Biochar stability and agroecosystem sustainability

Biochar stability and
agroecosystem
sustainability
Kimetu JM, Lehmann J, Ngoze SO, Mugendi DN, Kinyangi
JM, Riha S, Verchot L, Bationo A, Thies J and Pell A
Immediately after clearing
for cultivation
Primary forest
Forest soil
Degraded soil
Decline in soil C stocks with continuous cereal cropping
Total organic C (%)
10.0
8.0
6.0
4.0
2.0
0.0
0
20
40
60
80
100
Time of continuous cultivation (years)
120
Decline in crop yields concurrent with carbon decline
Increase of Carbon to improve Productivity
7
LR yield
SR yield
5
-1
Grain yield (Mg ha )
6
4
3
2
1
0
0
20
40
60
80
Years of cultivation
100
120
Ngoze et al., 2008, Global Change Biology, in press
Status of SOM
degradation
12 t C/ha/yr
Tithonia (C-to-N = 9)
Biochar (C-to-N = 380)
12 t C/ha/yr
Soil texture
Increasing organic matter improves soil productivity
12
Biochar
Tithonia
LSD0.05
Maize grain yield (t ha-1)
10
8
6
4
2
0
20
40
60
80
100
120
Time since conversion (years)
Kimetu et al., 2008, Ecosystems, 11: 726-739
Increased productivity with biochar is not related to
nutrient delivery
N
a
Tithonia
Biochar
Control
a
a
250
200
b
80
Total P uptake (kg ha-1)
300
-1
Total N uptake (kg ha )
350
b
150
b
b
100
b
b
50
0
5
a
a
20
a
b
b
a
a
b
b
b
b
b
b
50
0
5
35
105
b
b
35
105
a
Ca
a
100
35
a
40
100
K
200
150
a
5
-1
250
60
0
105
Total Ca uptake (kg ha )
-1
Total K uptake (kg ha )
300
35
P
80
a
60
40
b
b
a
a
a
b
20
b
0
5
Time since conversion (years)
35
105
Kimetu et al., 2008, Ecosystems, 11: 726-739
Recovery (% of added C found in soil)
C recovery in highly degraded soils
Calculated using δ13C
Repeated application for 3 seasons over 2 year period (n = 3)
Absolute SOC change (mg g-1)
600.0
500.0
400.0
Greater proportion
of C in stable
fractions per unit C
respired with
biochar than with
tithonia
Stable (Organo-mineral) fraction
Stabilized (Intra-aggregate) fraction
Labile (Free light) fraction
300.0
200.0
100.0
0.0
-100.0
-200.0
Tithonia Biochar Tithonia Biochar Tithonia Biochar
5
20
Time since conversion (years)
105
n = 1; pooled sample
from 3 replicate farms
Maize grain increase relative to control (%)
250
Highly degraded soils
200
Biochar
Tithonia
150
100
50
Year1
Year2
Season
Year3
Maize grain increase relative to control (%)
300
250
Moderately degraded soils
Biochar
Tithonia
200
150
100
50
0
Year1
Year2
Season
Year3
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Reverting carbon loss also increases
crop yields
Greatest efficiency in SOC and yield
increases was realized in the most
degraded soils
Greater sustainability in SOC and
yield increases with biochar than
tithonia
Unanswered questions:
- Why is biochar so stable in soil? What are
the molecular mechanisms of stabilization?
- What are the differences in stabilization
mechanisms for different biochars?
- What are the mechanisms by which crop
yields increased with biochar?
`
Symposium organizers for invitation
`
Collaborators (Chris Barrett and David
Mbugua)
`
The Rockefeller Foundation and the National
Science Foundation for core funding
`
ICRAF for helping in logistics
`
Field and laboratory technicians
`
Farmers
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