Gilles LEMAIRE

INRA, Lusignan France

Grasslands and ecosystem services within agro-ecosystems

Necessity for a multidisciplinary and multiscale approach

New paradigms for grassland sciences

- Ecosystem services, the benefits human societies and individual peoples can obtain from ecosystem functioning: provisioning, regulating, cultural and supporting

-Trade-offs between “grassland productivity” for human food and fiber production and other “services”

- Grasslands have to be analysed not only as a source for feeding domestic herbivores, but also as a way for production “ecosystem services”.

Role and environmental impacts of grassland areas

Direct effects:

Soil protection (erosion, SOM, biology, structure...)

Water quality (nitrate, phosphate, pesticides...)

Air quality (CO2 sequestration, N2O ?, NH3 ?)

Biodiversity (vegetation, soil fauna and flora, insects...)

Interactions with management systems

Herbivores

Scientific Objectives

Soil Organic Matter

Greenhouse gases

Biodiversity

CO2

N2O

NOx

Vegetation Microorganisms Micro-Meso-fauna

Water Quality

NO3-

DOC Pesticides...

4C, N, P cycles4C sequestration

Soil biology

SOM Biochemistry

Managementpractices

Vegetation

Climate changes

Soil Organic Matter

(SOM)

Soil properties

Soil fertility

Regulation of C, N, P…cycles

Environnemental impacts:

Nitrate leaching

Greenhouse gases : N2O, CO2

Agronomical impacts:

CO2 sequestration

Fonctions of SOM

Soil organic matter

Green litter

Brown litter

Input

Chemical protectionPhysical protectionPhysicochemical protection

Labile SOM poolIntermediate SOM poolStable SOM poolRhizodeposition

DungCO2

DOC

Inputs of fresh organic matter within grassland

ecosystem

Coupling C and N Cycles

Soil organic matter represents 2/3rd of the total terrestrial carbon

80

40

0

60

20

C:Nratio

Net immobilisation

Net mineralisation

Time

During the decomposition of OM of residues there is a decline in C:N ratio through CO2 losses…and then a phase of net immobilisation followed by a phase of net mineralisation of N depending on the C:N ratio of residues at origin.

0

1

2

3

4

Annual crops Grasslands

Gross Min. Gross Imm. Net Min.

N (

kg/h

a/j

)

Aita (1996) Loiseau et Thiéry (1992)

Comparison of N fluxes between croping system and

grassland

Plants

MOS Biomass

N mineral

Rootlitters

C/N 40-50

LeaflittersC/N 30

- Under grassland, there is a constant supply of litters with high C:N

- Then there is a high gross N immobilisation flux- In the same time plants have a more or less continuous N

absorption rate all along the seasons…- In consequence, NO3- cannot accumulate in soil > 3-5KgN.ha-

1, except after high level application of N fertilizer, and under urine patches…

- Then losses of N by nitrate leaching is very low even in winter…when stocking density remains not too high.

Trade-offProduction vs Environment

0

50

100

150

200

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300

0 200 400 600fertilisation (kg N efficace/ha)

N l

ixiv

ié (k

g N

/ha)

Pâture

Fauche

N leaching under grasslandsGrazing vs Cutting

Grazing:

High increase in N leaching when > 200 kgN/ha

Cutting:

Low N leaching when < 400kgN/ha

y = 8,77 e0,003x

r²=0.71

0

20

40

60

80

100

120

140

160

0 200 400 600 800 1000 1200

chargement (UGB.JPE/ha)

N li

xiv

ié (

kg N

/ha

)

Simon et al, 1997 ;Laurent et al.2000Vertès et al, 2002

Benoit et al., 1995

Effect of stocking density on N leaching

Vegetation

CO2

Mineral N

SoilOM

Microbes

MIT

Photosynthesis

N absorption

C-N coupling

Herbivores

CH4

Feces

Urine

C-N-P

N20NOxNH3

C-N decouplingNitrate

N

C-N couplingC-N decoupling

In grazing system C-N decoupling / C-N coupling

depends on stocking density

Above a threshold stocking density C-N decoupling excess the capacity of C-N recoupling of vegetation

and soil microbes

StrawRe-coupling

C-N

Compost

Cutting system with indoor feeding and association with cropping system through use of straw and

efficient compost production and recycling system could be highly intensified with reduced

environmental impacts

Hay-Silage

Control of GHGEmission ?

1. Permanent vegetation and soil microbes couple strongly C-N cycles

2. Grazing animals decouple C-N cycles and then provoke C and N emissions

3. Intensification at grazing reaches a limit beyond which environmental fluxes become too important according to stocking density

4. Cutting management is a way for a higher intensification of grassland…but high cost!!!

5. Decoupling C-N by animals indoor need to be acompanied by a re-coupling C-N within a coherent animal manure management

6. Comparison between grazing and cutting must be done at whole system level and not only at field or paddock level…

Role and environmental impacts of grassland areas

Indirect effects on cropping systems:

Control of weed communities and reduction of herbicide use;

Control of pests and diseases and reduction of pesticide use;

Recycling of nutrients and reduction of fertilizer use;

Improved soil structure and reduction of fuel energy use;

Heterogeneity of habitats and diversity of trophic chains;

LocalProcesses

IngeneeringSystems

Landscape

Soil-vegetation

Cropping systems

Forage systems

FarmsProduction systems

Territories

Biogeochemical CyclesEnvironnemental FluxesBiodiversitéExpérimentation, MonitoringModelisation

Conception-Evaluation of innovative systemsEnvironnemental balanceMulti function evaluation

Spatial integrationLand use system mosaïcCatchmentLandscape Ecology and biodiversityInteractions between farms

Multi-function and multi-scale approach

Stocks

Concentrates

GrasslandsFlux of foods

OMminerals

Exportations

Grassland area Croping area

Livestocksystem

Spatial interactions between grassland areas and cropping areas

Grassland

Stocks

Grassland

Grains

Preceding effect

Following effect

Livestocksystem

Exportations

Flux foodsOMminerals

Integration of grasslands within cropping systems

Field

Cropping system

Forage system

Livestock system

Analyse of local processes and Environment x Management interaction, What if ?

Conception and evaluation of cropping and forage systems, What is necessary for...?

Conception and evaluation of livestock systems from socio-economic and environment perspectives

Agro-Ecology Ingeneering

Interactions between cereal farms and livestock farms within a territory

- Fluxes of organic matter and nutriments among specialised farms and possibilities for more conservative biogeochemical fluxes by coupling more strongly C and N…

- Diversification of land use and management systems through:

- common crop rotation systems- exchanges of field- production and sell of hays …

G. Paillard-INRA C. Maitre-INRA

FarmCropsGrasslands Livestock

EnvironmentClimate SoilTopography

CatchmentWater quality Flux

BiodiversityLand useHabitat diversityTrophic networks

Contribution of Grasslands to Landscape Ecology

AtmosphereGHG emissionCO2 balance

Effects of grasslands on biodiversity at landscape level

*Cultivated areas with high diversity of crops host the richest diversdity

*>250 species of birds whose 173 prioritaries et 118 in danger

The decline of biodiversitywithin European agriculture plains

From BirdLife 2004

CNRS Chizé

1958 1990

During the last 30 years:decrease of livestock productiondecrease of grassland areasspecialization for cereal production systemsincrease in field sizereduction of the complexity of the landscape

mosaïc

clutch size

1,9

2,4

2,9

3,4

3,9

4,4

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

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50

60

Effect of reintroduction of grasslands on Little Bustard population within a cereal

cropping area CNRS Chizé

Conclusions1- Grasslands through soil-vegetation interactions allow a strong C-N coupling leading to very conservative C and N cycles and reduced fluxes to atmosphere and hydrosphere.

2- But grazing herbivores decouple greatly C and N, leading to increasing emission of GHG and nitrate leaching with stocking density.

3- Trade-off exists between grassland intensification and environment impacts.

4- Grassland areas can contribute to mitigate environmental impacts of intensive cropping system at landscape and regional levels

5- Mixed farming between arable crops and livestock production systems based on grasslands could help to reconcile high food production systems with high level of ecosystem services

Necessity of structuring the scientific community on continental ecosystem

across Europe

Scientific community on continental ecosystem is very fragmented across a high variety of ecosystem types and a high variety of scientific disciplines;

Most of the environmental problems (water quality, air quality, soils quality, climatic changes, pollutant, biodiversity problems…) require interdisciplinary approaches and long term observations, experimentations and data collection to enable simulation and forecasting the impacts of climate change and land use change on continental scale-ecology and to answer society questions.

Answering environmental questions requires coupling more than sophisticating analysis of individual elementary processes.

…, continue…

Research infrastructures implementation in experimental ecology, is a prerequisite for structuring research on continental ecosystems, enabling understanding of ecosystem responses to disturbance, providing pertinent knowledge for managing anthropogenic ecosystems in a sustainable way.

…and then… opportunities to merge European research projects with South American ones within a wider international network?

Thank you for your attentionand

for invitation