1. Winfried E.H. Blum, Georg J. Lair & Jasmin Schiefer
Limiting factors and time scales of soil carbon sequestration to mitigate climate change
Winfried E.H. Blum, Georg J. Lair & Jasmin Schiefer
Institute of Soil Research, Department for Forest and Soil Sciences
University of Natural Resources and Life Sciences (BOKU), Vienna/Austria

4. Organic carbon build-up during soil formation
total available organic carbon (OC)
soil organic carbon (SOC)
organic carbon content (t/ha)
time (year)

5. Critical Zone Observatory „Marchfeld“, Austria
Cropland
Forest
Grassland
Vienna
Bratislava
5 km

6. Vienna

7. Soils along the age gradient in the CZO “Marchfeld”3 3 2
increasing soil age 2 1 1
Chernozem
Topsoil >4000 years
Mollic Fluvisol
Topsoil ~350 years
Fluvisol on fine sediments
above gravel;
Topsoil 0-20 cm: <50 years

8. Texture, pH, organic C and CaCO3 content in topsoils (0-20 cm) under different land use
Ancient
floodplain
Close to
River

9. Soil formation with time based on build-up of A-horizons in the CZOAC C1 C2

10. Organic carbon accumulation in topsoils (0-20 cm) affected by different land use
Zehetner et al. (GBC 2009)

11. Annual C- Accumulation in topsoils (0-20cm) in kg ha-1 depending on soil age (stage of development)
(years)
C- Accumulation
(g m-2 a-1) (kg ha-1 a-1)
CO2- Sequestration
(kg ha-1 a-1)
0-50
(2t)
6140 (6.14t)
100
(1t)
3070 (3.07t)
200
(0.5t)
1535 (1.54t)
400
(0.1t)
307 (0.307t)

12. Calculation of C-sequestration in topsoils (0-20 cm) in
t ha-1 year-1, based on the experimental results
Example: Chernozem (0-20 cm depth, bulk density: 1.25 t m-3, 2% organic carbon)=50 t C ha-1
Soil age
(years)
C- Accumulation
0-50
2 t ha-1 a = % = ‰
100
1 t ha-1 a = % = ‰
200
0.5 t ha-1 a-1 = % = ‰
400
0.1 t ha-1 a = % = ‰

13. Stabilization of organic carbon in the clay fraction of cropland soils (<2µm) during soil formation
TG-analysis of the clay fraction of the topsoil (0-20 cm)
thermo-labile organic matter °C
thermo-stabile organic matter °C
Total organic C in the clay fraction (g/kg) :
62.9
61.4
60.6
68.4

14. Organic carbon content in clay sized fractions (<2 µm) of topsoils (0-10 cm) along the chronosequence
Corg accumulation in the cropland = 1.5 mg/kg/yr

15. 13C-NMR characterization of clay sized fractions
(< 2 µm) of topsoils (0-10cm) under cropping
acids, amides
aromatic groups
(lignin)
polysaccharides
(lignin, proteins)
lipids, hemicellulose

16. Soil organic carbon accumulation over time under forest,
modelled for 3 temperature scenarios (Roth-C, 0-10 cm)
- 1°C
+ 1°C
modelled for a 10 year old site using real climatic data

17. Summary and Outlook 1
C-sequestration is a slow process, resulting from the annual accumulation of plant and animal residues, their decomposition by metabolisation and mineralisation and their mixing with mineral soil material by bioturbation.
Main factors controlling these processes are:
quantity and quality of the organic residues depending on the prevailing nutritional conditions;
availability of reactive mineral surfaces for C-binding resulting from weathering processes;
the spheric position of these binding surfaces and their accessibility by microbes;
availability of water and temperature conditions for biological processes;
human interference trough soil management, changing the conditions for accumulation or decomposition of organic C.

18. Summary and Outlook 2
In A- horizons of soils older than 500 years most of the binding/accumulation positions for organic C are occupied. Further accumulation is only possible when new mineral binding positions become available or when organic C becomes recalcitrant or resistant against microbial decomposition.
The equilibrium between decomposition and accumulation of organic C is strongly influenced by climatic conditions. Increasing temperatures decrease the capacity of soils to sequester carbon.

19. Thank you!

20. 10 µm

23. 10 µm