Zomer et al. (2017). Global Sequestration Potential of Increased Organic Carbon in Cropland Soils

–

4

. Both land-use change to agriculture and agricultural production have and continue

to contribute significantly to the increase in atmospheric carbon dioxide (CO

2

), accounting for as much as 24% of

global greenhouse gas (GHG) emissions

5

. Almost 50% of all potentially vegetated land surface globally has been

converted to croplands, pastures and rangelands

–

4

. This land-use change and soil cultivation have contributed

136

±

55 petagrams of carbon (Pg C) to the atmosphere from change in biomass carbon since the beginning of

the Industrial Revolution, with depletion of soil organic carbon (SOC) accounting for a further contribution of

78

±

12 Pg C. This estimated 214

±

67 Pg C from the land-use sector compares to the estimated 270

±

30 Pg of C

contributed by fossil fuel combustion

6

as a historical carbon source. More recently soil organic matter also has

gotten increasing attention as a potentially large and uncertain source of carbon to the atmosphere in the future

in response to predicted global temperature rises

7

8

.

Soils, however, can act as both sources and sinks of carbon, depending upon management, biomass input

levels, micro-climatic conditions, and bioclimatic change. Substantially more carbon is stored in the world’s soils

than is present in the atmosphere. The global soil carbon (C) pool to one-meter depth, estimated at 2500 Pg C,

of which about 1500 Pg C is soil organic carbon (SOC), is about 3.2 times the size of the atmospheric pool and 4

times that of the biotic pool

,

. An extensive body of research has shown that land management practices can

increase soil carbon stocks on agricultural lands with practices including addition of organic manures, cover

cropping, mulching, conservation tillage, fertility management, agroforestry, and rotational grazing

. There

is general agreement that the technical potential for sequestration of carbon in soil is significant, and some con-

sensus on the magnitude of that potential

13

. On this basis, the 4p1000 initiative on Soil for Food Security and

Climate

14

, officially launched by the French Ministry of Agriculture at the United Nations Framework Convention

for Climate Change: Conference of the Parties (UNFCCC COP 21) in Paris, aims to sequester approximately

3.5Gt C annually in soils. Croplands will be extremely important in this effort, as these lands are already being

actively managed, and so amenable to implementation of improved practices

. Furthermore, because almost all

cropped soils have lost a large percentage of their pre-cultivation SOC

6

There are amendments to this paper

15

, they potentially represent a large sink

to re-absorb carbon through the introduction and adoption of improved or proper management aimed towards

increased SOC. However, carbon is rarely stored in soils in its elemental form, but rather in the form of organic

1

Key Laboratory for Plant Diversity and Biogeography of East Asia (KLPB), Kunming Institute of Botany, Chinese

Academy of Science, Kunming, 650201, Yunnan, China.

2

The Nature Conservatory (TNC), Santa Cruz, California,

USA.

3

International Center for Tropical Agriculture (CIAT), Nairobi, Kenya.

4

International Center for Tropical

Agriculture (CIAT), Cali, Colombia. Correspondence and requests for materials should be addressed to R.J.Z. (email:

r.zomer@cgiar.org

)

Received: 31 August 2017
Accepted: 2 November 2017
Published: xx xx xxxx

OPEN

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matter which contains significant amounts of other nutrients, above all nitrogen. Nutrients, biomass productiv-

ity, the type of vegetation and water availability, among other constraints therefore can be major limiting factors

inhibiting increases in soil carbon sequestration

. Further imperative to sequester carbon in soils arises from

the multiple co-benefits that are obtained from sequestration of carbon in soils that have been depleted of their

organic matter

17

. Soil fertility, health, and functioning are immediate consequences of the amount of soil organic

matter (and hence carbon) a soil contains; this is even more important for highly weathered soils, as is the case for

the majority of soils in the humid lowland tropics. Increasing carbon in soils also means improving its physical

properties and related ecosystems services, such as better water infiltration, water holding capacity, as well as

potentially increasing agricultural productivity and ecological resilience

,

In this analysis, we illustrate where carbon might be sequestered, and how much, if, through improved prac-

tices and management, we could increase SOC on agricultural land by a generally accepted (as attainable) moder-

ate to optimistic amount, based on the medium and high sequestration scenarios of Sommer and Bossio (2014).

These scenarios from Sommer and Bossio (2014) resulted in an 0.27 and 0.54% increase in SOC in the top 30 cm

of soils after 20 years, for the medium and high scenarios, respectively, that is, a 0.012 to 0.027% annual increase.

The low scenario in Sommer and Bossio (2014) was not used because it refers to sequestration rates estimated

primarily for unimproved pasture land. An implicit basic assumption is that in general, 50 to 70% of soil car-

bon stocks have been lost in cultivated soils

, such that the SOC status of almost all cultivated soils can be

increased. It is expected that these cropped soils will be able to sequester carbon for at least 20 years before reach-

ing saturation points and new SOC equilibriums

13

18

, while meta-analysis of field studies

14

suggests that in some

instances significant sequestration can continue for 30 or even up to 40 years before reaching new equilibriums.

We used the recently released ISRIC SoilGrids250m

global database of soil information, to identify and derive

basic soil characteristics, i.e. SOC and soil bulk density, and the FAO GLC-Share Land Cover database

20

to iden-

tify and calculate areal extent of the cropland landcover class. The analysis gives a spatially articulated estimate

of the distribution and increase of SOC if equal sequestration is reached, within the medium and high scenarios,

on all available cropland soils through improved practices. The results of this paper provide an estimate of what

the potential amount of sequestered carbon would be in terms of tons of carbon per hectare, spatially articulated

at 250 m resolution, and in terms of Pg C regionally and globally, allowing for a quantified discussion of the

importance of this carbon pool within on-going global discussions regarding mitigation potential within the

agricultural sector.

Results

Global Soil Organic Carbon Stocks on Croplands.

Estimates of global soil carbon stocks, trends and

sequestration potential

,

, particularly within the context of a warming climate

,

, are now central to impor-

tant discussions ongoing within various international fora, notably the discussions on including agricultural land

within mitigation strategies and protocols at the UNFCCC, and are the basis for the 4p1000 Initiative

14

. The spa-

tial distribution of SOC on croplands (Fig.

), and its contribution to total carbon stock, varies with latitude, and

differs substantially from that of carbon stored in above and below ground biomass

23

,

24

. Most of the world’s SOC

is stored at northern latitudes, particularly in the permafrost and moist boreal regions. In contrast, large areas

of cropland in India, across the Sahel, northern China, and Australia are found on low carbon density soils. An

overview of 27 studies

25

reports that 1500 Pg C can be regarded as a rough estimate of the global SOC pool (to one

meter depth; across all the world’s soils, more than 130 million km

2

), however with substantial variability among

both spatially- and non-spatially-explicit estimates and a range of from 500 to 3000 Pg C.

About 372,000 km

2

of cropland (Supplementary Figure S1), comprised of carbon dense soils (

>

400 t C/ha

and/or with a bulk density

<

1.0 g/cm

3

) and which are considered likely to lose SOC under any form of cropping

Figure 1. Soil organic carbon (SOC) in the top 30 cm, currently (T

0

), on all available cropland soils globally

(i.e. those not excluded from the analysis as high SOC soils or sandy soils). Maps were produced based upon

a geospatial analysis of datasets from the SoilsGrids250 database

, using ESRI ArcGIS software (version 10.3;

www.esri.com

).

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management, and sandy soils unlikely to sequester carbon due to high sand content (

>

85%), were excluded from

the analysis as “unavailable” (Table

). In particular, it is highlighted that high SOC soils, while accounting for

only 2% of total cropland area, account for almost 6% (8.48 Pg C) of total global cropland SOC stocks, and require

a set of management options aimed toward conservation and maintenance of carbon stocks

25

. These areas are pri-

marily peatlands in South East Asia, Russia, some in North America, South America, Europe, Australia/Pacific,

and Andosols in South America. Cultivation of peat soils has been shown to contribute significantly to global

emissions from agriculture

26

. Tropical and temperate peatlands account for a disproportionate share of terrestrial

carbon stocks considering their more limited area globally

27

, with peatland drainage, concentrated in Europe and

Indonesia, reported to account for nearly a third of all cropland emissions

28

.

Globally, cropland stores more than 140 Pg C in the top 30 cm of soil, almost 10% of the total global SOC pool.

About 94% of this carbon (131.81 Pg C) is stored on the 15.9 million km

2

(98% of global cropland) identified as

potentially available for enhanced carbon sequestration through improved soil management and farming prac-

tices

. Global distribution of SOC is strongly influenced by temperature and precipitation

15

29

. SOC is generally

lower in the tropics where it is hotter and/or drier, and higher in the cooler, wetter, more northerly, and to a some-

what lesser extent, southerly, latitudes (Fig.

). Lal (2002) cites several studies showing an exponential decrease

in SOC with increase in temperature. This is reflected by low SOC values found across much of the equatorial

belt (e.g. less than 100 t C/ha), with the highest carbon density soils (400 t C/ha or more) found in the northern

croplands and farmed peat soils of the United States, Canada, Europe and Russia (see Supplementary Table S1).

The regions of North America, Eurasia (Russia) and Europe currently store the greatest amount of carbon on

cropland, each with more than 21 Pg C, and all together accounting for over 50% of all SOC stocks on cropland

globally (Table

). By contrast, Central America, North Africa, and the Australian/Pacific region have very low

amounts of stored SOC, together comprising 6.48 Pg C or just over 4.6% of the global total. Western Asia, South

Asia, Southeast East Asia and East Asia each have moderate amount ranging from 4.38 Pg C to 9.14 Pg C, but

together accounting for just less than 2% of global total. South America, even having a fairly large amount of

farmland, has a moderate 9.42 Pg C. Almost 12 Pg C, more than 8.5% of the global total, is found in Africa, with

the highest concentrations found in the Eastern and Central regions. Nationally, Russia with its vast northern

tracts of carbon dense agricultural land has the largest total amount of SOC stored on cropland more than 21.9 Pg

C (almost 17% of the global total), followed by the United States (18.9 Pg C), China (8.4 Pg C), India (6.4 Pg C),

and Brazil (5.0 Pg C) (Supplementary Table S2).

Sequestration Potential of Increased Soil Organic Carbon Stocks on Croplands.

Our analysis

shows that if the SOC content in the 0–30 cm depth layer of all available cropland increased from 0.27% to 0.54%,

i.e. from the Sommer and Bossio (2014) medium to high scenarios, from 0.56 to 1.15 t C/ha/yr could be seques-

tered (Table

), which translates to 0.90 to 1.85 Pg C/yr globally, for at least the 20 years that sequestration can be

expected to continue. This estimate of total sequestration potential on cropland soils compares well to and is in

the range of other recent estimates for agricultural areas

,

,

,

. The annual increment (on a per hectare basis)

ranged from 0.50 up to 1.28 t C/ha across the various regions (see Supplementary Figures S2–S9), however total

amounts of sequestered carbon vary widely, due to the varying amount of cropland across regions. North America

showed the highest potential for total carbon storage, globally, with between 0.17 and 0.35 Pg C (0.60 to 1.22 t/ha)

sequestered annually (Table

2

; Fig.

2

). South Asia and Europe showed approximately the same total sequestration

potential (0.11–0.23 Pg C/yr), second highest among regions, even though European soils are already fairly car-

bon dense on average (106 t C/ha). Low levels of SOC on croplands across South Asia (44 t C/ha), much of it with

serious degradation issues, provide the opportunity to sequester 0.62–1.28 t C/ha/yr on over 2.9 million km

2

of

land, accounting for 2.2 to 4.5 Pg C/yr of carbon storage. Likewise, Africa, taken altogether with over 2.6 million

km

2

of cropland, shows a large potential for soil carbon storage, ranging from 0.15 to 0.31 Pg C/yr. South Asia and

North Africa show the highest potential for carbon storage on a per hectare basis (0.62–1.28 t C/ha), although

North Africa has very little cropland and hence only a small potential for total carbon soil sequestration.

Among countries of the world, the United States showed the highest total annual potential in SOC (1.2–2.6 Pg

C), with an average increase of 0.62–1.27 t C/ha/yr on over 2 million km

2

of cropland. However, India, with about

the same high average increase per hectare (0.63–1.27 t C/ha/yr) on over 1.6 million km

2

of cropland, shows a

potential total annual increment ranging from 1.0 to over 2.1 Pg C. Likewise, China and Russia, each with about

1.2 million km

2

of cropland, both have a large potential to increase total carbon storage, ranging from 0.63 to over

1.3 Pg C annually each. Many smaller countries exhibit high per hectare annual increments, although their total

Cropland Soils

(30 cm depth)

Soil Organic Carbon

Average Soil Organic Carbon per Hectare

Cropland

Area

Current After 20 Years

Annual Increase

Current After 20 Years

Annual Increase

Scenario

T

0

Medium

High

Medium

High

T

0

Medium

High

Medium

High

PgC

PgC/yr

tC/ha

tC/ha/yr

km

2

Available Soils 131.81

149.84

168.87 0.90

1.85

82

93

105

0.56

1.15

15,935,304

High SOC Soils 8.34

252

331,227

Sandy Soils

0.14

34

40,999

Total

140.28

16,307,531

Table 1. Soil organic carbon (SOC) for all available cropland soils globally (i.e. those not excluded from the

analysis as high SOC or sandy soils), showing both the global totals and the global averages per hectare, at current

status (T

0

), and after 20 years for both the medium and high sequestration scenarios, and their annual increment.

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C sequestration is low due to small areas of cropland. For example, 45 countries are in the higher range above 0.58

to 1.2 t C/ha, however, many of these are found in drier climates where water and biomass availability may be a

limiting factor.

Discussion

The Role of Soil Organic Carbon Stocks on Cropland.

Increasing soil organic carbon on the vast areas

of cropland globally which are already intensively managed

is more immediately practical and likely than on the

other available landuse types, e.g. forestry or grazing land. On these croplands adoption of improved management

practices offers the opportunity to sequester significant amounts of carbon in the near term, and potentially to

make an important contribution to global mitigation efforts. The 4p1000 Initiative has identified an aspirational

sequestration target of 3.5 Pg C/yr to provide substantive global mitigation. Our estimates suggest that from 26%

up to 53% (0.90–1.85 Pg C) of this target could be reached in the top 30 cm of cropland soils alone, and continue

over at least 20 years after adoption of SOC enhancing management, such as incorporation of organic manures,

Cropland Soils (30 cm depth)

Soil Organic Carbon

Average Soil Organic Carbon

Cropland Area

Current

After 20 Years

Annual Increase

Current

After 20 Years

Annual Increase

Scenario

T

0

Medium

High

Medium

High

T

0

Medium

High

Medium

High

Region

PgC

PgC/yr

tC/ha

tC/ha/yr

km

2

Australian/Pacific

3.75

4.50

5.29

0.04

0.08

57

68

80

0.57

1.16

659,834

Central America

1.22

1.37

1.52

0.01

0.02

87

98

109

0.53

1.09

139,742

Central Asia

5.01

5.40

5.81

0.02

0.04

136

146

158

0.53

1.08

369,061

East Asia

9.14

10.52

11.97

0.07

0.14

72

83

95

0.54

1.12

1,262,134

Eastern and Southern Africa

5.64

6.80

8.02

0.06

0.12

53

64

76

0.55

1.13

1,055,461

Europe

21.05

23.26

25.60

0.11

0.23

106

117

128

0.55

1.14

1,995,564

North Africa

1.51

1.83

2.17

0.02

0.03

58

71

84

0.63

1.28

258,602

North America

28.07

31.52

35.16

0.17

0.35

97

109

122

0.60

1.22

1,260,786

Russia

21.94

23.19

24.52

0.06

0.13

174

184

194

0.50

1.02

1,235,827

South America

9.42

10.72

12.09

0.06

0.13

76

87

98

0.53

1.08

1,753,039

South Asia

7.68

9.87

12.18

0.11

0.22

44

56

69

0.62

1.28

852,619

SouthEast Asia

8.15

9.06

10.03

0.05

0.09

96

106

118

0.53

1.10

1,307,174

West and Central Africa

4.83

6.35

7.95

0.08

0.16

37

49

61

0.58

1.19

891,532

Western Asia

4.38

5.44

6.57

0.05

0.11

49

61

74

0.60

1.23

2,893,928

Global

131.81

149.84

168.87

0.90

1.85

81.61

92.82

104.66

0.56

1.15

15,935,304

Table 2. Regional Analysis of Available Soils: Soil organic carbon (SOC) for all available cropland soils by

region (i.e. those not excluded from the analysis as high SOC or sandy soils), showing both the regional totals

and the regional averages per hectare, at current status (T

0

), and after 20 years for both the medium and high

sequestration scenarios, and their annual increment.

Figure 2. Annual increase in soil organic carbon (SOC) in the top 30 cm, on all available cropland soils

globally (i.e. those not excluded from the analysis as high SOC or sandy soils) under the medium scenario (i.e.

an increase in percent SOC of 0.27 over 20 years). Maps were produced based upon a geospatial analysis of

datasets from the SoilsGrids250 database

, using ESRI ArcGIS software (version 10.3;

www.esri.com

).

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cover cropping, mulching, conservation tillage, some types for agroforestry practices, rotational grazing, or other

practices known to increase soil carbon at the decadal scale. This requires that croplands increase SOC storage

between 0.55–1.15 t/ha/yr. However, as Sommer and Bossio (2014) point out, adoption can be expected to be

phased in over a period of years, with delays in roll out as various countries, production systems and farm types

may be slower to adopt improved practices. Likewise, our estimates do not account for differences in climate and

important soil process issues, notably nutrient and water limitations, biomass production and turnover rates.

However, given the large amount of cropland potentially available, sequestering carbon via increases in the soil

component on agricultural land is an achievable and potentially effective route to quickly increasing CO

2

seques-

tration in the near term. For comparison, above-ground losses due to tropical land use conversion are currently

estimated at 0.6–1.2 Pg C yr-1

30

. A strategy of enhancing agriculture with soil carbon enriching improved prac-

tices, e.g. via appropriate policy mechanisms, thus offers significant potential to mitigate landuse related carbon

emissions and provide an opportunity for agricultural production to positively contribute to global mitigation

efforts. SOC may be either enhanced by, or enhance above- and below-ground biomass carbon on agricultural

land

24

, allowing for synergistic increases in on-farm carbon stocks. Agroforestry systems and planting trees, for

example, may increase soil carbon sequestration

Multiple Benefits from Enhanced Soil Organic Carbon Stocks on Cropland.

The benefits of

increasing soil organic matter in croplands goes far beyond climate change mitigation potential. Facilitation

of increased SOC through improved farming and soil conservation practices, enhancing resilience through

improved fertility status and water holding capacity, also provide important adaptation benefits

31

. It is generally

recognized that changes in the moisture regime (e.g. drought or heavy precipitation events) can significantly

impact crop productivity

32

. These climatic conditions are mitigated by SOC

,

, which adds structure, improves

water infiltration and holding capacity, increases cation exchange capacity, and impacts soil fertility, a major con-

trolling factor of agricultural productivity and both regional and household food security

34

. Soil conditions have

dramatic effects on the abundance and efficiency of N-fixing bacteria

35

, which are vitally important in cropping

systems that lack fertilizer inputs

36

. Thus increased SOC through improved management practices is likely to add

substantial resilience to croplands and farming systems, particularly during drought years or increased seasonal

variability, helping to avoid edaphic (soil related) droughts that result from land degradation

37

.

For the most part, agricultural practices that increase soil organic matter are supportive of enhanced food

production and other ecosystem services. This is in contrast to other proposed negative emission strategies, such

as afforestation (plantations of fast growing trees) and BECCS (bioenergy and carbon capture and storage) that

will entail destruction of huge amounts of natural ecosystems or productive agriculture land if implemented at

scales large enough to impact CO

2

in the atmosphere

38

–

40

. Given that hundreds of millions of small farmers for

their subsistence depend upon croplands around the world, mitigation benefits of enhanced SOC storage must be

recognized as only one significant component of an array of multiple benefits to achieve.

Despite the large technical potential to sequester carbon in soils, there are often significant limitations to

achieving that potential in any particular place and within specific farming systems, including lack of biomass and

other inputs

. In addition, there may be tradeoffs with productivity, food security or hydrologic balances

34

41

, as

well as concerns regarding other GHGs, such as N

2

O

. As with any efforts to sustain notable changes in practice

significant understanding of cultural, political and socioeconomic contexts are required

. Enhanced understand-

ing of land potential is also necessary to target limited resources

37

. While numerous constraints to achieving the

technical potential of soil carbon sequestration exist, there are cases in which far higher sequestration rates are

proposed than commonly accepted, even for annual cropping systems

42

. Refining our understanding of the tech-

nical potential for carbon sequestration in soils, and the practical implementation of improved soil management

and farming practices aimed towards increasing SOC, offers a strategy for mitigation within the land use sector in

the near-term, with potentially positive implications for food security and ecological resilience in the long-term.

Methods

Three publicly available global geospatial datasets were used for this study:

Soils Data.

The recently released Soils Grid 250 m is a global database of soil properties at a spatial resolution

of 250 m, provided by ISRIC World Soil Information. Datasets for SOC (g/kg), bulk density (kg/m

3

) and sand

content (weight %), at several depths and depth layers, from 0–30 cm, were utilized in the analysis

Landcover Data.

The Global Land Cover SHARE Beta-Release v1.0 (GLC_SHARE) fractional landcover

geospatial database, provides an estimate of the percent of cropland area within a 1 km grid cell, and was used to

identify cropland extent. The designation “cropland” is an aggregated category based upon the UN Land Cover

Classification System, which includes herbaceous crops, woody crops, and multiple or layered crops. This dataset

was resampled to allow for the analysis and geoprocessing at the finer 250 m (0.002083333 degree) resolution of

the soils data

20

.

Administrative Boundaries.

The GADM database of Global Administrative Areas v 2.8 was used to ana-

lyze results by regions and countries

43

.

The geospatial analysis uses the equation for potential carbon sequestration delineated in Sommer and Bossio

(2014) as the estimate of the potential attainable increase of SOC on croplands after twenty years. These starting

estimates, i.e. 0.27 increase for the medium scenario and 0.54 increase for the high scenario, are used to deter-

mine the estimate of SOC sequestration potential in tons of carbon (or Pg C), on a grid cell by grid cell basis. The

SoilsGrid250m SOC and bulk density datasets were used to parameterize the conversion from SOC as a percent

of the top 30 cm soil depth layer, to SOC in t C (or PgC for the global results). Only the medium and high seques-

tration scenarios pertinent to croplands are presented, since the low scenario in Sommer and Bossio (2014) refers

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to sequestration rates for unimproved pasture land. SOC sequestration. We have estimated the increase after a

20-year time span in order to provide an operational description of the linear portion of the SOC sequestration

curve, noting that the rate of increase is likely to decrease sometime thereafter and eventually reach a new equi-

librium (Fig.

3

).

The increase in %-SOC in response to improved management or other sequestration measures was described

in Sommer and Bosio (2014) with a four-parameter sigmoid function of the form:

=

+

−

a

e

SOC

1

(1)

0

t t

b

0

where

SOC

0

is the initial soil organic carbon content (%),

a

and

b

are empirical constants and

t

the time expressed

in years.

t

0

is the year where the slope of the curve is largest, i.e. the annual sequestration rate highest. The param-

eters for the two scenarios (based upon Sommer and Bossio 2014), were:

= .

=

.

=

= .

=

a

b

t

a

b

t

Medium: SOC

0 71;

0 697;

11 5;

4

High:

SOC

0 60;

1 20;

9 8;

7

0

The percent increase of SOC after 20 years (T

20

) was calculated from this curve for the two scenarios as:

= .

Medium: T

0 269663

High:

T

0 553936

20

Bulk density was used to first convert SOC (t/ha) (as presented in the SoilsGrid250m data) into SOC (%). The

estimated percentage increase was then added, and the result was then converted back in SOC (t/ha).

High SOC soils were mapped in a separate layer by identifying grid cells with a weighted average bulk density

(0–30 cm) equal to or less than 1.0 kg/m

3

, and/or any gird cells with more than 400 t C/ha. These high carbon soils

were excluded from further analysis. Sandy soils were mapped in a separate layer by identifying grid cells with

sand content (at 15 cm) equal to or greater than 85%, and likewise, were excluded from further analysis.

All result grids converted to World Sinusiodal projection to allow for area calculations. The GLCShare –

Dominant (Class 2

=

Cropland) dataset, in percent area of a 1 km grid cell, was resampled to 250 m and multiplied

times the various results (t/ha) to calculate actual total tC in each grid cell, i.e. given the actual area of agricultural

land in that grid cell. The sum of grid cells was then multiplied by the number of hectares to provide regional and

country zonal statistics. A full description of the geospatial methodology used to calculate the agricultural area,

percent SOC, the conversion to tons per hectare, and the aggregation of tons of SOC on cropland is given in the

Supplemental Materials. Results datasets are archived and available from Harvard Dataverse, accessible from the

following link: DOI:

10.7910/DVN/HYFICT

. High resolution maps are available online at:

http://ciat.cgiar.org/

global-soil-carbon

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Acknowledgements

Funding for this study was provided by the International Center for Tropical Agriculture (CIAT) and the CGIAR

Research Program on Water, Land and Ecosystems (WLE), with additional support provided. The Nature

Conservancy, and by the Center for Mountain Ecosystems Studies (CMES), Kunming Institute of Botany and the

Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant Number QYZDY-SSW-

SMC014).

Author Contributions

D.B., R.Z. and R.S. designed the study; R.Z. performed the geospatial analysis, R.Z., D.B., R.S. and L.V. analyzed

the data sets; R.Z., D.B., R.S. and L.V. wrote the paper; R.Z. produced all maps, tables and figures.

Additional Information

Supplementary information accompanies this paper at

https://doi.org/10.1038/s41598-017-15794-8

.

Competing Interests: The authors declare that they have no competing interests.

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