Soil Organic Matter – Soil Fertility – Climate Change
Johannes Lehmann Department of Crop and Soil Sciences, Cornell University
Soil Organic Matter – the “old”(?) view Humus, usually black or brown in color, is a collection of very complex organic compounds which accumulate in soil because they are relatively resistant to decay. (Brady and Weill, 2008)
Schulten and Schnitzer, 1998, Biol Fert Soils 26, 1-15
Soil Organic Matter – criticisms
‘‘One may feel justified in abandoning without reservation the whole nomenclature of ‘humic acids’ … beginning with the ‘humins’ … and ending with … ‘fulvic acid.’ These labels designate, not specific compounds, but merely certain preparations which may have been obtained by specific procedures.” (Waksman, 1936)
Alkaline extraction is able to: (i) dissolve not yet degraded plant materials (ii) induce chemical alterations such as hydrolyses or condensation
reactions (iii)allow organic materials to become oxidized by air (Kleber and Johnson, 2010)
In Search of Humics
10 μm
Energy [eV]280 285 290 295
Abs
orba
nce
(arb
itrar
y un
its)
289.3
a
287.3288.6
286.7285.0
b
c
d
e
f
g
h
i
k
a b
c d
e f
g h
i k
Total Soil
285.0
286.7
Principle Component Analysis
Lehmann et al, 2008, Nature Geo 1, 238-242
Humic Substance Extract
Synchrotron-based NEXAFS-STXM 10μm
‘Humification’
Traditional view (until early 1990s): - Microbial re-synthesis - Recalcitrance - Organo-mineral “complexes”
‘New’ view: - Physical occlusion - Interaction with mineral surfaces - Pore filling
Schmidt et al, 2011, Nature 478, 49-56
Soil Organic Matter Loss with Cultivation
Solomon et al., 2007, GBC
0 20 40 60 80 100
0
20
40
60
80
100
0 20 40 60 80 100
SOC
rem
aini
ng (%
)
0
20
40
60
80
100
0 20 40 60 80 100
0
20
40
60
80
100
0 20 40 60 80 100
Tota
l N re
mai
ning
(%)
0
20
40
60
80
100
a) Kakamega forest
b) Nandi forest e) Nandi forest
d) Kakamega forest
R2 = 0.96k = 0.14
R2 = 0.89k = 0.23
R2 = 0.98k = 0.16
R2 = 0.97k = 0.14
Years of cultivation
(chronosequence, Oxisol/Ultisol, Western Kenya)
Soil Organic Matter Loss with Cultivation
compiled from Solomon et al., 2007, GBC Own unpubl data
Years0 20 40 60 80 100 120
Car
bon
(% o
f prim
ary
vege
tatio
n)
0
20
40
60
80
100
120Lethbridge, CANPendleton, USAFree State Province, SAMafungautsi, ZIMNandi, KEN
Soil Organic Matter – Soil Fertility
Years of cultivation
0 20 40 60 80 100 120
Gra
in y
ield
(Mg
ha-1)
0
1
2
3
4
5
6
7
LR yield SR yield
Ngoze et al., 2008, GBC14: 2810-2822
(chronosequence, Oxisol/Ultisol, Western Kenya N=3)
Fertilizer Responses – Fertilizer Needs Primarily N limitation even in “fertile” soils with high SOC and SON
y
N rate (kg N ha-1)
0 20 40 60 80 100 120 140
Gra
in y
ield
(Mg
ha-1
)
0
2
4
6
8
10
Old conversionMedium conversionYoung conversion
P rate (kg P ha-1)
0 20 40 60 80 100 120
Gra
in y
ield
(Mg
ha-1
)
0
2
4
6
8
10
Old conversionMedium conversionYoung conversion
y
Ngoze et al., 2008, GBC
(chronosequence, Oxisol/Ultisol, Western Kenya N=3)
SOC and Watershed Dynamics
Recha et al., 2012, Earth Interactions, publ online
Soil Organic Carbon and Water Losses
2007 2008Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov
Rainfall (m
m day
-1)
0
20
40
60
80
100
120
140
Dis
char
ge (m
m d
ay-1
)
0
2
4
6
8
10
2007 2008Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov
Rainfall (m
m day
-1)
0
20
40
60
80
100
120
140
Dis
char
ge (m
m d
ay-1
)
0
2
4
6
8
10
2007 2008Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov
Rainfall (m
m day
-1)
0
20
40
60
80
100
120
140
Dis
char
ge (m
m d
ay-1
)
0
2
4
6
8
10
2007 2008Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov
Rainfall (m
m day
-1)
0
20
40
60
80
100
120
140
Dis
char
ge (m
m d
ay-1
)
0
2
4
6
8
10
Forest 5 year
10 year 50 year
B
D
A
C
Recha et al., 2012, Earth Interactions, publ online
SOC: 10.8% Discharge: 16% of rainfall
6.9% 25%
3.6% 29%
2.8% 33%
Nutrient Losses
Forest 5 year conversion
10 year conversion
50 year conversion
NO3- 1.18 2.68 27.09 29.16
TDP 0.09 0.03 0.29 0.98
K 1.06 3.68 5.44 7.61
Ca 21.43 25.66 31.46 46.22
Mg 8.93 9.42 9.23 16.38
Recha et al., submitted
Fertilizer-N: 0 0 ~40 ~40† Fertilizer-K: 0 0 0 0 Plant uptake Ca: 20 †for area applied
(kg/ha)
Short-term Storm Flow Paths
Overland flow: 14% of stream flow
18%
21% 25%
(using end-member mixing analysis)
Recha et al., submitted
Mitigation by SOC Management? Direct Proof? Experimentation on watershed scale needed (confounding factors: compaction, foot paths, buildings, soil productivity etc)
Incubation period (days)
0 100 200 300 400
Cum
ulat
ive
C m
iner
aliz
atio
n (m
g C
O2-
C g
-1C
)
0
20
40
60
80
100
120
140
160
Forest5 yrs
20 yrs
35 yrs
105 yrs
LSD0.05
Soil Organic Matter Stability and Stabilization Even though SOC contents are low in long-term cultivated soils, proportional C loss is high = stability is low
SOC (%): 2.2 2.1 3.3 6.0 10.5
Kimetu et al., 2009, Soil Biol Biochem 41, 2100-2104
Incubation, N=3 Oxisol, Kenya
SOC Increase by Added Organic Matter
Time of continuous soil use (years)
0 20 40 60 80 100 120
Tota
l min
eral
ized
C (m
g g-1
soil)
3.0
4.0
5.0
6.0
7.0
8.0
9.0
xey x 02.08.302.4 2.0 ++= −
965.02 =R
Lowest amount of SOC does not necessarily result in lowest increase in mineralization after OM input
Apparent Cmin increase after OM addition of 8 t C/ha Incubation, N=3 Ultisol, Kenya
drawn after Kimetu et al., 2009, Soil Biol Biochem 41, 2100-2104
0 20 40 60 80 100
0
20
40
60
80
100
a) Kakamega forest
R2 = 0.98k = 0.16
Years of cultivation
SO
C (%
initi
al)
Conservation Farming
Maize Zambia, 280 farms 2nd year CF
Gatere, 2012, thesis
Grain yield (t ha-1) Farming System
Region I Region II Region III All Sites
(796 mm) (900 mm) (1050 mm)
Traditional 1.3 (0.04) 1.0 (0.04) 1.6 (0.11) 1.2 (0.04)
Conservation 1.5 (0.07) 1.0 (0.04) 1.4 (0.09) 1.2 (0.04)
P value 0.40 0.72 0.51 0.22
Observations 83 165 32 162
Lack of inputs (OM and nutrients): Where from? Competing uses
Management to increase SOC
No “one-size-fits-all”! Site-specific solutions
Olander et al., 2011, TAGG report
Soil Carbon Sequestration
Variability ≠ Uncertainty Scientific certainty judged by soil scientists
Olander et al., 2011, TAGG report
Removal of Atmospheric Carbon
Global Regional Local Local+ C storage benefit
Project Impact Beyond Climate
Afforestation/reforestation
Higher
Lower
ForestmanagementSequestration in buildings
Biomass burial
No till agriculture
BiocharConservation agriculture
Fertilizationof land plantsCreation of wetlands
Bioenergy with CCS
Blue carbon
Direct CO2 injection
Weathering
Carbon absorbing cement
Direct air capture
Ocean fertilization
Rel
ativ
e E
stim
ated
Tot
al S
tora
ge P
oten
tial
Red: Sink creationBlack: Emission reduction
Little transboundaryissues
Transboundaryissues
Lehmann, unpubl. adapted for IPCC Special Report 2012 on Geoengineering
Agricultural Carbon
Filling the Knowledge Gaps
Compare with food policy strategy: Sachs et al., 2010, Nature 466, 558-560 And combating degradation: Cowie et al., 2011, Land Degr Dev
Soil/Plot Level Landscape Level Global Level
Calibration with Measurements Improvement of Prediction
Scaling of Results
Stronger Guidance for Management and Policy
No other phase of chemistry has been so
much confused as that of humus (Waksman, 1936)
Storm Flow Nutrient Losses
K
NO3
Recha et al., submitted
Soil Organic Matter
What about the Kimetu paper with biochar and tithonia and C mienralization?
Time (days)
0 100 200 300 400 500
CO
2-C (g
/ m2 )
0
500
1000
1500
2000
2500
T. diversifoliaBiocharControlForest
(a) Soils with low organic matter
Time (days)
0 100 200 300 400 500
CO
2-C (g
/ m2 )
0
500
1000
1500
2000
2500
T. diversifoliaBiocharControlForest
(b) Soils with high organic matter
Soil Organic Matter – the early days
humus, Latin for ground, earth, soil human, from soil, as opposed to god ‘‘. . .we may reap greater harvests if the earth is quickened again by frequent, timely, and moderate manuring’’ (De Re Rustica, Columella, AD 70) Soil organic matter as a concept separate from soil by Wallerius (1761)
Soil Organic Matter – the early days Achard (1786) Chemische Untersuchung des Torfs: (i) Peat does neither dissolve in plain water nor in an organic solvent (turpentine oil). (ii) Adding H+ (i.e., strong acid) to the water does not increase the solubility of peat. (iii) About one half of peat material is soluble when OH (i.e., strong base) is added to the system.
Soil Organic Matter – the “old”(?) view Humus, usually black or brown in color, is a collection of very complex organic compounds which accumulate in soil because they are relatively resistant to decay. (Brady and Weill, 2008)
Schulten and Schnitzer, 1998, Biol Fert Soils 26, 1-15
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Soil Organic Matter – the “old”(?) view
In soil science, refers to any organic matter that has reached a point of stability, where it will break down no further and might, if conditions do not change, remain as it is for centuries, if not millennia (Wikipedia, 2012)
Humus has a characteristic black or dark brown color, due to an accumulation of organic carbon
Soil Organic Matter – criticisms
‘‘One may feel justified in abandoning without reservation the whole nomenclature of ‘humic acids’ … beginning with the ‘humins’ … and ending with … ‘fulvic acid.’ These labels designate, not specific compounds, but merely certain preparations which may have been obtained by specific procedures.” (Waksman, 1936)
Alkaline extraction is able to: (i) dissolve not yet degraded plant materials (ii) induce chemical alterations such as hydrolyses or condensation
reactions (iii)allow organic materials to become oxidized by air (Kleber and Johnson, 2010)
Soil “Humic Substances” here and there
Energy [eV]280 285 290 295 300 305 310
Abs
orba
nce
(arb
itrar
y un
its)
Embrapa (Brazil)
Franz Josef (New Zealand)
289.3
Arnot (USA)
Barro Colorado (Panama)
McGowen (USA)
Nandi (Kenya)
287.3
288.6286.7
285.0
C=C C=O C-C
Lehmann et al, 2008, NGS 1, 238-242
NEXAFS STXM, point spectrum defocused
Total organic carbon
Chemical Heterogeneity
lignin amylopectin
albumincuticle
Florida peat HA (IHSS)
Sum of individual compounds
NMR using heteronuclear single quantum coherence experiments
Kelleher and Simpson, 2006, ES&T 40, 4605-4611
Fine-scale spatial heterogeneity
Young and Crawford, 2004, Science 304, 1634-1637
microorganisms 3.5 cm by 1 cm, by computer tomography
2 cm
600 µm
Spatial heterogeneity 10 μm
Total C Aromatic C Aliph. C
Carbox. C Phenolic C Cluster Map NEXAFS with STXM 500nm step size
Lehmann et al, 2008, NGS 1, 238-242
In search of humics
10 μm
Energy [eV]280 285 290 295
Abs
orba
nce
(arb
itrar
y un
its)
289.3
a
287.3288.6
286.7285.0
b
c
d
e
f
g
h
i
k
a b
c d
e f
g h
i k
Total Soil
285.0
286.7
Principle Component Analysis
Lehmann et al, 2008, NGS 1, 238-242
Humic Substance Extract
What is (not) organic matter?
Lehmann et al, 2008, NGS 1, 238-242
Singular Value Decomposition
a
b
10 μm
c
d
Black Carbon Microbial Carbon
Plant Carbon Total Carbon
Fine-scale heterogeneity
Milne et al, 2011, Eur. J. Soil Sci. 62, 617-628
Transect A
Fine-scale heterogeneity
Milne et al, 2011, Eur. J. Soil Sci. 62, 617-628
Aromatic C compared to Carbox. C
Distance (μm)
Wav
elet
Cor
rela
tion
Distance (μm)
Aliphatic C compared to Carbox. C
Co-located at small scales, part of the same molecule?
Not part of the same molecule Possibly indicating the difference between positions in one pore
Fine-scale heterogeneity
Correlation with principle component 1
Cor
rela
tion
with
prin
cipl
e co
mpo
nent
2
Milne et al, 2011, Eur. J. Soil Sci. 62, 617-628
Fine-scale heterogeneity
a b
a
Mineral
Pore
Pore
b
‘Humus’ is dead – what’s next?
More than just nomenclature: If ‘humus’ does not exist, what about ‘humification’????
RothC model
‘Humification’
Traditional view (until early 1990s): - Microbial re-synthesis - Recalcitrance - Organo-mineral “complexes”
- Physical occlusion - Interaction with mineral surfaces - Pore filling
Selective preservation?
Schmidt et al, 2011, Nature 478, 49-56
Aromaticity of “humic acids”
Orlov and Sadovnikova, 2005, redrawn by Kleber and Johnson, 2010
Black carbon and soil carbon stocks
Rodionov et al 2010, GBC
Black carbon in soils
60% BC
Mao et al., unpubl. data
Black humic and fulvic acids?
1 2 31 2 3
(a)
(b)
(c)
(d)
Heymann et al., unpubl.
Organo-mineral “interactions”
Torn et al., 1997, Nature 389, 170-173
Co-location with minerals
Lehmann and Solomon, 2009, Elsevier
CH3 C=C
Al-O O-H (kaolinite)
Synchrotron-based FTIR-ATR, 7 μm aperture
Surface coating of minerals? McGowen Forest Nandi Forest Lago Grande Forest
2 μm
2 μm
2 μm
Lehmann et al., 2007, Biogeochemistry
Pore-filling or surface-coating?
1. 2. 3. 4.
clay mineral
organic matter
Lehmann et al., 2007, Biogeochemistry
Distribution of mineral elements
40 nm
Fe
STEM and EELS-based identification (electron energy loss spectroscopy)
O in aluminosilicate
Chia et al., unpubl. data
Location of Organic Matter and Minerals
O Fe C Fe C
Chia et al., unpubl. data
Forms of Fe
∆E = 1.25 eV
Fe L2,3 EdgeFe Map
∆E = 1.25 eV∆E = 1.25 eV
Fe L2,3 EdgeFe Map
Chia et al., unpubl. data
Distribution of Fe forms
Fe Comp 1“Fe 3+” ish
Comp 2Reduced valence
“Fe 2+” ish or lower
Fe 2+ ishFe 3+ ish
Fe Comp 1“Fe 3+” ish
Comp 2Reduced valence
“Fe 2+” ish or lower
Fe 2+ ishFe 3+ ish
Chia et al., unpubl. data
Fine-scale heterogeneity
Chia et al., unpubl. data
Carbon K edge
Different C forms associated with Fe2+? Component 2: Si,Al,O as an insulator?
Humus is dead,- long live …
Wershaw, 2004, USGS Report
Humification is dead,- long live …
Schmidt et al, 2011, Nature 478, 49-56
A final Good-Bye?
Is it murder? Was it inevitable? What will the consequences be? Do we need a new nomenclature? New textbooks? Get rid of IHSS? No other phase of chemistry has been so much confused as that of
humus (Waksman, 1936)
The People Conspiring Many collaborators and friends, such as Markus Kleber, Ingrid Koegel-Knabner, Michael Schmidt, Margaret Torn, Susan Trumbore and many others, the gang from Kloster Ittingen. Our entire lab group, more than others Dawit Solomon, James Kinyangi, Karen Heymann, Lena Dathe, Kelly Hanley, Akio Enders. Collaborators on EELS: David Muller, Chee Chia, Stephen Joseph All those paving the way in the past decades.
With condolences
•With sadness (and confusion?), we announce that •our friend, the concept of
•Humus •* Ancient times, † 2005(?)
•passed away after a long and fruitful life. It came so slowly that we hardly noticed it, but all of a sudden
the concept of soil “humus” faded. We have learned a lot from it, and will miss it.
•Funeral is ongoing •Flowers may be thrown onto any soil outside.