Norwegian Institute for Agricultural and
Environmental Research
Division for Soil and Environment

• Cover 7-10 % of agricultural soils in Norway
• Uneven distribution due to climate conditions:
– 2-3 % in south-east
– 12-15 % in north and west
• Subsidence and C-loss has been known for a century
– An agricultural problem
– Relation to climate change and greenhouse gas emission the last 2 years in Norway
• No systematic/extensive survey of C-loss from cultivated peat soils in Norway
• Rough estimates can be obtained

Estimates from 3 methods are compared
1.
Long-term monitoring of peat subsidence
2.
Changes in ash contents
3.
Soil CO
2 flux measurements

• Subsidence includes:
– Compaction
– Soil loss
• Data required for calculating C loss:
– Initial and final bulk density
– Initial and final C-concentration
Not always available
•Material from a study in western Norway:
•11 fields – 1300 observation points – 30 years
•Mean annual subsidence 1.86 cm
•Assumptions:
•50 % of the subsidence due to C loss
•Mean C concentration 40 %
Estimated loss: 0.77 kg C (2.85 kg CO
2
) m -2 y -1

Assumption:
• Increase in mineral content is due to:
– C loss
– Lime and fertilizer application

2. Changes in ash contents
The OM loss can be calculated from the equation:
OM loss
MF fin


MF fin

BD fin

Thick




1

1



 
MF ini
= measured final mineral content
1

MF fin


BD fin

Thick

MF ini
= measured initial mineral content (can be estimated from adjacent uncultivated peat)
BD fin
= final bulk density
Thick = layer thickness
Not required:
•Initial bulk density
•Bulk density of deeper layers
•Subsidence measurements

2. Changes in ash contents
Calculations based on material from the mentioned study in western Norway:
11 fields – 1300 observation points – 30 years
• Available data:
– Final mineral content
– Initial mineral content
– Final bulk density
• Assumptions:
– Thickness of the influenced layer was assumed to be 20 cm
– Correction for increase of lime content: 0.4 % CaO (mean value from the soil database)
• Results:
Final mineral content:
- Initial mineral content
11.1 %
4.5 %
- Increased lime content: 0.4 %
= Increase due to degradation: 6.2 %
Estimated carbon loss: 0.75 kg C (2.75 kg CO
2
) m -2 y1

2
Small chambers (25 x 25 cm)
Sampling interval: 2 weeks
Period: August 2003 – November 2004
(Not December- March)

3. Soil CO
2 flux measurements
Gross respiration (emission)
+ Yield removed kg C m -2 y -1
1.15
0.38
- Gross photosynthesis* 0.94
= Net C loss (ecosystem balance) 0.6 (2.2 kg CO
2
)
*Estimated from: net plant producivity/above ground net plant productivity (NPP/ANPP=1.4) net plant productivity/gross plant productivity (NPP/GPP=0.55)

1.
Monitoring of peat subsidence
2.
Changes in ash contents
3.
Soil CO
2 flux measurements
Advantages Disadvantages
High precision of total long-term C loss
Cheap – few parameters required
Initial data and long term monitoring required
Less precision expected
Uniform peat layer a precondition
Temporal variability of CO
2 loss
Relation to other greenhouse gases
More expensive
Many replicates necessary
Photosynthesis estimates required

1.
Monitoring of peat subsidence: 0.77 kg C m -2 y -1
2.
Changes in ash contents: 0.75 kg C m -2 y -1
3.
Soil CO
2 flux measurements: 0.6 kg C m -2 y -1
Likely estimate: 0.6 – 0.8 kg C m -2 y -1

• Cultivated peatlands the last 100 years in Norway:
– 150,000 – 200,000 ha (15-20 % of cultivated area)
• From the soil database:
– Organic soils: 6.3 % of soil samples, whereof 2/3 have 20-40 % SOM (mixed mineral-organic soil)
• Estimated peat area in agricultural use: 70,000-
100,000 ha
• Estimated total annual carbon loss from cultivated peatlands:
– 2 - 4 million tons CO
2 y -1 ,
– 5 - 10 % of the total human induced CO
2 emission
• The emission will be reduced as the peat is converted to mineral soils

Limited options for areas under cultivation:
–
–
>90 % used for grass production
Raising ground water table hardly feasible
Restoration of abandoned cultivated peatland
• Natural processes
– Shallow peat soils over bedrock or stone rich moraine
–
–
Too low slope for further drainage
Difficult drainage because of low permeability
• Deliberate actions
– Commitments to WTO can lead to surplus of cultivated land -
Unfavourable climate conditions
– Encouragements for set aside land and C sequestration
• Options
– No management - high ground water table
–
–
Deep/shallow drainage
Afforestation/bioenergy production
• Main challenge:
– minimize CH
4 emission

• Little attention to cultivated peat soils as a source of
CO
2 emission
• No systematic survey of C loss has been conducted
• Calculations by three methods indicate a loss of
– 0.6 – 0.8 kg C m 2 y -1
– 2 - 4 million tons CO
2 y -1
– 5-10 % of the total human induced CO
2
Norway emission in
• Future challenge:
– Restoration of abandoned cultivated peatlands
– Maximize C accumulation and minimize CH
4 emission