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.