carbon sequestration in soils of central asia

land degradation & development

Land Degrad. Develop. 15: 563–572 (2004)

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ldr.624

CARBON SEQUESTRATION IN SOILS OF CENTRAL ASIA1

R. LAL*

Carbon Management and Sequestration Center, FAES/OARDC, The Ohio State University,School of Natural Resources, Columbus, OH 43210, USA

Received 4 December 2003; Revised 15 January 2004; Accepted 18 February 2004

ABSTRACT

Problems of frequent drought stress, low soil organic carbon (SOC) concentration, low aggregation, susceptibility tocompaction, salinization and accelerated soil erosion in dry regions are accentuated by removal of crop residues, mechanicalmethods of seedbed preparation, summer clean fallowing and overgrazing, and excessive irrigation. The attendant soildegradation and desertification lead to depletion of SOC, decline in biomass production, eutrophication/pollution of waters andemission of greenhouse gases. Adoption of conservation agriculture, based on the use of crop residue mulch and no till farming,can conserve water, reduce soil erosion, improve soil structure, enhance SOC concentration, and reduce the rate of enrichmentof atmospheric CO2. The rate of SOC sequestration with conversion to conservation agriculture, elimination of summerfallowing and growing forages/cover crops may be 100 to 200 kg ha�1 y�1 in coarse-textured soils of semiarid regions and 150to 300 kg ha�1 y�1 in heavy-textured soils of the subhumid regions. The potential of soil C sequestration in central Asia is 10 to22 Tg C y�1 (16� 8 Tg C y�1) for about 50 years, and it represents 20 per cent of the CO2 emissions by fossil fuel combustion.Copyright # 2004 John Wiley & Sons, Ltd.

key words: greenhouse effect; soil C sequestration; desertification control; soil quality; climate change

INTRODUCTION

Central Asia comprises five countries covering a total area of 400 million hectares (Mha) and a population of about

60 million (Batyrov, 1999; FAO, 2002). The arable land area is only 38 Mha. The per capita arable land area ranges

from 0�11 ha in Tadjikistan to 1�9 ha in Kazkhastan. Agriculture is primarily dependent on irrigation covering

96 per cent of arable land in Uzbekistan, 8 per cent in Khazkhastan, 78 per cent in Kyrgyzstan, and 100 per cent in

Tadjikistan and Turkmenistan. Irrigation efficiency is low and salinization and desertification are the most severe

problems throughout the region (Babaev, 1983, 1999; Esenov and Redjepbaev, 1999; Funakawa et al., 2000).

Increase in secondary salinization and desertification are strong indications that prevalent land use and manage-

ment systems are unsustainable.

Regional and national fossil fuel emissions in central Asia have steadily declined since 1992. Regional

emissions of 116 Tg C y�1 (Tg¼ teragram¼ 1012 g¼ 1 million tonnes) in 1992 declined to 74 Tg C y�1 in 1998

(Marland et al., 1999, 2001), which represents only 1�2 per cent of the global emissions estimated at 6300 Tg C y�1

(IPCC, 2001). In addition to fossil fuel combustion, emission of greenhouse gases (GHGs) is also caused by land-

use conversion, soil cultivation and other agricultural practices. Emission of GHGs from terrestrial/agricultural

Copyright # 2004 John Wiley & Sons, Ltd.

�Correspondence to: R. Lal, Carbon Management and Sequestration Center, FAES/OARDC, The Ohio State University, School of NaturalResources, Columbus, OH 43210, USA.E-mail: [email protected]

Contract/grant sponsors: Winrock International; Land O’Lakes, Inc.1This paper is based on the presentation at the International Workshop on ‘Conservation Agriculture for Sustainable Wheat Production inRotation with Cotton in Limited Water Resource Areas,’ 13–18 October 2002, Tashkent, Uzbekistan.

ecosystems is exacerbated by inappropriate land use, soil mismanagement and anthropogenic perturbations that

create an ecological imbalance and exacerbate soil degradation.

The term climate change, or global warming, refers to the acceleration of the natural greenhouse effect by

anthropogenic activities leading to changes in the earth–atmosphere system. The climate change, 0�6� 0�2�Cincrease in earth’s mean temperature during the 20th century and 1 to 4�C projected to increase during the 21st

century, is caused by an increase in the concentration of GHGs in the atmosphere. Anthropogenic perturbation of

the global C and N cycles is responsible for the increase in atmospheric concentration of CO2, CH4 and N2O

(IPCC, 2001). World soils play an important role in the global carbon (C) and nitrogen (N) cycles and can buffer or

accentuate the rate of climate change. In this context, it is important to assess the significance of land-use

conversion and soil/vegetation management in central Asia on emission of GHGs, and of the potential of

restorative measures and adopting recommended management practices (RMPs) on soil C sequestration to

mitigate the projected climate change.

The objective of this manuscript is to describe soil processes that affect C dynamics, and discuss the importance

of conservation agriculture in C sequestration in dry regions of central Asia. Application of the basic principles of

soil C dynamics is discussed in the context of this region, where soil degradation and desertification are severe

problems.

SOILS AND THE GLOBAL CARBON CYCLE

There are five principal sources of C emission: fossil fuel combustion, cement manufacture, land use change,

deforestation and soil cultivation. The magnitude of emission from these sources varies over time. Global emission

was 5�0� 0�5 Pg (1 Pg¼ petagram¼ 1015 g¼ 1 billion metric tonnes) from fossil-fuel combustion and

1�7� 0�8 Pg from land-use change in the 1980s compared with 6�3� 0�6 Pg from fossil fuel combustion and

1�6� 0�8 Pg from land-use change in the 1990s. During the 1990s, the known sinks were the atmosphere absorbing

3�2� 0�2 Pg and ocean uptake of 1�7� 0�5 Pg. There is a residual terrestrial sink estimated at 2�3� 1�3 Pg. There

are numerous speculations about the nature and location of this terrestrial sink (IPCC, 2001).

World soils constitute the third largest global C pool after oceanic (38 000 Pg) and geologic (5000 Pg,

comprising 4000 Pg of coal, 500 Pg of gas and 500 Pg of oil) pools. The soil C pool, estimated at 2500 Pg to 1-

meter depth (Eswaran et al., 2000) is about 3�3 times the atmospheric pool (760 Pg) and 4�5 times the biotic pool

(560 Pg). The atmospheric pool is increasing at the rate of 3�2 Pg C y�1 (IPCC, 2001) at the expense of the soil,

geologic and biotic pools.

The soil C pool comprises two principal components: soil organic carbon (SOC); and soil inorganic carbon

(SIC). The SOC pool includes highly active humus and relatively inert charcoal C, and to 1-m depth is estimated at

about 1550 Pg (Batjes, 1996). The SOC pool is a key determinant of soil quality (i.e., its biological productivity

and environment moderating capacity) and is a major source or sink for atmospheric CO2 and other GHGs. The

SOC pool can be conceptually divided into three broad categories: the labile or active pool with a mean residence

time (MRT) of less than 1 year; intermediate pool with MRT of several decades or centuries; and passive pool with

MRT of millennia.

The SIC includes elemental C and carbonate minerals such as calcite, dolomite and gypsum. The magnitude of

the SIC pool to 1-m depth is estimated at about 750 to 950 Pg, and is an important constituent of soils of the arid

and semiarid regions. There are two types of carbonates in soil: the primary or lithogenic carbonates; and the

secondary or pedogenic carbonates. The primary carbonates are derived from the weathering of parent material,

and the secondary carbonates are formed through the reaction of atmospheric CO2 with Caþ2 or Mgþ2 brought in

from outside the local ecosystem. Formation of secondary carbonates is an important mechanism of soil C

sequestration (Lal and Kimble, 2000; Glazovskaya, 1996).

SOIL CARBON AS A SOURCE OF ATMOSPHERIC CO2

During the period 1850 to 1998, 405� 60 Pg of C has been emitted as CO2 into the atmosphere globally (IPCC,

2000). Of this, 270� 30 Pg of C was emitted from fossil fuel burning and cement production (Marland et al.,

564 R. LAL

Copyright # 2004 John Wiley & Sons, Ltd. LAND DEGRADATION & DEVELOPMENT, 15: 563–572 (2004)

1999), and 136� 55 Pg of C from land-use change (IPCC, 2000). Until 1970, more C was emitted from land-use

change than fossil-fuel combustion. Presently, about 20 per cent of the total emissions (1�6 Pg out of a total

emission of 7�9 Pg) are from land-use change, principally by deforestation in the tropics. There are two distinct

sources of C emission from land-use change: release of C from vegetation or the biotic pool; and emission of C

from soil or the pedologic pool. Release of C from the vegetation following deforestation or conversion of natural

to managed ecosystems is caused by biomass burning and microbial decomposition. Emission of C from soil is

caused by mineralization/oxidation of soil organic matter in SOC pool and acidification of carbonates in the

SIC pool.

Cultivation of virgin soils is not as conspicuous a source of atmospheric CO2 as is fossil-fuel combustion. The

SOC pool is in a steady-state equilibrium under native vegetation cover because input of C through the biomass

(leaf liter, detritus material, and roots) is balanced by decomposition and other losses. The magnitude of the SOC

pool under native vegetation cover depends on climate, parent material, landscape position and slope aspect

(Jenny, 1980; Kovalyova and Yevdokimova, 1996; Glaser et al., 2000). The SOC pool ranges from 38 Mg C ha�1

for soils of arid regions (Aridisols) to 1170 Mg C ha�1 for Histosols or wetland soils (Eswaran et al., 2000). Most

mineral soils contain 80 to 100 Mg C ha�1. In Kyrgyzstan, Kovalyova, and Yevdokimova (1996) observed that the

SOC pool was a function of altitude and terrain. In southwest Tien Shau, Kazakhstan, and Vladychensky (1996)

observed a strong link between density of juniper forest cover and the SOC pool.

FACTORS AFFECTING DEPLETION OF SOC POOL

The loss of SOC is accentuated by deforestation, land-use conversion and attendant soil degradation and

desertification, which are severe problems in central Asia (Kharin, 2002; Funakawa et al., 2000; Makulbekova

and West, 1996; Maul et al., 1993; O’Hara, 1997). Soil humus content is a strong indicator of the susceptibility of

soil to degradation (Savich et al., 1999). Deforestation has been a serious problem in the mountainous region of

Uzbekistan (Alibekov, 2000). In Kyrgyzia, Glaser et al. (2000) observed that conversion of native vegetation to

pasture led to a loss of 30 per cent of total organic C compared with the native Juniperus turkestania forests.

Plowing depletes the SOC pool through increase in the rate of mineralization and acceleration of soil erosion. In

Kazakhstan, McNab (1997) reported that summer fallowing caused a rapid mineralization of soil organic matter.

Also in Kazakhstan, excessive grazing (Vladychensky et al., 1995) and degradation of rangeland (Makulbekova

and West, 1996) have been reported to cause depletion of SOC pool. Excessive and inappropriate irrigation has

caused widespread salinization and depletion of water resources (Orlovsky et al., 2000).

CAUSES OF SOIL DEGRADATION IN CENTRAL ASIA

There are several factors responsible for land degradation and desertification. Important among these is

inappropriate irrigation, leading to salinization and depletion of water resources. Excessive irrigation has caused

degradation of irrigated cropland. Cotton is grown under irrigated conditions in all countries in central Asia, and

there was a rapid expansion of irrigated land area in these countries between 1950 and 1986. During this period,

the irrigated land area increased from 2�28 Mha to 4�17 Mha in Uzbekistan, 0�36 Mha to 0�70 Mha in Tajikistan,

and 0�45 Mha to 1�35 Mha in Turkmenistan (Babaev and Zonn, 1999). Between 1940 and 1986, land area under

cotton production increased by 122 per cent in Uzbekistan, 196 per cent in Tajikistan and 330 per cent in

Turkmenistan (Critchlow, 1991). Excessive irrigation has caused drastic shrinkage of the Aral Sea and severe

problems of soil salinization. Urgent measures need to be taken to curtail salinization and degradation of irrigated

farmlands (Kharin, 1996).

Uncontrolled and excessive grazing is responsible for degradation of rangelands. For example, the juniper

forests of Kyrgyzstan are very heavily grazed (Vladychensky et al., 1995). Increases in grazing pressure

have a strong impact on the SOC pool and erosion hazard. Soil degradation is initiated by dehumification,

breakdown of structure, compaction and loss of biodiversity. These conditions make soil prone to accelerated

erosion. The data in Table I show that degraded areas in grazed pasture lost 19�0 Mg C ha�1 in a pasture site in

Kyrgyzstan.

CARBON SEQUESTRATION 565


Plowing and excessive tillage is another factor that exacerbates the problem of soil degradation and reduces the

SOC pool. Plowing depletes the SOC pool by increasing mineralization and the risks of soil erosion. Most soils

lose one-third to two-thirds of their SOC pool upon conversion from natural to agricultural ecosystems because

input of C is less than the losses due to mineralization, erosion and leaching. The rate of SOC loss is generally

more in the tropics than in temperate regions (Lal, 2001). The loss of SOC from cropland may be 60 to

80 Mg C ha�1 in humid climates and 10 to 40 Mg C ha�1 in semiarid and arid climates. The historic loss of SOC

from soils of the world was estimated at 55 Pg by IPCC (1995). Lal (1999) estimated the historic loss of SOC at 66

to 90 Pg of which 19 to 32 Pg is due to accelerated soil erosion. It is because of this loss that most agricultural soils

contain less SOC than their potential. The difference between the potential and actual SOC pool or the sink

capacity can be filled through conversion to a restorative land use and adoption of recommended management

practices (RMPs).

The land use data for central Asia includes 38 Mha under arable land and 249 Mha under permanent pasture

(FAO, 2002). Assuming a modest loss of 8 to 12 Mg C ha�1 from arable land and 4 to 6 Mg C ha�1 from permanent

pasture, the historic loss of SOC from soils of central Asia may be 1 to 2 Pg. In addition, some emission may have

also occurred from the SIC pool. Thus, the C sink capacity of soils in central Asia is 1 to 2 Pg over about a 50-year

period.

CONSERVATION AGRICULTURE AND SOC SEQUESTRATION

An important strategy of soil C sequestration is to reverse the degradative trends, restore degraded soils and

ecosystems, and adopt RMPs on cropland and grazing land. Adopting sustainable land use is an important strategy

of SOC sequestration (Singer et al., 2000). Sustainable management of cropland involves:

* adopting conservation tillage and reducing intensity and frequency of plowing;

* eliminating summer fallow;

* using integrated nutrient management options including manuring and judicious use of fertilizers; and

* reclaiming degraded (salinized, eroded, desertified) lands.

Research conducted in central Asia has documented the impact of several ameliorative measures on

improvement in soil quality and increase in SOC pool (Table II). Conservation agriculture in the broadest sense

(e.g., elimination of intensive tillage and summer fallow, integrated nutrient management, efficient use of irri-

gation water, improved cropping systems) and phytoremediation of degraded soils and ecosystems are important

options in enhancing production and SOC sequestration. Afforestation and improving degraded rangelands are

equally important (Kuliev, 1996; Lalymenko and Shadzhikov, 1966). The SOC concentration is often higher

underneath the shrubs than around them (Zayed, 2000). Tree species affect phenolic acid contents and the SOC

pool (Faituri, 2002). Improving pastures is another option in increasing SOC concentration. Teryukov (1996)

observed in western Kazakhstan that improved pastures should comprise a mixture of shrub species and perennial

grasses. Grasses are especially important to enhancing soil fertility. In Uzbekistan, Mirzaev (1984) observed that

Table I. Loss of soil humus by grazing in the southwestern Tyan-Shan region of Kyrgyzstan (recalculated from Vladychenskyet al., 1995)

Grazing Location Humus Soil bulk SOC pool at 0–15 cmconcentration (%) density (mg m�3) depth (Mg C ha�1)

Protected Path 3�27 1�28 36�4Degraded area 5�15 1�11 49�7Undamaged area 5�54 0�91 43�9

Grazed Path 2�23 1�37 26�6Degraded area 2�02 1�36 26�1Undamaged area 5�08 1�02 45�1

Assuming humus contains 58% C.

566 R. LAL


green manures (winter pea, winter rape) together with N and P fertilizers and perennial grasses increased soil

organic matter content. There are several options for restoring degraded soils in the desertified Aral Sea basin

(Dimeyova, 2000; Meirman et al., 2000; Muradov, 2000; Karibayeva, 2000; Baitulin, 2000). In addition to SOC,

there is also a potential for sequestering secondary carbonates, especially in irrigated agriculture (Glazovskaya,

1996; Jumeshov, 1999).

Principal benefits of conservation farming with residue mulch include increasing the available water storage in

the root zone by enhancing infiltration rate and reducing soil temperature (Bakajev et al., 1981), reducing

evaporation losses (Al-Darby et al., 1990) and improving water-use efficiency (Lopez and Arrue, 1997). However,

conservation farming or no till does not always produce the best yield, and the appropriate tillage methods may be

soil and crop specific (Suleimenov and Lysenko, 1997; Barajev and Sulejmenov, 1979; Hemmat and Oki, 2001).

One of the principal benefits of conservation farming is an increase in the SOC pool. The effectiveness in

enhancing the SOC pool and improving crop yield is accentuated by including legume-based rotations (with

medicago, vetch or other legumes), elimination of summer fallow, and controlled grazing (Jenkinson et al., 1999;

Murrillo et al., 1998; Al-Fakhry, 1988).

The data in Table III from Cordoba, Spain, show the benefits of SOC enhancement by eliminating fallow,

growing continuous wheat, or wheat in rotation with legumes, and adopting conservation tillage. In some

inherently-poor soils, conversion from natural to agricultural/managed ecosystems can enhance the SOC pool

(Wahba et al., 1999). Use of manures and biosolids is an effective strategy for increasing the SOC pool even in

soils of arid regions (Shalweer et al., 1998; Abdel-Nasser and Hussein, 2001). In Egypt, Labib et al. (2001)

observed that the SOC concentration was greater in soils growing cotton than those being intercropped. Several

experiments conducted in northwest Africa have demonstrated the positive effects of conservation tillage systems

on enhancement of the SOC pool (Mrabet, 2000; Mrabet and Franzluebbers, 2002; Mrabet et al., 2001a, 2001b;

Bessam et al., 2001; Saber and Mrabet, 2002). The data in Table IV from semiarid regions of Morocco show a SOC

sequestration rate of 305 kg C ha�1 y�1 upon conversion from plow tillage to no tillage, and 102 to

270 kg C ha�1 y�1 upon adoption of continuous cropping, which including forages/legumes in the rotation cycle

(Mrabet et al., 2001a, 2001b). Bessam and Mrabet (2003) reported that after four years of no-till an extra

5�6 Mg ha�1 of SOC was sequestered in the 0–25 cm layer, and after 11 years the SOC pool increased further to

Table II. Technological options for soil restoration and carbon sequestration in central Asia

Technology Soil/terrain/ecosystem Region/country Reference

Afforestation Foothill plains Balkan range Lalymenka and Shadzhikov (1996)INM Chernozen Central Asia Kogut et al. (1998)Phytomelioration Degraded pasture Kazakhstan Teryukov (1996)Rangeland restoration Volga–Ural sands Kazakhstan Makulbekova and West (1996)Soil reclamation Solonetz soils Kazakhstan Okorokov and Abileva (1995)Conservation/minimum tillage Light and heavy soils Kazakhstan, Karabayev (2000); Kaskarbayev

Monocco et al. (2001); Suleimenov et al.(1994, 2003); Barajev andSudeimenor (1979); Mrabet (2002)

Eliminating summer fallow Black soils Kazakhstan Suleimenov et al. (1997)Integrated nutrient Irrigated crops Kyrgyzstan, Zoloev et al. (1993);management/compost Spain Coelho et al. (2000)Organic farming Ecological agriculture Tajikistan, Odinayev (1995); El-Shalweer

Egypt et al. (1998)No till farming Irrigated agriculture in Turkmenistan Babaev and Ovezliev (1994)

sandy desert areasAfforestation Desertification control Turkmenistan Kuliev (1996)Agroforestry Plain and montaine Uzbekistan Alibekov (2000)Integrated water resource Irrigated agriculture Uzbekistan Sokolov (1999)managementPhytomelioration Degraded rangeland Uzbekistan Reizvikh and West (1995)



7�21 Mg ha�1. These rates are comparable to those reported from elsewhere in semiarid regions (Lal, 2001), and

may be applicable to the soils of central Asia. Comparing data from 276 paired treatments globally, West and Post

(2002) reported that a change from conventional tillage to no-till can sequester SOC at the rate of

570� 140 kg ha�1 y�1.

THE POTENTIAL OF SOIL CARBON SEQUESTRATION

Estimates of the potential of soil C sequestration shown in Table V indicate the possibility of soil C sequestration in

the range of 10 to 23 Tg C y�1 for about a 50-year period. The data in Table VI is another estimate of the soil C

Table III. Effects of six years of tillage and rotationtreatments on SOC concentration in 0–30 cm depth underrain-fed Mediterranean conditions in Cordoba, Spain

Treatment SOC (g kg�1)

A. TillageNo tillage 5�34aConventional tillage 5�28a

B. RotationContinuous wheat 5�51aWheat–sunflower 5�34aWheat–chickpea 4�99bWheat–faba bean 5�45aWheat–fallow 5�10b

Source: Recalculated from Lopez-Bellidu et al., 1997. Figuresfollowed by the same letter in column 2 are statistically similar.

Table IV. SOC pool as affected by wheat rotation and tillage for 11 years in a semiaridarea of Morocco

Treatment SOC pool in 2 m Rate of SOC change(Mg C ha�1) (kg C ha�1 y�1)

A. RotationContinuous wheat 36�39a 246Wheat–fallow 34�80b 102Fallow–wheat–forage 36�65a 270Fallow–wheat–corn 33�68c —Fallow–wheat–lentils 36�43a 250

B. TillageNo tillage 37�28a 305Conventional tillage 33�92b 0

Source: Recalculated from Mrabet et al., 2001a, 2001b. Figures followed by the same letter incolumn 2 are statistically similar.

Table V. Estimates of the potential of soil carbon sequestration in central Asia

Land use Area (Mha) C sequestration rate (kg ha�1 y�1) Total potential(Tg C y�1)

SOC SIC Total

Irrigated cropland 10�3 50–100 20–50 70–150 0�72–1�55Rain-fed cropland 27�9 20–50 10–20 30–70 0�84–1�95Permanent pasture 248�7 20–50 10–20 30–70 7�46–17�41Forest and woodland 16�1 50–100 10–20 60–120 0�98–1�93Total 303�0 10�00–22�84

SOC sequestration rates are based on data by Mrabet et al. (2001a, 2001b), Jenkinson et al. (1999) and Lal (1999, 2001).

568 R. LAL


sequestration potential based on the land use and the need for soil and ecosystem restoration. The potential for soil

C sequestration by this approach is 11�3 to 20�7 Tg C y�1 with a mean of 16� 6�6 Tg C y�1. This potential is over

and above that of C sequestration in the biota. The average soil C sequestration potential of about 16 Tg C y�1 is

20 per cent of the CO2 emissions from fossil-fuel combustion.

The modest potential, as it may seem, has several agronomic, economic and environmental implications:

* Agronomically, an increase in humus content will enhance soil quality and improve agronomic/biomass

productivity.

* Economically, soil C sequestered can be traded in the international market under the Kyoto Protocol using the

provision of Clean Development Mechanism. Even at a modest price of $10 Mg�1, the soil C sequestration

potential in central Asia is worth US$100–230 million per year.

* Environmentally, soil C sequestration offsets 20 per cent of the CO2 emission from fossil-fuel combustion, and

decreases the rate of enrichment of atmospheric CO2. Thus, soil C sequestration is truly a win–win situation.

Restoration of degraded soils and ecosystems and adoption of conservation farming are important options in

achieving this goal.

CONCLUSIONS

There is a vast potential for C sequestration in dryland ecosystems (Squires et al., 1995; Lal, 2002). The potential

for soil C sequestration in central Asia is relevant to the Clean Development Mechanism (CDM) under the Kyoto

Protocol. Realization of this potential, however, necessitates identification and implementation of policies that

facilitate/encourage restoration of degraded soils and ecosystems, and adoption of conservation farming and other

recommended agricultural and forestry practices. There is also a strong need for commodification of C so that it

Table VI. The potential for SOC sequestration by adopting improved management in different ecoregions of central Asia

Land use Conservation Rational utilization Amelioration Totaland rational with partial of theutilization amelioration whole area

(a) Land area (Kharin, 1996) (Mha)Forests 22�561 10�438 0�672 33�671Rangeland 16�997 7�145 0�492 24�634Irrigated farmland 0�867 7�025 0�780 8�762

(b) Rate of SOC (SIC) sequestration(kg C ha�1 yr�1)

Forests 200–300 (20–50) 100–200 (10–20) 300–400 (20–50)Rangeland 100–200 (50–100) 50–100 (20–50) 100–200 (20–50)Irrigated farmland 150–250 (100–200) 100–150 (100–150) 200–300 (100–200)

(c) Total SOC sequestration (Tg C y�1)Forests 4�51–6�77 1�04–2�08 0�20–0�27 5�75–9�12Rangeland 1�70–3�40 0�36–0�72 0�05–0�10 2�11–4�22Irrigated farmland 0�13–0�22 0�70–1�05 0�16–0�23 0�99–1�50Total 6�34–10�39 2�10–3�85 0�41–0�50 8�85–14�84

(d) SIC sequestration potential (Tg C y�1)Forests 0�45–1�13 0�10–0�20 0�01–0�03 0�56–1�36Rangeland 0�85–1�70 0�14–0�36 0�01–0�02 1�00–2�08Irrigated farmland 0�09–0�17 0�70–1�05 0�08–0�16 0�87–2�43Total 1�39–3�00 0�94–1�61 0�10–0�21 2�43–5�87

Grand total of SOC and SIC 7�73–13�39 3�04–5�46 0�51–0�71 11�28–20�71

Numbers in parenthesis are SIC sequestration rates. SOC and SIC sequestration rates are based on Lal (1999, 2001), Mrabet et al. (2001a,2001b), Jenkinson et al. (1999), Murillo et al. (1998) and Lal and Kimble (2000).



can be traded in the international market. Identification of C sequestration bright spots, soils and ecosystems with a

large potential to sequester C and the associated practices to achieve that potential, is a researchable priority for the

region.

acknowledgement

Financial support for travel to Uzbekistan was provided by the Winrock International and Land O’Lakes, Inc.

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