sohi ibi newcastle 2008 evaluating mechanisms

7/25/2019 Sohi IBI Newcastle 2008 Evaluating mechanisms

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International Biochar Initiative

2nd annual meetingNewcastle, UK, 7-11th September 2008

Evaluating mechanisms oforganic matter-biochar

interaction in soil

Dr Saran SohiRothamsted Research, Harpenden, UK

[email protected]

www.rothamsted.bbsrc.ac.uk/aen/CarbonCyclingCentre for Bioenergy and Climate Change

Cross-Institute Programme in Sustainable Soil Use


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Outline

Hypotheses:

Biochar increases other organic matter in soil

Modelling can decipher the underlying process

1. Introduction: soil organic matter, modelling

2. Experimental approach (using terra preta)

3. Results and conclusions


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Organic matter, carbon & soil structure

Watts et al., Rothamsted Research


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Organic matter in soil

Plants are the dominant source

- but supplemented by management Decomposition is inevitable and rapid

- but necessary to deliver key benefits

Only a few percent of soil mass is organic- but offers manageable properties

Soil is always a harsh, complex habitat- but infinitely diverse

Biochar is a fundamentally distinct

component of soil organic matter


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Purpose of soil C models

Embody understanding of crop, climate

and soil texture effects on decomposition Provide the universal formula predicting

organic matter trajectory and equilibrium


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Universal soil modelling concept

0

2

46

8

10

0 50 100

0

1

23

4

5

0 50 100

0.0

0.20.4

0.6

0.8

1.0

0 50 100

0.0

0.40.8

1.2

1.6

2.0

0 50 100

SoilC

t/ha

SoilC

t/ha

time (yrs) time (yrs)

Pool 1 Pool 2

Pool 3 Pool 4


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Universal soil modelling concept

0

4

8

12

16

20

0 50 100

Soil

Ct/ha

time (yrs)


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Field experiments simulated

Soil C

(tonnes /hectare)

corn &grass

cornonly

grass

border

natural

pasture

80

0

30

60

1860 20001930

Data from the Morrow Plots, a long-term field experiment in Illinois

RothC simulation at Rothamsted by K Coleman


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Biochar changes everything: the universal

understanding no longer applies

But:


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Example 1: Waite plots, Australia

K. Coleman et al. Geoderma 81(1) 29-44

Assuming 10tC/ha plant input Assuming 3tC/ha in IOM


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Example 2: Terra preta soils, Brazil

Sites and data (provisional) from INPA, Brazil, with Cornell UniversityRothC simulation at Rothamsted by K Coleman

Adjacent 52 78 % 8.0 5.7

Terra Preta 84 63 % 12.7 4.5 +212 %

Adjacent 68 33 % 10.7 5.0

Terra Preta 156 46 % 23.6 6.5 +201 %

Adjacent 53 37 % 7.9 3.3

Terra Preta 88 21 % 14.3 4.0 +98 %Adjacent 54 65 % 7.5 3.9

Terra Preta 104 11 % 18.1 3.8 +204 %

Location

Adjusted :

default inertC (%)

-

-

-

-Site 1

Site 2

Site 3

Site 4

totaltC/ha Clay

Explanatory

C input

(Defaultmodel; tC/yr)

Measured

litter C

input(tC/yr)


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One obvious impact of biochar

Pool of inert carbon is enhanced

But changes in other soil characteristics

suggest fundamental changes to soil organic

matter cycling


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Less added carbon respired in biochar soil

0

1

2

3

4

5

6

7

8

0 100 200 300 400 500

Days of incubation

mgCO2-C

/ day

(minus

control)

terra preta

adjacent soil

Measurements at Cornell by B Liang


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Modelling using measurable pools

Objectives:

To discriminate and evaluate points of impact

To compare impacts of different biochar

products under different conditions

Experimental protocol and linked model already

in place from organic matter studies in normalsoils


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Soil physical fractionation

15 g soil + 90 ml NaI

solution (1.80 gcm-3)

Dissolved organic matter

Organomineral (heavy)

Density separation Free organic matter (light)

Sohi et al. 2001, Soil Science

Society of America Journal 64(3)

Ultrasonic dispersion

Density separation Intra-aggregate (light)


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Experimental design

Three ancient terra preta oxisols

enriched in biochar, limited recent agriculture

Three adjacent oxisols (no biochar) no evidence of agriculture

Laboratory incubation 18mth at 30C with/out isotope-labelled sugarcane leaves

Periodic sampling fractionation (C,N, 13C and 15N measured)

including a biochar fraction

measurement of respiration (CO2)


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Less added carbon respired in biochar soil

0

1

2

3

4

5

6

7

8

0 100 200 300 400 500

Days of incubation

mgCO2-C

/ day

(minus

control)

terra preta

adjacent soil

Measurements at Cornell University by B. Liang


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But more rapid transfer in labile fractions

Added (labelled) C:

Fate of most active soil

fraction free organic matter

fasterin terra preta

Association with protected

intra-aggregate) fractions is

more rapid

0

20

40

60

80

100

1 10 100 1000

Days of incubation

AddedCinfra

ction(%)

Oxisol

Terra Preta

0

20

40

60

80

100

1 10 100 1000Days of incubation

AddedCin

fraction(%)

Oxisol

Terra Preta


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Yet: more stabilisation..

Also: the mobile, labile

soluble fraction much

larger

But not in the biochar-

enriched sub-fractionbiochar-rich

fraction

other

organomineral

0.0

0.5

1.0

1.5

2.0

Oxisol Terra preta

AddedC

(mgC/gsoil)

Organomineral fraction

contained much morestraw carbon:


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Conclusions from model analysis

* Turnover of free organic matter is tripled

* More organic matter processed through aggregates

* Microbes concentrate in aggregates, organomineral

* Efficiency of microbial C incorporation is halved

* Transfer between fractions increasingly abiotic

* Microbial mortality rate is much slower

* Turnover of soluble organic matter greatly reduced


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Simulation captures contrasting dynamics

More rapid accumulation of organic matter

into stable organomineral pool in terra preta

Simulated dynamics of carbon resulting from enrichment of soil with biochar

Oxisol Oxisol with biochar

0

5

10

15

20

-10 40 90 140 190 240 290 340 390 440 490

Days of incubation

C in

fraction

(mg / g

soil)

CO2

Soluble

Free

Intra-aggregate

Organomineral

0

5

10

15

20

-10 40 90 140 190 240 290 340 390 440 490

Days of incubation

C in

fraction

(mg / g

soil)

CO2

Soluble

Free

Intra-aggregate

Organomineral


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Terra Preta study: conclusions

Less CO2 emitted after straw addition

Transfer of organic matter through pools

of increasing stability much more rapid

An extra 15% of added organic matter(straw) transferred to the most stable pool

Results from model optimisation support a

predominantly abiotic process


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Experimental considerations, challenges

Biochar contains an active fraction and aged

biochar is not simple to manufacture Response and equilibration of microbial

population could be relatively slow


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Acknowledgements

Johannes Lehmann & Biqing Liang, Cornell University

Helen Yates & Kevin Coleman, Rothamsted ResearchJohn Gaunt, Carbon Consulting LLC

Rothamsted Research receives grant-aided support from the Biotechnology

and Biological Sciences Research Council (BBSRC) in the UK

sohi ibi newcastle 2008 evaluating mechanisms

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