Agriculture Reference
In-Depth Information
Experimental design
The experiment was established in a growth room (16 h photoperiod,
20-15
C and 80% humidity) as a two-factor experiment (split plot) in a
randomized complete block design. The atmospheric CO
2
concentrations
(ambient and elevated) were considered as the main plot and the sub-plot
N fertilization rates (low and high) were arranged randomly within each
main plot. Every CO
2
level was replicated four times, and each N
fertilization level was replicated twice within each CO
2
unit.
Treatments were designated as follows: N
0
(ACO
2
) = low N input
(10 kg N ha
−1
) at ambient CO
2
concentration (369
°
mol mol
−1
CO
2
);
N
1
(ACO
2
) = high N input (170 kg N ha
−1
) at ambient CO
2
concentration
(369
±
2
µ
mol mol
−1
CO
2
); N
0
(ECO
2
) = low N input (10 kg N ha
−1
)at
elevated CO
2
concentration (716
±
2
µ
mol mol
−1
CO
2
); and N
1
(ECO
2
)=
high N input (170 kg N ha
−1
) at elevated CO
2
concentration (716
±
4
µ
±
4
µ
mol
mol
−1
CO
2
).
Total N for high N input was split into two doses of 80 and 90 kg
Nha
−1
applied at days 2 and 16, respectively. Total N for low N input was
applied once at day 16. Nitrogen was applied as NH
4
NO
3
.
Analysis
Soil cores were sealed daily to allow gases to accumulate in the enclosed
headspace. After 1 h, two 5-ml gas samples were removed from the
headspace atmosphere using gas-tight Hamilton syringes. These samples
were analysed for N
2
O by gas chromatography. At harvest, plant shoots
were excised at the soil surface, and the soil core removed intact from the
microcosms. The soil adhering to the roots after shaking was defined as
rhizosphere soil, which typically represented a 1 mm thick layer on the root
surface. Samples of rhizosphere soil were recovered after washing the roots
in distilled water and filtering the combined root washing through a
membrane filter (0.45
m). Plant material was analysed for total dry weight
and total N uptake. Rhizosphere soil was analysed for total dry weight (oven
dry at 105
µ
C), ninhydrin N microbial biomass (Jorgensen and Brookes,
1990) and denitrification enzymatic activity (Smith and Tiedje, 1979).
The data were analysed by two-way ANOVA using the Genstat 4.0
Statistical Package. Significant main effects were separated with paired
Student's
t
-test (
P
< 0.05).
°
Results and Discussion
gN
2
O-N m
−2
h
−1
) recorded on day 1
in all treatments (Fig. 4.12.1) were probably associated with the disruption
The very high N
2
O fluxes (741-849
µ
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