Download - Global Soil Week - Richard Young
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The potential of mixed and all-grass farming to reverse soil degradation
in Europe
Richard YoungGlobal Soil Week, Berlin
21 April 2015
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Soil quality
Global carboncycle
• Food security• Resilience• Less disease
Global warming:Turning the tideor runawayclimate change
Soil Organic Matter
Soil degradation and winderosion Suffolk, UK
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Tempting claims
‘Nearly 90 percent of the technical mitigation potential of agriculture comes from soil carbon sequestration.’
(FAO 2009)
‘Reduce agriculture’s emissions by 1.1 - 4.3 Gt CO2 e’ Mostly due to no-till crop production.
(UNEP 2013) ‘A 10% increase in soil carbon stocks would cancel out 30 years of anthropogenic emissions.’FAO 2009. Food Security and Agricultural Mitigation in Developing Countries:Options for Capturing SynergiesUNEP 2013. The Emissions Gap ReportVarious
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Cropland and dust storms
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Yangtze, Yellow, Mississippi and Paraná rivers carrying topsoil to the sea
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Arable cropping leads to approx. 60% soil carbon loss (FAO)
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Commodity crops – ignoring the ‘rule of return’
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UNEP report in 2013 restates claim thatno-till agriculture increases SOC, and estimate that agricultural emissions could bereduced by up 4.3 bn tonnes CO2 p.a. with89% of this from no-till agriculture.
Powlson et al. 2014 find, from meta-analysisof published studies, that apparent and actualincreases of SOC in top layers of soil arefrequently offset by losses at deeper levels,and further compounded by changesin soil density (i.e. top 5 cm getting less dense,lower levels getting more dense).Most optimistic estimate would be 0.4 GtCO2e in the top soil, but mostly cancelled bylosses deeper down. Min-till/no-till can reduceerosion in all-arable systems but unlikely to‘invisible’ losses of CO2 and N2O.
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SOC changes following land use change, Rothamsted
40
30
20
10
01960
90
1940
70
50
80
100
60
20001980
Year
Org
an
ic C in
soil, t h
a-1
Started arable
Started grass
Johnston et al (2009) Advances in Agronomy 101, 1-57
Trial 1☐ Grass kept as grasso Grass converted to arable Arable kept as arable Arable converted to grass
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UK grass leys under 5 years old
• 1977 30% of farmland• 1999 18% of farmland• 2013 <8% (7.56%) of farmland
77 & 99 Hatch et al. 2002 Grassland re-sowing and arable-grass rotations in the United Kingdom etc.13 Defra 2014 Farming statistics
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58%
8%
7%
27%
UK Farmland 2013
Permanent Pasture Grass leysCommon Grazing Arable crops
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Kirkgaarde et al. undated. Management practices forBuilding soil carbon. CSIRO
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Estimates
• European grassland sequestering 760 kg/ha yr across almost 200 sites (Soussana et al 2014)
• Organic farms sequestering 560kg C/yr (Azeez 2009)
• Other estimates typically 200 kg C/yr or less
Sousanna et al 2014. The role of grassland in mitigating climate change.EGF Conference, AberystwythAzeez, 2009. Organic farming and soil carbon. Soil Association
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Higher OM equals higher yields
Johnston et al. 2009. Soil organic matter: It’s importance in sustainable agriculture andcarbon dioxide fluxes, Advances in Agronomy 101: 1-57
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But, adding organic matter to cropland is not the best answer
Organic matter still declines onsandy and sandy loam cropland soils, thoughWill increase on clay soils. However,more than 75% of the added carbon is lost to the atmosphere.
Better to add composted OM to grasslandthen rotate with arable crops as intraditional mixed farming systems.(However, all Rothamsted researcharable-based and this has not beentested in a controlled study in the UK)
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Continuous arable with fallows
Continuous arable
3 year grass/clover ley
Woburn Ley/Arable Experimentsandy loam soil, 7% clay, 60 years
3 years “treatment” cropping followed by2 years arable “test” crops
Johnston et al (2009) Advances in Agronomy 101, 1-57
“Treatment”cropping
3 year grass ley + N
%C increase ≈ 0.23%
With thanks toProfessor David Powlson
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Trees have as much below ground, as wood above ground.
Some species of grass have 3 times as much root material below ground as grass above ground.
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Rooting depth of Grass, legumes and herbs
Ryegrass 0.6mTimothy & Meadow fescue 0.75mWhite clover 0.75m.Tall fescue 1.1m.Cocksfoot 1.2mBirdsfoot trefoil 1.3m.Smooth Meadow grass & Vetch 1.5m.Alsike clover 2.mSweet clover 2.5m.Red clover & chicory 3m.Sainfoin 4m.Lucerne 5-6m.
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Methane
• UN FAO “Livestock’s Long Shadow claimed in 2006 that livestock are responsible for 18% of anthropogenic GHG emissions , more than transport
• Figure revised down to 14.5% in 2013• Other estimates put total farming contribution at ‘8 –
10.8%’, excluding LUC. FAO 2013 only included LUC for S. America.
• Impression given that ruminants mostly responsible for this due to their methane emissions
• Let’s just put this in context
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Global Warming: A Closer Look at the Numbers, from www.geocraft.com
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Wetlands31%
Enteric Fermentation17%
Fossil Fuels15%
Oceans etc7%
Rice6%
Landfill & Waste water11%
Termites4%
Other Agriculture4%
Manure2%
Biomass Burning2%
WetlandsEnteric FermentationFossil FuelsOceans etcRiceLandfill & Waste waterTermitesOther AgricultureManureBiomass Burning
Methane – all sources
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Industry29%
Transport15%
Land Use Change15%Agriculture
7%
Energy Supply13%
Residential11%
Commercial7%
Waste3%
Global Anthropogenic GHG Sources
Knapp J R et al. 2013. Enteric methane in dairy cattle production,J. Dairy Sci 97:3231-3261
(5.5% Methane)