the static fertilisation experiment, Bad Luchstädt, after
reversing high and no-input treatments (Source: Körschens 2009)..............................................................81
Figure 31 Soil organic carbon and nitrogen levels in the main treatments of the static fertilisation experiment, Bad
Luchstädt [0–30 cm, average of all crops 1989–1992] (re-drawn from Körschens 2003)...........................81
Figure 32 Development of soil organic carbon levels in manured and unmanured treatments of the nutrient depletion
trial in Thyrow over a 40-year period (Source: Ellmer, 2008).....................................................................82
Figure 33 Effect of manure use on soil organic carbon levels and percentage manure carbon sequestered in five
European long-term (> 50 yrs) field experiments (re-drawn from Körschens 2006)....................................85
Figure 34 Soil organic carbon levels without and with optimum fertilisation in ten long-term field experiments in
Germany (Source: Körschens 2009).............................................................................................................85

The benefits of using compost for mitigating climate change
Office of Environment and Heritage NSW
VIII
Figure 35 Long-term effect of organic soil amendments on SOC of un-cropped heavy clay in Holland (Source: Zwart
2003) .............................................................................................................................................................89
Figure 36 Changes in dry matter ash free mass of different mulch materials during 12 months in a warm semi-arid
environment (Source: Drawn from Data in Valenzuela-Solano and Crohn 2006) .......................................95
Figure 37 Changes in the organic matter content of humic acid and the fulvic fraction during the composting of
separated cattle manure (Source: Inbar et al. 1990*) ..................................................................................98
Figure 38 Biochemical characterisation of 29 garden organics composts from France (Source: Metzger 2003)......100
Figure 39 Cumulative decomposition of composted (filled symbols) and uncomposted (open symbols) organic
amendments in soil from Washington (WA) and Oregon (OR) (Source: Gale et al. 2006).........................102
Figure 40 Cumulative CO2 emissions from compost (lemon tree prunings + yeast) in soil at different compost ages [0,
4, 7, 9, 13 and 25 weeks] (Source: Garcia-Gomez et al. 2003) ..................................................................102
Figure 41 Cumulative CO2 emissions from fresh and mature biowaste compost in sand during 112 Days at various
temperatures (Source: Chodak et al. 2001).................................................................................................105
Figure 42 Effect of compost use on soil organic matter levels relative to control [average of five field sites in Norfolk,
UK] (Source: Davison 2008).......................................................................................................................108
Figure 43 Effect of annual compost use (9 and 12 Years) on soil organic matter levels [average of five field sites in
Germany] (Source: Haber et al. 2008) .......................................................................................................110
Figure 44 Correlation between organic matter added in compost over 9 and 12 years, and organic matter in soil
[average of five field sites in Germany] (Source: Haber et al. 2008).........................................................110
Figure 45 Long-term effect of organic soil amendments on soil organic matter levels in heavy fluviatile clay in
Holland (Source: De Haan and Lubbers, 1984, cited in Zwart 2003)........................................................112
Figure 46 Soil carbon retention following compost use (5 x 30 m3 ha-1) in vegetable production in sandy soil (Source:
Paulin et al. 2005).......................................................................................................................................116
Figure 47 A simplified carbon sequestration model for compost use (Source: Favoino and Hogg 2008)..................118
Figure 48 Accumulation of soil organic carbon following annual application of one tonne Carbon per hectare in
compost with an assumed turnover time of 10, 27 or 40 years (Source: Smith et al. 2001)........................121
Figure 49 Cumulative release of NO3-N from fresh (left) and mature (right) biowaste compost at various temperatures
(Source: Chodak et al. 2001) ......................................................................................................................127
Figure 50 Development of nitrogen use efficiency at different compost and mineral nitrogen application rates during
four cropping cycles [average of all trials at five sites, except for fourth rotation at three Sites] (Source:
Haber et al. 2008) .......................................................................................................................................133
Figure 51 Comparison of compost nitrogen use efficiency between crop rotation with high (corn for silage) and low
(corn for grain) Nitrogen demand [average of 2nd–4th Rotation] (Source: Haber et al. 2008)...................134
Figure 52 Nitrogen use efficiency of biowaste compost applied in autumn 2005 during the following three wheat
crops at three UK sites (Source: Bhogal and Chambers 2009) ..................................................................135
Figure 53 Increase in soil nitrogen (0–30 cm) after application of 5x30 m3 of garden organics –chicken manure
compost on sandy soil, compared to nitrogen added in compost (Source: Paulin et al. 2009)...................136
Figure 54 Potential accumulation of soil nitrogen following long- term annual compost application at 8 t DM ha-1
(top) and associated increasing nitrogen mineralisation potential (bottom) (Source: Amlinger et al. 2003b)
138
Figure 55 Estimated humus production capacity (kg C t-1 FM) of various organic soil amendments (Source:Siebert
and Kehres 2008)...................................................................................................................