Soils and Carbon...Environment regulation: Global C cycle 6 2 0.1 107 105 60 60 120 0.4 Global...
Transcript of Soils and Carbon...Environment regulation: Global C cycle 6 2 0.1 107 105 60 60 120 0.4 Global...
Soils and Carbon: quantity
impacts
global implications
David Powlson Lawes Trust Senior Fellow
Department of Sustainable Soils & Grassland Systems
Rothamsted Research, UK
Spot the
Difference!
Contains organic matter
No organic matter
SOM
Soil
quality
Global carbon
cycle
• Food security
• Sustainability
Climate change:
• mitigation
OR
• worsening
• Aggregate formation & stability
• Water infiltration & retention
• Erosion risk
• Nutrients supply: N, P, S
• Nutrient retention (CEC)
• Substrate for microbes and fauna
• …..
SOM influences virtually all soil properties – usually more is better
• Total SOM content is difficult to increase in
arable/horticultural soils
slow; changes over years – decades
• Difficult to measure changes in short term
or even direction of change
• Increasing SOM may not be farmers’
highest priority
cf economics, timing, labour issues
BUT …
Two (complementary) approaches to studying soil organic matter (SOM):
What it IS • Chemical structure
• Chemical/physical interactions with inorganic particles
What it DOES • Quantity in soil
• Influence of management practices
• Influence on soil physical properties
• Root growth, crop yields
• Source of nutrients & CEC
• Biology
Chemistry
Dynamics, Impacts
Formation of lignin - one component of SOM
Powlson, Smith, De Nobili
(in Soil Conditions and Plant Growth,
Eds. PJ Gregory & S Nortcliff, 2013)
Chemical functional groups in soil as revealed by 13C-NMR spectroscopy
Fontaine et al (2007) Nature 450, 277-288
SOM quantity • Inputs
• Outputs
• Equilibrium concept
• Influence of land management and agricultural practices
OM inputs and outputs
Powlson, Smith, De Nobili (in Soil Conditions and Plant Growth,
Eds. PJ Gregory & S Nortcliff, 2013)
Incoming OM processed by fauna and microbes
– a suggestion that SOM derived entirely from microbial metabolites
Agriculture and SOM
• Clearing natural vegetation to create land
for agriculture is almost always bad for soil
organic matter!
• But we do have to eat!
• Soils are part of our ecosystem with
important roles in providing “ecosystem
services”
• “Provisioning services” are among the
ecosystem services – food, fibre, fuel
Limited options for increasing (or even maintaining) SOC
• Land use change
arable → forest, grass, perennial crops
• Inter-crops, cover crops (less bare soil)
• Add organic materials manures, AD digestate, compost, crop residues, …
• Reduced tillage?
• Improved crop growth fertilizers, disease control, irrigation, …
• Crops with larger/deeper roots
• Biochar?
Converting forest to agriculture,
Ethiopia chronosequence
Effects of deforestation and subsequent cultivation on the SOC fraction derived from
natural forest (Cf), and from agricultural crops (Cc) in the 0–10 cm soil layer along a
chronosequence of farm fields converted from tropical dry Afromontane forest.
Leminih et al (2006)
Agriculture, Ecosystems & Environment 109, 9-19
Morrow Plots, Illinois Clearing Prairies (natural grassland) for agriculture
Points: measured Lines: RothC simulation
0
10
20
30
40
50
60
70
80
1860 1880 1900 1920 1940 1960 1980 2000 2020
Year
SOC (t/
ha t
o 1
5cm)
Bluegrass
Border
Continuous
Corn
Corn-oats
-clover
C lost to
atmosphere
Gollany et al (2011) Agronomy Journal 103, 234-246
40
30
20
10
0
1960
90
1940
70
50
80
100
60
20001980
Year
Org
an
ic C
in
so
il, t
ha
-1
SOC changes following land use change, Rothamsted
Started arable
Started grass
Johnston et al (2009) Advances in Agronomy 101, 1-57
Movement towards new equilibrium SOC content
Broadbalk Wilderness
- Woodland reversion
since 1882
Soil pH gradient,
pH 8.3 to 4.0
Hoosefield - Spring barley
since 1852
Broadbalk - Winter wheat
(continuous & rotation)
since 1843
Exhaustion Land since 1856
P & K studies
(rates of run-down and
recovery)
Fosters Ley-arable
(crop rotations)
since 1949
> 250,000 grain, straw, herbage,
soil, fertilizer and manure samples,
some dating back to 1843.
Rothamsted Sample Archive ( Refurbished 2009)
Broadbalk Soil organic C in selected treatments
Points – measured data Lines – RothC simulation
Bellamy et al (2005) Nature 437, 245-248
England & Wales. SOC changes, 1978-2003
England & Wales. SOC changes, 1978-2003
Range of original SOC
g kg-1
% of area
Rate of change of SOC g kg-1 yr-1
0-20 19 0.34
20-30 21 0.13
30-50 28 -0.10
50-100 20 -0.68
100-200 6 -2.18
200-300 2 -4.00
>300 5 -7.37
Bellamy et al (2005) Nature 437, 245-248
-
+ Increased crop yields,
straw return
Changes in soil organic C, Java, 1930 to 2010
Minasny et al (2011) Global Change Biology 17, 1917-1924
Is soil carbon disappearing?
1930-1970: deforestation. Conversion to plantations (tea, rubber), then annual crops
1960-1970: rice, low input
1970 onwards: intensification of cropping. Increased inputs, residue returns
Minasny et al (2011) Global Change Biology 17, 1917-1924
SOM fractionation
• Classic humic and fulvic acids – extraction
with alkali, precipitation with acid.
• Particle size
• Density
• Combined particle size and density
• Biological - microbial biomass
So
il o
rgan
ic C
(%
)
0
1
burnt
incorporated
So
il t
ota
l N
(%
)
0.00
0.05
0.10
Bio
mass C
(kg
ha
-1)
0
50
100
150
200
250
300
350
400
Bio
mass N
(kg
ha-1
)
0
15
30
45
60
75
%C %C %N BC BC BN BN%N
Straw incorporation experiment, spring barley, Denmark
(18 years)
Powlson et al (1987) Soil Biology & Biochemistry 18, 159-164
No measurable effect
on soil total C or N
40% increase in microbial biomass
- “early warning”
Influence of SOM quantity on soil physical
properties
Highfield Reversion Experiment
N
Fallow
Arable
Grass
Acknowledgement:
Chris Watts, Rothamsted Research
1
2
3
4
1945 1955 1965 1975 1985 1995 2005
% o
rgan
ic C
in
so
il
permament grass
arable
bare fallow
Reduction in organic carbon in arable and fallow soil
compared to grassland
The benefits of SOM may not be directly proportional to total content
Soils repeatedly wetted and compressed
Treatment SOC %
Bulk density Mg m-3
Plastic Limit
%
Grass 3.2 1.39 18.2
Arable 1.5 1.71 23.0
Fallow 1.1 1.84 34.4
Highfield Experiment
20 mm aggregates collected from surface 10 cm. Soil: Chromic Luvisol, Batcombe Series.
25% clay, 58% silt, 17% sand
Review of straw experiments
• 25 experiments,
– 6-56 years, Europe, North America, Australia
• All had “straw returned” and “straw removed” treatments.
• Mainly wheat or barley, some maize, sorghum
• Straw removed
– mainly baled, in a few cases burned.
Powlson, D.S., Glendining, M.J., Coleman, K., Whitmore, A.P. (2011)
Agronomy Journal 103, 279 – 287
Total SOC Small changes from straw return or removal.
Only significant in 6 out of 25 experiments (mainly <10%)
Microbial biomass (and other “active fractions”
within total SOC) Changes in response to straw return/removal proportionately much greater than total SOC
Soil physical properties Larger impacts - aggregate stability, penetrometer resistance
- even when no measureable change in total SOC
Similar results with “conservation agriculture” in Southern Africa and South Asia
Results
Influence of SOM on crop yields
After:
Continuous arable
3 year grass ley + N
3 year grass/clover ley
Winter wheat Spring barley
Johnston et al (2009) Advances in Agronomy 101, 1-57
SOM influencing crop yield through N supply
Broadbalk Soil organic C in selected treatments
Points – measured data Lines – RothC simulation
0
1
2
3
4
5
6
7
8
9
10
1840 1860 1880 1900 1920 1940 1960 1980 2000 2020
Gra
in, t/
ha a
t 85 %
dry
matt
er
Cont wheat Unmanured
Cont wheat FYM
Cont wheat N3PK
1st wheat FYM+N2 (+N3 since 2005)
1st wheat Best NPK
Fallowing Liming
Herbicides
Fungicides
Red Rostock Red Club Sq. Master Red Standard Sq. Master
Cappelle D.
Flanders Apollo
Hereward Brimstone
1st Wheat
Cont. wheat
Modern cultivars
FYM
Broadbalk wheat yields, varieties and major changes
NPK
Grain yield of winter-sown wheat: not very sensitive to SOC concentration, despite improved soil structure in FYM treatment (10 month growing season)
Example of SOM influencing crop yield –
through soil structure or water availability?
Hoosfield spring barley - changing yield trends with changes in variety
1976-79
Julia
1988-91
Triumph
1996-99
Cooper
2004-2007
Optic
Johnston et al (2009) Advances in Agronomy 101, 1-57
FYM
FYM FYM
FYM
PK
PK PK
PK
Modern cultivars of spring-sown barley (high yield potential): grain yield is sensitive to SOC concentration (5-6 month growing season)
FYM applied 2001 – 2006 only
Soil C and climate change
(Burial)
107
Environment regulation: Global C cycle
62
0.1
105107
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60
120
0.4
Global carbon: stocks and flows
Vegetation (560)
Soil (1500)
1000 million tonnes per year
(Pools) 1000 million tonnes
flows
Ocean (38000)
Atmosphere (720)
(Burial)
107
Environment regulation: Global C cycle
62
0.1
105107
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60
120
0.4
Global carbon: stocks and flows
Vegetation (560)
Soil (1500)
1000 million tonnes per year
(Pools) 1000 million tonnes
flows
Ocean (38000)
Atmosphere (720)
C sequestration
Either: Greater movement from atmosphere to land (increased plant growth) Or Decreased movement from land to atmosphere (slower SOM decomposition)
Where the opposite to sequestration is happening
Deforestation in Brazil down 23% - only 2040 km2 in last 12 months!
Oil palm, SE Asia, on high-C soils - for biofuel - to decrease GHG emissions!
Brazil - Cerrado native vegetation
Was Cerrado - now soybeans
- mainly for export to Europe and China
C loss from:
1. Clearing natural vegetation
2. Soil organic C
Arable Forest
Poulton et al (2003) Global Change Biology 9, 942 - 955
Broadbalk and Geescroft Wildeness sites, Rothamsted.
Formerly arable fields.
Reverted to (semi) natural vegetation from 1881.
pH 4.4 in 1999 pH 7.4 in 1999
roots
soil
trees
litter
Poulton et al (2003) Global Change Biology 9, 942 - 955
C sequestered
in trees + soil
Re-vegetation: loess plateau, NW China
New vegetation
Inter-crops, cover crops
• Less bare soil
• Genuine C sequestration (additional
transfer of C from atmosphere to soil)
• In addition to numerous other benefits
• Provided water is not limiting total biomass
production
Legume inter-cropping
Adding manure or straw to soil
Increases SOC content.
BUT - is it climate change mitigation through soil C sequestration?
• Depends on alternative fate of manure or straw.
• Manure – mostly applied to soil anyway – so usually no additional C retention in soil.
• Straw - if alternative is burning in the field, then soil C retention from straw application is genuine climate change mitigation.
Does no-till sequester C ?
Nature Climate Change (2014) 4, 678-683
Impact of 26 years reduced tillage on soil C (Brazil)
0 5 15 20 25 0
5
10
15
20
30
40
Soil
depth
(cm)
1.0 2.0
Carbon content (mg/g soil)
0
Whole soil Free light fraction
Machado et al (2003)
Soil Use and Management
19, 250-256
+ 50 % +100 %
10
- - - - - Dashed lines = Conventional tillage; Solid lines = no-tillage
Impact of zero tillage on SOC: meta analysis
– 23 studies, 47 site comparisons, 237 data points
Angers & Eriksen-Hamel (2008)
Soil Science Society of America Journal 72, 1370-1374
(SOC in no till – SOC in ‘full inversion tillage’) / SOC in ‘full inversion tillage
Reduced tillage
“No-till agriculture can deliver significant
benefits for farmers and sustainability in
many (though not all) situations: reduced
GHG emissions are a small but important
additional benefit, not the key policy driver
for its adoption.”
Powlson et al (2014) Nature Climate Change 4, 678-683
Concluding comments • SOM content influences virtually all soil properties
• Source of nutrients for crops.
• Source of energy for microbes.
• Chemical structure is complex and difficult to define – derived from microbial metabolites.
• Arable agriculture normally leads to a decline in SOM cf natural vegetation.
• Various practices can slow the decline – but quite difficult to achieve increases.
• Small changes in SOM content can have disproportionately large impacts on soil properties.
• A major pool of C in biosphere.
Thanks for your attention