Agriculture Reference
In-Depth Information
5-10 cm depth. No interaction between soil temperature and elevated CO
2
was observed.
No significant difference was observed for N mineralization at the
0-5 cm depth between the CO
2
treatments, but elevated CO
2
resulted in
a significant reduction in N mineralization at the 5-10 cm depth for the
30-day period (Table 4.11.4). No significant difference was observed
between ambient CO
2
and elevated CO
2
treatments for CO
2
emission at
the different time periods and soil depths. However, because of the
increased level of soil total C present under elevated CO
2
, a significant
reduction was observed with elevated CO
2
for C turnover at both time
periods for the 0-5 cm soil depth, compared with ambient CO
2
(Table
4.11.4).
Our findings indicated that the effects of elevated CO
2
on plant decom-
position processes observed with isolated plant material (i.e. little difference
observed between CO
2
emission, but a reduction in N mineralization with
elevated CO
2
(Torbert
et al
., 1995, 1998)) could be observed with soil sam-
ples collected following a 5-year elevated CO
2
field experiment. Nitrogen
cycling within the plant-soil system will probably be altered with elevated
CO
2
and may be the controlling factor for C storage in these systems.
Results from this study indicate that nutrient cycling may be increased
in these agroecosystems with an increase in soil temperature and, since
there was no observed temperature by CO
2
treatment interaction, changes
in residue quality will not greatly reduce nutrient availability to growing
plants and may reduce the impacts predicted from global warming.
Furthermore, increased biomass production with elevated CO
2
will
probably result in increased soil C storage since no significant increase in
CO
2
emission was observed and a significant reduction in C turnover was
Table 4.11.4.
Effect of atmospheric CO
2
and soil depth on CO
2
emission, N mineralization and C
turnover
1
.
C mineralized (mg kg
−
1
)
N mineralized (g 100 g
−
1
)
C turnover (g 100 g
−
1
)
CO
2
level
0-5 cm
5-10 cm
0-5 cm
5-10 cm
0-5 cm
5-10 cm
30 days
Ambient
158
a
104
a
8.6
a
1.5
a
4.1
a
4.4
a
Elevated
171
a
91
a
8.5
a
0.9
b
3.6
b
4.0
a
60 days
Ambient
387
a
306
a
16.7
a
3.9
a
10.0
a
12.9
a
Elevated
407
a
285
a
17.7
a
3.7
a
8.8
b
12.5
a
1
Values represent means of three replicates. Means within a column followed by the same letter do
not differ significantly (0.10 level).
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