Agriculture Reference
In-Depth Information
1981) and 2.78-4.80 for Oxisols and Ultisols of the humid tropical forest zone
of Sumatra (van Noordwijk
et al
., 1997). Under intensive multiple-rice cropping,
the soil organic mater may increase until a new steady state level is reached after
some years. Table 3.12 gives an example for a rice-rice system over five crops
in 2 years compared with a maize-rice system. However, very large soil organic
matter contents do not develop.
Evidently rates of decomposition are greater than expected for simple anaerobic
decomposition. Figure 3.10 shows comparable rates of organic matter decompo-
sition in soils that were kept continuously flooded or well-drained under otherwise
similar, tropical conditions for 3-4 years (Neue and Scharpenseel, 1987). Clearly,
Table 3.12
Carbon balances for rice-rice and maize-rice cropping systems over five
consecutive crops in 3 years at IRRI, Laguna, Philippines. Except for short stubble all
straw was removed from the fields and no organic manures were applied. Values are t C
ha
−
1
±
SEs
Cropping system
Rice-rice
Maize-rice
N fertilizer (kg ha
−
1
)
0-0
190-100
0-0
190-100
Initial SOC
a
19
.
13
±
0
.
83
19
.
41
±
0
.
27
19
.
22
±
0
.
79
19
.
38
±
0
.
97
Final SOC
20
.
97
±
0
.
49
22
.
15
±
0
.
54
19
.
01
±
0
.
40
19
.
83
±
0
.
43
Change in SOC
+
1
.
84
±
0
.
44
+
2
.
74
±
0
.
67
−
0
.
22
±
0
.
50
+
0
.
46
±
0
.
96
(% change)
(
+
10
)
(
+
14
)
(
−
1
)
(
+
2
)
C from crop residues
4
.
93
±
0
.
18
7
.
72
±
0
.
21
4
.
15
±
0
.
28
7
.
09
±
0
.
18
C mineralized
3
.
09
±
0
.
56
4
.
98
±
0
.
47
4
.
37
±
0
.
56
6
.
63
±
0
.
87
(% of crop residues)
(63)
(64)
(105)
(94)
a
SOC, soil organic carbon.
Source
: Witt
et al
. (2000). Reproduced with kind permission of Kluwer Academic Publishers.
(a) well drained
(b) submerged
100
100
Aquept
Aquoll
Aquult
Tropept
Tropept
Humult
30
30
10
10
3
3
0 0 0 0 0 0
0 0 0 0 0 0
Time (months after straw incorporation)
Figure 3.10
Decomposition of
14
C-labelled rice straw in (a) well-drained upland
soils and (b) continuously submerged lowland soils under tropical conditions (adapted
from Neue and Scharpenseel, 1987). Reprinted with permission from Elsevier
