Carbon sequestration in sub-tropical soils under rubber plantations in north-east India potx

Carbon sequestration in sub-tropical
soils under rubber plantations in
north-east India
Debasis Mandal and K. R. Islam
Indian Rubber Research Institute, Tripura, and
University South Centers, USA
Widespread deforestation for fuelwood,
timber and forage is an on-going process
in the south-east Asian countries
(Islam et al 1999).
Deforestation transfers C
directly to the atmosphere,
and affects the mechanism
to hold
C in soil (Chambers et
al. 2001).
Rubber plantations were raised as a secondary
forest in the Indian state of Tripura since 1975 to
improve degraded lands, generate income for
locals, and meet increasing demand for rubber.
It is expected that reforestation of degraded
lands may act as tropospheric
CO
2
sink
(Wallace 1994, Islam et al. 1999).
This study was conducted to evaluate the
impact of rubber plantations on
C fractions,
stocks, and sequestration in reforested

degraded sub-tropical forest lands in
Tripura, India.
Materials and methods
Site: 10,412 ha of
rubber plantations
of different ages at
Kunjaban,
Agartala, NE India
Soil Ultisol
Texture Clay loam
Porosity 0.41
m
3
m
-3
pH 4.5+0.3
Sample plots from 5, 10, 15, 20, 25, and 30 yrs
old rubber plantations with a control (initial).
Standing biomass and annual C flow as litter-fall
Soil sampled at 0 - 15 and 15 - 30 cm depths
Oxidizable organic C (C
OX
)
Non-oxidizable C (C
NOX
)
Total C (C
T
)
Bulk density

C concentration and stocks
Data analysis by SAS as 7 (age) x 2 (soil depth)
factorial combination at p<
0.05.
Results and Discussion
Table 1: Standing biomass of
different ages of rubber plantations
_______________________________________
Plantation
Shoot Root Total
age (year) ____ biomass (Mg ha
-1
)____
_______________________________________
0 (initial) 16.8c 4.2d 21.0c
5 29.3c 13.6c 42.3c
10 121.3b 26.6b 145.9b
15 156.0ab 29.4ab 185.5ab
20 160.4ab 32.4a 193.4a
25 160.7ab 31.9a 192.9a
30 161.7a 29.9ab 191.6a
______________________________________
LSD
P>0.05
39.8 7.1 41.6
Table 2: Biomass C of different ages
of rubber plantations
___________________________________________
Plantation
Shoot Root Total

Age (year) _____ biomass C (Mg ha
-1
) ______
___________________________________________
0 7.2b 1.9d 9.1b
5 12.6b 5.7c 18.4b
10 52.3a 11.1b 63.3a
15 67.1a 13.2ab 80.3a
20 69.2a 14.5a 83.7a
25 69.2a 14.3a 83.5a
30 69.5a 13.3a 82.9a
___________________________________________
LSD
P>0.05
19.7 3.2 20.9
Years after plantation
0 102030
Litter-fall (Mg ha
-
1
yr
-
1
)
0
2
4
6
8
Biomass

Carbon
Years after plantation
0102030
Bulk density
(g cm
-3
)
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
0-15-cm depth; y = 1.6 - 0.003*X
r
2
=0.57*
15-30-cm depth: y = 1.61- 0.002*X
r
2
=0.37ns
Years after plantation
0 102030
C
OX
conc
(g kg
-

1
)
0
5
10
15
20
25
0-15 cm: y = 7.47 + 0.41*X
r
2
=0.84**
15-30 cm: y = 4.83 + 0.40*X - 0.008*X
2
r
2
=0.76*

Years after plantation
0102030

C
NOX
conc (g kg
-
1
)
0
5
10

15
20
25
0-15 cm: y = 10.6 + 0.33*X - 0.01*X
2
r
2
=0.33ns
15-30 cm: y = 12.5 + 0.5*X- 0.01*X
2
r
2
=0.57*
Years after plantation
0 102030
C
T
conc (g kg
-
1
)
0
5
10
15
20
25
30
35
0-15 cm: y = 18.1 + 0.74*X - 0.01*X

2
r
2
=0.88**
15-30 cm: y = 17.3 + 0.89*X - 0.018*X
2
r
2
=0.63*
Years after plantation
0 102030
C
OX
stock (Mg ha
-1
)
0
10
20
30
40
50
60
0-15-cm depth
y = 17.85 + 205.6*(-0.0046*X)
r
2
= 0.94***
15-30-cm depth
y = 10.94 + 12.8*(0.113*X)

r
2
= 0.73*
Years after plantation
0 102030
C
NOX
stock (Mg ha
-1
)
0
10
20
30
40
50
60
0-15-cm depth
y = 26.3 + 3.13*(1-exp(-0.19*X)
r
2
= 0.1ns
15-30-cm depth
y = 30.32 + 15.13*(1-exp(-0.088*X)
r
2
= 0.55*
Years after plantation
0102030
C

T
stock
(Mg ha
-1
)
0
20
40
60
80
0-15-cm depth
y = 43.02 + 34.49*(1-exp(-0.055*X)
r
2
= 0.91***
15-30-cm depth
y = 41.35 + 27.88*(1-exp(-0.097*X)
r
2
=0.76*
Years after plantation
0 102030
Profile C stock
(Mg ha
-
1
)
0
20
40

60
80
100
120
140
160
C
Oxi
= 29 +56.9*(1-exp(-0.037*X)
, r
2
=0.93***
C
NOxi
= 56.45 + 17.22*(1-exp(-0.122)
, r
2
=0.37ns
C
T
= 84.35 + 60.2*(1-exp(-0.076*X
, r
2
=0.85**
Years after plantation
0 102030
C
ox
sequestration (kg ha
-1

yr
-1
)
0
200
400
600
800
1000
1200
1400
0-15 cm: y = 872.8 - 2.33*X
r
2
=0.99***
15-30 cm: y = 1354.2 - 56.4*X + 0.84*X
2
r
2
=0.98***
Years after plantation
0102030
C
Nox
sequestration (Mg ha
-
1
yr
-
1

)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0-15 cm: y = 1.36 - 0.026*X
r
2
=0.99***
15-30 cm: y = 1.13 - 0.06*X + 0.001*X
2
r
2
=0.98***
Years after plantation
0 102030
C
T
sequestration (Mg ha
-1
yr
-1
)
0.0
0.5
1.0

1.5
2.0
2.5
3.0
0-15 cm: y = 2.23 - 0.028*X
r
2
=0.99***
15-30 cm: y = 2.49 - 0.12*X + 0.002*X
2
r
2
=0.98***