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- Dr Saran Sohi 1,2, Dr John Gaunt 1,2,3, Dr Elisa
Lopez-Capel 4,
- Helen Yates 1 & Prof Johannes Lehmann 2
- 1 Agriculture & Environment Division, Rothamsted
Research, UK
2 Dept. of Crop & Soil Sciences, Cornell
University, NY
- 3 GY Associates, Harpenden, UK
- 4 Civil Eng. & Geosciences, University of Newcastle, UK
- saran.sohi@bbsrc.ac.uk
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- Placing approaches to SOC modeling in the context of black C
- Outline:
- Why do we need (SOC) models?
- What type of SOC models do we have?
- Can they be modified to account for black C (BC)?
- What other models can be developed to explain the effects of BC?
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- Originally: to make generalizations about land-use impacts on SOC
content
- Sustainability of production
- Descriptive, site-specific, and plot scale
- Recently: to predict net changes in SOC from changing agronomic management
- diverse landscapes, regional scale
- carbon sequestration
- So far we are using the same models
- Will new models allow mechanisms of stabilization to be elucidated?
- What is the impact of black C on SOC turnover
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- Organic matter added to soil decomposes
- Decomposition is not proportional to what is there i.e., not first-order
- How is the actual relationship represented in models
- How the relationships are tested
- CO2 (measuring where organic matter goes - sensitive in
short term)
- SOC (measuring what is left - changes slowly, easy to measure)
- How are these relationships affected by black C?
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- Predictive, and versatile descriptive models imply and must embody some:
- universal or defined
reactivity-distribution
- These distributions will be impacted by the presence of abundant black
C
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- Existing models work by allocating SOC to discrete, linked pools of
defined & contrasting ‘reactivity’
- These pools cannot be measured but from extensive parameterization we
know their likely size in typical soils (given information on site,
texture and climate)
- Descriptions of C accumulation and equilibriums in long term
experiments under contrasting conditions
- Prediction of C accumulation and equilibriums at sites with known
management history
- Extended to forest systems
- Integrated with GIS for regional scale predictions
- These models are not able to automatically account for atypical and/or
black soils…..
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- Recent studies suggest (Schmidt et al., Skjemstad et al.)
- black C is a ubiquitous constituent of soil organic carbon (SOC) in agricultural
soils
- black C is not only significant, but an often major (or even dominant)
constituent of SOC
- If black C comprises stable or most stable C, its abundance must
strongly affect SOM reactivity profiles
- SOC accumulation
- SOC equilibrium
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- Context
- Soil C stocks
- C sequestration
- Feedback effects
- Description, prediction, spatial
- Sensitivity (land-use or agronomic level)
- Spatial resolution (soil type or climatic zone)
- Time-scale & time-step (field or lab incubation experiments)
- Empirical, mechanistic
- Model initialization
- Assessing intervention
- Issues addressed:
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- Context
- Descriptive and spatial modeling
- Land-use level
- Regional scale projections
- Time-scale of decades; time-step of months (field data)
- Empirical model
- Revised ‘rules’ for initialization
- Issues addressed:
- C-sequestration potential (re-assessed)
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- Models based upon relevant (distinct) and verifiable (measurable) pools
offer a tool for elucidating underlying mechanisms of C stabilisation
- Our simulations using SOMA would account explicitly for black C present
in each pool
- Black C appears not to be characterized by a single physical location
within the soil matrix (Glaser et al., 2000)
- Success would not be entirely dependent upon relevant black C
measurement techniques
- The impact on the reactivity of each pool can be inferred
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- Simple modification to existing models e.g. RothC, re-defining the
inert/passive fraction
- Re-optimizing new mechanistic models e.g. SOMA for soils with/without
known amounts/types of black C
- > Strategies for purposeful amendments that maximise soil C
stabilisation
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