biomasss

Question 1

Biochar

Answer 1

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

Question 2

Wastewood

Answer 2

we don’t have enough biomass in the UK so they import wood chip from North America so they have a carbon footprint

Question 3

Production of biochar

Answer 3

requires slow pyrolysis

Question 4

How much carbon can be stored as biochar

Answer 4

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

Question 5

Indirect benefits of biochar

Answer 5

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

Question 6

Risks/ problems associated with biochar

Answer 6

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

Question 7

UK biomass crops

Answer 7

• Miscanthus

- short rotation coppice willow/ poplar

Question 8

Miscanthus

Answer 8

grows rhizomes
reaches 3 M
Yields up to 25 T ha more usually 8-10 T ha in the UK

Question 9

Carbon neutrality

Answer 9

’carbon neutral means that through a transparent process of calculating emissions, reducing those emissions and offsetting residual emissions- net carbon emissions equal zero’’

Question 10

How carbon neutral is energy derived from bioenergy crops?

Answer 10

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

Question 11

Which soil processes determine system sustainablity

Answer 11

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)

Question 12

Why is soil carbon important

Answer 12

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

Question 13

Carbon storage

Answer 13

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)

Question 14

Production of N fertiliser

Answer 14

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

Question 15

Nitrous oxide

Answer 15

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)

Question 16

Denitrification

Answer 16

bullshit

Question 17

Why can some bioenergy crops promote C storage in soil?

Answer 17

• 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

Question 18

Terra Preta soil

Answer 18

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

Question 19

Carbon in Terra Preta and oxisol

Answer 19

part of elevated SOM is black C
derived from incomplete combustion
of vegetation

pottery in upper horizons may
suggest soils are man-made

Question 20

SOC

Answer 20

soil organic carbon

Question 21

soil organic carbon importance:

Answer 21

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

Question 22

carbon storage

Answer 22

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)

Question 23

C storage vs sequestration

Answer 23

Turnover time:

<10 years

100s years

1000s years

Biochar: turnover >1000s years?