Carbon sequestration potential in European croplandshas been overestimated

P E T E S M I T H *, O L O F A N D R E N w , T H O R D K A R L S S O N w , PA U L A P E R A L A z,K R I S T I I N A R E G I N A z, M A R K R O U N S E V E L L § and B A S VA N W E S E M A E L §

*School of Biological Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK,

wDepartment of Soil Science, SLU, PO Box 7014, S-750 07 Uppsala, Sweden, zMTT Agrifood Research Finland, Environmental

Research, FIN-31600 Jokioinen, Finland, §Department of Geography, Universite catholique de Louvain, Place Pasteur, 3 B-1348

Louvain-la-Neuve, Belgium

Abstract

Yearly, per-area carbon sequestration rates are used to estimate mitigation potentials by

comparing types and areas of land management in 1990 and 2000 and projected to 2010,

for the European Union (EU)-15 and for four country-level case studies for which data are

available: UK, Sweden, Belgium and Finland. Because cropland area is decreasing in

these countries (except for Belgium), and in most European countries there are no

incentives in place to encourage soil carbon sequestration, carbon sequestration between

1990 and 2000 was small or negative in the EU-15 and all case study countries. Belgium

has a slightly higher estimate for carbon sequestration than the other countries exam-

ined. This is at odds with previous reports of decreasing soil organic carbon stocks in

Flanders. For all countries except Belgium, carbon sequestration is predicted to be

negligible or negative by 2010, based on extrapolated trends, and is small even in

Belgium. The only trend in agriculture that may be enhancing carbon stocks on crop-

lands at present is organic farming, and the magnitude of this effect is highly uncertain.

Previous studies have focused on the potential for carbon sequestration and have

shown quite significant potential. This study, which examines the sequestration likelyto occur by 2010, suggests that the potential will not be realized. Without incentives for

carbon sequestration in the future, cropland carbon sequestration under Article 3.4 of the

Kyoto Protocol will not be an option in EU-15.

Keywords: arable land, carbon mitigation, carbon sequestration, cropland management, Kyoto Protocol,

soil organic carbon

Received 23 May 2005; and accepted 28 July 2005

Introduction

Croplands (i.e. lands used for the production of arable

crops), cover about 1/3 of Europe’s land surface and are

estimated to be the largest biospheric source of carbon

loss to the atmosphere in Europe each year. The crop-

land estimate is the most uncertain among all land-use

types (Janssens et al., 2003). It is estimated that crop-

lands (in Europe as far east as the Urals) lose 120–

300 Tg C yr�1 (Janssens et al., 2003, 2005), with the mean

for the European Union (EU-15) of 78 (SD: 37) Tg C yr�1

(Vleeshouwers & Verhagen, 2002). National estimates of

cropland CO2 fluxes for some EU countries are of

similar magnitude on a per-area basis (Sleutel et al.,

2003), but other estimates are lower (Dersch & Boehm,

1997). The EU-15 estimates for the CO2 cropland emis-

sions ( � 78 Tg C yr�1) are of the same order of magni-

tude as the reported emissions of N2O from agricultural

soil ( � 60 Tg C-eq. in 2000) and CH4 from agriculture

( � 50 Tg C-eq. in 2000; Smith et al., 2004).

The values for CO2 flux suggest that cropland soil

carbon stocks in general are continuing to decline,

perhaps as a result of recent (decadal) land-use change.

However, values for net changes in land use during the

past 20–30 years do not suggest a large-scale conversion

to cropland from other land uses, but may not show all

areas that have undergone a change as they report only

net changes. An alternative reason for the high C loss

from agricultural soils in some regions may be changesCorrespondence: Pete Smith, tel. 1 44 (0)1224 272702,

fax 1 44 (0)1224 272703, e-mail: pete.smith@abdn.ac.uk

Global Change Biology (2005) 11, 2153–2163, doi: 10.1111/j.1365-2486.2005.01052.x

r 2005 Blackwell Publishing Ltd 2153

of agricultural management (e.g. manure use) over

recent decades (Sleutel et al., 2003). The values for

cropland soil carbon loss are highly uncertain (Janssens

et al., 2003) and there is clearly scope to reduce the

uncertainty surrounding these estimates.

In Europe, most soils are out of equilibrium as they

have been affected by past land use/management prac-

tices. Management practices affecting green house gas

(GHG) emissions from agricultural areas include

changes between arable and grassland, grassland and

forest, etc., cropland management such as tillage, rota-

tions, fertilizer use, use of legumes, the type of fertilizer

applied, farm management pattern, grassland manage-

ment such as ley systems (cut or grazed), and water

management, etc.

The political context for agricultural GHG mitigation

arises from the Kyoto Protocol to the 1992 United

Nations Framework Convention on Climate Change

(UNFCCC) and its subsequent elaboration at the 7th

Conference of Parties (COP7) leading to the Marrakech

Accords. This allows biospheric carbon sinks (and

sources) to be included in attempts to meet Quantified

Emission Limitation or Reduction Commitments for the

first commitment period (2008–2012), as outlined in the

Kyoto Protocol (available at: www.unfccc.de). Under

article 3.4 of the Kyoto Protocol, the activities of forest

management, cropland management, grazing land

management and re-vegetation are included. Soil car-

bon sinks (and sources) can therefore be included under

these activities.

Previous estimates of mitigation potential have often

been confounded by differing constraints considered by

different authors. Some authors quote biological poten-

tials (Metting et al., 1999), others quote potentials as

limited by available land or resources (Smith et al.,

2000b), and others also consider economic and social

constraints (Cannell, 2003; Freibauer et al., 2004; Smith,

2004a). Smith (2004b) provided a figure to show how

these estimates of mitigation potential differ, and

how the potential is reduced by a number of constraints

(Fig. 1).

An analysis of the estimates presented in Freibauer

et al. (2004) and the assumptions used by Cannell (2003)

suggest that the realistic sustainable (or conservative)

achievable potential of GHG mitigation (taking into

account limitations in land use, resources, economics,

and social and political factors) may be about 10–20% of

the biological potential. Although this value is derived

predominantly from expert judgment, it may be useful

in assessing how different estimates of GHG mitigation

potential can be compared and how they might realis-

tically contribute to GHG stabilization.

The aim of this paper is to use available data, and

extrapolation of current trends, to estimate agricultural

soil carbon sequestration achieved during the 1990s and

that likely to be achieved by 2010, in the first Kyoto

Commitment period, for four case study countries and

for the EU-15.

Materials and methods

Previously published estimates of yearly per-area miti-

gation potentials for Europe were used to derive best

estimates, and ‘low’ and ‘high’ per-area estimates of the

mitigation potential of a range of cropland management

practices. These estimates, the sources from which they

were derived and any further assumptions used are

given in Table 1.

Having derived yearly per-area mitigation potentials

for various management practices, the areas under the

different management practices for the EU-15 (Table 2)

and four case study EU countries, UK (Table 3), Sweden

(Table 4), Belgium (Table 5) and Finland (Table 6), were

multiplied by the yearly per-area carbon sequestration

rates for each management practice given in Table 1, to

estimate the cropland soil carbon sequestration for each

country/region examined. The fate of soil C in lands

converted from croplands is not accounted for in this

study and could either be increasing or decreasing, but

that is beyond the scope of this study, which assesses

only cropland soil carbon sequestration. Tables 2–6

show the areas under each cropland management prac-

tice for each region for 1990, 2000 and 2010. Data

sources and assumptions made are given in the table

footnotes.

Results and discussion

Estimates of carbon sequestration (expressed as

t C cropland ha�1 yr�1, to allow different areas to be

GHG mitigation potential

Biological potential

Biologically/physically constrained potential (e.g. land suitability)

Maximum value Minimum value

Economicallyconstrainedpotential Socially/politically

constrainedpotential − estimated realistically achievablepotential (~10% of biological potential)

Fig. 1 Impact of different constraints on reducing the green

house gas (GHG) mitigation potential from its theoretical biolo-

gical maximum to lower, realistically achievable potentials

(adapted from Smith, 2004b).

2154 P. S M I T H et al.

r 2005 Blackwell Publishing Ltd, Global Change Biology, 11, 2153–2163

compared) for 2000 and 2010 (compared with 1990) are

shown in Figs 2 and 3.

The low (and also negative) carbon sequestration

estimates for the EU-15 and all countries reflect that in

many countries total cropland area and/or areas under

carbon enhancing management have decreased from

1990 to 2000. Based on current trends, or on expert

judgement of the most likely trend, extrapolation to

2010 suggests that this trend will not be reversed by

2010. The only potentially C enhancing practice that has

increased from 1990 to 2000 is organic farming, and this

practice is set to increase further between 2000 and

2010. It should be noted, however, that although organic

farming might increase soil organic carbon (SOC) in the

areas where it is practiced (Foereid & H�gh-Jensen,

2004), a simple redistribution of the organic resource

available will not result in a net gain in SOC at the

country level, as gains on the organically managed field

may be balanced by losses on the field to which the

organic resource would otherwise have been applied.

For this reason the low per-area C sequestration esti-

mate of zero is used as the size of the resource redis-

tribution effect is not known.

Belgium is the only country examined in which

cropland management might have increased cropland

soil carbon sequestration from 1990 to 2000 and where

Table 1 GHG mitigation options for croplands. Low best and high estimates of per-area mitigation potential

Management

Potential rate

t C ha�1 y�1 t C ha�1 y�1 t C ha�1 y�1

Low estimate Best estimate High estimate Notes

Zero-tillage 0 0.4 0.4 1

Reduced tillage 0 0.2 0.2 2

Set-aside 0 0.2 0.2 2

Riparian zones/buffer strips 0 0 0 3

Convert to permanent crops an perrenial grasses 0 0.6 0.6 4

Improved management of permanent crops 0 0 0 3

Deep rooting crops 0 0.6 0.6 4

Solid animal manure (FYM) 0.2 0.4 1.5 5

Slurry 0.2 0.4 1.5 6

Crop residues 0.1 0.7 0.7 7

Sewage sludge 0.1 0.3 0.3 7

Composting 0.2 0.4 1.5 6

Improved rotations 0.17 0.5 0.76 8

N fertilization (inorganic) 0.1 0.2 0.3 9

Irrigation 0.05 0.075 0.1 9

Drainage 0 0 0 3

Bioenergy crops (soil) 0 0.6 0.6 10

Annual bioenergy crops (soil) 0 0 0 11

Extensification/deintensification 0 0.5 0.5 1

Organic farming (arable) 0 0.5 0.5 12

Convert arable to woodland 0.3 0.4 0.5 1

Convert arable to grassland 0.3 1.75 1.9 13

Convert grassland to arable �1.7 �1.35 �1 13

Convert permanent crops to arable �1.7 �1.35 �1 13

Convert forest to arable �0.6 �0.6 �0.6 12

Convert cropland to urban 0 0 0 3

Notes: (1) From Smith et al. (2000b) and Freibauer et al. (2004). (2) Assumed to be half of the no-till potential of Smith et al. (2000b) and

Freibauer et al. (2004). (3) No data on which to base an estimate. (4) As in Freibauer et al. (2004), assumed to be the same as bioenergy

crops. (5) Low and best estimates from Smith et al. (2000b) of dm basis; high estimate from Vleeshouwers & Verhagen (2002). (6)

Assumed to be as for FYM on a dm basis – low and best estimates from Smith et al. (2000b) on dm basis; high estimate from

Vleeshouwers & Verhagen (2002). (7) Low estimate from IPCC (2000), best and high estimates from Smith et al. (2000b) and Freibauer

et al. (2004). (8) Range from IPCC (2000) – best estimate is rough mean from this range. (9) Range from Lal et al. (1998). (10) From

Smith et al. (2000b). (11) No evidence that these are different from any different from other crops. (12) From Freibauer et al. (2004).

(13) Range from Vleeshouwers & Verhagen (2002) and Freibauer et al. (2004).

FYM, farm yard manure; GHG, green house gas; dm, dry matter.

CARBON SEQUESTRATION POTENTIAL IN EUROPEAN CROPLANDS OVERESTIMATED 2155

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it is projected to increase further to 2010 (Dendoncker

et al., 2004), although low and best estimates of yearly

per-area SOC change suggest a loss or very modest

increase. Estimated increases in SOC derived from the

high estimates of yearly per-area SOC change are at

odds with previous findings of Sleutel et al. (2003)

for Flanders (Northern Belgium), which suggested

significant decreases in SOC between 1990 and 2000.

Although, in a later study, Sleutel (2005) found

lower SOC losses based on a re-sampling exercise, the

decline in SOC nevertheless persisted. The loss in

Belgium is predicted to continue to 2012, even in

the presence of carbon sequestering management prac-

tices (Sleutel 2005). Other evidence shows that

actual losses of SOC may be missed by the methodology

applied here. Although Swedish and Finnish mineral

soils are thought to be close to equilibrium as sugges-

ted here, cultivated organic soils may be losing

significant amounts of SOC through oxidation and

subsidence of between 0.8 and 8.3 t C ha�1 yr�1 (Nyka-

nen et al., 1995; Maljanen et al., 2001, 2004; Lohila et al.,

2004).

Table 2 Areas under each cropland management practice in the EU-15

Management

EU-15 area under this management (ha)

1990 2000 2010 Notes

Total cropland area 77 998 000 74 740 000 71 618 110 1

Zero-tillage 1169 970 1121100 1 074 272 2

Reduced tillage 1169 970 1121100 1 074 272 2

Set-aside 7 799 800 7 474 000 7 161 811 3

Riparian zones/buffer strips 0 0 0 4

Convert to permanent crops and perrenial grasses 0 �360 000 �360 000 5

Improved management of permanent crops 0 0 0 6

Deep rooting crops 0 0 0 4

Solid animal manure (FYM) 10 334 735 9 903 050 9 489 400 7

Slurry 10 334 735 9 903 050 9 489 400 7

Crop residues 7 643 804 7 324 520 7 018 575 8

Sewage sludge 5 693 854 5 456 020 5 228 122 9

Composting 4

Improved rotations 0 0 0 10

N fertilization (inorganic) 0 0 0 11

Irrigation 0 0 0 10

Drainage 0 0 0 10

Bioenergy crops (soil) 12

Annual bioenergy crops (soil) 12

Extensification/deintensification 4

Organic farming (arable) o2 283 638 2 283 638 4 567 276 13

Convert arable to woodland 0 1177 710 1177 710 14

Convert arable to grassland 0 4

Convert grassland to arable 0 4

Convert permanent crops to arable 0 4

Convert forest to arable 0 4

Convert cropland to urban 0 4

Notes: (1) From FAO statistics for 1990 and 2000; same change 2000–2010 assumed as for 1990–2000. (2) 1990 value assumes 50 : 50

split of the reduced/no-till area; total 5 3% of cropland (from Smith et al., 2000b); assumed no change to 2000 as no incentives to

increase reduced tillage so also assume no change to 2010. (3) Assume to be 10% of cropland (Smith et al., 2000b). (4) No data

available. (5) 2000 value from Freibauer et al. (2004); assumed no change 2000–2010. (6) Permanent crops only; no evidence for

change since 1990. (7) From Smith et al. (2000b) for 20 t dm ha�1 yr�1; assumed constant for 1990–2010; assume 50 : 50 slurry to solid

FYM. (8) From Smith et al. (2000b) for 10 t dm ha�1 yr�1; assumed constant for 1990–2010. (9) From Smith et al. (2000b) for

1 t dm ha�1 yr�1; assumed constant for 1990–2010. (10) No evidence of any change. (11) From FAO statistics there is a 30 kg N ha�1

drop in fertilizer application rates 1990–2000 so the trend is away from increased fertilization; therefore, assumed to be zero. (12)

Actual amounts are very small in 1990; assumed to negligible. (13) Year 2000 value is from FAO 2003 data; area (ha) under organic

agriculture is scaled by 0.514 for conversion from UAA to cropland. (14) Values from Freibauer et al. (2004); 37% of the new forest is

from arable land.

FYM, farm yard manure; dm, dry matter; EU, European Union.

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The results presented here are based predominantly

on carbon sequestering management options, and as

such do not account explicitly for other trends in SOC,

such as long-term decreases identified from soil re-

sampling exercises. As such, the method used here

may tend to over-estimate SOC sequestration potential.

Of the case studies examined, Belgium is the country

most actively encouraging soil carbon sequestration

through, for example, policies to encourage green

manuring and composting (Sleutel 2005), lending

support to the suggestion that Belgium could be in-

creasing cropland SOC stocks slightly. However, it is

also known that sources of organic matter (e.g. animal

manure) to add to cropland soils are decreasing (Sleutel

Table 3 Areas under each cropland management practice in the UK

Management

Area under this management (ha)

1990 2000 2010 Notes

Total cropland area 6 686 000 5 928 000 5 255 937 1

Zero-tillage 100 290 88 920 78 839 2

Reduced tillage 100 290 88 920 78 839 2

Set-aside 668 600 592 800 525 594 3

Riparian zones/buffer strips 0 0 0 4

Convert to permanent crops (area under permanent crops shown) 79 000 45 000 25 650 5

Improved management of permanent crops and perrenial grasses 0 0 0 4

Deep rooting crops 0 0 0 4

Solid animal manure (FYM) 885 895 885 895 885 895 6

Slurry 885 895 885 895 885 895 6

Crop residues 655 228 580 944 515 082 7

Sewage sludge 488 078 432 744 383 683 8

Composting 9

Improved rotations 0 0 0 4

N fertilization (inorganic) 0 0 0 10

Irrigation 0 0 0 4

Drainage 0 0 0 4

Bioenergy crops (soil) 11

Annual bioenergy crops (soil) 11

Extensification/deintensification 9

Organic farming (arable) o240 385 240 385 12

Convert arable to woodland 0 9

Convert arable to grassland 0 9

Convert grassland to arable 0 9

Convert permanent crops to arable 0 9

Convert forest to arable 0 9

Convert cropland to urban 0 9

Notes: (1) FAO values used for 1990 and 2000; for 2010 values the same change for 2000–2010 as for 1990–2000 is assumed. (2) The

1990 value assumes a 50 : 50 split of the reduced/no-till area; total assumed to be 3% of cropland (Smith et al., 2000b); assumed no

change to 2000 as no incentives to increase no-till area so no change to 2010 is also assumed. (3) Assume 10% of cropland (Smith et al.,

2000a, c). (4) No evidence of significant change. (5) Permanent crop area in UK in 1997 was 57% of what it was in 1990 – i.e.

permanent crop area is decreasing; 2010 values assume the same change for 2000–2010 as for 1990–2000. (6) From Smith et al.

(2000b, c) for 20 t dm ha�1 yr�1; assumed constant for 1990–2000 as cattle plus swine numbers in UK remain unchanged from 1990 to

1997 (difference of o0.6%; FAO statistics from EarthTrends, 2003); assumed same level of manure available – as cropland area

decreases, a larger proportion of area can be covered at the same rate so we assume the same area as in 1990 receives manure at

20 t dm h�1 yr�1; same assumption for 2000–2010; 50 : 50 slurry to solid FYM assumed. (7) From Smith et al. (2000b, c) for

10 t dm ha�1 yr�1: as cropland area decreases, cereal straw production also decreases in proportion; assumed constant percent of

available cropland for 1990–2010. (8) From Smith et al. (2000b, c) for 1 t dm ha�1 yr�1; assumed constant for 1990–2010. (9) No data.

(10) From FAO statistics (EarthTrends, 2003); there has been a 30 kg ha�1 decrease in fertilizer application rates 1990–2000 so the

trend is away from increased N fertilization; therefore assumed to be zero. (11) Actual amounts are very small in 1990; assumed to

negligible. (12) The 2000 value is from EarthTrends (2003: FAO statistics) as the percentage of utilizable agricultural area (UAA) in

2003 ([ � 4% of UK UAA] scaled by 0.3537 to get from UAA to cropland area in UK).

FYM, farm yard manure; dm, dry matter.

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2005), which, it has been suggested, has led to a

decrease in SOC (Sleutel et al., 2003). Other studies

(Lettens et al., 2004; Dendoncker et al., 2004), suggest a

lower SOC stock in croplands in Flanders, with an

increase in SOC for croplands in Flanders between

1950 and 1970, followed by a slight decrease in the

Table 4 Areas under each cropland management practice in Sweden

Management

Area under this management (ha)

1990 2000 2010 Notes

Total cropland area 2 844 592 2 705 981 2 570 682 1

Zero-tillage 0 0 2

Reduced tillage 0 0 2

Set-aside 193 387 247 733 260 120 3

Riparian zones/buffer strips 0 0 4

Convert to permanent crops and perrenial grasses 0 0 2

Improved management of permanent crops and perrenial grasses 0 0 2

Deep rooting crops 611 435 468 163 468 163 5

Solid animal manure (FYM) area (assuming 20 t dm ha�1 yr�1) 384 000 247 500 198 000 6

Slurry area (assuming 20 t dm ha�1 yr�1) 431 000 615 500 621 850 6

Crop residues 978 779 978 779 929 840 7

Sewage sludge (tonnes dm) 46 200 46 200 46 200 8

Composting 0 0 9

Improved rotations 0 0 9

N fertilization (inorganic) 1 326 000 1 326 000 1 313 613 10

Irrigation 0 0 9

Drainage 0 0 11

Bioenergy crops (soil) 15 079 15 079 16 587 12

Annual bioenergy crops (soil) 2

Extensification/deintensification 0 0 9

Organic farming (arable) 183 000 183 000 201 300 13

Convert arable to woodland 69 306 136 955 14

Convert arable to grassland 9

Convert grassland to arable 9

Convert permanent crops to arable 9

Convert forest to arable 9

Convert cropland to urban 9

Notes: (1) SCB (2001), Farms with more than 2 ha, including leys and grassland; 2010 decrease by 5% from 2000 calculated from

trends in Backstrand (2003) and Burmann et al. (2003). (2) No data given. (3) SCB (1991) and SCB (2001), 1990 value including black

fallow, green fallow and other not utilized land, 2000 black and green fallow; increase in 2010 by 5% of 2000 area calculated from

trends in Backstrand (2003) and Burmann et al. (2003). (4) Included in set aside. (5) SCB, winter cereals, sugar beet, rape oil seed

included; by 2010 energy crops increase but a decrease in grain and oil seed so net effect is no change from 2000; calculated from

trends in Backstrand (2003) and Burmann et al. (2003). (6) SCB (1992) and SCB (2002), data from 1991and 2001, respectively; in 2001

including all manures from ‘other animals’; areas calculated from dm tonnes assuming application rate of 20 t dm ha�1 yr�1; solid

manure projected to decrease to 80% of 2000 value by 2010; for slurry in 2010 there is a 5% decrease in the total of slurry plus FYM,

but more is now produced as slurry leading to an increase by 2010; calculated from trends in Backstrand (2003) and Burmann et al.

(2003). (7) SCB (1999), data only available from 1997; areas with incorporated crop residues; no other data so assume 1990 same as for

2000; for 2010 there are less crops and less residues coupled with a 5% increase in the burning of crop residues for energy, hence the

decrease; calculated from trends in Backstrand (2003) and Burmann et al. (2003). (8) SCB (2002); no other data so assume 1990 and

2010 same as for 2000. (9) No data so assume none or no change. (10) SCB (2002) data for 2001; no other data for 1990 so assume as for

2000; for 2010 the decrease in N fertilization is in proportion to the decrease in crop area and the increase in set aside and organically

farmed area; calculated from trends in Backstrand (2003) and Burmann et al. (2003). (11) In principle all arable land. (12) SCB (2001)

energy forest; no other data for 1990 so assume same as for 2000; for 2010 there is projected to be a 10% increase in bioenergy crop

area; calculated from trends in Backstrand (2003) and Burmann et al. (2003). (13) SCB (2002); no data for 1990 so assume same as for

2000; for 2010 the organic area is projected to increase by 10%; calculated from trends in Backstrand (2003) and Burmann et al. (2003).

(14) Estimated as 50% of the area reduction in arable land for 2000 and 2010; calculated from trends in Backstrand (2003) and

Burmann et al. (2003).

FYM, farm yard manure.

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Table 5 Areas under each cropland management practice in Belgium

Management

Area under this management (ha)

1990 2000 2010 Notes

Total cropland area 760 559 864 075 864 075 1Zero-tillage 0 12 373 24 745 2Reduced tillage 0 12 373 24 745 2Set-aside 1478 23 549 27 750 3Riparian zones/buffer strips 0 0 10 580 4Convert to permanent crops and perrenial grasses 0 0 0 5Improved management of permanent crops and perrenial grasses 12 310 17 326 17 326 6Deep rooting crops 0 0 0 5Solid animal manure (FYM) 470 265 612 342 612 342 7Slurry 7Crop residues 0 0 0 8Sewage sludge 13 500 0 0 9Composting 1275 14 125 14 125 10Improved rotations 5240 4498 101 917 11N fertilization (inorganic) 0 0 0 12Irrigation 25 690 25 690 25 690 13Drainage 75 594 75 594 75 594 13Bioenergy crops (soil) 0 10 000 10 000 14Annual bioenergy crops (soil) 0 10 000 10 000 14Extensification/deintensification 0 0 0 15Organic farming (arable) 715 99 00 16 500 16Convert arable to woodland 658 308 5900 17Convert arable to grassland 53 1421 1421 18Convert grassland to arable 0 71 680 71 680 19Convert permanent crops to arable 0 0 0 5Convert forest to arable 0 0 0 5Convert cropland to urban 233 398 398 18

Notes: (1) Cropland assumed to be the same in 2010 as in 2000. (2) The total for no-till and reduced till (49 490 ha) is assumed to besplit 50 : 50 between zero and reduced till, assuming adoption over 20 years for suitable soils (418% clay and nonhydromorphous;Arrouays et al., 2002); also assume 2000 value is midway between 1990 and 2000 value. (3) 1990 and 2000 data from INS (1990, 2000);set-aside rose sharply in the early 1990s as a result of the EU CAP reforms and is currently fluctuating; estimates for 2010: 10% of the2000 cereal area. (4) For 2010, the Walloon region gives subsidies for a max of 8% of the cultivated area under the headlandconservation scheme; we assume again an uptake rate of 0.35. (5) No data. (6) 1990 and 2000 data from INS (1990, 2000) for thesurface of orchards; nearly all orchards have grass strips (assume 2010 same as 2000). (7) N data from ‘manure book-keeping’ andspread the manure produced until it reaches legal limits. These limits become more severe over time. As there is a difference inagriculture between Flanders and Wallonia, manure cannot be exchanged between the regions meaning that Flanders producesmore than enough manure to cover all grasslands and croplands, and the Walloon region produces enough manure to maintainfertility in grasslands, but not all croplands receive enough manure. (8) There is an import of straw for animal bedding: 1.18 Tg(1990) and1.14 Tg (2000) cereal straw produced and 2.80 Tg (1990) 2.77 Tg (2000) required for bedding based on requirements peranimal, time spent in housing and type of housing (Dendoncker et al., 2004). (9) Sewage sludge is only spread in the Walloon region;90% is applied to arable land, however it is expected that the spreading will soon be forbidden. (10) Based on Flanders: 75 kt wastecomposted in 1991 and 675 kt in 1998, Walloon region 156 kt waste in 1998. We assume that 1 kg waste produces 0.17 kg dm compost(Kiely, 1997, p. 661) and application rates of 10 Mg dm ha�1. (11) 1990 and 2000 data from INS (1990, 2000) (winter rapeseed): For2010, we assume a maximum calculated as follows: the whole area of winter cereals to include a cover crop and maize in the Walloonregion to be under-sown with grass over an adoption period of 20 years i.e. 35% of the area (Dendoncker et al., 2004); subsidies forcover crops are available in both regions, whereas subsidies for maize are restricted to the Walloon region. (12) All agricultural landis fertilized: N fertilizers decreased from 125 kg ha�1 in 1990 to 115 kg ha�1 in 1995 so trend away from increased fertilization; assumezero. (13) INS (2000) data: this is the area that can be irrigated using the available equipment. We assume that cropland is irrigatedand not grassland and assume 2010 same as for 2000. As there is no evidence of a change between 1990 and 2000, 1990 valuesassumed to be the same as 2000. (14) INS (2000): rapeseed for the production of nonalimentary oil in 1994 for the Walloon region2010: Flemish and Walloon policies; assuming 50% annual crops and 50% perennial crops; 1990 values assumed to be the same as2000. (15) Probably not relevant in the Belgian context as less intensive systems will convert to organic farming (see note 16). (16)Based on overall areas of organic farming, assuming a ratio of 0.55 cropland and 0.45 grassland (same as for conventional farming)(Dendoncker et al., 2004). This could be an overestimation for 2000 as extensive cattle breeding converted first to organic farming.(17) 1990 and 2000 data from INS (1990, 2000); For 2010; 6300 refers to the EU ‘on farm woodland’ scheme. 5500 to Flemish policies(10 000 ha by 2020) assuming reforestation of 0.55 arable and 0.45 grassland for Flanders. The mean of this value is used here, i.e.5900 ha. (18) 1990 and 2000 data from INS (1990, 2000); land used for nonagricultural purposes (280 220 ha). (19) Belgium lostgrassland and gained cropland, while the total area remained the same.

FYM, farm yard manure; dm, dry matter; CAP, Common Agricultural Policy; EU, European Union.

CARBON SEQUESTRATION POTENTIAL IN EUROPEAN CROPLANDS OVERESTIMATED 2159

r 2005 Blackwell Publishing Ltd, Global Change Biology, 11, 2153–2163

1990s (with an overall decrease in croplands in the

Walloon region).

Our results show the importance of assessing carbon

sequestration potential at the national/regional level as

well as at larger (EU-15 wide) scales, as local manage-

ment, and hence estimates of the mitigation potential,

can be very different. For some management practices

no data are available and here values are based on

expert judgment/extrapolation, introducing large un-

certainties into national estimates. Activity data (i.e.

Table 6 Areas under each cropland management practice in Finland

Management

Area under this management (ha)

1990 2000 2010 Notes

Total cropland area 2 088 200 2 005 700 1 842 000 1

Zero-tillage 5000 30 000 500 000 2

Reduced tillage 5000 380 000 3

Set-aside 182 800 181100 325 000 4

Riparian zones/buffer strips 0 8874 17 748 5

Convert to permanent crops and perrenial grasses 0 0 0 6

Improved management of permanent crops and perrenial grasses 0 0 0 7

Deep rooting crops 0 0 0 7100

Solid animal manure (FYM) 327 418 236 068 169 969 8

Slurry 139 195 129 632 120 726 8

Crop residues 2 088 200 2 005 700 1 842 000 9

Sewage sludge 13 3 1 10

Composting 0 0 0 7

Improved rotations 0 0 0 7

N fertilization (inorganic) 2 081 448 1 858 277 1 659 034 11

Irrigation 0 0 0 12

Drainage (%) 86 86 90* 13

Bioenergy crops (soil) 0 5000 373 000 14

Annual bioenergy crops (soil) 0 3500 145 000 15

Extensification/deintensification 0 0 0 7

Organic farming (arable) 6752 147 423 147 423 16

Convert arable to woodland 8545 5782 3912 17

Convert arable to grassland 0 0 0 7

Convert grassland to arable 0 0 0 7

Convert permanent crops to arable 7634* 0 0 18

Convert forest to arable 0 0 0 7

Convert cropland to urban 0 0 0 7

Notes: (1) Finland area of crops (ha) (including cereals and cultivated grass). Yearbook of Farm Statistics 2000 and 2001 (utilized

agricultural area in 2001 in Finland was 2 216 900 ha). Scenario: Expert judgement, National Expert: Heikki Lehtonen, MTT Agrifood

Research Finland. (2) Expert judgement, National Expert: Laura Alakukku, MTT Agrifood Research Finland. (3) The area of reduced

tillage (ha) in 2000. National Expert: Eila Turtola, MTT Agrifood Research Finland. (4) Yearbook of Farm Statistics, 2001, Scenario: Expert

judgement, National Expert: Heikki Lehtonen, MTT Agrifood Research Finland. (5) In 2002, the area of riparian zones was 4724 ha

and the area of buffer strips was 4150 ha (if width of the strip is 3 m), National Expert: Eila Turtola, MTT Agrifood Research Finland.

(6) The area of green fallow was 134 072 ha in 1995, 111 678 ha in 1999 and 121 529 ha in 2002. National Expert: Eila Turtola, MTT

Agrifood Research Finland. (7) No data available. (8) Total N in manure divided by the maximum allowed application rate

(kg N ha�1); 2010 value assumes same change 2000–2010 as for 1990–2000. (9) Residues mostly left on soil. (10) Total N in sludge

divided by the maximum allowed application rate. (11) Total cultivated area minus area of organic farming. (12) Irrigation is very

rare in Finland. (13) Yearbook of Farm Statistics 2002, Expert judgement, National Expert: Aulis Ansalehto [according to Laikari (1989)].

(14) Leinonen et al. (2003); reed canary grass for solid fuel, forage crops grown for biogas, spring turnip rape for diesel fuel, cereal for

fuel ethanol (cereal straw harvested from 200 000 ha excluded from scenario). (15) Leinonen et al. (2003); spring turnip rape for diesel

fuel, cereal for fuel ethanol. (16) Yearbook of Farm Statistics 1998 and Yearbook of Farm Statistics 2002; assumed stays same as for 2000.

(17) Finnish Statistical Yearbook of Forestry 2002; 2010 value assumes same change 2000–2010 as for 1990–2000. (18) Area converted to

arable was 10 088 ha in 2000 (Ministry of Agriculture and Forestry). It is not known whether this area comes from permanent crops,

abandoned land, peatlands or other forms of land-use.

FYM, farm yard manure.

*Yearbook of Farm Statistics.

2160 P. S M I T H et al.

r 2005 Blackwell Publishing Ltd, Global Change Biology, 11, 2153–2163

data on areas under different management practices)

need to be improved to allow better estimates of the

potential for C sequestration under cropland manage-

ment to be made. These data sources should be im-

proved in line with recommendations outlined in the

IPCC Good Practice Guidance for Land Use, Land-Use

Change and Forestry (IPCC, 2003).

The estimates presented here, of negligible cropland

C sequestration in most countries, and for the EU-15 as

a whole, based on measured trends in areas under each

management practice in Table 1 from 1990 to 2000, and

on projections of current trends to 2010, are in sharp

contrast with biological mitigation potentials reported in

previous studies (Smith et al., 2000b; Vleeshouwers &

Verhagen, 2002; Freibauer et al., 2004). Figure 4 shows

the estimates of previous studies of C mitigation poten-

tial in Europe under various assumptions. The differ-

ence between the estimates presented in this study and

those reported in previous studies, is that the previous

studies aimed to show what could be achieved. As

highlighted in many of these studies, without active

encouragement, changes in cropland management

practice will not occur. This study suggests that in the

four case study countries (with the possible exception of

Belgium) and in the EU-15 as a whole, cropland man-

agement has not increased soil C sequestration signifi-

cantly since 1990 and is not predicted to increase it

significantly by 2010, because of the lack of implemen-

tation of C sequestering management in croplands.

Given the recognized biological, economic, social, poli-

tical and institutional constraints on the implementation

of soil carbon sequestration measures, the scale of

carbon sequestration in agriculture will rely more upon

overcoming these constraints than upon filling in gaps

in our scientific and technical knowledge. Carbon se-

questration needs to be encouraged by policy measures

Country/region

EU-15 UK Sweden Belgium Finland

t C h

a−1

yr−1

seq

uest

ratio

n es

timat

e

−0.15

−0.10

−0.05

0.00

0.05

0.10

0.15

0.20

0.25Low estimateBest estimateHigh estimate

Fig. 2 Yearly cropland soil carbon sequestration estimates by

2000 compared with 1990 for EU-15, UK, Sweden, Belgium and

Finland. Positive values indicate an increase in soil organic

carbon (SOC). Low, best and high estimates refer to SOC

sequestration estimates made using the low, best and high yearly

per-area SOC stock change values.

Country/region

EU-15 UK Sweden Belgium Finland

t C h

a−1

yr−1

seq

uest

ratio

n es

timat

e

−0.2

−0.1

0.0

0.1

0.2

0.3

0.4Low estimateBest estimateHigh estimate

Fig. 3 Yearly cropland soil carbon sequestration estimates by

2010 compared with 1990 for EU-15, UK, Sweden, Belgium and

Finland. Positive values indicate an increase in soil organic

carbon (SOC). Low, best and high estimates refer to SOC

sequestration estimates made using the low, best and high yearly

per-area SOC stock change values.

Study

Study 1 Study 2 Study 4Study 3

C s

eque

stra

tion

pote

ntia

l by

2010

(T

g C

yr−

1 )

−20

0

20

40

60

80

100

120

140

160

180

200Low estimateHigh estimate

Fig. 4 Estimates of cropland soil carbon sequestration potential

in EU-15 from previous studies and from this study. Study 1 is

from Vleeshouwers & Verhagen (2002) with the low estimate for

straw incorporation and the high value for conversion of all

cropland to grassland. Study 2 is from Smith et al. (2000b) with

values scaled from geographical Europe (including Baltic States

but excluding Russia) to EU-15 as per Smith et al. (1997). The low

estimate is from the combined land management scenario with

extensification of surplus arable land and straw incorporation;

the high estimate is for the combined ‘optimal’ scenario (see

Smith et al., 2000b for further details). Study 3 is from Freibauer

et al. (2004) with values assessed for realistically achievable

potential by 2010 (about 1/5 of the estimated biological poten-

tial). Study 4 is this study, with values based on measured trends

from 1990 to 2000 and extrapolations to 2010. Positive values

indicate an increase in soil organic carbon.

CARBON SEQUESTRATION POTENTIAL IN EUROPEAN CROPLANDS OVERESTIMATED 2161

r 2005 Blackwell Publishing Ltd, Global Change Biology, 11, 2153–2163

requiring action at the governmental (national and EU)

level. Ultimately, however, management is implemen-

ted at the farm scale by farmers and land managers.

Managing the diverse interests of the range of interested

parties (policy makers, farmers, land managers, envir-

onmental groups and the wider public) will not be easy.

It is likely that a combination of measures will be

required to overcome the many constraints to GHG

mitigation in agriculture, and may include incentives,

regulations and education.

Acknowledgements

We are grateful to the CarboEurope GHG project which funded ameeting at which this study was devised, and to Jean-FrancoisSoussana and Sloan Saletes who organized the meeting at INRA-Clermont Ferrand, France. We also thank the national expertslisted in the table footnotes who provided many of the valuesused in this study.

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