This presentation was presented during the 1 Parallel session on Theme 2, Maintaining and/or increasing SOC stocks for climate change mitigation and adaptation and Land Degradation Neutrality, of the Global Symposium on Soil Organic Carbon that took place in Rome 21-23 March 2017. The presentation was made by Mr. Axel Don, from Thünen Institute of Climate-Smart Agriculture -Germany, in FAO Hq, Rome

1. GLOBAL SYMPOSIUM ON SOC
March 2017
Land management impact on soil organic
carbon stocks – what do we really know?
Axel Don
Thünen Institute of Climate-Smart Agriculture, Braunschweig, Germany

2. Axel Don
73% of the land surface is managed land
Luyssaert et al. 2014,
Nature climate change
Fraction of plant
cover conversion
as measure for
land-use change
and land-
management
intensity

3. Axel Don
Land-use change vs. land management
Grassland WetlandForestCroplandLand-use
Land management
Land-use change
pasture
hay
meadow
conv.
tillage
no
tillage

4. Axel Don
Land-use changes in Europe
Land-use changes: 25% of EU since 1900. >15% of EU since 1950.
Fuchs et al. 2013, Biogeosciences

5. Axel Don
0 20 40 60 80 100 120
0
50
100
150
200
age
change
0 50 100 150 200
-80
-60
-40
-20
0
age
change
Cropland to grasslandGrassland to cropland
N = 89N = 176
Cropland to grassland and vice versa
 Slow in fast out
 Conversion of cropland to grassland has long-term potential to sequester carbon
Time since conversion [years] Time since conversion [years]
RelativeSOCstockchange[%]
RelativeSOCstockchange[%]
Poeplau, Don et al. 2011, GCB

6. Axel Don
50 100 150 200
-20
0
20
40
60
80
100
age
change
0 50 100 150 200
-50
0
50
100
age
change
N = 100
N = 45
with forest floor
RelativeSOCstockchange[%]
RelativeSOCstockchange[%]
Time since conversion [years] Time since conversion [years]
 Afforestation of grasslands causes a transitional C loss
 SOC sequestration only in the forest floor Poeplau, Don et al. 2011, GCB
Afforestation of grassland
only mineral soil

7. Axel Don
0 50 100 150
0
50
100
150
200
age
change
0 20 40 60 80 100 120
0
50
100
150
200
age
change
N = 70 N = 59
RelativeSOCstockchange[%]
RelativeSOCstockchange[%]
Time since conversion [years] Time since conversion [years]
Poeplau, Don et al. 2011, GCB
Afforestation of cropland
 30 % of soil carbon is sequestered in the forest floor

8. Axel Don
C-input
C-output
or
NPP,
Harvest,
Fire
Decompostion
Mircrobial activity
C-stabilisation
Controls on soil organic carbon

9. Axel Don
 Sampling depth was often too shallow
 Missing data on bulk density
 Missing mass correction
Ploughing depth
No-tillageConventional
tillage Temperate zone:
61% North American
studies
35% European studies
In total 116 studies
Minimum duration of tillage
treatment: 5 years
Reducing C-mineralisation with no tillage ?
Soil carbon
Soil
depth

10. Axel Don
0 10 20 30 40
-4-202
x
y
0 10 20 30 40
-0.50.00.51.01.52.0
x
y
On average +0.15 ± 0.11 Mg C ha-1 yr-1
N=86, not significant
No-tillage Minimum tillage
On average +0.16 ± 0.10 Mg C ha-1 yr-1
N=36, not significant
SOCsequestration[MgCha-1yr-1]
SOCsequestration[MgCha-1yr-1]
Duration of treatment [years] Duration of treatment [years]
Soil carbon sequestration with low tillage

11. Axel Don
Greenhousegasbalance[kgCO2eq.ha-1yr-1]
-1500
-1250
-1000
-750
-500
-250
0
250
500
750
1000
No-tillage
Minimum tillage
SOC
N2O
Diesel
Herbicide
Total
Field greenhouse gas balance low tillage
 Soil carbon effect is offset by more N2O emissions

12. More C-input, e.g. with cover crops
 Cover crops are grown during
winter season
 Grown at around 5% of all
croplands in the EU/North America
 We estimated, that 25 % of the
agricultural area worldwide could
be used for cover crop cultivation.
 Aiming at reducing nitrate
leaching, less erosion

13. Meta-analysis of 37 world wide studies
(139 pairs of cover crops vs. no cover
crops).
Poeplau and Don 2015, Agric. Ecosys. & Environ.
 Cover crops increased SOC stocks
by 0.32±0.08 Mg C ha‐1 yr‐1.
 We predicted an average SOC stock
accumulation at equilibrium of
16.7 ±1.5 Mg C ha‐1.
Cover crop effect on soil carbon stocks

14. Axel Don
Human appropriated fraction of NPP
Haberl et al. 2007, PNAS

15. Axel Don
Conclusions
 Soil carbon accumulation is slow –
carbon loss can be fast
 No tillage in the temperate zone seems to be
no climate mitigation measure
 More C input is the main control on soil
carbon
 More NPP (e.g. via cover crops) can enhance
soil carbon
Thank you for your attention!

16. Axel Don
0 10 20 30 40
-20020406080
x
y
0 10 20 30 40
-40-20020
x
y
+6.5 ± 2 % relative SOC stock change
No-tillage Minimum tillage
+5.6 ± 3 % relative SOC stock change
RelativeSOCchange[%]
RelativeSOCchange[%]
Duration of treatment [years] Duration of treatment [years]
IPCC default
IPCC default
Low tillage effects on soil carbon
Don and Poeplau, in prep.

17. Axel Don
0
20
40
60
80
100
0
0.2
0.4
0.6
0.8
1.2
1.0
No-tillage Minimum tillage
additionalN2
O[kgN2
O-Nha-1
]
N2
Oemissionincrease[%]
N=35 sites
+86% ± 26 +63% ± 31
N=9 sites
44 sites
65% from North America
27% from Europe
Average measurement
duration: 9 months
Average measurement
frequency: every 10th day
Nitrous oxide (N2O) emissions
Don and Poeplau, in prep.