Fate of biochar applied to a Colombian savanna Oxisol during the

Fate of biochar applied to a Colombian savanna Oxisol during the

Fate of biochar applied to a Colombian savanna Oxisol
during the first and second years
Julie Major1, Johannes Lehmann1, Marco Rondon2
1Department
2formerly
of Crop and Soil Sciences, Cornell University, Ithaca NY 14853,
International Center for Tropical Agriculture (CIAT), Palmira, Colombia (now IDRC, Ottawa, Canada)
Introduction
Biochar can conceivably be lost from soil by surface erosion, abiotic or biotic degradation and leaching of small particles,
although abiotic degradation is extremely slow under normal field conditions. In field situations, irrigation and rain water
would most likely be responsible for surface erosion and leaching of biochar particles of various sizes. Here, we used isotope
signatures to assign sample C to its sources. We measured the amounts of C from biochar as well as resident organic matter
that were mineralized to CO2 and found in soil samples to 2m depth. Hypotheses:
(i) Applied biochar will be found in soil below the initial incorporation depth.
(ii) CO2 evolution will be reduced by biochar applications, due to an increased C:N ratio.
Materials and Methods
A field experiment was established in the Oriental Savanna of Colombia (N 04º10’15.2”, W 072º36’12.9”) on a Tropeptic Haplustox (delta 13C ~12‰).
Average annual temperature is 26°C, annual rainfall is 2200mm and 95% falls in the rainy season which extends from April to November. In December
2004, biochar (delta 13C = -29‰) was produced by piling mango tree prunings. Savanna vegetation was mowed in December 2004, and a RCBD with 3
replicates was established with unamended plots and plots where 26 t * ha-1 biochar was applied and disked in (2ND YEAR PLOT) to 10cm depth. In
April 2006 more biochar was made from mango and applied to an adjacent lot in the same fashion (1ST YEAR PLOT). Soil was sampled in the “2 year
plot” to 2 m depth in May and December 2006, i.e. after the effects of 1 and 2 rainy seasons (years). Throughout the 2006 rainy season soil respiration
was measured using soda lime traps (2 traps per plot). Chambers were 27.3 cm in diameter and soda lime was exposed for 24 h weekly for 19 weeks
and then bi-weekly. Laboratory analyses consisted of determining respired CO2 by soda lime mass difference, dissolving soda lime to capture and
analyze absorbed CO2 for C isotopes in a C/N analyzer, and grinding air-dried soil also for soil C isotope analysis.
Results and Discussion
Biochar application increased soil respiration
Biochar increased biomass production by 189%
Year 1
Year 2
300
300
biochar
control
1200
189%
biochar
control
1000
800
% increase
93%
600
292%
400
200
150
100
200
0
1
ep
3S
t.
1
c
1O
t.
ov
8N
.
ec
6D
.
6
3
1
180
20
30
40
50
60
70
X Data
0
Control
13 t biochar * ha-1
-1
26 t biochar * ha
-1
130 t biochar * ha
140
160
20
-35
-30
-25
-20
-15
-5
80
100
100
After 2 years
140
After 2 years
120
Biochar value
140
160
18%
3
2
Increase in respired C
1
Biochar
Control
6A
Year 1
0
0
0
80
120
4
pr.
4
y
Ma
e
un 5 July A
2
8J
.
ug
S
13
.
ep
O
11
ct.
8N
.
ov
.
ec
6D
Isotope signatures did not change between treatments
-10
20
60
60
5
160
40
40
.
.
t.
ov Dec
Oc
6
8N
11
0
.
.
t.
pt.
ov
ec
Oc
Se
8N
6D
11
13
-10
-15
-20
-25
Year 2
0
-5
Surface soil value
Biochar
Control
Biochar value
Delta 13C (‰)
130 t biochar * ha-1
120
Delta 13C (‰)
140
100
Soil Depth (cm)
Soil depth (cm)
13 t biochar * ha-1
26 t biochar * ha-1
.
ep
This C was most likely derived from
resident OM and NOT biochar
After 1 year
80
Control
Biochar
Control
y
e
ly
g.
Ma Jun 5 Ju 2 Au
8
18
40
80
Increase in respired C
2
40
120
42%
4
20
100
S
13
-1
5
0
60
Cumulative C evolved (t C*ha )
7
6
20
After 1 year
.
e
un 5 July Aug
2
8J
Year 2
7
-1
Cumulative C evolved (t C*ha )
Year 1
No significant difference in
Delta 13C was observed
between the 1st and 2nd year
0
pr. May
6A
4
This lead to 60% more C being lost from
biochar plots after 2 years
l
f
Tota Grassesroad leaLegumes
B
0
10
100
50
.
y
e
ly
ug
Ma Jun 5 Ju
2A
8
18
No significant increase in C
content between the 1st and
2nd year was observed below
the surface
0
150
0
Biochar did NOT migrate down the soil profile
60
200
50
1244%
0
biochar
control
250
-1
CO2 evolved in 24 h (Kg*ha )
250
-1
CO2 evolved in 24 h (Kg*ha )
Above-ground biomass (g * 2 m-2)
5 months after biochar application
-5
-10
-15
-20
Biochar
Control
-25
160
180
0
10
20
30
40
50
60
-30
70
-35
C content (mg C * g soil-1)
-30
-25
-20
-15
Delta 13C (‰)
-10
-5
-30
0
ay une July Aug.
9
18 M11 J
13
1N
ov.
6D
ec.
pril
6A
une July 3 Aug.
2
11 J 9
6D
ec.
Conclusions
•As demonstrated by the C isotope data, biochar applied to the soil surface had not significantly (α=0.05) migrated downward, 2
years after application.
•While biochar application caused increases in soil respiration (60%) and thus greater loss of non-biochar C, simultaneous
increases in above ground plant biomass (378% for 2 years) more than offset C losses and rather contributed a net C gain in the
system.
1