Agriculture Reference
In-Depth Information
Table 4.3.1.
Nitrogen input-output budget (mg N m
−
2
) for the leached soil cores.
Input in rain
Output in leachate
Net retention/loss of N
Cores
±
vegetation
1
Net TDN
leached
3
NH
4
+
NO
3
−
NH
4
+
NO
3
−
DON
NH
4
+
NO
3
−
Min. N
2
6.5
°
C+
149
90
10
a
198
a
237
a
−
139
a
108
a
−
31
a
206
a
6.5
°
C
−
149
90
11
a
290
a
63
b
−
138
a
200
a
−
62
b
125
a
15
°
C+
149
90
17
a
419
b
230
a
−
132
a
329
b
197
c
427
b
15
°
C
−
149
90
8
a
555
b
52
b
−
141
a
465
b
324
d
376
b
Means within the same column followed by a common letter are not significantly different
(P< 0.05).
1
+ = with vegetation and
−
= no vegetation.
2
Min = mineral N (NH
4
+
+ NO
3
−
).
3
TDN = total dissolved nitrogen.
The DON flux from the soil cores displayed a contrasting pattern to the
inorganic N flux. The DON flux was approximately four times larger from
the cores with than without vegetation, and temperature appeared to have
no influence upon the flux (Table 4.3.1). Thus, although the net inorganic
N flux was larger from the cores without vegetation, the net TDN flux was
larger from the cores with vegetation at both temperatures. In addition, the
amount of DON, and DOC, leached from the cores with vegetation was
similar regardless of whether net N immobilization or net N mineralization
was occurring within the soil (Table 4.3.1).
Discussion
Origin of DON
In the incubation experiment, the relative sizes of the DON and mineral
N pools initially were very similar, yet during incubation net mineralization
was observed at all temperatures, whereas the DON pool size varied little
over the 8-week incubation experiment and showed little response to tem-
perature. Thus, there was no apparent accumulation or depletion of DON
over the course of the incubation study. Other studies have found that
DON, extracted with 0.01 M CaCl
2
, remained relatively constant during
incubation while mineral N increased linearly (e.g. Appel and Mengel,
1990). For this to occur, the DON pool may be maintained by and in equi-
librium with a large reserve of organic N. The rate of transfer between these
pools
would
need
to
be
comparable
with
the
sum
of
the
rates
of
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