Grassland management strategies to
mitigate and adapt to climate change
Donal O'Brien
Livestock Systems Department, Animal and Grassland,
Research and Innovation Centre, Teagasc, Moorepark, Fermoy,
Co. Cork
Introduction
• Grasslands are a key European ecosystem
• Cover 33% of agricultural area
• Over 65% in some countries e.g. Ireland and the UK
• Demand for food products from grassland is rising
• 1.4%-2% growth beef and dairy demand
• Food products from grassland are carbon intensive
• Increasing concerns over climate change
• Need to adapt and mitigate greenhouse gas (GHG)
State of grasslands
• Majority of world's grassland on poor
quality soil
• Overgrazing common problem
• Soil Erosion
• Weed Encroachment
• Several drivers of overgrazing
• Population growth
• Urbanization
• Breakdown of transhumance system
Grassland and climate change
• Pastures are vast stores of Carbon
• Store 50% more carbon than global forests
• Can contribute to climate change mitigation via
sequestration
• World's grassland can sequester up to 3 Gt of C/year
• Debatable how long grassland can sequester C
• IPCC consider grassland management key tool to reduce
agricultural greenhouse gas (GHG) emissions
• Management also key to adapt to climate stress
Climate management strategies for grassland
• Optimize grazing intensity
• Mixed species grassland
• Improve productivity
• Nutrient management
• Restoring degraded lands
Optimize grazing intensity
• Under or over grazing adversely effect grassland C stocks
• Carbon loss from soil
• Reduced rates of soil C sequestration
• Correct stocking rate where imbalance occurs
• Grass budgeting
• Pasturebase - Online grazing tool Grass
growth
• Match grass supply and demand
• Remove excess forage and conserve
• Feed conserved forage during deficits
Herd
Demand
Mixed swards
• Introducing new species with high productivity reduces
emissions
• Improves soil organic C
• Reduce N fertilizer requirements and costs
• Deep rooted grasses with high productivity have greatest
potential to increase soil organic C stocks
• Greatest impact of low productivity swards or
savannahs
• Added benefit of improving resilience and biodiversity
Improve productivity
• Aim to increase food output from grassland
for the same level of input
• Plant breeding - Higher producing grass
cultivars
• Irrigation
• Fertilization rate
• Measurement is key to benchmark
performance
• Farmer discussion groups
• Online tools - Farm profit monitor
Improve productivity – Plant Breeding
Wilkins and Humphreys, 2003
Effect of milk yield
Gerber et al. 2011
Nutrient management
• Soil C sequestration positively correlated to mineral N
• Increase artificial N ferilizer use
• Introduce or increase sward legume content
• Intensively managed swards sequester over 2 t C/ha more
than extensive systems
• But excess N fertilizer application increases N2O emissions
• Must match fertilizer application to plant growth
Nutrient management – Use of legumes
•Clover can substantially reduce emissions
• Replaces mineral N
• Little or no N2O associated with biological N fixation
16
16
Measured
Simulated
Milk production
14
12
10
14
12
10
8
8
6
6
4
4
2
2
0
0
GG+FN GWC+FN GWC-FN
G-B
Milk Production (t ha-1 yr-1)
N2O Emissions (kg N ha-1 yr-1)
•Clover can fix up to 120 kg N ha-1
WC-B
Li, Humphreys, Lanigan (2011) PloS-one
Restoring degraded lands
• Large areas of pasture land operating well below
potential
• Improve productivity
• Increase soil organic C
• Key practices to restore degraded lands
• Reseeding or replanting of grasslands
• Improving soil fertility via manure application
• Retaining crop residues
• Conserving water and irrigation
Carbon footprint and grassland
• Key measure of food product is carbon footprint
• Greenhouse gas emissions/unit of food
• Measured using IPCC and life cycle assessment - ISO
approved method
• Simulates on and off-farm sources and sinks of GHG
from grassland farms
• Correct application of LCA uses appropriate unit and
distributes footprint across farm products
• Fat and protein corrected milk and meat
IPCC (National GHG inventory)
Dairy Farm
Harvesting
Housing
Cultivation
Grazing
Soil
Milk Meat
Manure
GHG
NH3
NO3
Life Cycle Assessment
Dairy Farm
Off-farm Inputs
•Fertilizer
•Pesticides
•Feedstuff
•Livestock
•Fuel
•Electricity
•Machinery
•Etc..
Harvesting
Cultivation
Housing
Grazing
Soil
Manure
GHG NH3 NO3
Milk Meat
GHG
NH3
NO3
Effect of GHG accounting method on
grazing and confinement systems
t CO2e/t milk solids
16
14
Other inputs
12
Fertiliser
10
Concentrate
8
6
Indirect N loss
4
Grazing returns
2
Managed Manure
0
LCA
Grass
LCA
Confine
IPCC
Grass
IPCC
Confine
Enteric fermentation
Mitigation objective?
O’ Brien et al.,2011 Accepted
Reduce Global GHG emissions or maximise National
compliance
Carbon footprint and grassland
• Typically global studies report grassland systems have
above average C footprint
• But temperate grassland systems have the lowest C
footprint e.g. New Zealand or Irish grazing systems
• Pan European studies show grassland to be most C
footprint efficient for milk
• Include land use emissions
• Include soil organic sequestration
• But for meat comparisons are difficult - Large diversity of
beef and sheep systems
High performance comparison
• Carbon footprint of milk from grazing systems
amongst the lowest in the world
• Most global comparisons only consider
regional or national average farms
• Goal - Compare carbon footprint of milk from
high performance dairy systems
• Irish Grazing System (Horan et al., 2004, 2005)
• UK Confinement System (Garnsworthy et al. 2012)
• USA Confinement System (DairyMetrics)
Farm Information
Item
Irish
UK
USA
Milk yield, kg/cow
6,262
10,892
12,506
Fat, %
4.47
3.95
3.58
Protein, %
3.55
3.14
3.17
Replacement rate, %
18
34
38
Live weight, kg
543
613
680
Concentrate, kg DM/cow
320
2,905
3,355
N fertilizer, kg N/ha
250
106
53
Carbon footprint of milk of high performance
dairy systems
+4%
+6%
Carbon footprint and grassland
• Within nations or regions large variability in C footprint of
similar grassland farming systems
• British dairy farms C footprint range 0.8-2.8 kg of
CO2/litre of milk
• Irish beef farms C footprint range from 7.4-24 kg of
CO2/kg of live weight
• Grassland management practices can be implemented to
improve productivity and C footprint
• Nutrient management
• Extending the grazing season
Irish Carbon audits
• 124 dairy farms successfully audited 2011-12
• But not representative of Rep. of Ireland
• West and North-West excluded
• Livestock inventory and milk production
• Electronic - DAFM, ICBF, Co-ops
• Annual on-farm survey
• Animal feeding plan
• Fertiliser use and manure management
• Fuel, Chemical, Water use etc…
Histogram of Carbon Footprint of Milk of
124 Irish Dairy Farms
25%
15%
Mean: 1.11
SD: 0.13
2.5%: 0.90
97.5%: 1.38
Skew: 0.85
10%
5%
kg CO2-eq/kg fat and protein corrected milk (FPCM)
1.80
1.73
1.66
1.58
1.51
1.44
1.36
1.29
1.22
1.14
1.07
0.99
0.92
0.85
0.77
0%
0.70
FPCM produced
20%
2.00
2.00
1.80
1.80
Kg CO2-eq/kg FPCM
kg CO2-eq/kg FPCM
Grazing management and C footprint of
Irish dairy farms
1.60
1.40
1.20
1.00
1.60
1.40
1.20
1.00
0.80
0.80
0.60
0.60
0%
20%
40%
60%
Farm N efficiency
150
200
250
300
Grazing days
Relationships between Farm Measures and
Carbon Footprint of Milk
• No single farm measure explained variation between
farms carbon footprints of milk
• Stepwise multiple regression - Carbon footprint of
milk best explained by:
• Farm N efficiency, milk yield/cow, grazing season
and replacement rate (R2 = 0.75)
• Mitigation is possible by management changes
• Improving total genetic merit via EBI
• Legumes – White clover
National abatement potential
• National potential assessed via MACC
• Dairy and Agricultural Sector
• Menu of Irish mitigation measures
• National research only
• Measures ranked by their individual costs
• IPCC and LCA approaches applied
• Baseline assumes 50% increase in milk output by
2020 relative to 07-09 (Food Harvest 2020)
Marginal abatement cost curve
Conclusions
• Grassland climate management strategies are
available and economically viable
• Postulated Barriers to implementation
• Social - Insecurity of tenure
• Technical - Climate change and GHG emissions
• Economic – Rising costs of fertilizers
• Need to quantify and capture the effective potential of
management
Thank you for your
attention