Organic carbon in soils - Meeting climate change and food security challenges - knowledge and action - ADEME
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Organic carbon
in soils
Meeting climate change
and food security challenges
Local authorities and farming sector
knowledge and action
Editorial
Soil carbon: what
are the issues
for climate and GIS Sol
agriculture? in brief
Jérôme Mousset Created in 2001, GIS Sol
Head of the agricultural (sol being the French
and forestry service, ADEME word for soil) is a French
T.P.
scientific network focused
Soil is the living base for agricultural and forestry on soils. The network
includes the French
production and a limited resource which cannot be
National Institute for
renewed at the human scale. Increasingly, land is in
Agricultural Research
demand and there is tension between different land (INRA), the French
uses. Changes in production practices, ploughing Environment and Energy
up of grassland, loss of arable and wooded land for Management Agency
urbanisation, increased use of biomass...There are (ADEME), the Ministry
of Agriculture, Food and
so many changes which, if not taken into account,
Forests, the Ministry
could affect soil quality and lower soil carbon stocks. of Ecology, Sustainable
Nevertheless, soil is a considerable asset in strategies Development and Energy,
for mitigating climate change. But this issue lacks the Institute of Research
visibility and, in order to raise awareness among for Development (IRD)
and the National Institute
territorial administrators, decision makers, farmers
for Geographical and
and foresters, ADEME has enlisted the help of experts, Forestry Information
scientists, advisers and representatives of public (IGN).
authorities to produce this brochure. GIS Sol is seeking to
This brochure aims to clarify the role of soil in mitigating create and manage an
information system on
the greenhouse effect and, furthermore, to highlight
French soils, including
the environmental benefits of better management
data about their spatial
of organic matter. A healthy, living, well-balanced soil distribution, their
containing organic matter can increase production characteristics and
potential, contribute to optimising the use of agricultural changes in their quality. It
works in the knowledge
inputs, filter water from these pollutants and increase
that soil is a limited and
biodiversity. This idea of environmental and economic
non-renewable resource
services chimes exactly with the principles of at the human scale.
agroecology.
2l Soil and carbon
Contents
Issues Points of view
04. oil, a carbon pool essential for the
S 20. Reconstructing carbon stocks
climate Many benefits to highlight
06.
Continuously providing soil with Evaluation
organic matter
22. Measuring changes
08. Organic matter: providing at the field scale
environmental services 24. Measurement tools
Points of view at the territorial scale
10. Carbon storage in soils: Perspectives
rising awareness 26. Improving and sharing
references
Impacts and levers for action
27. An international dynamic
12. Changes in land use: the need to combine food security and climate
to preserve carbon-rich soils change mitigation
14. F orest soils: rationalising the Research
increase in harvested wood
28. ADEME supports research
16. Agricultural soils: acting on organic for better agricultural and
matter inputs and losses environmental management
18. Agricultural practices of soil organic matter
according to their cost 30. Soil organic carbon matters
and efficacy in the European Union
This document has been edited Communication service: Brochure Ref.8575 to download on
by ADEME Sylvie Cogneau www.ADEME.fr/mediatheque
Technical coordination: Writting and design: Terre-Écos ADEME
For ADEME Cover picture: Vivescia 20, avenue du Grésillé -
Agricultural and Illustrations : Gana Castagnon BP 90406 49004 Angers
forestry service: Printed by: Cedex 01
Thomas Eglin, agronomy and Pure impression certificated PEFC, Registration of copyright:
environmental engineer Iso 14001, Imprim’vert, Print ©ADEME Editions, November 2015
environnement ISBN : 979-10-297-0209-9
Any complete or partial representation or reproduction made without the consent of the author or his legal successors is illicit, according to the Code of intellectual property (Art L 122-4) and
constitutes an imitation repressed by the penal code. The only authorisations are (Art L 122-5) copies or reproductions strictly reserved for private use of the copyist, and not intended for a collective
use, as well as analyses and short quotations justified by the critical, educational or informational character of the work into which it is incorporated, only if, however, the articles L 122-10 and L
122-12, relative to the reproduction by reprography, of the same code, are respected.
Soil and carbon l3
Issues
Soils, a carbon pool essential
for the climate
In the form of organic matter, soils store two to three times more carbon than the
atmosphere. Therefore their use creates fluxes in CO2 and has consequences on
climate change. Today, the challenge is to limit carbon losses linked to changes
in land use and to increase carbon stocks by promoting suitable agricultural and
forestry practices.
C
arbon dioxide (CO2) is equivalent of two to four years’
the main greenhouse carbon emissions. In France, 3 4 per 1,000
gas (GHG) linked to to 4 billion tonnes of carbon are A ‘4 per 1,000’ annual
human activities. At stored in the first 30cm of soil, increase of organic matter
in soil would be enough to
the global scale, nearly 35 billion which is three times more carbon
compensate for the global
tonnes of CO2 were emitted in than is present in forestry woods. emissions of greenhouse
2013 through the consumption The levels of carbon stocks are gases (see page 27)
of fossil fuels such as oil, gas highly variable, depending on land
and coal, and through cement use, soil type and climate. The storage, integrating changes in
production. Terrestrial ecosys- trend shows a general reduction in soil carbon stocks, has become
tems mitigate these emissions organic matter in agricultural soils, compulsory for European Union
by capturing more than a third though there are large regional Member States. From 2013, this
through photosynthesis. and territorial differences. has included variations linked to
The evolution of carbon stocks forestry practices and, from 2021,
PRESERVING STOCKS in French soils remains very will include those linked to the
OF ORGANIC MATTER uncertain because of the many management of cropland and
Organic matter in the soil is the mechanisms involved and the pastures. This decision is evidence
largest reservoir of organic carbon, difficulty of measuring them: of the first step towards the future
even greater than plant biomass. the extension of forest areas, integration of land use issues in
Worldwide, the first metre of soil development of urban areas, European Union commitments to
contains between 1,500 and conversion of grassland into reducing GHG emissions. Within
2,400 billion tonnes of organic cultivated areas and changes carbon markets, voluntary carbon
carbon. Losses of these soils and in agricultural practices. And to offsetting schemes represent a
the organic matter they contain this we can add climate change, way of valuing carbon storage
throws into question their role a phenomenon which encourages in soils. Currently, at the inter-
as a carbon sink and increases plant production and boosts the national scale, the number of
emissions. A reduction of only 5% degradation of organic matter. such initiatives and reductions in
in carbon stocks represents the GHG emissions are very limited
TAKING CARBON because of the diverse nature of
FLUXES INTO ACCOUNT emissions and uncertainties over
3 to 4 billion tonnes With the adoption of decision storage levels. More reliable and
of carbon are stored in the 529/2013/EU in 2013, keeping cheaper evaluation methods are
first 30cm of French soils
accounts of GHG emissions and needed.
4l Soil et carbon
Dessin A
Carbon stocks and fluxes at the global scale
+ Atmosphere
4 829
+
7.8
+ - -
1.1 2.6 2.3
Vegetation
Average fluxes Fossil
G. Castagnon
XX 350 to 550 Ocean
for 2000 - 2009, carbon
in billion tonnes 1001 to 1940
Soils 40 000
per year 1500 to 2400
XX Stocks for 2011,
estimated in Fossil carbon • Emissions linked to land use change Carbon dissolution in the
billion tonnes
emissions and deforestation sea and carbon fixation by
• Carbon assimilation by plants and soils marine organisms
source IPCC 2013
The atmosphere contains 829 billion tonnes of carbon, among which 240 result from human activities, starting from
the year 1750. The most important annual flux is linked to industrial and urban areas with 7.8 billion tonnes, to which
is added the flux linked to land use change and deforestation, up to 1.1 billion tonnes. These emissions are partially
compensated by carbon assimilation through photosynthesis, as well as carbon dissolution in the oceans (2.6 and
2.3 billion tonnes respectively). Some 4 billion tonnes of carbon are added in the atmosphere every year.
Dessin C
Dessin C
Variations in organic carbon stocks depending on land use in France
Urban areas Vineyards Orchards and Grasslands Forest
Urban areas Vineyards Orchards and
farmlands Grasslands Forest
farmlands
35 tC/ha
˜˜
Variable 50 tC/ha
˜˜
35 tC/ha 80 tC/ha 80 tC/ha
˜˜ ˜
Variable
G. Castagnon
50 tC/ha 80 tC/ha 80 tC/ha
˜
source GIS sol
XX Estimate of carbon stored within the 30 first centimetres of soil
XX Estimate of carbon stored within the 30 first centimetres of soil
Organic matter stocks in forests, grasslands and low vegetation growing in highlands are large, whereas stocks
are quite low in vineyards, farmlands and Mediterranean zones. Quantifying stocks is difficult in urban areas;
nevertheless, a significant amount of carbon could be stored under green spaces. Carbon stored in forest litter is not
taken into account.
Soil and carbon l5
Issues
Continuously providing soil
with organic matter
Soil organic matter can be defined as ‘everything that is alive or was alive in the
ground’. Organic matter undergoes a degradation which leads to mineralisation.
Carbon contained in organic matter is largely released into the atmosphere
in the form of a gas. So, in order to maintain carbon stocks, there must be
compensation for these losses. Here we explain further...
O
rganic matter enters released into the atmosphere*. and tropical forests, the storage
the soil in a ‘fresh’ To a lesser extent, losses of of organic matter in the soil
form: plants (fallen organic matter are also due to happens with the same rapidity
leaves, crop resi- leaching of dissolved organic as its degradation. In agro-
dues, root exudates etc.), micro- matter, water and wind erosion, ecosystems this balance can
organisms or dead animals. A and fire. be disturbed by many factors,
large part is quickly decomposed: which can favour the accumu-
in a few months, organic matter THE INFLUENCE OF lation of organic material or, on
is mineralised by decomposers CLIMATE AND SOIL the contrary, its mineralisation.
such as fungi and bacteria, CHARACTERISTICS Rainfall and temperature play a
and transformed into carbon In the soils of some large ecosys- major role. For example, low or
dioxide (CO2) which is quickly tems, such as African savannas high humidity levels can hinder
Dessin
How isBorganic matter formed and degraded?
Organic matter inputs Organic matter losses
Agricultural Ploughing Water Fire
spreading and harvest erosion
Crop residues, CO2
CH4
plant covers
Endogenous Exogenous
inputs
G. Castagnon
inputs Microbial
OM OM
Root inputs OM activity
Leaching
Apart from root inputs, the major source of organic matter inputs is from the surface. On the other hand,
organic matter degradation is mainly an underground mechanism, ensured via microbial activity. Possibilities
for action can involve both increasing inputs and reducing losses.
6l Soil et carbon
A.D.
Roots contribute a lot to carbon storage in soil
the activity of decomposers in
soils which naturally accumulate
more organic matter than others.
Expert opinion
Conversely, a 10°C increase Éric Blanchart
in temperature can double Research director
or even triple microbiological French Institute of
activity. Climate change, which Research for Development
currently stimulates plant pro-
ductivity (temperature and CO2
Structure and nature of soils influence organic
concentration in the atmosphere) matter stability
and mineralisation of organic “While the major share of organic matter is quickly mineralised,
matter, has an impact on car- a more modest quantity can undergo three mechanisms which
bon storage which is difficult to can help it stabilise and resist mineralisation. First possibility,
assess. Finally, the physical and a chemical transformation: some microbes can transform
chemical characteristics of soil organic matter into complex carbon molecules, difficult to
degrade chemically. The second option consists in integrating
reduce mineralisation through
organic matter in aggregates, in order to create a physical
their ability to ‘protect’ organic barrier against microorganisms’ action. Third possibility: if soils
matter (see box). are rich in clays and carbonates, these elements can react with
organic matter, creating a physico-chemical protection against
FARMERS: MANAGERS mineralisation. Finally, even if organic matter can be protected
OF ORGANIC MATTER and remain stable for a long time – up to several thousand
When harvesting, farmers remove years – it always ends up mineralised .”
large amounts of plant mate-
rial. This means the quantity
of organic matter returned to fore, mineralisation. Given the matter and adapting losses to
the soil is limited. Furthermore, important role of organic matter a minimum.
practices such as ploughing and its positive influence on *Some organisms (autotrophic, anaerobic) can
consume CO2 before it is released in the atmosphere.
aerate the soil and encourage the environment, the idea is to However, they are very few of them and so this
microbial activity and, there- maintain high inputs of organic mechanism is considered as minor.
Soil and carbon l7
Issues
Organic matter: providing
environmental services
Organic matter in soils is essential for the proper functioning and
sustainability of agricultural and forest ecosystems. Organic matter ensures
soil stability, carbon storage, water quality, biodiversity etc. Some of these
services depend on the quantity of organic matter contained in the soil
while others depend on the mineralisation of organic matter.
O
rg a nic m at te r
provides multiple Bio-indicators to evaluate organic matter dynamics
environmental ser-
Bacteria and fungi degrade organic matter, nematodes
vices. First of all,
regulate microorganism populations and earthworms
organic matter is a food source structure soils...The ADEME ‘Soil quality bio-indicators’
for organisms living in the soil, programme aims to provide a better understanding of the role
microorganisms and fauna. A of soil-living organisms, in order to supply public and private
soil with a high organic matter stakeholders with tools for monitoring and characterising
content encourages the pres- soil quality. The monitoring of many variables linked to soil
ence of these animals and plants, ecosystems, in different agro-climatic conditions, has made
it possible to evaluate the impact of managing soil organic
which are both numerous and
matter on biodiversity. The abundance of fungi and microbial
varied, and therefore enhances groups and the diversity of nematodes have been identified
biodiversity. as early indicators of changes in a soil’s organic quality.
MINERALISATION,
POSITIVE FOR PLANT ... THOUGH effect. Nitrate and phosphate
NUTRITION... COMPENSATION IS ions released represent profi-
Organisms living in the soil feed NEEDED TO MAINTAIN table nutrients for plants but,
on organic matter, and hence CARBON STOCKS AND if not assimilated, they can be
contribute to its decomposition LIMIT CONTAMINANT transferred to water flows. Mine-
and mineralisation. Yet, organic TRANSFERS ralisation can also free organic
matter acts as a sponge in the The mineralisation of organic and metallic contaminants which
soil: it adsorbs and contains matter has other effects. First of were trapped in organic matter.
various elements which are all, it produces simple molecules Therefore it is important that
released once mineralised. In such as greenhouse gases stocks of organic matter are pro-
agricultural and forest ecosys- (CO2, N 2O or CH4, depending gressively replenished, through
tems, plants benefit from the on the degradation conditions), plants or exogenous inputs which
cations and mineral elements which are mainly released into comply with regulations. If these
released as they contribute to the atmosphere* and therefore stocks are maintained, the ser-
their nutrition. contribute to the greenhouse vices provided by mineralisation
8l Soil et carbon
Expert
opinion
Claire Chenu
Teacher-researcher and
FAO soil ambassador
AgroParisTech
Multifunctional
Both the presence and
degradation of organic
matter are very important.
© CLUZEAU Daniel/INRA
It is a real ‘turntable’
for the cycles of major
elements (carbon,
nitrogen and phosphorus)
and pollutants in soil
ecosystems. It acts as a
A soil profile made of soil clods and aggregates is a complex living filter for the environment
system, providing habitat for soil microflora and fauna. by storing natural
contaminants, not only
organic but metallic and
can be ensured, carbon stocks environment. Indeed, crop roots synthetic. When degraded,
remain constant and contaminant benefit from aerated soils and the organic matter benefits
transfers can be limited. infiltration of water is enhanced, the environment in a
avoiding problems such as runoff different way, by providing
PROVIDING and erosion. a nutrient supply for
Dessin E
STRUCTURE FOR SOIL
Finally, the maintenance of a
* Very few microorganisms are able to consume
these gases in the soil.
plants and enhancing soil
biodiversity.
certain quantity of organic matter
is essential to soil structure, as
well as its stability when faced
with rainfall. In effect, organic
Climate
G. Castagnon
Carbon storage
matter acts like ‘glue’ in the soil. It
aggregates mineral particles and
also provides a food supply for
organisms (microorganisms,
Water flow
and quality
earthworms) whose acti-
vities are also beneficial
Retention of water Soil organic Mg 2+
Ca2+
matter
and pollutants K+
for soil structure. Therefore,
organic matter contributes
Chemical
directly and indirectly to soil Soil fertility
structure, which profits biological and soil
both agriculture and the activity structure
Soil and carbon l9
Points of view
Carbon storage in soils:
rising awareness
Dominique Arrouays,
Research
Research engineer and
and public scientific coordinator of the
policy are Global Soil Map Programme,
joining forces Infosol Unit of the National
to boost Institute for Agricultural
carbon in Research (INRA), Orléans.
French soils
and therefore
better combat
climate
change.
Joseph Lunet, project leader
T
responsible for agriculture
he general public may not and forest in the Ministry of
yet be fully aware of the Sustainable Development
importance of soils as a (Energy and Climate Head
carbon pool and a tool Office, Greenhouse Mitigation
for mitigating climate change. Department).
However, the business com-
munity and the political sector in improving knowledge about and past land use, climate, clay
have started to show an interest. the mechanisms and amounts content, soil depth and agricul-
“In the agricultural and forestry of carbon involved. He explains: tural and forestry practices as
sectors, awareness is rising,” “The French state supports public the main sources of variations
explains Dominique Arrouays, research programmes which aim in carbon levels in French soils.
an INRA researcher specialising to improve our knowledge, under “The potential for increasing
in soil. He adds: “It probably isn’t the supervision of GIS Sol(1). stocks is not necessarily found in
so true for actors in the parks Working on a better knowledge the most carbon-weak areas,” he
sector and those working in of carbon fluxes in farmland and explains. “It might be more useful
regional planning.” At the Ministry forest soils is essential.” to preserve or increase already
of Sustainable Development, high stocks, rather than try and
Joseph Lunet confirms that MAINTAINING OR create new ones in areas where
present policies do consider ENRICHING ALREADY the potential for stabilisation is
the major role played by soils. LARGE STOCKS low. Furthermore, region-specific
According to him, public autho- For the moment, Dominique actions exist, depending on the
rities are especially prominent Arrouays considers present business sector.”
10l Soil et carbonMap of carbon stocks in French soils
Thanks to the Soil Quality Measurement Network (known by its
French initials RMQS – www.gissol.fr), soil carbon stocks have
been mapped. They seem greater in highlands and livestock
areas. The network does not provide a value for carbon stocks in
urban areas (shown in white on the map). However, the inventory
of national greenhouse gas emissions suggests that urban areas
“
could contain half the stocks of grassland areas. It takes into
account, among others,
gardens and urban
parks. France would like to
see the land-use sector
included in future
international climate
agreements.
“
Organic carbon stock
(Kg/m²)
More than 13 and ecologically important
Between 10 and 13
Between 7.5 and 10 areas, ban the destruction of
Between 4 .5 and 7.5
Less than 4.5 some natural meadows, limit
Urban area clearance of wooded areas and
tackle urban sprawl etc.
The representative of the Ministry
of Sustainable Development adds
source : Meersmans et al. 2012 that the issue of carbon and soil
is not currently at the heart of
“
climate-related policies, “because
GROWING soil carbon is poorly taken into
IMPORTANCE OF In the agricultural account within the framework of
INCENTIVE MEASURES and forestry sectors, the Kyoto Protocol”. According
According to Joseph Lunet, awareness is rising. It to him, France would like to
support measures which aim needs to be developed see that the land-use sector is
to preserve or increase carbon
stocks in agricultural soils are
increasingly important, especially
“
in the parks sector and
regional planning.
“included in future international
climate framework agreements,
post 2020”. That way, policies
with the new 2014-2020 CAP could take greater account of
(Common Agriculture Policy), and incentive measures to protect or
through France’s ‘Loi d’avenir’ increase soil carbon stocks.
legislation for agriculture and
forests. Indeed, these policies
(1) Group of scientific interest including INRA,
support incentives for the pres- ADEME, IGN, IRD and the Ministries of Agriculture
ervation of permanent grassland and Environment.
Soil and carbon l 11Impacts and levers for action
Changes in land use: the need
to preserve carbon-rich soils
The reconstruction of organic carbon stock in the
soil takes several decades. This means we should
focus on protecting those areas which contain the
highest stocks, and on controlling urbanisation.
T
urning grassland into land, permanent grassland has
cropland leads to a deple- seen the biggest impact, with
tion in soil carbon, while a loss of 1.6Mha, mostly for
afforestation of cropland conversion to crop cultivation.
increases carbon storage. Accor-
ding to the Ministry of Agriculture’s CONTROLLING LAND
annual agricultural statistics, USE
the main land-use changes in Although afforestation increases
France between 1990 and 2010 carbon stocks, urbanisation and,
included a 0.6 million hectare in particular, soil sealing leads to
(Mha) increase in afforested a loss of organic matter and soil
land, but also an increase in functions which are very difficult,
© A.D.
urbanised land of 1.4Mha. These if not impossible, to reverse.
land-use changes have been to In all cases, in order to preserve
Ploughing up grasslands for crop
the detriment of farmland, cau- French soil carbon stocks and
cultivation causes carbon losses.
sing a net loss of 1.3Mha over maintain ecosystems which act
The Common Agricultural Policy
encourages farmers to preserve
20 years, and a 0.7Mha loss of as carbon sinks, natural environ-
grasslands. natural land. Within agricultural ments should be protected and
Carbon stock evolution, depending on land-use change
40 During the first twenty years which
More than 400,000ha of
follow a change in land-use, carbon
is lost twice as fast as it is stored.
Carbon storage (tC/ha)
grassland have been ploughed 20
Only after several decades or even
in France since 2000, and more than a century can carbon
1.6Mha since 1990. 0 storage compensate carbon losses.
(source: Agricultural Statistics).
-20
In France, 70,000ha far-
Source: Arrouays and al. 2002
mland hectares have been -40
cropland -> forest
cropland -> grassland
lost between 2006 and 2014, 0 20 40 60 80 100 120 forest -> cropland
according to Teruti-Lucas. Application period (years) grassland -> cropland
12l Soil et carbonA => F : 190
F=> Natural lands (N) : 815
N=>F : 584
Changes of land-use
N => A : 395
Farmland: A=>N : 238
between 2006 and 2014, in France
28 000 thousand hectares Land-use changes create carbon fluxes. The current
resolution of spatial monitoring and lack of knowledge
concerning urban land limits the precision of
measurements.
Urban land:
5100 thousand hectares
190
524
G. Castagnon
815
395 238
584
Natural land and forests:
21800 thousand hectares
F luxes in thousands Source: Teruti-Lucas survey
of hectares from 2006 to 2014, including
2014 surfaces.
livestock systems should preserve
Antonio Bispo
grasslands. Regarding agriculture,
agro-environmental measures
Expert Soil and environment
deter the ploughing of grassland
after five years. The French
opinion engineer at ADEME
Safer(1) group can also intervene
to pre-empt lands threatened by
Integrating carbon stocks in GHG environmental
urbanisation. Other regulatory assessments in land-use policies
levers are foreseen in the codes “Any change in land use, whether it is for non-food crops or for
dealing with urbanisation, rural urbanisation, can have consequences, not only in France but
areas and the environment, also in developing countries. So, deforestation may intensify in
and within the framework of the order to maintain the offer of raw materials on world markets.
Within the framework of a working group launched in 2010,
ALUR law(2). They involve various
the impact of French policies promoting bio-fuels on farmland
mechanisms, such as protection
use and CO2 emissions has been evaluated. This research is
zoning, pre-emption and norms now being extended and is integrating different scenarios
on urban densification. and drivers in land-use changes, such as urbanisation and
agricultural objectives, both at a national scale and worldwide.
Competition for different land uses is a major issue for public
(1) Real estate development and rural establishment
policies.”
companies
(2) Law for access to housing and renewed urban planning.
Soil and carbon l 13Impacts and levers for action
Forest soils:
rationalising the increase
in harvested wood
The demand for and
disruption of forest
soils is lower than
for farmland, and
they evolve slowly.
Nevertheless, their
fertility is limited
and very dependent
on natural flows of
elements and organic
matter. An increase
in wood demand for
energy purposes needs
to be accompanied by
measures seeking to
© A.D.
protect them.
The medium and long-term effects of wood harvesting intensification
on carbon stocks are not well known. The impacts of different practices
strongly depend on soil characteristics.
I
n chemical terms, forest soils much carbon stored in the soil long-term evolutions, especially
are generally the poorest within as there is in the trees. under the influence of changes
a territory, or those whose in forestry practices.
physical characteristics are the SUSTAINABLE In the future, the foreseeable
most unfavourable to agriculture. FORESTRY PRACTICES increase in wood demand - for
Unlike agricultural soils, they Carbon stocks evolve more energy or material needs - will
undergo no or very little altera- slowly in forest soils than in encourage the intensification of
tion due to human activity. As a agricultural soils. Usually, they forest harvesting. The impact of
result, organic matter is highly are assumed to be stable, but this intensification on stocks is
accumulated in the litter and very little monitoring has been uncertain; it could lead to oppo-
surface layers of soil. In temperate conducted to make it possible sing effects on litter production
forests, there is approximately as to know their true medium and and the integration of harvest
14l Soil et carbonwaste in the soil. Nevertheless, a for ADEME.
Laurent
greater harvest of forest residuals,
which includes young trees and
Expert Augusto
branches remaining on land
after harvesting and pruning of
opinion INRA researcher
trees, for energy needs, directly
decreases soil intakes of carbon.
Indicators to protect soil fertility
The ADEME guide* on ‘The
“The challenge for research consists in finding logistical
sustainable harvesting of forest levers in order to mobilise underexploited woodland, but
residuals’ recommends that not also in finding good compromises to manage forests which
all of the above-ground biomass are increasingly in demand. The latter have to preserve their
should be taken: a portion of the various functions, such as wood production, biodiversity
residuals should be left on the reservoirs and carbon storage. In this context, maintaining
organic matter stocks in forest soils is essential, because
ground at each harvest, and resi-
unlike other countries, French forests receive practically no
duals should be collected once,
inputs to contribute to soil fertility. Yet, half of the forests are
maybe twice, in the stand’s life. former farmlands reforested in the middle of the 19th century,
These recommendations were because they were too poor or difficult to cultivate. In order
made in order to preserve the to preserve this capital, the challenge consists in finding the
mineral chemical fertility of forest right balance between exported wood and the wood left on
soils and reduce soil compaction, the ground. Today, research projects are seeking to develop
but are also valuable in preserving indicators so forest managers can improve their harvesting
practices.”
carbon stocks.
Gestion Forêts * The guide will be updated on the basis of the collective
expertise RESOBIO coordinated in 2013 by GIP ECOFOR
E lements in the GHG balance
in the wood sector
Harvesting larger quantities of forest wood could limit
G. Castagnon
increases in carbon stocks in the soil and trees. For a
complete evaluation of the GHG balance in the wood
sector, we need to take into account carbon storage in
wood products (construction and furniture) as well as
substitutions of other materials and fossil fuels.
50 year 200 year
forest forest
rotation rotation Construction
and furniture
• Replaces fossil
materials
• Stores carbon
Energy
• Replaces fossil
energies
Soil and carbon l 15Impacts and levers for action
Agricultural soils:
acting on organic matter
inputs and losses
To boost carbon levels in agricultural soils, two
specific actions have been identified: favouring
practices which increase stocks of organic matter
and limiting those which increase losses of organic
matter.
A
ccording to INRA esti- of intermediate crops in crop
mates in 2002 and rotations, grassing between rows
2013, the maximum in vineyards and orchards, and
potential of additional extending the lives of temporary
carbon storage in agricultural grasslands.
soils should reach 1 to 3 million The planting of hedges and grass
tonnes a year over 20 years. and flower strips enriches the
This storage could compensate soil in organic matter alongside
a significant proportion - some their role as biodiversity reser-
© A.D.
3 to 4% - of France’s annual voirs, ecological corridors and
greenhouse gas emissions, but buffer zones between crops
In order to return higher amounts would require a very pro-active and water courses. With the
of organic matter to the soil, it approach. introduction of rows of trees in
is necessary to favour soil cover The practices which should fields and pastures, agroforestry
by including intermediate crops be implemented involve either techniques lead to an increase of
in the rotation and grassing increasing inputs of organic the carbon stocks in soils as well
between the rows in vineyards matter or reducing losses. as in wood. In low productivity
and orchards. grasslands (grazing land, high
SUPPLYING MORE mountain pastures and moor-
ORGANIC MATTER land), moderate intensification
In France, less than 1% of The first action identified to practices can be implemented.
cultivated land is directly
increase soil carbon stocks is For crops and grasslands which
sown.
to increase plant production have already been intensified,
4.6Mha is cropped using and return more organic matter the concern is not to increase
simplified cultural techniques, to the soil. To achieve this, it is inputs but to better preserve crop
a third of the cultivated area. necessary to promote the use of residues. Finally, the application
(Source: Arvalis Institut du Végétal). soil cover through the inclusion of organic matter from urban
16l Soil et carbonsources or of manure could be sowing and more or less deep preserve part of the possible gain
an interesting solution at the interventions. Their impact on in carbon stocks and, above all,
local scale, provided low-carbon carbon stocks has often been save on fuel.
soils are prioritised and it meets overestimated.
existing regulations. Based on the monitoring of
experiments conducted by the
Expert
SLOWING CARBON
LOSSES
international scientific community,
only direct sowing provides an
opinion
Hedges and soil cover also effect average increase over plou- Jérôme Labreuche
carbon stocks, by reducing runoff ghing (0.15 tonnes of carbon Agro-equipment centre
and losses due to erosion. storage per year). This result manager at Arvalis- Plant
Putting an end to ploughing is highly variable depending Institute
would lead to an increase in on the situation. Moreover, field
soil-carbon levels as colder trials led by Arvalis over 40
and wetter surface conditions years on the Boigneville site
and better physical protection in Essonne (south of Paris),
in the aggregate slows down show that after a 2t/ha annual
Taking better
the mineralisation of organic organic carbon storage over 24 account of
matter. According to the Arvalis years, direct sowing does not practices which
plant institute, 34.4% of France’s differ from ploughing after 40 enhance organic
cultivated land is currently crop- years. Furthermore, ploughing matter inputs
ped using simplified cultural is sometimes necessary for The implementation of
techniques (no-till or low-till), agronomic reasons (see box). intermediate nitrate-
trap crops (INTCs) during
mainly autumn crops. Low- According to INRA, occasional
long interculture periods
till techniques include direct ploughing every five years would has been encouraged by
regulatory obligations.
This farming practice
When ploughing is improves soil humic
justified balance, especially
since carbon storage
According to the Arvalis
by INTCs has recently
plant institute, ploughing
been reappraised.
is most often conducted
There is also a trend for
for spring crops and on
keeping these crops for
soils low in clay content.
a longer time-period,
It provides security for
and planting them in
spring crops, as ploughing
areas where it is not
encourages crop emergence
necessarily compulsory.
and improves soil structure
Another evolution in
in situations where there
practices has been
is a significant risk of soil
spotted: in cereal
compaction (late harvesting or loamy soils). It is also the case
production areas, some
that for easy-to-plough soils this practice is not often called into
farmers do not hesitate
question. In a context where weed control is increasingly complex,
to add organic inputs to
ploughing is recommended, especially where there is strong
the soil.
pressure from grass weeds.
Soil and carbon l 17Impacts and levers for action
Agricultural practices
according to their cost
and efficacy
In 2013, INRA analysed the potential of agricultural practices for mitigating French
GHG emissions. Agroforestry, no-till, extending the life of temporary grasslands
and maintaining permanent soil cover appear to be the most effective levers for
stimulating carbon storage. Here we present the lessons learned.
T
en different actions have at less than €25 per tonne of matter: increasing the life of
been identified by INRA CO2-equivalent avoided. temporary grasslands (1.44Mt
for limiting agricultural CO2-equivalent per year) and
emissions of three major UNDERSTANDING ALL extending the grazing period.
greenhouse gases (CO2, N2O THE BENEFITS Extending grazing periods also
and CH4) over the next 15 years. Other moderate-cost measures influences other GHGs because
These measures have to be stimulate the storage of organic part of the manure usually emitted
pragmatic and avoid yield losses
beyond 10%. Added together, they Estimation of impacts of agricultural practices
could lead to a 32 million tonne on carbon storage
CO2-equivalent reduction per
year by 2030. These measures
also include economic factors.
Those which aim at reducing
Permanent Hedges and
Moderate
CO2 emissions together with Agroforestry
High
plant cover plant strips
High
increasing farmers’ revenues act Cost
mainly on economies in the use Increase in plant productivity >
of fossil fuels and carbon storage
nisms Increase in organic matter physical protection >
in soils and biomass. Mecha in C
e d Reduced carbon losses due to leaching and erosion >
involv age
Regarding carbon sequestration stor
in the soil, the most effective miti-
gation measures are occasional
of Between 0,1 Hedges Between 0,1 and 1,35,
ploughing (3.77Mt CO2-equivalent al units
Potenti storage and 0,35 • In grasslands: 0,14 including
per year) and agroforestry (1.53Mt carbon ears in In croplands: 0,25 approximately 2/3 in
y
CO2-equivalent per year). However, over 20 study, • Plant strips the soil
A
the long-term impact of occasional the INR a/year. 0,5±0,3
in tC/h 13 ;
ploughing needs to be clarified et al. 20
(Pellerin )
ay s et al. 2002
(see p.17). The cost-efficiency of Arrou
these measures remains modest
Note :
• A tonne of carbon stored is the equivalent of around 3.66 tonnes of CO2 captured.
• Agricultural land in France covers around 28.2Mha.
18l Soil et carbonExpert Sylvain Pellerin
Coordinator of the INRA study: ‘Ten measures
opinion to reduce GHG emissions through agricultural
practices’
“For the first time, we have measured and quantified GHG emissions mitigation potential, and the
related costs. Carbon storage is favoured by moderate-cost measures, such as no-till or agroforestry. In
order to improve the carbon-storage dimension of these practices, inventory methods have to progress.
Today, only land-use change impacts are measured.”
in the barn, and the emissions environmental aspects, such biomass represent 30% of the
of N 2 O and CH 4 associated as conserving the quality of potential mitigation of GHG
with it, will be reduced. The water, soils and biodiversity, of emissions, when including
planting of hedges, intermediate which the economic impact has their effects on CH4 and N2O
crops, permanent grassing in not been taken into account in emissions, and the substitution
vineyards and orchards and this study. of fossil fuels. Beyond the date
introducing flower or plant set in this study - 2030 - car-
strips (2.77Mt CO2-equivalent CARBON STOCKS bon stocks will reach a ceiling
per year) have a higher cost, CAPPED IN THE and net CO2 fixation will end.
mainly because of the working MEDIUM-TERM However, the other effects of
time required. Nevertheless, Overall, the levers relating to mitigation, such as savings in
these measures benefit other carbon storage in soil and fuel, will continue.
Grassing in Grassland Spreading of Return of
Moderate
Moderate
Moderate
No-till
Moderate
vineyards management techniques effluents and crop residues
High
and orchards compost
Increase in plant productivity > Increased return of organic matter to the soil
Reduced carbon losses due to leaching and erosion >
Lower mineralisation if the ratio C/N is high
• For permanent soil • Increase in temporary • Transition to direct Between 10 and 50% 0,15 for 7 tonnes
covers in orchards: grasslands’ lifetime sowing, 0,15 of the carbon input, of straw
0,5±0,3 (< 5 ans): 0,15 • Transition to ploughing according to type of
• For permanent soil • Moderate every five years: 0,10 input.
covers in vineyards: intensification • Shallow tillage: no
0,3±0,2 of poor permanent additional C storage
• For temporary soil grasslands: 0,4
covers in vineyards:
0,16
Soil and carbon l 19Points of view
Reconstructing carbon stocks
Many benefits to highlight
Practices which favour the storage of organic
matter or which preserve carbon already existing
in the soil are better perceived in the field if they
combine several environmental benefits. Different
tools and levers are available to make their
implementation easier. Here we explain.
raising programmes based on the
multiple environmental benefits.”
Sandrine Leménager, project
Sandrine Leménager, leader at the soil division at the
project leader on soil agriculture, food and territorial
subjects at the head policies department (known
office of Agriculture, by its French initials DGPAAT)
Food and Territorial of the Ministry of Agriculture,
Policies (DGPAAT)
identifies new opportunities to
at the Ministry of
better take into account issues
Agriculture.
relating to soil carbon and cli-
mate. The timetable provides
Jean-Luc Fort, head of the
F
evidence: “2015 is a pivotal year,”
armers are aware of the agronomy and environment she says. “France is hosting
importance of carbon sto- service at the Poitou- the 21st climate conference,
Charentes Chamber of
rage, particularly in regard Paris Climat 2015 (Cop21). It
Agriculture and coordinator
to its benefits for biological is also the International Year
of the ‘Sols et Territoires’
activity and overall soil fertility. of Soils. The 2014-2020 CAP
Combined Technology
Yet the role of organic matter in (Common Agricultural Policy)
Network.
in environmental assessments is strongly prioritises measures
poorly taken into account. “The which ensure greenhouse gas
time required for reconstructing Agriculture, and coordinator of mitigation through carbon storage
carbon stocks is so long that the Sols et Territoires (soil and in soils, such as the preservation
this issue isn’t enough to trigger land) Combined Technology of pasture, soil cover, areas of
corrective measures in agricul- Network. ecological interest…Finally, the
tural practices,” says Jean-Luc “On the other hand, technical fight against the urbanisation
Fort, manager of the agronomy bodies, agricultural advisers and of farmland and forest helps to
and environment service at the cooperatives are involved in plenty protect the ecosystem services
Poitou-Charentes Chamber of of development and awareness- provided by soil carbon storage.”
20l Soil et carbonContext
Measures encouraging carbon storage
Measures Levers
Ongoing discussions about organic residues and current policy
Organic matter inputs
“
promoting farm-sourced organic matter.
Intermediate crops, Nitrates Directive and implementation legislation.
Grass or flower strips CAP- greening: zones of ecological interest
Using only the
Grassing in vineyards
carbon storage angle is CAP, agro-environmental measures
and orchards
not enough to encourage CAP, agro-environmental measures
Hedges, Agroforestry Art. 23 of 2014-2020 rural development regulation
favourable farming CAP - greening: zones of ecological interest
“
systems. We need a
multifunctional point of
view.
Preservation of
permanent pasture
CAP - greening: no ploughing of permanent pasture classed
as sensitive, and for other areas if Member State wishes. The
diminution rate of permanent pasture must not exceed 5%
nationally.
PRIORITISING INCENTIVE they are based on the environ- aspects. Innovative crop mana-
MEASURES mental benefits and economic gement techniques combining
According to Sandrine Leména- compensations obtained, and several environmental goals are
ger, approaching carbon issues not only on the administrative very welcome since they also
through agricultural practices management of a problem. include agricultural and eco-
which favour its storage is the “We need to turn this around, nomic interests. In our region,
entry point. The practices identi- to value the agricultural and lucerne (alfalfa) is a perfect
fied concern soil cover, notably economic benefits of a better example of positive synergy: we
intermediate crops, flower or consideration of environmental use lucerne as a low-input crop
grass strips, inputs of organic which benefits the rotation with,
“
matter and the development in parallel, the maintenance of
of agroforestry, but also hedge Measures which livestock which feed on it and
maintenance and afforestation. add value to the crop.”
encourage carbon
She insists: “There are tools to This synergy can even go beyond
encourage the implementation of storage meet the goals the farming sector. Among
each measure, particularly within of the French agro-
“ the selected measures which
the CAP. Some are incentives, ecological project. increase organic matter, San-
others are statutory, but there is a drine Leménager favours the
clear tendency to better take into spreading of organic matter
account soil and carbon issues inputs, “on the condition that
within agricultural practices.” their safety and agronomic value
For Jean-Luc Fort, the agro- have been demonstrated. The
environmental measures included Ministries of Agriculture and
in the second pillar of the CAP of Sustainable Development
(Common Agricultural Policy) are working to this end,” she
are relevant levers, because adds.
Soil and carbon l 21Evaluation
Measuring changes
at the field scale
At the field scale, the influence of the actions implemented on soil carbon
stocks can be assessed through direct measurements and estimated with
the help of models. The latter can help agricultural advisers in changing
agricultural practices. Below is an overview of the tools and norms available.
T
he impact of field manage-
Estimation of Example of norm Objective
ment on soil carbon stocks
Isolate particular organic
can be quantified using material (plant residues in
Organic matter dynamics NF X31-516, 2007
direct measurements, course of decomposition) and
before and after the implemen- organo-mineral complexes
Soil microbial biomass NF EN 14240-1 et -2, 2011
tation of new practices. Estimate the microbial activity
Soil respiration NF EN 16072, 2011
of organic matter degradation
Certain enzyme activities NF EN 23753-1 et -2, 2011
DIRECT
Earthworms NF EN 23611-1, 2011
MEASUREMENTS TO Value the number and
Mites and springtails NF EN 23611-2, 2011
EVALUATE RESULTS diversity of invertebrates
Enchytraeid worms NF EN 23611-3, 2011 involved in organic matter
Direct measurement methods dynamics (e.g. earthworms,
require particular caution (see Nematodes NF EN 23611-4, 2011 nematodes)
box ‘Expert opinion’). We have to Total macro-fauna PR NF ISO 23611-5, 2010
Annie Duparque
Expert Head of agronomy at Agro-Transfert Ressources
opinion and Territories, and partner in the RMT Sols et
Territoires (soil and land combined technology
network).
Carbon dynamics: three key points to bear in mind
“In order to assess carbon dynamics, we need a relevant sampling procedure. Different measures have
to be made on the same soil amount, and bias must be avoided due to the spatial heterogeneity of
organic matter content in farm fields.
“We need to be careful on three different points: recording the samples’ locations with a GPS, and
returning to the exact same place for further measurements five to seven years later; to rationalise the
sample depth according to the depth of tillage, and keeping it unchanged from one measurement to
another; if possible, to determine the soil bulk density through the depth of the sample.
“Carbon content analysis of preliminarily air-dried samples is performed by a laboratory. Then, the
organic carbon stock (t/ha) can be calculated by multiplying carbon content with the mass of soil,
estimated via depth sampling and bulk density.”
22l Soil and carbonAgriculture Chamber of Oise (60)
The evaluation
of carbon
dynamics in
cultivated
soils requires
the following
of a precise
protocol.
wait between five and 10 years USING MODELLING TO practices (crop rotation patterns,
before the impacts of changes GUIDE AGRICULTURAL residue management, organic
in agricultural practices can be PRACTICES inputs, intermediate crops, tillage,
observed. Analytical methods Thanks to models such as AMG, irrigation) and on soil and climate
can be used for an early esti- established in France by INRA in characteristics. Specific models are
mation of changes in organic Laon (02), we can also simulate also available for France’s overseas
matter (see chart opposite). In changes in agricultural practices. territories, such as the Web Mor-
order to predict the effects of Agro-Transfert-RT, INRA and part- Gwanik application developed for
inputs of exogenous organic ners in the agricultural sector have Guadeloupe, which are designed
matter (liquid manure, fertiliser, developed a decision support sys- to include the specificities of the
compost) on carbon stocks, bio- tem integrating this model, called climate, farming systems and soils
degradability indicators based on Simeos-AMG. Designed for use found in the country’s outermost
the biochemical composition of in agricultural advisory services, it regions. Used within the framework
inputs have been developed and simulates and displays the expected of energy performance plans,
standardised. An example is the changes in soil organic carbon ADEME’s tool Dia’ Terre® can
organic matter stability indicator stocks in the long-term (20, 30, 50 include soils in farm greenhouse
(NF XPU 44-162, 2009). years etc.), depending on agricultural gas assessments.
Simeos-AMG, a simulation tool for agricultural advice use at different scales
Vegetable production, silt soils (rotation: potatoes/wheat/peas (canning)/beetroot/wheat/carrot)
CURRENT SYSTEM A SCENARIO Organic matter content evolution
in the tilled layer of the soil
• Ploughing: 2 years out of 3 (Reduced C losses)
• Ploughing depth: 28cm • No ploughing 9,25 1,85
Organic C content (g/kg)
• Green fertilisers: (1 year out of 2)
1 year out of 3 9,00 1,80
• Reduction of ploughing
OM content (%)
depth to 22cm 8,75 1,75
B SCENARIO
C SCENARIO 8,50 1,70
(Inputs of humic
substances) • Input of green waste 8,25 1,65
current system
• Input of green waste compost: 8,00 a scenario
1,60
b scenario
compost: 10t/ha over 10t/ha over 6 years c scenario
6 years • One ploughing removed 7,75 1,55
0 6 12 18 24 30
• Green fertiliser: 1 year and reduction of depth to
Years
out of 2 22cm Source agro-transfert RT, Duparque et al, 2011
Soil and carbon l 23Evaluation
Measurement tools
at the territorial scale
Direct measurements, national databases, modelling, etc.: evaluation tools
offer the possibility of monitoring the impacts of public policies and predicting
changes in soil carbon stocks.
A
s for fields, soil carbon MEASUREMENT RMQS is based on the moni-
stocks can be moni- NETWORKS AT THE toring of 2,200 observation sites,
tored at the territorial NATIONAL SCALE divided according to a 16km
level thanks to direct In France, two main networks, per side grid across the whole
measurements and modelling. complementary in their design, territory. This network supplies
Using direct measurements are managed within the framework average data and representative
requires the introduction of of GIS Sol: RMQS (soil quality values of carbon stocks for the
sampling networks. measurement network) and main land uses (forests, crops,
BDAT (soil analysis database). permanent pasture etc.). Analyses
Expert Olivier Scheurer
Lecturer at the Institut Polytechnique LaSalle
opinion Beauvais, and partner in the RMT Sols et Territoires
(soil and land combined technology network).
Net balance of CO2 emissions for the cultivated red Modelling offers the possibility
soils in Vienne, calculated from simulated changes of estimating the effects of
over 50 years.
modifications to cropping systems
Balance Balance at small regional agricultural levels
(tC/ha/yr) (tC/ha/yr)“Within the work conducted in Sols et Territoires(1),
Red soil - 86 -0.05 0.01 we showed that it was possible to apply the AMG
Average depth -0.10 -0.05 model for carbon dynamics in agricultural soils,
Shallow 0.07 0.13 based on a spatial inventory of ‘soils, cropping
Deep -0.10 -0.03 systems, and current organic carbon content’. To
Without With achieve this inventory, pre-existing databases
intermediate intermediate were used: CAP data, pedological regional
crops crops references (RRP) and the soil analysis database.
Nevertheless, local agronomic expertise is
necessary to group these data. The chart (left) shows a model application in Poitou-Charentes (Vigot,
2012): the introduction of intermediate crops limits carbon losses and even increases stocks depending
on the soil type in question.” (1) www.sols-et-territoires.org
24l Soil and carbonA.D.
We can analyse the consequences of changes in cropping systems on carbon stocks thanks to models
at the agricultural territorial level.
are also conducted to charac- extending these changes to all complete and extrapolate direct
terise agronomic parameters, French farmland comes with measurements. This is the case
contamination levels and soil great uncertainties linked to the for the methods developed
biodiversity. Thanks to the first temporal and spatial diversity by INRA, working with Citepa
sampling campaign between of the sampling and analytical (a technical centre studying
2001 and 2011, carbon stocks methods. In France, there are other atmospheric pollution), based on
in mainland France and the observation networks integrating the GIS Sol database, in order
French West Indies have been soil carbon measurements too. to feed national inventories for
evaluated. Starting from 2015, a For example, the Renecofor GHG emissions. Other tools have
new sampling campaign will be network monitors 102 forest sites been developed for use at the
conducted in order to observe in mainland France. The SOERE territorial scale. The Simeos-AMG
changes in stocks. All the RMQS network (observation and expe- tool made it possible for the AMG
samples are conserved at INRA’s rimentation system for long-term model to be implemented at the
national soil sample conservatory environmental research) brings agricultural territorial level in Loiret
in Orléans. together different sites chosen to and Poitou-Charentes (see box).
BDAT is a database which estimate the long-term impacts of The ABC’Terre project (Reacctif
gathers the results of soil ana- climate and agricultural practices. ADEME 2012) continues this work,
lyses conducted by farmers. The and will also lead to the deve-
database groups around two MODEL-BASED lopment of a calculation method
million samples taken since 1990. EVALUATIONS for GHG emissions balances,
Thanks to the data collected, it The implementation of observa- integrating soil carbon balances
has been shown that agricultural tion networks is limited due to at the agricultural territorial level.
soils tended to lose approximately their cost and the length of time This project will also improve
6Mt of carbon per year between required. Therefore, in order to ADEME’s Climagri® tool, used
1990 and 1995, and 1999 to evaluate policies which impact in greenhouse gas diagnoses
2004. However, these changes on soil management and carbon within territorial climate-energy
are spatially highly variable and stocks, modelling is needed to plans (PCEAT).
Soil and carbon l 25You can also read
