A high-resolution spatially-explicit methodology to assess global soil organic carbon restoration potential21 March 2017Luuk Fleskens, Michel Bakkenes, Coen Ritsema, Ben ten Brink, Klaas Oostindie, Gudrun Schwilch

Rationale Urgent need for spatial data to guide initiatives on

restoration and prevention of land degradation: what practices are available, possible and feasible in each location, and how do they perform?

Much research exists on restoration opportunities, but the bulk of it concentrates on local scales.

A new approach is therefore much needed that, based on the state of knowledge, enables a global outlook on opportunities and challenges of SOC restoration.

Methodology

We model the global SOC restoration potential in the top 30-cm of soil as a full-scale SOC Restoration scenario by aggregating the effects of the most effective restoration category in each location.

SLM and reforestation practices can affect SOC in two ways:Restoring SOC and Preventing SOC loss

Establishing SOC restoration potential requires: i) restoration and prevention trend lines considering time

after investment (literature review)ii) SOC restoration ceilings (S-World)iii) Current levels of soil loss and SOC loss (NDVI+S-World) iv) Classification of restoration measures and developing an

allocation mechanism for these categories of restoration measures (WOCAT and data review)

C Sequestration potential: restoration + prevention of SOC losses

SLM effect on SOC – relation of SOC increase with timeLiterature reviewRelationship between the number of years and the increase of Soil Organic Carbon (SOC)(Mg/ha) for those cases exhibiting a sequestration rate greater or equal than 0.25 Mg/ha, or where the total SOC increase is greater or equal than 7.5 Mg/ha

This function is used to map C restoration potential

Current SOC levels, trend and potential SOC content30 arcsec (~1 km2) global datasets:• Current soil organic carbon (SOC) content

Based on S-World; functional interpolation modelling based on harmonised global soil profiles. Stoorvogel et al. (2017a) Land Deg Dev in press)

• Current rate of soil degradation (SOC loss and soil depth loss) Based on trend analysis and projection of bias-corrected NDVI analysis. Schut et al. (2015) PLOS One 10(10): e0138013

• Potential soil organic carbon (SOC) content Based on S-World; analyses of soils under natural land use classes and best possible agricultural management given current land use. Stoorvogel et al. Stoorvogel et al. (2017b) Land Deg Dev in press)

SLM category typesWOCAT Broad

CategoriesWOCAT

Sub-classifications

WOCAT Broad categories

Categorisation used (number of practices included)

Agronomic

Cropping management

Conservation agriculture

Reduced tillage (44)

Soil improvement

Manuring/composting Soil improvement (42) Integrated soil fertility management

Vegetative

Cover crops Vegetative cover (33) Cross-slope barriers (vegetative)

Vegetative barriers (43)

Agroforestry Agroforestry (38) Sustainable planted forest management

Reforestation in savannahs* (29) Assisted natural regeneration* (6) Smallholder woodlots* (6) Forest plantations *(6)

Structural

Water management

Water harvesting

Floodwater harvesting Water harvesting (36)

Macrocatchment Microcatchment Rooftop/courtyard

Irrigation

Drip irrigation Irrigation (24) Smallholder irrigation

management Cross-slope barriers (structural)

Terraces Terracing (29) Bunds Bunds (45)

Gully rehabilitation Gully rehabilitation (26) Management

Grazing land management

Integrated crop-livestock management

Grazing land management (39)

Pastoralism and rangeland management

Forest management

Sustainable forest management in drylands Sustainable rainforest management

Combination

Miscellaneous

Other Multi-faceted intensification (19)

Trends and opportunities

Classification used

SOC restoration potential per technology category*

*Based on WOCAT expert opinion, assuming a 5-year assessment lag period

SOC Increase (%)Soil loss reduction (%)

Applicability of SLM categories (examples)

Agroforestry

Terraces

Water harvesting

Bunds

Considering land use, slope, elevation, precipitation, biome, soil depth, soil texture, population density, distance to roads/ports/etc (at 1 km2 resolution)

Most effective restoration technology per location/pixel

Soil organic carbon restoration potential until 2050

SOC restoration potential 2050

Calculations based on following assumptions:

• Excludes conversion of any agricultural land to forest• Considers only the top 30 cm of soil as responding to

management

Total global SOC restoration and prevention: 22 Gt C

Conclusions1. We present a first, high resolution (30 arc second) and

spatial-explicit assessment of the global SOC restoration potential.

2. A theoretical full-scale Restoration scenario considering both restoration of historical and prevention of ongoing SOC losses, amounts to 22 Gt by 2050.

3. Comparing our results to findings by others, the potential contribution of SOC restoration to climate change mitigation is low, mainly governed by SOC ceilings associated to current land use.

4. A variety of restoration technologies can be deployed for restoration. There are some interdependencies that were not considered (e.g. use of compost/manure may be limiting; livestock exclusion may lead to degradation surrounding areas)