biomasss Flashcards
Biochar
Biochar is the porous, carbonaceous solid produced in the thermo-chemical conversion of biomass under oxygen-depleted conditions and which has physiochemical properties suitable for safe and long-term storage of carbon in the environment and, potentially, soil improvement
Wastewood
we don’t have enough biomass in the UK so they import wood chip from North America so they have a carbon footprint
Production of biochar
requires slow pyrolysis
How much carbon can be stored as biochar
US systems:
Pyrolysis of residues from forest used for timber
Conversion of abandoned cropland to biomass plantation, pyrolysis of biomass
Pyrolysis of crop residues
= 10 % of annual US fossil fuel emissions
Global potential for billion tonne sequestration
of C within 30 years
Indirect benefits of biochar
Long term stable pool of C
Limits soil nutrient losses
Promotes water storage
Protects organic C by reducing decomposition, promoting C storage
Reduces greenhouse gas emissions from soil
Risks/ problems associated with biochar
High rates of application reduce crop yields
Contains low concentrations of toxic polyaromatic hydrocarbons and dioxins
Is there enough land to make enough biochar to make a difference?
Destruction of forests to make biochar or grow biochar plantations
Loss of arable land from food production
UK biomass crops
- Miscanthus
- short rotation coppice willow/ poplar
Miscanthus
grows rhizomes
reaches 3 M
Yields up to 25 T ha more usually 8-10 T ha in the UK
Carbon neutrality
’carbon neutral means that through a transparent process of calculating emissions, reducing those emissions and offsetting residual emissions- net carbon emissions equal zero’’
How carbon neutral is energy derived from bioenergy crops?
Answer depends on:
Crop yield (i.e. CO2 uptake from atmosphere)
Fossil fuel use during cultivation and transport of crop
Net effects on soil C and N cycling
Which soil processes determine system sustainablity
Fluxes of greenhouse gases CH4,CO2,NO, N2O mineralisation
Conversion of C and N into soil organic matter storage
Balance of mineralisation vs storage depends on climate, soil type and soil management (inputs, cultivation)
Why is soil carbon important
Key component of soil organic matter which:
Acts as a source of nutrients for crops
Supports above and below ground food webs
Controls soil structure; helps determine water storage, protects against erosion
Sorbs nutrients and pollutants, acting as an environmental buffer
Cimate change. Soil is a key source/ sink of CO2
Carbon storage
Balance between storage and mineralisation of C in soil depends on:
Quantity and quality of inputs (leaf litter, root turnover, rhizodeposits)
Temperature and moisture, which determine decomposition rate
Soil characteristics which control stabilisation (e.g. clay content, N availability)
Management (cultivation)
Production of N fertiliser
Haber-Bosch process (1909) N2 from air fixed to NH3 using iron catalyst
NH3 oxidised to NO3 for use as fertiliser
Current industrial fixation of N as fertiliser is 80 Tg yr; may reach 135 Tg yr by 2030
1-2 % of the worlds total energy consumption is spent making N fertiliser
Nitrous oxide
Present as a trace gas in the atmosphere
Long atmospheric life span (120 years)
310 more powerful as a greenhouse gas than CO2 (on a per molecule basis)
Denitrification
bullshit
Why can some bioenergy crops promote C storage in soil?
- High inputs of litter
- Litter has high C:N ratio and decomposes slowly
- No tillage protects SOC and soil biota
- Low inputs of N and P fertiliser ensure low N and P availability, limiting microbial activity and mineralisation of C
Terra Preta soil
Central America: typically 20 ha areas highly enriched in SOM and black C
Mineralogy identical to surrounding soils, but contain higher SOM, nutrient and water holding capacity than surrounding soil
Carbon in Terra Preta and oxisol
part of elevated SOM is black C
derived from incomplete combustion
of vegetation
pottery in upper horizons may
suggest soils are man-made
SOC
soil organic carbon
soil organic carbon importance:
Key component of soil organic matter which:
Acts as a source of nutrients for crops
Supports above and below ground food webs
Controls soil structure; helps determine water storage, protects against erosion
Sorbs nutrients and pollutants, acting as an environmental buffer
Cimate change. Soil is a key source/ sink of CO2
carbon storage
Balance between storage and mineralisation of C in soil depends on:
- Quantity and quality of inputs (leaf litter, root turnover, rhizodeposits)
- Temperature and moisture, which determine decomposition rate
- Soil characteristics which control stabilisation (e.g. clay content, N availability)
- Management (cultivation)
C storage vs sequestration
Turnover time:
<10 years
100s years
1000s years
Biochar: turnover >1000s years?
