Geoderma 122 (2004) 1 – 23
www.elsevier.com/locate/geoderma
Review article
Carbon sequestration in the agricultural soils of Europe
Annette Freibauer a,*, Mark D.A. Rounsevell b, Pete Smith c, Jan Verhagen d
a
Max-Planck-Institute for Biogeochemistry, P.O. Box 100164, 07701 Jena, Germany
Department of Geography, Université catholique de Louvain, Place Pasteur, 3, B-1348 Louvain-la-Neuve, Belgium
c
Department of Plant and Soil Science, University of Aberdeen, Cruikshank Building, Aberdeen, AB24 3UU, UK
d
Plant Research International, Business Unit Agrosystems Research, P.O. Box 16, 6700 AA Wageningen, The Netherlands
b
Available online 27 February 2004
Abstract
In this review, technical and economically viable potentials for carbon sequestration in the agricultural soils of Europe by
2008 – 2012 are analysed against a business-as-usual scenario. We provide a quantitative estimation of the carbon absorption
potential per hectare and the surface of agricultural land that is available and suitable for the implementation of those measures,
their environmental effects as well as the effects on farm income. Realistically, agricultural soils in EU-15 can sequester up to
16 – 19 Mt C year 1 during the first Kyoto commitment period (2008 – 2012), which is less than one fifth of the theoretical
potential and equivalent to 2% of European anthropogenic emissions. We identified as most promising measures: the promotion
of organic inputs on arable land instead of grassland, the introduction of perennials (grasses, trees) on arable set-aside land for
conservation or biofuel purposes, to promote organic farming, to raise the water table in farmed peatland, and—with
restrictions—zero tillage or conservation tillage. Many options have environmental benefits but some risk of increasing N2O
emissions. For most measures it is impossible to determine the overall impact on farm profitability. Efficient carbon
sequestration in agricultural soils demands a permanent management change and implementation concepts adjusted to local soil,
climate and management features in order to allow selection of areas with high carbon sequestering potential. Some of the
present agricultural policy schemes have probably helped to maintain carbon stocks in agricultural soils.
D 2004 Elsevier B.V. All rights reserved.
Keywords: Carbon sequestration; Kyoto protocol; Agriculture; Carbon; Management
1. Introduction
Abbreviations: CAP, Common Agricultural Policy of European
Community; ECCP, European Climate Change Programme; FAO,
Food and Agriculture Organisation; IGBP-DIS, International Geosphere – Biosphere Programme-Data and Information Services;
IPCC, Intergovernmental Panel on Climate Change; LFA, Less
Favoured Areas; NVZ, Nitrate Vulnerable Zones; SD, Standard
deviation; UAA, Utilised agricultural area.
* Corresponding author. Tel.: +49-3641-576164; fax: +493641-577100.
E-mail address: [email protected] (A. Freibauer).
0016-7061/$ - see front matter D 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.geoderma.2004.01.021
Carbon sequestration in agricultural soils is accountable under Article 3.4 of the Kyoto Protocol.
Principal challenges associated with the identification
and quantification of accountable activities still remain unanswered, which require political decisions to
be made. Here, as one of the prerequisites for carbon
accounting, the technical and economically viable
potentials for carbon sequestration in agricultural soils
of Europe by 2008 – 2012 are analysed against a
business-as-usual scenario. We provide a quantitative
2
A. Freibauer et al. / Geoderma 122 (2004) 1–23
estimation of the carbon absorption potential per
hectare, and for the total area of agricultural land that
is available and suitable for the implementation of
those measures, their environmental effects, as well as
the effects on farm income.
2. Carbon sequestration under business-as-usual
2.1. Land use and management change arising from
European policy
2.1.1. General effects
The principal aim of the Common Agricultural
Policy (CAP) mechanisms has been to maintain farm
incomes by manipulating producer prices (intervention, import duties), whilst imposing production controls (quotas or set aside). The 1990s, however,
experienced radical change in the structure of the
CAP with a move away from price support based on
production to area-based payments, and the introduction of a wealth of rural development and agri-environmental measures. Whilst these policies are likely to
influence land use and management in different ways,
it is also difficult to disaggregate direct policy effects
from the influence of other socio-economic trends.
These include, for example, technological change, the
effects of world markets and international agreements,
changing consumer preferences as well as soil and
water quality (Rounsevell et al., 2002).
2.1.2. Specific land use changes
Set aside following the 1992 MacSharry reforms is
one of the few land use changes that is a direct
consequence of policy. Current terms require 10%
set aside with a provision for voluntary set aside up to
a maximum of 50% of the arable area, although these
areas were different in the past. Set aside is important
because of the potential for soil C sequestration and
for fossil fuel off-set using biofuels planted on set
aside land (Smith et al., 2000a,b). Current estimates
suggest that 20% of set aside land is being used for
non-food crops, of which rapeseed for the production
of biodiesel accounts for 80% (Joaris, 2002).
There has been a clear decline in the area of
grassland in Europe since the 1960s. This has largely
resulted from the increased production of maize at a
time when livestock numbers were reduced due to the
implementation of milk quotas in 1984. Since the
early 1990s, however, grassland areas have remained
fairly stable. Two explanations seem plausible: the
1992 CAP price support reforms and the introduction
of agri-environmental and rural development measures. The MacSharry reforms effectively prevented
grassland to arable conversions by fixing the area of
land that was eligible for arable area payments. Thus,
only land that was in arable production on 31 December 1991, could claim the aid payment. The Less
Favoured Areas (LFA) policies have probably contributed to the maintenance of permanent pastures in
arid and upland grazing areas. Thus, the policy has
effectively maintained the status quo in many grassland areas and one could question what land use
would have existed if marginal areas were abandoned
or converted to other uses. It is possible that the return
of land to natural vegetation types would have led to
an increase in C stocks in the biomass whilst soil
carbon could have rather decreased (Guo and Gifford,
2002; Jackson et al., 2002).
The total area of woodland in Europe has increased
throughout the period of the CAP (Rounsevell et al.,
2002). Although woodland on agricultural land
accounts for only a small proportion of this area, recent
afforestation policies have contributed to a large increase. A total of 519,350 ha (excluding Belgium and
Fig. 1. Yearly C fluxes per hectare and in EU-15 under business as
usual scenario in the first commitment period 2008 – 2012
(Vleeshouwers and Verhagen, 2002). Positive sign: carbon sink;
negative sign: carbon source. Standard deviation (SD) of total flux
sum from cropland flux estimates. Yield data used were on a whole
country basis (FAO-data) and soil data (C and texture) were taken
from the IGBP-DIS soil map (Global Soil Data Task, 2000).
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Sweden) were afforested between 1993 and 1997 with
Spain alone accounting for 46% of this area. The area
of permanent crops (vineyards, orchards) in Europe has
reduced substantially since the mid 1970s (Rounsevell
et al., 2002). This was mostly because of reductions in
the area of vineyards between 1980 and 1995, which
was strongly influenced by the Community aid for the
grubbing-up of vines, and a shift either to better quality
3
wine production or the cultivation of other crops. Olive
plantation areas have tended to remain fairly stable
during this period, although there has been a trend of
replacing older systems with more up-to-date production methods.
Agri-environmental measures encouraged conversion to, and maintenance of, organic farming by
providing financial compensation to farmers for any
Fig. 2. Simulated carbon fluxes in soil organic matter in Europe (t C ha 1 year 1) in the commitment period 2008 – 2012 (business-as-usual
scenario). Simulations were made using the mean soil organic carbon content (SOC) reported by IGBP-DIS (Global Soil Data Task, 2000) and
its standard deviation (SD) as the initial situation in 2000 (Vleeshouwers and Verhagen, 2001).
4
A. Freibauer et al. / Geoderma 122 (2004) 1–23
losses incurred during conversion. The total area of
land devoted to organic farming is just under 2% of
the utilised agricultural area (UAA) of the EU-15, but
varies considerably between countries. Italy alone has
27% of the EU organic land, followed by Germany
(16%) Austria (12%) and Sweden (9%) (EC, 2001).
It is currently impossible to say how the nitrates
directive has influenced land use. In theory, the policy
affects the profitability of farm enterprises and, therefore, farmer land use decisions. Nitrate Vulnerable
Zones (NVZ) are implemented very differently in
different regions of Europe, and at the European scale
it is impossible to generalise about its effects on land
use. Limiting the addition of N fertiliser may also play
a role in reducing soil C contents, although this effect
may be negligible at the European scale since many
soils are N-saturated.
2.2. Baseline carbon sequestration
Whether agricultural soils are a sink or source of
carbon depends on the actual organic matter content in
the soil (Vleeshouwers and Verhagen, 2002). Establishing a baseline of carbon contents in the topsoil is
crucial when establishing whether agricultural land
was a sink or source in 1990. When assessing the
effects of mitigation options this question is of minor
importance, because a measure may result in an
enhancement of a sink or a reduction of a source.
To establish a baseline we need to look at changes in
management practices over time (e.g. increase of
fertiliser in organic farming systems). Area specific
data related to land use and carbon are presented in
Section 3. The only available spatially explicit European baseline was modelled by Vleeshouwers and
Verhagen (2002) with the CESAR model. A detailed
description of the model and considered environmental
factors is given in Vleeshouwers and Verhagen (2002).
The resulting variation of C stock changes under
business as usual estimated in Europe was high (Fig.
2). Assuming the use of inorganic fertiliser and removal of crop residues from the field, which is probably a
worst case scenario, Vleeshouwers and Verhagen
(2002) calculated average carbon fluxes under the
business as usual scenario in the 2008 –2012 commitment period for Europe. Per hectare values for grassland fluxes of carbon range from 1.81 to 2.31,
mean = 0.60, SD = 0.64 t C ha 1 year 1. Equivalent
figures for arable land were min: 2.93, max: 0.31,
mean = 0.83, SD = 0.40 t C ha 1 year 1 (Fig. 1).
Positive fluxes mean carbon uptake by the soil while a
negative sign indicates a carbon source (Fig. 2).
2.3. Variability and uncertainty
Ecosystem productivity as well as organic matter
decomposition are strongly determined by environmental conditions. Weather, soil type and past land
management have a direct effect on the carbon sequestering potential. This variability is reflected in the
decomposition rate as a function of soil temperature
and moisture (Vleeshouwers and Verhagen, 2002; Fig.
3). High decomposition rates occur in regions where
high temperatures in summer coincide with moist
conditions whereas low decomposition rates occur in
areas with low temperatures and wet conditions.
Regional differences in crop yield exist, but the
FAO data set does not contain such information.
Besides the spatial variation of C input from crop
residues, quality of data of soil carbon stocks due to
the high standard deviation in the IGBP-DIS database
and of land management, especially of manure application, residue management and tillage, is a point of
concern. For grassland production only a limited
amount of yield data is available, adding to the large
uncertainty associated with the spatial variability, the
same holds for farm management practices of grazing
and grass cutting. So far, only the uncertainty in soil
Fig. 3. Annual relative decomposition rates (% year 1 of total soil
organic matter) calculated by CESAR (Vleeshouwers and
Verhagen, 2001).
A. Freibauer et al. / Geoderma 122 (2004) 1–23
carbon stocks has been incorporated in the uncertainty
estimates in Figs. 1 and 2.
3. Potential measures for carbon sequestration in
agricultural soils
3.1. Options for sequestering carbon in mineral soils
In agricultural cropping systems, the larger part of
the carbon is stored in the soil. Input of carbon to soil is
determined by the net primary production and the
fraction of it remaining on the field. Loss of carbon is
determined by decomposition and loss of topsoil by
erosion. The rate of decomposition is controlled by
ambient temperature and soil physical and soil chemical
conditions. In general, low crop yields, high soil carbon
contents and high soil organic matter decomposition
rates enhance the loss of carbon from agricultural soils.
Evaluation of current and new management practices for carbon sequestration will focus on the input
and the output of soil organic carbon. Possible
changes of emissions of N2O and CH4 are important
when determining the greenhouse gas mitigation
effect of a given activity, especially when organic
amendments and no-till options are involved (Smith
et al., 2001a; 2000b). More research is needed in
order to better evaluate the overall greenhouse gas
effect of C sequestration measures.
This paper concentrates upon cropland and grassland management, though organic soils are also considered where they are used for agriculture. Management changes within a single land-use (e.g. reduced
tillage on cropland) as well as transitions between landuses are considered (cropland to grassland conversion).
Increasing the soil carbon content means increasing
the carbon input, decreasing the output or a combination of the two through improved management. Carbon sequestration can also occur through a reduction
in soil disturbance because more carbon is lost from
tilled soils than from soils that are less disturbed.
Measures for reducing soil disturbance include
reduced or zero tillage systems, set-aside land and
the growth of perennial crops. Measures for increasing
soil carbon inputs include the preferential use of
animal manure, crop residues, sewage sludge, and
compost on cropland instead of grassland, improved
rotations with higher carbon inputs to the soil, and in
5
some cases fertilsation/irrigation/livestock management to increase productivity. Switching from conventional arable agriculture to other land-uses with
higher carbon inputs or reduced disturbance (e.g.
bioenergy crop production, conversion to grassland,
natural regeneration) will increase soil carbon stocks
(Table 2). The potential for carbon sequestration of
these measures is discussed in Section 3.3.
Increased yields in the past have not produced
higher input of carbon in the soil. In contrast, increases
in yields were mainly achieved through changes in the
harvest index (Evans, 1993). So while grain yields
increased, the amount of crop residues was reduced.
3.2. Alternative use of peatlands
Virgin peatlands take up carbon at rates between
0.1 and 0.3 t C ha 1 year 1, but emit CH4 at
significant rates, turning them into a source of 0.16
(range: 0.14 –1.5) t ha 1 year 1 C-equivalents (Cannell and Milne, 1995) based on the following global
warming potentials: CO2 = 1, CH4 = 21, N2O = 310
(IPCC, 1996). The cultivation of peatlands releases
carbon by rapid peat oxidation, at a rate of 2.2 – 5.4 t C
ha 1 year 1 (min: 2.2, max: 31 t C ha 1 year 1;
Kasimir Klemedtsson et al., 1997; Freibauer, 2003).
Carbon losses increase with deep drainage and intensive mechanical soil disturbance, especially after deep
ploughing (Kasimir Klemedtsson et al., 1997). Whilst
CH4 emissions more or less cease completely after
drainage, N2O emerges at rates that exceed those from
mineral agricultural soils by a factor of 2 –10. In total,
average greenhouse gas emissions from agricultural
peat soils are estimated to range between 3.5 (2.2 –
5.2) t ha 1 year 1 C-equivalents in grasslands, 4.9
(3.3 – 6.5) in croplands, and 6.5 (3.8 – 9.5) under
potatoe or sugar beet (Freibauer, 2003).
Large variability in C losses is mainly caused by
differences in drainage, climate, fertility and peat type
(Aerts and Toet, 1997; Chapman and Thurlow, 1996;
Kasimir Klemedtsson et al., 1997). Decomposition
rates after drainage in eutrophic peats are higher than
in oligotrophic peats (Minkkinen et al., 1998). In the
context of carbon sequestration, the rationale for
alternative use of peatlands is the preservation of the
existing large carbon stocks in peat soils and the
reduction of anthropogenic greenhouse gas emissions
rather than an increase of soil carbon stocks in the short
6
A. Freibauer et al. / Geoderma 122 (2004) 1–23
term (Komulainen et al., 1999). On the other hand,
peat carbon losses may be compensated by enhanced
vegetation growth (Cannell et al., 1993; Minkkinen et
al., 1998), so only a full greenhouse gas budget reveals
the climatic benefit of rewetting drained peatlands.
Potential alternative uses of agricultural peat soils
include the avoidance of potatoes and sugar beet, avoidance of deep ploughing, maintenance of a more shallow
water table and the conversion of arable cropping to
permanent cultures as well as new crops on restored
wetlands.
3.3. Potential of different agricultural management
options for sequestering carbon in soils
The carbon sequestration potential in agricultural
soils has been estimated globally, emphasizing temperate croplands (Table 1).
Table 1
Carbon sequestration potential outside Europe
Measure
Cropland
Improved crop
production
and erosion
control
Improved
farming
on eroded
soils
Conservation
agriculture
Conservation
tillage
No-till
Eliminate
bare fallow
Region
Global
Potential soil
carbon
sequestration
rate (t C ha 1
year 1)
Reference
0.05 – 0.76
Watson
et al., 2000
Humid
Semi-arid
0.2 – 0.5
0.1 – 0.2
Lal, 1999a
Lal, 1999a
Drylands
Tropical
areas
Australia,
Canada,
USA
Drylands
Tropical
areas
Canada
0.15 – 0.3
0.3 – 0.8
Lal, 1999b
Lal, 1999b
0.2 – 0.4
Watson
et al., 2000
0.1 – 0.2
0.2 – 0.5
Lal, 1999b
Lal, 1999b
Model:
0.07 – 0.14
9 long-term
experiments:
0.16
Smith et al.,
2000a; 2000b
Janzen et al.,
1998, in
Smith et al.
2000a; 2000b
Watson
et al., 2000
Canada
0.17 – 0.76
Table 1 (continued)
Measure
Cropland
Organic
amendments
Mulch farming
or plant cover
Composting
Nutrient
management
Water
management
Cultivation after
land conversion
Slash and burn
conversion
Moimbo
woodland
conversion to
maize
cultivation
Continuos
cultivation
Grassland
Reduce
degradation
Improve grazing
management
Grassland and
pastures
Afforestation
Agroforestry
Wetland
Wetland
restoration
Conversion to
agriculture
Region
Potential soil
carbon
sequestration
rate (t C ha 1
year 1)
Reference
USA
0.1 – 0.3
Drylands
Tropical
areas
Drylands
Tropical
areas
Drylands
Tropical
areas
Drylands
0.05 – 0.1
0.1 – 0.3
Watson
et al., 2000
Lal, 1999b
Lal, 1999b
0.1 – 0.3
0.2 – 0.5
Lal, 1999b
Lal, 1999b
0.1 – 0.3
0.2 – 0.5
Lal, 1999b
Lal, 1999b
0.05 – 0.1
Lal, 1999b
Western
Kenya
Mozambique
10 (loss)
8 (loss)
Zimbabwe
2.7 (loss)
Kenya
0.9 (loss)
Woomer
et al., 1997
Woomer
et al., 1997
Woomer
et al., 1997
Woomer
et al., 1997
Global
0.024 – 0.5
Global
0.22 – 0.7
Drylands
0.05 – 0.1
Watson
et al., 2000
Watson
et al., 2000
Lal, 1999b
Tropical
areas
Tropical
areas
Tropical
areas
0.1 – 0.2
Lal, 1999b
4– 8
Lal, 1999b
0.2 – 3.1
Lal, 1999b
0.1 – 1.0
Watson
et al., 2000
1 to 19
(loss)
0.4 to 40
(loss)
Watson
et al., 2000
Range of
reported
values
Boreal and
temperate
Tropical
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Few studies have estimated agricultural soil carbon
sequestration potentials for Europe. Early estimates by
Smith et al. (1997a,b, 1998a,b) were based on 46
long-term experiments in Europe. Since these studies
collected together all available long-term experimental data on agricultural soil carbon sequestration in
Europe, we do not re-review that literature here.
Instead, we use these values, other estimates added
by Batjes (1996) and Nabuurs et al. (1999) and the
most recent estimates of Smith et al. (2000a;b) and
Vleeshouwers and Verhagen (2002) to provide up-todate estimates of agricultural soil carbon sequestration
potential in Europe. Based on values in the papers
listed above, which already include reviews of European measurements and long-term experiments, and
on our own calculations, estimates per hectare for
agricultural soil carbon sequestration potential in
Europe are presented in Table 2, including estimates
of uncertainty associated with these figures. All fluxes
are given as gross values without consideration of the
hidden C cost of the input involved. Carbon sequestration rates in Table 2 are at the high end of worldwide estimates (Table 1), but are restricted to a time
scale of few decades.
The figures given in Table 2 were largely derived
using statistical relationships that averaged across soil
types and climates from a large number of long-term
experiments. The carbon sequestration values were
also derived for average European arable soils. The
average stock of soil C was calculated for all nonorganic soils (i.e. less than 5% C); arable soils were
assumed to be placed at random on soils of different C
content, so the average stock of soil C in European
arable soils is equal the average C stock of nonorganic soils in Europe—about 53 t C ha 1 for 0–
30 cm depth (Smith et al., 2001b). As such, there is
much variability among climatic regions and soil
types. Whilst clay soils accumulate carbon relatively
quickly, sandy soils may accumulate practically no
carbon even after 100 years of high carbon inputs
(Christensen, 1996). Similarly, soils in colder climates
where decomposition is slower, may accumulate carbon more rapidly than soils in warmer climates.
According to Vleeshouwers and Verhagen (2002),
the highest sequestration rates through the application
of farm-yard manure were calculated for South – West
and South – East Europe (e.g. Spain and Turkey),
where low soil carbon contents occur together with
7
a dry summer season, which reduces the decomposition of soil organic matter, but in reality little manure
is available in this region. Conversion of arable land
into grassland and leaving behind cereal straw exerted
the greatest effect in Western Europe, where grassland
and cereal yields are highest. The effect of reduced
tillage was highest where relatively high soil carbon
contents occur simultaneously with relatively high
decomposition rates, like for example in the Netherlands and in North-Germany.
When calculating total carbon sequestration potentials for Europe, the area where it is feasible to carry
out a specific measure should be taken into account
(Smith et al., 2000a,b). For example, application of
farmyard manure is restricted by the amount, of
manure produced, and conversion of arable land to
grassland is restricted to the area of surplus arable
land. Finding better estimates for these values will be
an important step forward in assessing regional differentiation in the efficacy of carbon dioxide abatement options in European agriculture. European totals
based on estimates of the average gain of measures
and the average proportion of agricultural areas that
may be subjected to the measures were calculated by
Smith et al. (2000a,b).
The relative effects of the different measures in the
study by Vleeshouwers and Verhagen (2002) agree
well with Smith et al. (2000a,b., 2001a) and long-term
experiments referred to therein. Only the effect of
applying farm-yard manure to cropland calculated in
Vleeshouwers and Verhagen (2002) as 1.5 t C ha 1
year 1 clearly exceeds the one calculated by Smith et
al. (2000a,b, 2001a) as 0.4 t C ha 1 year 1 although
both studies apply farm-yard manure at 10 t fresh
matter per hectare and use similar humification rates.
However, the CESAR model tends to overestimate
carbon sequestration rates when the supply of organic
matter strongly increases (Vleeshouwers and Verhagen, 2002). In addition, Vleeshouwers and Verhagen
(2002) calculate the biophysical sequestration potential whilst the estimate of Smith et al. (2000a,b,
2001a) is partly constrained by resource availability.
Both studies rely on the assumption that farmyard
manure spread on cropland sequesters more carbon
than if spread on grassland, which has recently produced some controversy (Arrouays et al., 2002).
Compared to the business-as-usual scenarios, the
changes in carbon fluxes owing to the different
8
Table 2
Measures for increasing soil carbon stocks in agricultural soils and potential yearly soil carbon sequestration rates (t C ha
measures for increasing soil carbon stocks in agricultural soils for Europe (EU15) and limiting factors
Measure
1
year
1
) and total carbon sequestration potential of
Estimated
uncertainty
(%)
Reference/
notes
Total soil
carbon
sequestration
potential if all
agric. land used
(Mt C year 1)
Limiting factor
Soil carbon
sequestration
potential
(Mt C year 1)
given limitation
Soil carbon
sequestration
potential
(Mt C year 1)
by 2012
Reference/
notes
Cropland
Zero-tillage
0.4; 0.3 F 0.1
>50%; 0 to 0.7
1, 2
28
24
2.4
19
Reduced-tillage
< 0.4
H50%
3
< 28
< 24
< 2.4
19, 20
Set-aside
< 0.4
H50%
4
28
< 2.4
0
21
Perennial
grasses and
permanent
crops
Deep-rooting
crops
0.6
>50%
5
45
Suitable
land = 63 Mha
Suitable
land = 63 Mha
< 10% of arable
land; < 7.3 Mha
No incentives to
grow more
0?
0?
22
0.6
>50%
5
45
0?
0?
22
Animal manure
0.4; 1.5 F 0.1
>50%;
0.7 to 3.2
1
27
24
?
23
Crop residues
0.7; 0.2 F 0.1
1
26
5.5
?
23
Sewage sludge
0.3
>50%;
0.3 to 0.3
>50%
1
19
2.1
?
23
Composting
0.4
H50%
6
27
3
3?
24
Improved
rotations
Fertilisation
Irrigation
>0
Very high
7
0
Research and
breeding needed
for annual crops
Manure
available = 385 Mt
dm year 1
Surplus straw = 71
Mt dm year 1
Sewage
sludge = 8.1 Mt dm
year 1 = enough to
cover 8.1 mio ha at
1 t ha 1 year 1
13 – 22 Mt year 1
d.m = enough to
cover 6 – 11 mio ha
at 20 t ha 1 year 1
>0
0?
0?
25
0
0
Very high
Very high
8
8
0
0
0
0
0
0
0
0
25
25
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Potential
soil carbon
sequestration rate
(t C ha 1 year 1)
0.6
H50%
1
45
Extensification
0.5
H50%
1
39
Organic farming
0 – 0.5
H50%
9
0 – 39
Convert arable to
woodland
0.3 – 0.6
H50%
1, 18
45
Convert arable to
grassland
1.2 – 1.7;
1.9 F 0.6;
0.3 – 0.6
110%
(0.6 – 3.1)
10, 18
87 – 123
Convert grassland
to arable
1.0 to
1.7
H50%
11, 18
70 to
Convert permanent
crops to arable
1.0 to
0.6
1.7;
H50%
11, 18
12
Convert woodland
to arable
0.6
> 50%
18
Less than
0.1 – 0.5
H50%
12
7 to 37
Grassland
Increase the
duration of
grass leys
124
78
Assuming food
demand remains the
same—can use only
current set-aside =
7.3 Mha
Assuming food
demand remains
the same—can
use current set-aside
to extensify about
30% of arable
agriculture = 20 Mha
Currently 2% or
arable area = 1.5
Mha. Could increase
to 10% = 7.3 Mha.
Assuming food
demand remains the
same—can use only
current set-aside =
7.3 Mha
Assuming food
demand remains the
same—can use only
current set-aside =
7.3 Mha
Land-use change since
1990 calculated as
2.7 Mha
Land-use change since
1990 calculated
as 0.4 Mha
Negligible land-use
change since 1990
Assuming food
demand remains
the same – can
use only current
set-aside = 7.3 Mha,
which means a
doubling of leys in
existing rotations
4.5
0.9
26
11.4
?
27
3.9
< 3.9
28
4.5
< 4.5
29
9 – 12
0
30
3 since 1990.
Future = 0
0
31
0
32
0
0
33
0.8 – 3.5
0.8 – 3.5
30
0.4 since 1990
9
(continued on next page)
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Bioenergy crops
10
Table 2 (continued)
Measure
Estimated
uncertainty
(%)
Reference/
notes
Total soil
carbon
sequestration
potential if all
agric. land used
(Mt C year 1)
Limiting
factor
Soil carbon
sequestration
potential
(Mt C year 1)
given limitation
Soil carbon
sequestration
potential
(Mt C year 1)
by 2012
Reference/
notes
0.3 – 0.4
H50%
12
22 – 29
2.2 – 2.7
2.2 – 2.7
30
0.2
H50%
12
9
Assuming food
demand remains
the same – can use
only current set-aside,
extent of present
leys = 7.2 Mha
Opposes present
CAP to maintain
extensive grassland
0
0
25
H50%
12
Opposes present
CAP, uncertain
effect on climate
0
0
25
?
?
?
?
?
?
?
34
?
?
?
?
?
?
?
34
Revegetation
Abandoned arable
land
0.3 – 0.6
H50%
13
29, 18
Assuming food
demand remains
the same—can
use only current
set-aside = 7.3 Mha
4.5
< 4.5
35
Farmed organic soils
Protection and
restoration
Up to 4.6
Range 0 – 4.6
Spatial
variability
high
14
>10
>10
10
14
0
>50%
14
0 GHG: 0.5
Assuming all
cultivated organic
soils are restored =
4% of total
agricultural area
High yields and
financial returns
for sugar beets
and potatoes,
no incentive
0?
0?
14
Grassland
Change from short
duration to
permanent
grasslands
Increase of fertilizer
on nutrient poor
permanent
grassland
Intensification of
organic soils with
permanent
grassland
Livestock
management
Fire protection
Avoid row crops and
tubers
0.9 to 1.1
2 to 2
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Potential
soil carbon
sequestration rate
(t C ha 1 year 1)
Avoid deep
ploughing
More shallow
water table
>50%
14
0.8 GHG: 0.8
1.4 – 4.1
>50%
14
10 GHG: 10
Convert arable to
grassland
Convert arable to
woodland
1.4
>50%
14
0.8 GHG: 0.8
0.5 – 1.4
H50%
15
0.5 GHG: 0.8
New crops on
restored
wetlands
from arable
New crops on
restored wetlands
from grassland
Sheep grazing
on undrained
peatland
2.2 – 4.6
>50%
16
>2 GHG: < 2
0.8 – 3.3
>50%
16
6 GHG: 5
>2.2
>50%
17
>6 GHG:>8
>2.2
>50%
14
>6 GHG: >8
Abandon for
conservation
Traditional land-use
system, no incentive
Possibly attractive
on grassland
when new
melioration is
needed—50% of
grassland area
during first
commitment
period = 1.5 Mha
No incentive
0?
0?
14
4
4
14
0?
0?
14
Subsidies
compensate
income losses—
adoption rate max.
50% of arable
area = 0.3 Mha
Needs more
research and
demonstration
0.3
0.3
14
0?
0?
14
0?
0?
14
3
3
17
0?
0?
14
Needs more
research and
demonstration
Common practice
in Scotland and
Ireland, could
be linked to
subsidies for
extensification –
adoption rate
probably 50%
of grassland
area 1.5 Mha
No incentive
A. Freibauer et al. / Geoderma 122 (2004) 1–23
1.4
11
12
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Notes to Table 2:
The potential indicated is to a large extent non-additive. GHG: Greenhouse gas reduction in C-equivalents.
1. Smith et al. (2000a,b); per hectare values calculated using the average C content of arable top soils (to 30 cm) of 53 t C ha 1; Vleeshouwers
and Verhagen (2002). 10 t of farmyard manure (fresh matter) applied annually per hectare.
2. Uncertainty estimated from 95% confidence interval about the mean-statistical uncertainty of the mean only; actual uncertainty is higher.
3. Estimated from papers reviewed in Smith et al. (2000a,b).
4. Assumed to be the same as zero tillage figure of Smith et al. (2000a,b).
5. Assumed to be the same as for bioenergy crops figure of Smith et al. (2000a,b).
6. Assumed to be the same as animal manure figure of Smith et al. (2000a;b).
7. Minimal impact of arable rotations in papers reviewed in Smith et al. (2000a,b) but perennial crops in rotations may increase soil carbon
levels.
8. Net carbon impact of irrigation and fertilisation is minimal or negative when carbon costs of producing fertiliser and pumping irrigation water
are considered (Schlesinger, 1999).
9. Organic farming is increasing in Europe, but is not a single management practice. Within an organic farm, a combination of practices may be
used including extensification, improved rotations, residue incorporation and manure use. These will contribute to carbon sequestration
positively, but in different proportions depending of the degree of implementation of a given practice. Zero and reduced tillage are generally
incompatible with organic farming since increased tillage is frequently used to control weeds. It is, therefore, impossible to assign an exact
figure for the carbon sequestration potential of organic farming, but a range between the lowest and highest potential sequestration rate can be
given.
10. From Vleeshouwers and Verhagen (2002). Also based on figures from Rothamsted grass to arable conversions; for first 15 – 25 years after
conversion.
11. From figures of Jenkinson (1988) used by Smith et al. (1996). Also based on figures from Rothamsted grass to arable conversions; for first
15 – 25 years after conversion.
12. From French experiments by P. Loiseau, in Arrouays et al. (2002). Grassland area from EC (2001) for 1997, grassland on organic soils
estimated from Lappalainen (1996).
13. Per hectare value assumed to be the same as Rothamsted Geescroft natural regeneration (Poulton, 1996).
14. Calculated in this study. Carbon sequestration is from avoiding carbon loss from peats. Further benefit through reduced emission of N2O,
which is not compensated by increased CH4 emissions. GHG: Effect including N2O and CH4, given as CO2-equivalents.
15. Sites in Ireland, Scotland and Sweden (Byrne and Farrell, 2001; Cannell et al., 1993; Maljanen et al., 2001).
16. Typha: German constructed wetland (Kamp et al., 2001).
17. Garnett et al. (2000).
18. Land use change estimates also from Guo and Gifford (2002), Murty et al. (2002): relative changes in soil carbon stocks given in these
studies were linearly discounted over a 25-years period, assuming initial soil carbon stocks of 43 t C ha 1 in cropland and of 70 t C ha 1 in
grassland and forest (average for France, Arrouays et al., 2002).
19. Total figure for EU15 calculated from figures in Smith et al. (2000a; 2000b). Suitable land area from Smith et al. (1998a,b). Estimated
maximum of 10% adoption before 2008 estimated from uptake in the USA since 1970 in Lal et al. (1998).
20. Total figure for EU15 estimated to be lower than figure for zero-till calculated from figures in Smith et al. (2000a,b).
21. Set-aside has decreased during the 1990s. If at current levels (10% of arable area; Smith et al., 2000a,b) the potential would be 2.4 Mt C
year 1, but is likely to be negligible by 2012.
22. Total figure for EU15 based on per hectare value assumed to be the same as for bioenergy crops. There are no special incentives for
perennial crops so the prevalence of perennial crops is unlikely to increase.
23. Total figure for EU15 calculated from figures in Smith et al. (2000a,b). Total amount of manure and sewage sludge available from Smith et
al. (1997a,b) of surplus cereal straw from Smith et al. (2000a,b). Guestimate that only 20% of surplus cereal straw will be usable for
incorporation into the soil, with remaining straw either used for bioenergy combustion or not viable due to transport/economic constraints.
24. Total figure for EU15 based on per hectare value assumed to be the same as animal manure. Total compost dry matter from Enzo Favoino,
Monza/Italy, personal communication.
25. Assumed negligible benefit, e.g. Rounsevell et al. (2002).
26. Total figure for, and area available in, EU15 calculated from figures in Smith et al. (2000a,b). Uptake assumed to be 20% of maxiumum
potential by 2008 as for the UK (UNFCCC, 2001).
27. Total figure for, and area available in, EU15 calculated from figures in Smith et al. (2000a; 2000b).
28. Total area currently under organic production (2%) in EU15 taken from values given in Rounsevell et al. (2002), total area from those
calculated from Smith et al. (2000a; 2000b). Assuming that organic farming would remain profitable only if less than 10% of farm products
were produced organically.
29. Total figure for and area available in EU15 calculated from figures in Smith et al. (2000a, 2000b) and from ECCP (2001).
30. Total figure for EU15 from Vleeshouwers and Verhagen (2002). Available area ( < 10% set aside) from Smith et al. (2000a,b). Livestock
numbers are falling; unlikely to be greater demand for new grassland.
A. Freibauer et al. / Geoderma 122 (2004) 1–23
measures or climate change effects evaluated in Vleeshouwers and Verhagen (2002) were considerably less
sensitive to the initial soil carbon content. The reason
for this is that they are the resultant of the difference
between two carbon fluxes calculated with the same
initial value of soil carbon content. This favorably
affects the robustness of the estimates and the quantification of regional differences.
Inter-annual variability in climate affects yields and
hence, the amount of carbon returned to the soil, and
also decomposition rates. As illustrated by Vleeshouwers and Verhagen (2002), the effect of leaving
behind and incorporating straw residues varies. Even
when averaged over a period of 5 years, natural interannual variation in prevailing conditions and crop
yields may cause substantial variation in the effect
of the measure. This raises the question whether it
may be more appropriate to reward an activity aimed
at the increase of carbon rather than to reward its
actual effect on the carbon stock in the field, since the
latter may partly depend on the climatic conditions
beyond farmers’ influence.
3.4. Factors limiting carbon sequestration in soils
3.4.1. Mechanisms of carbon sequestration
Carbon sequestration is usually measured in terms
of the total carbon stored in the soil but how much
carbon is stored, and for how long this carbon can be
stored, depends upon the pools (active/labile vs.
recalcitrant/passive) and their recycling (Six et al.,
2001; Gleixner et al., 2002), form of stabilization
(chemical/physical) (Kaiser et al., 2002) and physical
location (inter/intra-aggregate vs. free) (Balesdent et
al., 2000; Six et al., 2001) of the carbon in the soil. It
is beyond the scope of this review to cover the huge
body of literature on these mechanisms. Instead we
13
Fig. 4. The accumulation of total soil carbon in silty clay loam soils
at Rothamsted, UK, when old arable land is sown to permanent
grass. Adapted from nitrogen content in Fig. 18.10 of Jenkinson
(1988), C/N ratio = 10.
focus on the practical management options available
to increase to total carbon content of the soil.
3.4.2. Sink saturation
Whilst the figures given in Table 2 are approximate
for a short period (5 years Kyoto Commitment Period), changes in carbon sequestration with time need to
be considered. Soil carbon sequestration is non-linear.
Long-term experiments show that increases in soil
carbon are often greatest soon after a land-use or landmanagement change is implemented (Smith et al.,
1997a,b and papers quoted therein). As the soil reaches a new equilibrium, the rate of change decreases,
so that after between 20 and 100 years a new equilibrium is reached and no further change takes place
(Fig. 4).
This phenomenon is sometimes referred to as sink
saturation (Watson et al., 2000). Whilst soil carbon
levels may not reach a new equilibrium until 100
years after land-use or land-management change
(Smith et al., 1996), carbon sequestration potential
Notes to Table 2 (continued):
31. Total area available in EU15 calculated from figures in Smith et al. (2000a,b) and EC (2001). About 3 Mha of permanent pasture have been
lost since 1990. 60% of the 0.5 Mha afforested between 1993 and 1997 under regulation 2080/2092 came from permanent grassland = 0.3 Mha.
This leaves a total area of grassland to arable conversion of about 2.7 Mha from 1990 to present. Further change from grassland to arable is
unlikely to occur due to stable food demand.
32. Loss of area of permanent crops (vineyards, olives, orchards) does not necessarily mean conversion to arable land, the land could be
abandonded and revegetated. Therefore worst-case estimate.
33. Loss of carbon when converting woodland to arable similar to or smaller than converting grassland to arable (Guo and Gifford, 2002).
Actually, afforestation has occurred meaning that the net change will be positive.
34. No reliable data.
35. Same figure as for conversion of arable to woodland.
14
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Table 3
Potential environmental side effects of the soil carbon sequestration options
Measure
Cropland
Zero-tillage
Reduced-tillage
Set-aside
Perennial grasses and permanent crops
Deep-rooting crops
Animal manure
Crop residues
Sewage sludge
Composting
Improved rotations
Fertilisation
Irrigation
Bioenergy crops
Potential environmental side effects
Some increase in pesticide usage but less fossil fuel used (included in
calculations). N2O emissions may increase as soils may become more
anaerobic leading to more N2O production from denitrification.
When these potential increases in N2O are converted to carbon equivalents and
included in the calculations, the total mitigation effect in terms of the global
warming potential is reduced by about 50 – 60% compared to when only soil carbon
sequestration is considered (Smith et al., 2001a).
As for zero tillage.
More weeds in years following set-aside—more herbicide usage possible.
Improved biodiversity for some species possible.
Improved biodiversity for some species possible.
Improved continuity of soil pores to greater depth, enhanced deep infiltration.
Potentially a number of environmental side effects associated with the significantly
increased transport required for this measure (Smith and Smith, 2000). Increased
transport emissions which are about 30% of sequestered carbon if average distance
moved is 100 km. But increased demand for fuel, increased particulate losses from
combustion of fuel, if fitted with catalytic converters, increased ammonia and other
gaseous emissions from transport etc. (ECCP, 2001). On the positive side possible
trace gas benefits (compared to applying the manure to grasslands) and
improved soil structure and water holding capacity (Smith et al., 2001a).
Possible slight increase in N2O emissions due to more organic material in
the soil as a source of mineralisable N (Smith et al., 2001a).
Possible slight increase in N2O emissions due to more organic material
in the soil as a source of mineralisable N. Non-regulated sewage sludge
or any other waste can have negative environmental effects such as the
build-up of heavy metals and organic pollutants. The sludge could, however,
be applied at below the safe EU limits (Smith et al., 2001a).
Environmental benefits from application of urban composts including the avoided
use of chemical fertilizers and pesticides, improved tilth, positive effect on
trace minerals. Possible slight, increase in N2O emissions due to more organic
material in the soil as a source of mineralisable N, but not confirmed by
measurements. Also possible N2O emissions during composting process.
If carefully planned, could reduce nitrate leaching.
Increased N2O emissions due to addition of extra reactive N to the soil.
CO2 carbon costs of fertiliser production can be greater than the soil carbon
sequestration benefit (Schlesinger, 1999).
CO2 carbon costs of pumping irrigation water can be greater than the soil
carbon sequestration benefit (Schlesinger, 1999).
This is a measure that the UK Government believes can mitigate emissions
of CO2 from fossil fuels and has introduced the Energy Crops Scheme under
the England Rural Development Programme to support these activities.
Expenditure of £ 30 m over the seven year life of the programme will
support planting of crops and setting up of producer groups for short-rotation
coppice growers. Because the biomass fuel chain results only in some GHG
emissions (sometimes nearly C-neutral-depending on the biomass chain,
considered), energy crops can make a significant contribution to Government
targets on renewable energy and climate change. The Prime Minister recently
announced a further £ 50 m support for renewable energy from biomass and
offshore wind. This is not carbon sequestration since the carbon is rapidly
burnt to substitute for fossil fuels. The IPCC calls this ‘‘carbon substitution’’,
replacing fossil carbon by ‘‘recent’’ carbon (ECCP, 2001). May also improve
biodiversity and leisure and amenity value of the arable land
(Smith et al., 2001a).
A. Freibauer et al. / Geoderma 122 (2004) 1–23
15
Table 3 (continued)
Measure
Cropland
Extensification
Organic farming
Convert arable to woodland
Convert arable to grassland
Convert grassland to arable
Convert permanent crops to arable
Convert woodland to arable
Grassland
Increase the duration of grass leys
Change from short duration to
permanent grasslands
Increase of fertilizer on nutrient poor
permanent grassland
Potential environmental side effects
Wildlife benefits, animal welfare benefits, improved soil structure
(Smith et al., 2001a).
Potential benefits due to reduced fertilizer production (hence less CO2
produced), more fuel carbon used as physical methods are used to reduce
weeds in place of herbicides, possible wildlife benefits, animal welfare
benefits, improved soil structure, potentially more nitrate leaching and N2O
emissions (depending on time of application of manure).
Benefits potentially high if afforestation is sensitive to regional habitats
and landscapes. Biodiversity and landscape will not be improved by
commercial monocultures. This requires abandonment of agricultural land.
Afforestation is already part of agroenvironmental schemes in some member
states (ECCP, 2001). May improve biodiversity and leisure and amenity value
of the land (Smith et al., 2001a).
Potentially high benefits depending on end use and type of restored grassland
habitat. May reduce leaching.
Lose soil carbon. Of minor importance. The arable land area has been largely
fixed since 1992.
Lose soil carbon.
Lose soil carbon.
May reduce leaching. Beneficial for soil structure and erosion protection.
May reduce leaching. Beneficial for soil structure and erosion protection.
Intensification of organic soils with
permanent grassland
Livestock management
Fire protection
Increased N2O emissions due to addition of extra reactive N to the soil. CO2
carbon costs of fertiliser production can be greater than the soil carbon
sequestration benefit (Schlesinger, 1999).
May enhance productivity. Uncertain benefit for CO2, and risk of increased
N2O emissions (cf. above).
May reduce soil degradation and compaction.
Improve biodiversity in fire prone areas.
Revegetation
Abandoned arable land
Same as for ‘‘convert arable to woodland’’.
Farmed organic soils
Protection
Avoid row crops and tubers
Avoid deep ploughing
More shallow water table
Convert arable to grassland
The potential for GHG reduction is high. If the reduction of N2O and CO2
emissions originally emitted from peat oxidation is included, the overall
effect is >1.4 Mt C-equivalents year 1 if an adoption on 10% of farmed
peatlands of either of the measures (1) no roots and tubers, (2) abandon
tillage, (3) recultivation, is achieved (ECCP, 2001).
Frequent and intensive soil disturbance under vegetables, potatoes, and
sugar beets and enhances N mineralisation (Klemedtsson et al., 1999).
In several Swedish studies, N2O emissions were higher than under cereals.
Avoid a pulse in soil aeration. However, this means to abandon the traditional
practice in many regions with a sandy mineral layer underneath the peat and
makes the soil less workable.
This will restrict the choice of arable crops and will probably be restricted to
grasslands.
Best in conjuntion with a more shallow water table.
(continued on next page)
16
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Table 3 (continued)
Measure
Farmed organic soils
Convert arable to woodland
New crops on restored wetlands from arable
New crops on restoredwetlands from grassland
Sheep grazing on undrained peatland
Abandon for conservation
Potential environmental side effects
Afforestation of peat soils under arable crops only if provided that a more
shallow water table than before is maintained. There will be also some
extra benefit through carbon sequestration in wood and wood products
(Cannell and Milne, 1995). The afforestation of grasslands will only show
long-term benefits. However, Swedish studies suggest that in the first years of
afforestation greenhouse gas emissions may be higher (Maljanen et al., 2001).
Also Birch planted as short-rotation coppice increased carbon losses and
greenhouse gas emissions due to the lowering of the water table by intensive
respiration (Å. Kasimir Klemedtsson, personal communication, 2001).
Further research is needed before afforestation of peat soils can be
recommended as option with short-term and long-term benefits. Unfortunately,
a recent EU research proposal in this direction was not funded.
Typha produced for industrial raw material on rewetted, formerly drained, fens
reduces the emission of greenhouse gases, retains water and probably reactivates
the function of peatlands as a sink of nutrients in the landscape
(Wild et al., 2001). However, economic viability and large-scale applicability
still remain to be proven.
Same as for new crops on restored wetlands from arable.
Abandon drainage and use native grass sod for extensive sheep grazing.
Sheep-grazing and rotational burning are widely practised on blanket peat
moorlands in the United Kingdom. In a study of Garnett et al. (2000), light
sheep-grazing did not affect rates of C accumulation over 30 years in blanket
peat, but decadal burning of moorland reduced C sequestration.
Peatlands need decades to recover from drainage and to regain the original
vegetation cover. Nevertheless, the restoration will rapidly stop peat oxidation.
Manifold conservation and recreation benefits.
may be minimal after 20 years. Twenty years is also
the period used by the IPCC for national greenhouse
gas inventories (IPCC, 1997). Soil carbon sequestration does not have unlimited potential to offset CO2
emissions and the yearly benefits will continue for
about 20– 50 years. The final level at which the soil
carbon stabilises depends upon the ability of the soil
to stabilise carbon (related for instance to its cation
exchange capacity or clay content), the prevailing
climate determiing soil moisture and temperature,
the quality (decomposability) of the carbon added to
the soil, and the balance between the carbon input to
the soil and the carbon lost through respiration.
3.4.3. Non-permanence
Soil carbon sequestered in arable soils is nonpermanent. By changing agricultural management or
land-use, soil carbon is lost more rapidly than it
accumulates (Smith et al., 1996). For soil carbon
sequestration to occur, the land-use or land-management change must also be permanent. Whilst agricul-
tural soils that are tilled every few years may contain
more carbon than the same soils cultivated every year
(Smith et al., 1997a,b and papers quoted therein),
much of the benefit of reduced tillage is lost by
ploughing, when compared to a permanent management change. The impacts of such practices can be
estimated; for example permanent set-aside or zerotillage might result in a carbon sequestration potential
of 0.4 t C ha 1 year 1, whilst set-aside or zero-till
which is ploughed every 3– 4 years would have a
carbon sequestration potential that is much lower. For
practical purposes, however, in order to implement a
meaningful carbon sequestration policy on agricultural land, management changes must be permanent.
3.4.4. Availability of land and adoption of measures
Other factors limiting the implementation of soil
carbon sequestration measures are the availability of
suitable land and soils and the availability of limited
resources such as the amount of sewage sludge,
animal manure or cereal straw available. In a recent
A. Freibauer et al. / Geoderma 122 (2004) 1–23
review comparing bioenergy offsets with carbon sequestration potential, Cannell (2003) estimated the
biological potential, realistically achievable potential,
and a conservative achievable potential for carbon
sequestration. In Table 2, we give the total estimated
carbon sequestration potential for Europe of each of
the measures, taking account of limitation in suitable
land/resources, etc. (between the biological potential
and realistically achievable potential according to the
definitions of Cannell, 2003). Where possible, the
potential attainable by the end of the first Kyoto
Commitment Period (2012) is estimated (between
the realistically achievable and conservative achievable potential as defined by Cannell, 2003), though
more work needs to be done in estimating social and
economic limitations to the implementation of these
measures.
4. Potential environmental side effects of soil
carbon sequestration measures
A number of potential side-effects of agricultural
carbon mitigation measures were described by Smith
et al. (2001a) and expanded upon by the European
Climate Change Programme (ECCP, 2001). In Table
3, we summarise these results and add new findings
for the extra land management changes suggested
here.
A main consideration for many agricultural practices is the impact on the trace gases N2O and CH4
and impacts on other nitrogen losses. Given that
organic matter contains nitrogen as well as carbon,
increasing the soil carbon content also provides more
substrate for N loss by leaching and N2O emission.
For practices that potentially increase denitrification
(e.g. no-till), these N2O losses can be substantial and
may impact the overall greenhouse gas mitigation
potential significantly (Smith et al., 2001a). Other
practices, such as conversion to woodland, may have
significant positive side effects such as increased
biodiversity.
5. Effects on farm income
Since the Treaty of Rome, the underlying principle
of the CAP has been to maintain farmer incomes. This
17
principle has continued into the 1990s, and each new
policy whether related to production, rural development or agri-environment has had some mechanism
for compensating farmers for potential losses in income following the implementation of the policy.
AGENDA 2000 (EC, 1997), for example, has been
estimated to have increased average farm incomes by
4.5% (Mortimer, 1998). Furthermore, policies such as
the Less Favoured Areas (LFAs) have as their main
aim the maintenance of incomes in disadvantaged
areas, i.e. where farming would otherwise not be
viable. There are, however, regional disparities in
these effects with northern European countries (except
Ireland) benefiting from higher LFA subsidy payments than in the south. Some incomes in simple
LFAs in France and Germany, for example, are even
higher than the EU average. Thus, in general the effect
of post 1990 policies on farmer incomes has been
positive or neutral.
5.1. Factors affecting farm profitability of soil carbon
sequestration measures
In addition to the effect of specific CAP policies on
farmer incomes, one can also examine the potential
effects of soil C sequestration measures based on land
management. At present, we can describe only qualitatively the impact of these measures on farm profitability and/or costs. Some potential impacts are
described in Table 4.
Many carbon sequestration measures have potential positive and negative effects on farm profitability.
For a few, a net positive impact of farm profitability
is expected, whilst for the restoration of drained
organic soils, a net negative impact is expected (see
Table 4). Within the rural development policy (agrienvironmental scheme), a measure for no tillage in
combination with a mulch-seed system exists e.g. in
Germany, where between 25 and 60o ha 1 is paid
for this measure. Within the ECCP, 20o for the
reduction of 1 t CO2 ( 73o per t C) is assumed to be
cost effective. Taking this figure and an absorption
potential of 0.3 t C ha 1 year 1, 22o could be paid
for 1 ha of agricultural land (ECCP, 2001). The
economic benefits from CO2 sequestration by themselves could finance additional ‘‘agri-environmental
measures’’. The agricultural sector could receive
additional benefits from ‘‘emission trading’’. In the
18
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Table 4
Factors affecting farm profitability of soil carbon sequestration measures
Measure
Cropland
Zero-tillage
Reduced-tillage
Set-aside
Perennial grasses and
permanent crops
Deep-rooting crops
Animal manure
Crop residues
Sewage sludge
Composting
Improved rotations
Fertilisation
Irrigation
Bioenergy crops
Extensification
Potential positive effects on farm
profitability
Potential negative effects on
farm profitability
Overall effect on
farm profitability
In dry areas may improve
productivity via improved
moisture retention
In wetter areas more risk of
fungal attack, reduced emergence
and crop failure. High initial
equipment investment cost.
In wetter areas more risk of
fungal attack, reduced emergence
and crop failure.
Unless subsidised, reduced area
available for production
Less flexibility to respond to
market changes
+ or
unclear,
regionally specific
In dry areas may improve
productivity via improved
moisture retention
Possible better long term
soil fertility
Possible better long term
soil fertility
Possible better long term
soil fertility
Possible better long term
soil fertility
Possible better long term
soil fertility
Possible better long term
soil fertility
Possible better long term
soil fertility
Possible better long term
soil fertility
Improved production
Improved production
Depends on price of other fuels.
Potential improved
long-term fertility
Potential improved long-term
fertility
Premium paid for organic products
+ or
unclear,
regionally specific
+ or
+ or
+ or
+
+
Possible harmful effects of sludge
may reduce long-term soil fertility
+ or
+
+
Small increase in fertilizer cost
Cost of irrigation water and fuel
to pump it
Less flexibility to respond to
market changes
+
+ or
+ or
+ or
+ or
+ or
+ or
Convert arable to woodland
Possible subsidies to improved
leisure and amenity value of the land
Convert arable to grassland
Convert grassland to arable
Convert woodland to arable
Depends on relative product values
Depends on relative product values
More land available for production
Less intensive production may lead
to reduced per hectare profits
Long-term commitment and less
flexibility to respond to market changes
Reduced area available for production
and less flexibility to respond to
market changes
Depends on relative product values
Depends on relative product values
Initial clearance costs
Depends on relative product values
Depends on relative product values
+ or
Depends on relative product values
Depends on relative product values
+ or
Improved production
Small increase in fertilizer cost
+
Improved production
Small increase in fertilizer cost
+
Organic farming
Grassland
Increase the duration
of grass leys
Change from short duration
to permanent grasslands
Increase of fertilizer on nutrient
poor permanent grassland
Intensification of organic soils
with permanent grassland
+
+ or
A. Freibauer et al. / Geoderma 122 (2004) 1–23
19
Table 4 (continued)
Measure
Grassland
Livestock management
Fire protection
Revegetation
Abandoned arable land
Potential positive effects on farm
profitability
Potential negative effects on
farm profitability
Overall effect on
farm profitability
Possibly higher labour costs.
Productivity may increase
Increased labour cost
Labour costs could be lower.
Productivity may decrease
Product lost to fire less regularly
+
+ or
Possible subsidies for improved
leisure and amenity value of the land
Less land for production
+ or
Farmed organic soils
Protection and restoration
USA, farmers already have contracts with the industry, offering CO2 credits resulting from changing
their land-use systems. If the USA does not participate in the future in the Kyoto Protocol, a lower price
per tonne CO2 is expected on the CO2 market due to
a reduced demand for CO2 credits (ECCP, 2001).
However, with present market prices as low as 3o
per t CO2 (0.82o per t C) the economic benefit per
hectare is negligible.
Another example of measures that promote the
accumulation of organic matter in the soil occurs in
some regions of Italy, where under the scope of rural
development plans (2000 – 2006), farmers are subsidised for the application of organic fertilisers, in
particular composted products, by between 155 and
220o ha 1 (ECCP, 2001).
6. Summary and conclusions
The direct effect of CAP measures on carbon
sequestration in agricultural sinks cannot always be
quantified due to interactions with other socio-economic drivers. Indirectly, however, some productionrelated policies and the agri-environmental schemes
have probably helped to maintain carbon stocks in
agricultural soils. Specific effects include the increase
in carbon stocks through afforestation subsidies, the
encouragement of organic farming, and the introduction of set aside with its scope for biofuel production
with perennial species.
Farm-yard manure, which partly consists of straw,
is likely to be more resistant to decomposition than
Less land for production
pure animal manure. In Vleeshouwers and Verhagen
(2002), conversion into grassland is the most effective carbon mitigation option, which endorses the
main conclusion by Smith et al. (2000a,b, 2001a)
implying that putting surplus arable land into longterm alternative land-use, suitable for climate change
abatement is the most effective land use option in
agriculture.
Conversely, however, LFA schemes may have contributed to the maintenance of lower than natural
carbon stocks in ecosystems of extensive grazing areas
which might otherwise have been abandoned and
revegetated by species that assist carbon sequestration.
There is a realistic potential to sequester up to
16– 19 Mt C year 1 in agricultural soils of EU-15
during the first commitment period, which is equivalent to 2% of its anthropogenic CO2 emissions.
Promising policy measures in all three categories of
FCCC/CP/2001/13/Add.1, 2002 (Table 5) imply ancillary environmental and economic benefits:
– Cropland management: Promotion of increased C
input from organic amendments, organic farming,
conservation tillage;
– Grazing land management: Maintain a more shallow
water table and rewet grasslands on peat soils;
– Revegetation: permanent revegetation of set-aside
areas with perennial grasses or woody bioenergy
crops instead of rotational fallow.
Because of regional differences in soil, site, and
climatic conditions a substantial spatial component
20
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Table 5
Most promising policy measures (summary of Table 2, cropland only)
Policy measure
Potential per unit
area t C ha 1 year
1
Potential in
EU-15 during
first commitment
period Mt C year
Environmental
side effects
Impact on farm
income
More N2O from
organic amendments?
Accounting of N in
organic input as fertiliser
required to avoid nitrate
losses. Erosion control and
reduced nitrate leaching
under cover crops.
Benefits for wildlife,
biodiversity, amenity
Positive long-term
tendency due to better
soil fertility, easy
implementation
1
1
Promote organic
input on arable land
instead of grassland
(crop residues, cover
crops, FYM, compost,
sewage sludge)
0.3 – 0.8
5.5
2
Permanent
revegetation of arable
set-aside arable land
(e.g. afforestation)
or extensivation of
arable production
by introduction of
perennial components
Biofuel production
with short-rotation
coppice plantations
and perennial grasses
on arable set-aside land.
Promote organic farming
0.5 – 1.9 (mean: 0.6)
4.1
0.5 – 1.9 (mean: 0.6)
4.1
Much greater additional
benefit from substitution
of fossil fuels by
bioenergy
Regionally specific, positive
if linked to subsidies or
emerging markets
>0 to 0.5
3.8
Benefits for wildlife,
biodiversity, amenity,
but risk of more N2O
loss from incorporation
of legume residues
Benefits for wildlife,
biodiversity, amenity,
water retention, reduced
N2O losses
Risk of more N2O, more
pesticides, very small C
sink in reduced tillage
systems, erosion control
Positive due to premium
and growing market
3
4
5
Promote permanently
shallow water table in
farmed peatland
1.4 – 4.1
4.1
6
Zero tillage/conservation
tillage
>0 – 0.8
< 2.5
in the net sequestration potential may be expected.
Consequently, uncertainties in European scale estimates are large (>50%). To support the development of climate policies, regional estimates of the
carbon mitigation potential of land-management
strategies are helpful. Such estimates should be
supported by regional specific data on soil, climate,
land cover, land management and ecosystem productivity. These data are, however, not readily
available and quality of the available data varies
strongly. The resolution of the FAO data, as used
Regionally specific,
positive if linked to
compensation payment
for nature protection
Regionally specific, positive
if linked to compensation
payment for nature protection
Site and region specific,
increased production risk for
farmer positive only if linked
to good erosion control
and better soil fertility
in here is too coarse and produces an unbalanced
picture. Creating data sets on above mentioned
topics covering Europe at a high (sub-country)
resolution will improve estimates and allow selection
of areas with high carbon sequestering potential.
Acknowledgements
This paper was based on a report produced under
Contract No. 2001.40.CO001 within the framework of
A. Freibauer et al. / Geoderma 122 (2004) 1–23
the Communication on ‘‘EU policies and measures to
reduce greenhouse gas emission: Towards a European
Climate Change Programme (ECCP)’’, COM (2000)
88, Working Group Sinks, Subgroup Soils.
References
Aerts, R., Toet, S., 1997. Nutritional controls on carbon dioxide and
methane emission from carex-dominated peat soils. Soil Biol.
Biochem. 29, 1683 – 1690.
Arrouays, D., Balesdent, J., Germon, J.C., Jayet, P.A., Soussana,
J.F., Stengel, P. (Eds.), 2002. Contribution à la lutte contre
ĺeffet de serre. Stocker du carbone dans les sols agricoles de
France? Expertise Scientific Collective. Rapport d́expertise
réalisé par INRA à la demande du Ministère de ĺEcologie
et du Développement Durable. October 2002. INRA, Paris,
France.
Balesdent, J., Chenu, C., Balabane, M., 2000. Relationship of soil
organic matter dynamics to physical protection and tillage. Soil
Tillage Res. 53, 215 – 230.
Batjes, N.H., 1996. Total carbon and nitrogen in the soils of the
world. Eur. J. Soil Sci. 47, 151 – 163.
Byrne, K.A., Farrell, E.P., 2001, Carbon balance of peatland forests
in Ireland. Presentation at Budapest Meeting of COST Action
E21, Contribution of Forests and Forestry to Mitigate Greenhouse Effects, Budapest 26 – 28 Apr 2001, http://www.bib.
fsagx.ac.be/coste21/report/2001-04-26.html.
Cannell, M.G.R., 2003. Carbon sequestration and biomass energy offset: theoretical, potential and achievable capacities
globally, in Europe and the UK. Biomass Bioenergy 24,
97 – 116.
Cannell, M.G.R., Milne, R., 1995. Carbon pools and sequestration
in forest ecosystems in Britain. Forestry 68, 361 – 378.
Cannell, M.G.R., Dewar, R.C., Pyatt, D.G., 1993. Conifer plantations on drained peatlands in Britain: a net gain or loss of
carbon. Forestry 66, 353 – 369.
Chapman, S.J., Thurlow, M., 1996. The influence of climate on
CO2 and CH4 emissions from organic soils. Agric. For. Meteorol. 79, 205 – 217.
Christensen, B.T., 1996. The Askov long-term experiments on animal manure and mineral fertilizers. In: Powlson, D.S., Smith,
P., Smith, J.U. (Eds.), Evaluation of Soil Organic Matter
Models Using Existing, Long-Term Datasets. NATO ASI,
vol. I38. Springer, Heidelberg, Germany, pp. 301 – 312.
EC, 1997. European Commission, Agenda 2000 for a wider
stronger EU. COM (97) 2000, Office for Official Publications
of the Community, Luxembourg, 15/07/1997. DOC/97/6 – 97
pp. (vol. I), DOC/97/7 – 90 pp. (vol. II), DOC/97/8 – 59 pp.
(vol. III).
EC, 2001. European Commission, Agriculture in the European
Union: Statistical and Economic Information 2000, http://
europa.eu.int/comm/agriculture/agrista/2000/table-en/
index.htm.
ECCP, 2001. European Climate Change Programme (ECCP)
21
Working Group 7—Agriculture. Mitigation potential of Greenhouse Gases in the Agricultural Sector, http://europa.eu.int/
comm/environment/climat/eccp.htm.
Evans, L.T., 1993. Crop Evolution, Adaptation and Yield. Cambridge Univ. Press, Cambridge.
FCCC/CP/2001/13/ Add.1, 2002. Report of the Conference of the
Parties on its seventh session, held at Marrakesh from 29 October to 10 November 2001. Addendum. Part two: Action taken
by the Conference of the Parties. Volume I. United Nations
Framework Convention on Climate Change, United Nations
Office at http://maindb.unfccc.int/library/.
Freibauer, A., 2003. Biogenic Emissions of Greenhouse Gases from
European Agriculture. Eur. J. Agron. 19 (2), 135 – 160.
Garnett, M.H., Ineson, P., Stevenson, A.C., 2000. Effects of burning
and grazing on carbon sequestration in a Pennine blanket bog,
UK. Holocene 10, 729 – 736.
Gleixner, G., Poirier, N., Bol, R., Balesdent, J., 2002. Molecular
dynamics of organic matter in a cultivated soil. Org. Geochem.
33, 357 – 366.
Global Soil Data Task, 2000, Global Soil Data Products CD-Rom
(IGBP-DIS) International Geosphere – Biosphere Programme—
Data and Information Services. http://www.daac.ornl.gov/SOILS/
igbp.html.
Guo, L.B., Gifford, R.M., 2002. Soil carbon stocks and land use
change: a meta analysis. Glob. Chang. Biol. 8, 345 – 360.
IPCC, 1996. Global Change 1995— The Science of Climate
Change. Contribution of Working Group I to the Second Assessment Report of the Intergovernmental Panel on Climate
Change, Intergovernmental Panel on Climate Change. Cambridge Univ. Press, Cambridge.
IPCC, 1997, IPCC Guidelines for National Greenhouse Gas Inventories. Workbook. Paris, Intergovernmental Panel on Climate
Change.
Jackson, R.B., Banner, J.L., Jobbágy, E.G., Pockman, W.T., Wall,
D.H., 2002. Ecosystem carbon loss with woody invasion of
grasslands. Nature 418, 623 – 626.
Jenkinson, D.S., 1988. Soil organic matter and its dynamics. In:
Wild, A. (Ed.), Russell’s Soil Conditions and Plant Growth, 11th
Edition. Longman, London, pp. 564 – 607.
Joaris, A., 2002. Non-food and energy crops, a long tradition and
potential for the future. European Commission Fact Sheet,
http://europa.eu.int/comm/agriculture/envir/report/en/n-food-en/
report.htm.
Kaiser, K., Eusterhues, K., Rumpel, C., Guggenberger, G., KögelKnabner, I., 2002. Stabilization of organic matter by soil minerals—investigations of density and particle-size fractions
from two acid forest soils. Z. Pflanzenernahr. Bodenkd. 165,
451 – 459.
Kamp, T., Gattinger, A., Wild, U., Munch, J.C., 2001. Methane and
nitrous oxide emissions from drained and restored peat in the
Danube valley. Verhandlungen der Gesellschaft für Ökologie,
vol. 31. Parey, Berlin, p. 193.
Kasimir Klemedtsson, Å., Klemedtsson, L., Berglund, K., Martikainen, P., Silvola, J., Oenema, O., 1997. Greenhouse gas emissions from farmed organic soils: a review. Soil Use Manage. 13,
1 – 6.
Klemedtsson, L., Kasimir Klemedtsson, Å., Esala, M., Kulmala, A.,
22
A. Freibauer et al. / Geoderma 122 (2004) 1–23
1999. Inventory of N2O emission from farmed European peatlands. In: Freibauer, A., Kaltschmitt, M. (Eds.), Approaches to
Greenhouse Gas Inventories of Biogenic Sources in Agriculture.
IER-Forschungsbericht, vol. 53, pp. 79 – 94.
Komulainen, V.M., Tuittila, E.S., Vasander, H., Laine, J., 1999.
Restoration of drained peatlands in southern Finland: initial
effects on vegetation change and CO2 balance. J. Appl. Ecol.
36, 634 – 648.
Lal, R., 1999a. Soil management and restoration for C sequestration
to mitigate the accelerated greenhouse effect. Progress Environ.
Sci. 1, 307 – 326.
Lal, R., 1999b. Global carbon pools and fluxes and the impact
of agricultural intensification and judicious land use. Prevention of Land Degradation, Enhancement of Carbon Sequestration and Conservation of Biodiversity Through Land Use
Change and Sustainable Land Management with a Focus on
Latin America and the Caribbean. World Soil Resources
Report 86. FAO, Rome, pp. 45 – 52.
Lal, R., Kimble, J.M., Follet, R.F., Cole, C.V (Eds.), 1998. The
potential of U.S. cropland to sequester carbon and mitigate the
greenhouse effect. Ann Arbor Press, Chelsea, MI, p. 128.
Lappalainen, E., 1996. Global Peat Resources. Saarijärven Offset
Oy, Saarijärvi, Finland.
Maljanen, M., Hytönen, J., Marttikainen, P.J., 2001. Fluxes of N2O,
CH4 and CO2 on afforested boreal agricultural soils. Plant Soil
231, 113 – 121.
Minkkinen, K., Vasander, H., Jauhiainen, S., Karsisto, M., Laine, J.,
1998. Post-drainage changes in vegetation composition and carbon balance in Lakkasuo mire, Central Finland. Plant Soil 207,
107 – 120.
Mortimer, D., 1998. Current land management and stewardship
schemes in the EU and their implications for land use. Working
Paper No. 1, Jackson Environment Institute, University College
London, pp. 24.
Murty, D., Kirschbaum, M.U.F., McMurtrie, R.E., McGilvray, H.,
2002. Does conversion of forest to agricultural land change soil
carbon and nitrogen? A review of the literature. Glob. Chang.
Biol. 8, 105 – 123.
Nabuurs, G.J., Dolman, A.J., Verkaik, E., Whitmore, A., Daaman, W., Oenema, O., Kabat, P., Mohren, G.M.J., 1999.
Resolving Issues on Terrestrial Biospheric Carbon Sinks in
the Kyoto Protocol Dutch National research Programme on
Global Air Pollution and Climate Change, Bilthoven, The
Netherlands (410 200 030: 100 pp.).
Poulton, P.R., 1996. Geescroft Wilderness, 1883 – 1995. In:
Powlson, D.S., Smith, P., Smith, J.U. (Eds.), Evaluation of
Soil Organic Matter Models using Existing, Long-Term
Datasets. NATO ASI, vol. I38. Springer-Verlag, Heidelberg,
pp. 385 – 390.
Rounsevell, M.D.A., Audsley, E., Mortimer, D., 2002. The impact
of the Common Agricultural Policy on land use in Europe, in
Land Cover and Land Use. In: Verheye, W.H. (Ed.), Encyclopedia of Life Support Systems (EOLSS), Developed Under the
Auspices of the UNESCO, EOLSS Publishers, Oxford, UK.
Schlesinger, W.H., 1999. Carbon sequestration in soils. Science
284, 2095.
Six, J., Guggenberger, G., Paustian, K., Haumaier, L., Elliott, E.T.,
Zech, W., 2001. Sources and composition of soil organic matter
fractions between and within soil aggregates. Eur. J. Soil Sci.
52, 607 – 618.
Smith, P., Smith, T.J.F., 2000. Transport carbon costs do not negate
the benefits of agricultural carbon mitigation options. Ecol. Lett.
3, 379 – 381.
Smith, P., Powlson, D.S., Glendining, M.J., 1996. Establishing
a European soil organic matter network (SOMNET). In:
Powlson, D.S., Smith, P., Smith, J.U. (Eds.), Evaluation
of Soil Organic Matter Models using Existing, Long-Term
Datasets. NATO ASI Series I, vol. 38. Springer-Verlag, Berlin,
pp. 81 – 98.
Smith, P., Powlson, D.S., Glendining, M.J., Smith, J.U., 1997a.
Using long-term experiments to estimate the potential for carbon
sequestration at the regional level: an examination of five European scenarios. Agrokém. Talajt. 46, 25 – 38.
Smith, P., Powlson, D.S., Glendining, M.J., Smith, J.U., 1997b.
Potential for carbon sequestration in European soils: preliminary
estimates for five scenarios using results from long-term experiments. Glob. Chang. Biol. 3, 67 – 79.
Smith, P., Powlson, D.S., Glendining, M.J., Smith, J.U., 1998a.
Preliminary estimates of the potential for carbon mitigation in
European soils through no-till farming. Glob. Chang. Biol. 4,
679 – 685.
Smith, P., Powlson, D.S., Glendining, M.J., Smith, J.U., 1998b.
Opportunities and limitations for C sequestration in European
agricultural soils through changes in management. In: Lal,
R., Kimble, J.M., Follett, R.F., Stewart, B.A. (Eds.), Management of Carbon Sequestration in Soil. Advances Soil Sci,
143 – 152.
Smith, W.N., Desjardins, R.L., Patty, E., 2000a. The net flux of
carbon from agricultural soils in Canada 1970 – 2010. Glob.
Chang. Biol. 6, 557 – 568.
Smith, P., Powlson, D.S., Smith, J.U., Falloon, P., Coleman, K.,
2000b. Meeting Europe’s climate change commitments: quantitative estimates of the potential for carbon mitigation by agriculture. Glob. Chang. Biol. 6, 525 – 539.
Smith, P., Goulding, K.W., Smith, K.A., Powlson, D.S., Smith,
J.U., Falloon, P.D., Coleman, K., 2001a. Enhancing the carbon sink in European agricultural soils: Including trace gas
fluxes in estimates of carbon mitigation potential. Nutr. Cycl.
Agroecosyst. 60, 237 – 252.
Smith, P., Smith, J.U., Powlson, D.S., 2001b. Soil Organic Matter
Network (SOMNET): 2001 Model and Experimental Metadata.
GCTE Report 7, Second Edition, GCTE Focus 3, Wallingford,
Oxon, 223 pp.
UNFCCC, 2001. 1 August 2000 submissions by Annex I Parties.
http://www.unfccc.de/resource/docs/2000/sbsta/.
Vleeshouwers, L.M., Verhagen, A., 2001. CESAR: a model for
carbon emission and sequestration by agricultural land use.
Plant Research International, Report no 36, Plant Research
International, P.O. Box 16 6700 AA Wageningen, The
Netherlands.
Vleeshouwers, L.M., Verhagen, A., 2002. Carbon emission and
sequestration by agricultural land use: a model study for Europe.
Glob. Chang. Biol. 8, 519 – 530.
Watson, R.T., Noble, I.R., Bolin, B., Ravindranath, N.H.,
A. Freibauer et al. / Geoderma 122 (2004) 1–23
Verardo, D.J., Dokken, D.J. (Eds.), 2000. Land Use, Land
Use Change, and Forestry. Cambridge Univ. Press, Cambridge, UK.
Wild, U., Kamp, T., Lenz, A., Heinz, S., Pfadenhauer, J., 2001.
Cultivation of Typha spp. in constructed wetlands for peatland
restoration. Ecol. Eng. 17, 49 – 54.
23
Woomer, P.L., Plalm, C.A., Qureshia, J.N., Kotto-Same, J.,
1997. Carbon sequestration and organic resources management in African smallholder agriculture. In: Lal, R., Kimble, J.M., Follett, R.F, Stewart, B.A. (Eds.), Management
of Carbon Sequestration in Soil. CRC Press, Boca Raton,
pp. 153 – 173.