To graze or not to graze?

AEGES
To graze or not to graze?
Grassland ecosystems represent an important contribution to the natural storage and recycling
of carbon. Here, Drs Cornelia Rumpel and Raia Silvia Massad introduce a project attempting to
uncover how management of grassland environments impacts their carbon storage capacity
Dr Cornelia Rumpel
Dr Raia Silvia Massad
Could you begin by outlining the main aims of
the AEGES project?
The general aim of the project is to reduce the
uncertainty associated with the prediction of
greenhouse gas emissions and levels of carbon
and nitrogen storage in agro-ecosystems.
Close collaboration between modellers and
experimental researchers shall lead to an
incorporation of recent developments in the
understanding of how carbon and nitrogen
cycling – processes such as decomposition,
nitrification and denitrification – influence
greenhouse gas balance models.
The project will take four different approaches
to achieve its aim. The first is to improve
greenhouse gas models and calibrate them
using data from other ongoing long-term
experiments. Then to study the effect of
agricultural practices on soil functioning.
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INTERNATIONAL INNOVATION
Additionally, AEGES will evaluate the capacity
of existing models to reproduce the effect of
different agricultural practices on soil organic
matter (SOM) storage as well as greenhouse gas
emissions at the field scale. Finally, the project
will propose management options for the
attenuation of greenhouse gas emissions from
agricultural systems.
This approach will allow us to generate practical
recommendations for farmers as well as decision
makers in order to apply management options
that lead to the attenuation of greenhouse gas
emissions from agricultural systems.
What types of ecosystem models are you
evaluating and how do these vary?
We are evaluating grassland systems in a variety
of pedoclimatic contexts which vary in the way
they are managed. We evaluate both permanent
and temporary grasslands of varying duration and
consider differences in management with respect
to the nitrogen input (levels of fertilisation) and
the way that grazing is managed – cutting versus
grazing for temporary grassland and animal
charge for permanent grassland.
Could you expand on the importance of
grasslands in landscapes with alternation of
crop land and grazing?
Temporary grasslands could be important
components of integrated livestock
management. Within the agricultural system
they could help to protect and restore soil during
the grassland phase due to the permanent
vegetation cover, leading to recovery of SOM
quantity and quality after the cropping phase. By
increasing quality and quantity of SOM, microbial
diversity and activity will be improved as well as
soil structure and water infiltration and storage.
Moreover, increased SOM will be beneficial for
nutrient delivery to plants and as a carbon source
for microorganisms.
Due to carbon and nitrogen sequestration in
soil, temporary grasslands may be important
for the attenuation of greenhouse gas emissions
within landscapes. Their presence may also make
the landscape more diverse, which could lead
to other important ecological benefits in terms
of environmental protection such as providing
habitats for animal or insect species.
How is overgrazing of land threatening soils in
areas of Europe? What can be done to tackle
this issue?
Overgrazing is threatening soils in some areas
of Europe because it leads to their degradation,
in particular because of reduction of their
organic matter content as a consequence
AEGES
of plant biomass removal, trampling and
compaction. This makes soils prone to erosion
and desertification. The issue may be tackled by
reasonable livestock management; adapting the
animal charge to the soil’s capacity to sustain
biomass production.
Collaboration forms an important part of
agricultural research. How are you working
alongside other projects to ensure that your
findings are shared and that you have a
positive impact in the sector?
We are working within the framework of the
SOERE ACBB observatory on environmental
research (www.soere-acbb.com). Under this
framework, we participate in general meetings
to share results obtained on the sites that we are
working on. At an annual meeting organised by
our funding agency ADEME, we share our findings
with the people involved in the other projects
funded under the framework of the REACCTIF
call. We also participate regularly in national and
international scientific meetings to discuss and
share our results.
Are there any outstanding questions that you
are seeking to address in the next stages of
your research?
We are interested in the mechanisms leading
to greenhouse gas emissions in the context of
grassland ecosystems. One of the questions
that we are particularly interested in is regarding
the kind of relationships that exist between
SOM composition, degree of stabilisation and
microbial functioning of soils.
The next top model
The French interdisciplinary project AEGES is integrating
information about soil functional diversity, carbon and nutrient
storage of grassland ecosystems into greenhouse gas emission
models to inform stakeholders about land management strategies
GRASSLAND IS DEFINED as an area of open
land where the vegetation is dominated by
species from the Poaceae family – the ‘true
grasses’. It covers roughly one-third of the
Earth’s surface and can be found naturally on
all continents with the exception of Antarctica.
Grasslands are of great economic consequence
as they are routinely used for grazing and raising
livestock, on which the human population
are dependent for meat, milk and other
dairy products. The integrity of the grassland
ecosystem can be maintained in particular areas
by human activity; grazing by reared animals,
grass cutting or manmade fires all discourage
colonisation of the grassland ecosystem by nongrass species such as trees and shrubs.
The soil found in grassland ecosystems can be
up to 6 m deep and some of the richest in the
world in terms of soil organic matter (SOM)
content and species diversity. The invertebrates,
microorganisms and fungi within the soil carry
out important ecosystem functions such as
improving soil structure, decomposing dead
organic matter to release nutrients, trapping
minerals and preserving soil moisture. As a
consequence of this biological activity, nutrient
cycling and the large-scale storage of organic
carbon in the soil, grassland ecosystems are
an important contributor to greenhouse gas
emissions when human-mediated management
strategies, such as overgrazing, and their
conversion into agricultural land result in the
release of this carbon store into the atmosphere.
In the context of increasing levels of atmospheric
carbon dioxide and consequential intensification
of the greenhouse effect, it is important that
grasslands can be effectively managed to
maintain, and perhaps even increase, their soils’
carbon storage potential.
In order to understand how this can be achieved,
it is necessary to develop methods for the
accurate and reliable quantification of carbon
and nitrogen fluxes within grassland ecosystems,
and to comprehend the effect that agricultural
practices have on the levels of these emissions.
This is the context of the multidisciplinary
research project ‘AEGES: Attenuation of
greenhouse gas emissions in grasslands’,
that is coordinated by Dr Cornelia Rumpel, a
research director at the Centre National de la
Recherche Scientifique (CNRS) in France, and
Dr Raia Sylvia Massad, a research scientist at
the Institut National de Recherche Scientifique
(INRA) – both based at INRA Versailles-Grignon.
The project will use an integrated modelling
approach of greenhouse gas (GHG) emissions,
carbon storage and ecosystem functioning to
reduce uncertainties around the prediction of
these processes to improve the accuracy of three
models: CERES-EGC, PaSim and ORCHIDEE. The
improved models will be used for nationwide
predictions of GHG emissions under different
land-management scenarios.
MANAGING SOIL ORGANIC MATTER
Permanent grasslands are under threat from
the expansion of intensive agriculture as
populations continue to expand and the need
for food increases. The loss of these ecosystems
causes disruption to the soil and can lead to
depletion of the carbon store and the release
of GHG into the atmosphere. On the other
hand, their introduction into cropping cycles as
temperate or ley grasslands can have positive
outcomes; the permanent soil cover will lead to
increasing SOM contents manure from grazing
animals is high in nitrogen which can facilitate
nutrient cycling and provide natural fertiliser
for the soil. In such a system, the various land
uses need to be carefully managed as, during
periods where crops are grown, soil erosion
increases – at the detriment of SOM content
– and the practice of monoculture and use of
inorganic fertilisers can reduce soil functional
biodiversity and thus restrict nutrient cycling.
WWW.RESEARCHMEDIA.EU
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INTELLIGENCE
AEGES
OBJECTIVES
To analyse the effects of grasslands on soil
organic matter dynamics and greenhouse
gas emissions.
PARTNERS
The aim of the project is to collect experimental data on how soil microbial
activity; nitrogen and carbon content and composition; and nutrient cycling
are influenced by different management strategies of grasslands, and use this
to inform existing greenhouse gas emissions and climate models
INRA, Unité de Recherche sur l’Ecosystème
Prairial
INRA-CNRS, Laboratoire d’Ecologie
Microbienne, Lyon
CNRS, Laboratoire des Sciences du Climat et de
l’Environnement
INRA, Unité de Recherche Pluridisciplinaire,
Prairie et Plantes Fourragères Centre INRA
Poitou-Charentes, Lusignan
FUNDING
French Environment and Energy Management
Agency (ADEME)
www.ademe.fr
CONTACT
Dr Cornelia Rumpel
Project Coordinator
CNRS
UMR 7618 Laboratoire de Biogéochimie et
Ecologie des Milieux Continentaux (BIOEMCO)
Campus AgroParisTech
Bâtiment EGER
78850 Thiverval-Grignon
France
T +33 130815479
E [email protected]
Raia Silvia Massad
Project Coordinator
INRA
UMR 1091 Environnement et Grandes Cultures
(EGC)
78850 Thiverval-Grignon, France
E [email protected]
CORNELIA RUMPEL received a Habilitation
in Geochemistry from Université Pierre et
Marie Curie, Paris, France in 2006. She leads
the ‘Soil organic matter’ group (six permanent
research scientists, four permanent technicians/
engineers) at the BIOEMCO laboratory,
Thiverval-Grignon, France. She is also a Director
of Research at the Centre National de Recherche
Scientifique (CNRS).
RAIA SILVIA MASSAD received her PhD from
Université Pierre et Marie Curie, Paris, France
in 2008. She is currently a researcher at the
National Institute for Agricultural Research
(INRA). Her research interests include modelling
the exchange of reactive nitrogen between the
land surface and the atmosphere with a focus on
agricultural ecosystems; upscaling from plot to
landscape and regional scales; and coupling with
chemistry and transport models.
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INTERNATIONAL INNOVATION
The periods where grasslands are left to develop
facilitates the recovery of SOM contents as well
as microbial and faunal diversity.
The soil microbial community is of vital
importance
for
determining
nutrient
availability, physical soil properties as well
as the soil’s susceptibility to emit GHG.
They decompose SOM, can generate longer
term stores of carbon and can improve soil
structure so it is more resistant to erosion and
loss of nutrients. Long-term establishment of
grassland encourages the soil layer to increase
in depth, improving its carbon storage capacity.
Furthermore, the benefits that arise from a
functionally diverse microbial community can
persist for years after the grassland is converted
for crop growth. This emphasises the potential
gains of interspersing a grassland growth phase
into periods of intensive crop cultivation, as
Rumpel explains: “The environmental benefits
and ecosystem services of grasslands have, up
to now, been analysed at a local scale; however
they may have global effects in terms of carbon
storage and GHG emissions depending on their
management and cropping cycle.” As a result,
the aim of this project is to collect experimental
data on how soil microbial activity; nitrogen
and carbon content and composition; and
nutrient cycling are influenced by different
management strategies of grasslands, and
use this to inform existing GHG emission and
climate models at a variety of scales from local
and national, to global.
IMPROVING THE MODELS
In France, 21 per cent of total GHG emissions
are from agriculture, and the grassland
ecosystem has a significant role to play in this
picture because it is characterised by large
stores of carbon in the soil. The integrity of
these stores and the extent to which carbon
is released into the atmosphere is dependent
on variables such as the age of the grassland,
load of livestock, grass cutting strategies
and extent of fertilisation. To understand
how these variables interact to determine
differential GHG emissions over space and
time, a combined modelling and experimental
approach will be used by the team who
focuses on the sites of the SOERE ACBB
environmental observatory. By explaining
carbon and nitrogen fluxes and identifying
indicators for the regulation of SOM, detailed
molecular information on SOM and microbial
community composition can be incorporated
into GHG and climate models to test different
land use scenarios involving temperate and
permanent grasslands. Furthermore, the
TREATMENT PLOTS AT SOERE ACBB, LUSIGNAN SITE
existing models will be integrated with new
data to develop a new model that is able
to predict GHG emissions across France
according to the chosen management
practices and ecosystem characteristics.
Massad explains her hopes for the project:
“We expect to offer advice on the possibility
of introducing temporary grasslands into crop
cycles, and provide grassland management
guidelines, to attenuate GHG emissions and
increase soil carbon storage”. By bringing
together modellers, soil microbiologists, soil
chemists and ecologists, this interdisciplinary
project will enable, for the first time, the
comparison between GHG flux and soil
processes over a period of several years.
FINDINGS TO DATE
Although the project is in its early stages, initial
results have been interesting and significant.
Firstly, in consideration of the stability of the
SOM content, the team has demonstrated a
certain resistance to disturbance caused by
grassland removal. Whilst this stress causes an
immediate change to SOM composition, its
integrity can recover over a two year period of
cropping to be similar to grassland conditions.
In a different area of investigation, it has been
shown that the species composition of the
grassland – for example, the introduction
of legume species – can increase its carbon
storage capacity as well as drought resistance.
Finally, and perhaps most significantly, it
is suggested that the presence of grazing
animals results in less carbon emissions from
the soil than a cutting regime.
On completion of the project, it is hoped that
the team will be able to integrate data on
GHG emissions from different management
practices at a national level to generate
practical recommendations for farmers to
enable them to limit the loss of carbon from
soil stores in agricultural systems.