Trade-offs between sequestration and bioenergy benefits

Nicolas VUICHARD (1,2) Philippe CIAIS (2)

Luca BELELLI (3) Riccardo VALENTINI (3)

(1) CIRED – Nogent (France)(2) LSCE/IPSL – Saclay (France)

(3) University of Tuscia – Viterbo (Italy)

Growing biofuels over abandoned croplands

in the former USSR

• Abandoned cultivated lands are suitable candidates for bioenergy production (Field, 2008)► Do not compete with food security► Dot not induce a carbon debt

• Bioenergy competes with soil C sequestration but has a higher environmental impact

• Is there an optimal onset time to start biofuel cultivation, given future climate change and management practices?

The end of the USSR resulted into one of the largest crop

abandonment of the 20th century

- 20 Mha

Hurtt et al., 2006

20 Mha

Soil carbon changes are impacted by

CropsRecovering grassland

Natural grassland

Soi

l car

bon

+ Climate + Climate

++ Management

+ Climate

++ Land-use legacy

1950’s 1990’s

A potential of 0.5 GtC could be sequestered

into the abandonned 20 Mha of croplands

New soil C data from abandonned crop fields in Russia

Goals

• Carbon benefit of sequestration by natural steppe recovery

• Carbon benefit of biofuel due to both:- biofuel can also sequester below ground C- biofuel harvest substitutes to Fossil Fuel

• Compare recovery vs. biofuel option

-> Use a spatially explicit process-basedmodel to address these questions

Model set-up

The ORCHIDEE global carbon-water-energy model

ORCHIDEESECHIBA

energy & water cyclephotosynthesis

t = 1 hour

LPJspatial

distributionof vegetation(competition, fire,…)t = 1 year

STOMATEvegetation & soil carbon

cycle(phénologie, allocation,

…)

t = 1 day

NPP, biomass,litterfall

vegetation types

LAI,roughness,

albedo

soil water,surface temperature,

GPP

rain, température, humidity,incoming radiation, wind, CO2

meteorological forcing

sensible & latent heat fluxes, CO2 flux, net

radiation

output variables

prescribed vegetation

vegetation types

Including crops in ORCHIDEE

Same Gridded climate and soil

data

STICS agronomic Model

Library of ≠ crop varieties

LUE growth

Biomass allocation and yield

Water and Nitrogen demand

No soil C balancescale : field , months

ORCHIDEE global modelGeneric ecosystem C dynamics

with land-use disturbances

scale : local => regional => global

1 year => 1000 years

Brisson et al. (2002)

LAIRoot profileIrrigation needs

Daily data assimilation of crop parameters into ORCHIDEE

• Input (spatially explicit) land-use statistics FAO

Including land-use change & land management

• Input N-fertilizer addition statistics USDA

• Simple agricultural parameterizationHarvest -> grains + straw exported

Tillage -> Mean Residence Time of soil C pools faster by 30%

time

1951 1993 Recovery period 2000

Orchidee-Stics Orchidee

Cultivation period

on arable land of former USSR

Results

Croplands100% instant. aband.

If croplands all maintained after 1993If croplands all abandoned in 1993Realistic abandonment scenario

g

C m

-2 y

r-1

Sink regional mean

Net Carbon Balance changes

agriculture

1951 1993

recovering grassland

2000

Orchidee-Stics Orchidee

Sink spatial patterns

Regional C gain from 1993 to 2000 373 gC per m2

Some grid points in the south are net sources, because NPP of steppes is

lower than soil carbon input from former crop fields

-> we really need spatially explicit modelling

Towards realistic estimates

Map of the C storage from 1993 to 2000

Abandoned cropland area from 1993 to 2000

C gain from 1993 to 2000 per m2

64 TgC in 8 years over 17 Mha

Sensitivity tests

• No fertilization during cultivation period

=> +37%• No tillage during cultivation period (no impact

on soil decomposition)

=> -25%• 10% of straw remained on plot

=> -15%

Biofuels on the steppe ?

Modelling Biofuel on the steppe

• Ethanol production from natural grassland biomass as in Tilman et al. (2006)►1 gC substitutes 0.42 gC

• Scenario: an abrupt switch to biofuels in 1990

• Compare scenario with sequestration by calculating the crossing time tcross

• tcross = time at wich biofuels deliver more C benefits than sequestration

Biofuel production vs steppe recovery sequestration

Soil C sequestration in natural steppe

Total Bioenergy production

Soil C sequestered with Bioenergy production

tcross

tcross spatial patterns in yrs after 1990

Timing of bioenergy implementation• If we wait 60-years after abandonment to

install biofuels ?

• Trajectories change... but same tcross

Soil C sequestration

Bioenergy production

Soil C released with bioenergy production

tcross

Sensitivity to C initial stocks

• Condition: MRT must remain constant over time• This condition could be challenged if

Warming accelerates decompositionTillage must be increased for cultivating biofuels

Tilling t0=just after abandonment

Tilling t0=60 years after abandonment

Never tilled

tcross tcross tcross

Conclusions

• Biofuel production looks suitable on abandoned croplands of former USSR

• Energy = 0.23 EJ per year (0.05% of world demand)

• Net Carbon balance of biofuelssink of 0.56 Gt C over 60 years- Carbon storage in biofuel soils = 0.08 GtC - Fossil carbon substituted = 0.48 Gt C

• Net Carbon Storage if steppe recoverysink of 0.3 Gt C over 60 years

Crossing date = 11 years, at which biofuels have a better carbon balance than steppe recovery

Crossing date is relatively insensitive to timing of implementation under some conditions (no soil warming)

Quick benefits

Perspectives

• Generalize to other ecosystems

• Priority = sugarcane in Brazil

• Calculate maps of carbon debt in the

eventuality of forest clearing

• Welcome collaborations with real experts !