The potential of mixed and all-grass farming to reverse soil degradation

in Europe

Richard YoungGlobal Soil Week, Berlin

21 April 2015

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

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

Cropland and dust storms

Yangtze, Yellow, Mississippi and Paraná rivers carrying topsoil to the sea

Arable cropping leads to approx. 60% soil carbon loss (FAO)

Commodity crops – ignoring the ‘rule of return’

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.

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

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

58%

8%

7%

27%

UK Farmland 2013

Permanent Pasture Grass leysCommon Grazing Arable crops

Kirkgaarde et al. undated. Management practices forBuilding soil carbon. CSIRO

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

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

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)

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

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.

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.

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

Global Warming: A Closer Look at the Numbers, from www.geocraft.com

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

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)