Seasonal effects of liming irrigation an
Biol Fertil Soils (1992) 13:130-134
Biology and Fertility
~
Q Springer-Verlag 1992
Seasonal effects of liming, irrigation, and acid precipitation
on microbial biomass N in a spruce (Picea abies L.) forest soil
M. von Liitzow 1'2, L. Zeiles a, I. Scheunert 1, and J.C.G. Ottow 2
1GSF - Institut ftir r
Chemie, Ingolst~idter Landstr. 1, W-8042 Neuherberg, Federal Republic of Germany
Zlnstitut for Mikrobiologie und Landeskultur, Justus-Liebig-Universit~it Giessen, Senckenbergstr. 3, W-6300 Giessen, Federal Republic of Germany
Received September 29, 1991
Summary. Seasonal effects of liming, irrigation, and acid
precipitation on microbial biomass N and some physicochemical properties of different topsoil horizons in a
spruce forest (Picea abies L.) were measured throughout
one growing season. The highest biomass N was recorded
in autumn and spring in the upper soil horizons, while
the lowest values were obtained in summer and in deeper
horizons. The clearest differences between the different
soil treatments were apparent in autumn and in the upper
horizons. Liming increased the microbial biomass N
from 1.7~ of the total N content to 6.8% (Olfl layer)
and from 1% to 2~ of the total N content in the Of 2
layer. The main inorganic-N fraction in the deeper horizons was NO 3 . An increase in cation exchange capacity
was observed down to the Oh layer, while soil pH was only slightly higher in the Olft and Of 2 layers after liming.
The effects of irrigation were less marked. The microbial
biomass N increased from 1.7~ of total N to 4.8% in the
Olfl layer and from 1070 to 2% of total N in the Of 2 layer. In the Olfl layer an increase in C mineralization was
observed. Acid precipitation decreased the microbial biomass N in the upper horizons from 4.8% of total N to
1.8O7o in the Olft layer and from 2o70 to 0.5~ in the Of 2
layer. No significant changes in soil pH were observed,
but the decrease in cation exchange capacity may result
in a decrease in the proton buffering capacity in the near
future.
Key words: Microbial biomass N - Spruce forest - Acid
deposition - Irrigation - Liming - Carbon mineralization - Picea abies
Acid "rain" (precipitation and deposition by interception) may affect unfertilized terrestrial ecosystems by increasing the total proton acidity in the long term. Since
soil microorganisms have a major effect on the decomposition of organic matter and provide an important
Offprint requests to: M. von LtRzow
sink/source ("pool") for plant nutrients in soil, changes
in this biomass following acid deposition may have important feedback effects on biogeochemical features, particularly in topsoils. Since microbial cells undergo a rapid
turnover, the soil microbial biomass may be regarded as
a relatively sensitive and labile fraction of the total soil
organic matter. Thus, changes in the biomass within a relatively short period should reflect ecological stresses long
before they can be detected by chemical analysis
(Powlson and Brookes 1987). In the present work, we
studied the effects of anthropogenic treatments, such as
liming, irrigation, and acid precipitation, on microbial
biomass N and on major chemical and physical properties of the soil under a 76-year-old spruce forest (Picea
abies L.) over one growing season (1986).
Materials and methods
Site and sampling
The spruce forest selected (76-year-old Picea abies L.) was located in the
state forest district Aichach, "H6glwald" (540 m above sea level), near
Augsburg, Germany (Kreutzer and Bittersohl 1986). The climate is characterized by a mean annual precipitation of 800ram (May-July
290 ram) and a mean annual temperature of 7.3 ~ (May-July, 14~
The soil was classified as a weakly acid (pH 4) Parabrown earth (orthic
luvisol). The parent material was derived from fine sediment of the upper Miocene (Molasse) and is covered by thin loamy loess deposits of
Quaternary origin. The acid humus (moder) is about 5 cm thick. The
litter (1) horizon, 4 - 5 cm thick, contains less than 10070 fine humus. The
subhorizons Olf 1 and Of 2 contain partially decomposed litter residues
of moderately matted structure. The Oh horizon (about 0 - 1 cm) comprises very dark brown to black, well humified organic material, containing more than 70~ fine organic matter with a gradual smooth
boundary. The Ah horizon (5 - 10 cm) has a subangular structure with
very few roots. Four different plots, each of 2500 m 2, were designed: (1)
Control plot; (2) limed plot, with 4 t ha -1 of dolomite powder (5507o
CaCO3, 40~ MgCO3) distributed by hand on the surface of the litter
2 years (April 1984) before the measurements started; (3) plot irrigated
with tap water (pH -5.5) at the rate of 180 mm.ha -1 year -1 in 15 portions (12 mm per event) during the growing season (May-October), using a sprinkler system (Perrot, ZA 30); (4) plot with acid irrigation,
treated as for plot 3 except that the tap water adjusted to pH 2.7-2.8
with sulphuric acid.
131
At regular intervals (April 9, July 14 and September 15, 1986) seven
samples were collected from different points in plot, from the Olf~,
Of 2, Oh, and Ah horizons. The seven subsamples were carefully mixed,
homogenized, sieved (2 mm), and used in a fresh state for biomass N
determinations. Living roots, organic particles, and other fragments
were removed by hand-sorting.
Physicochemical characterization
Air-dried samples were analyzed by standard methods in most cases
(Schlichting and Blume 1966). Water-soluble organic C was determined
as described by Burford and Bremner (1975). To determine NH2-N
and NO3-N, 10 g of the air-dried material was extracted with 100 ml
1070 K2SO4 solution (Navone 1964). Total C and N were measured by
heat conduction, as described by Ehrenberger and Gorbach (1973). Airdried mixed samples were ground to a fine powder in a steel burr mill
(Retsch, Haan, Germany) and analyses performed on a Carlo Erba
(ELA 1106, Rodana, Milano, Italy) auto-analyser. To measure exchangeable cations 3 g (Olf t, Of 2 Oh horizons) of 5 g (Ah horizon) of
the air-dried material was shaken with 75 ml 1 M NH4C1 for 1 h and
the soil extract was analysed with an inductively coupled plasma atom
emission spectrometer (ICP-AES; Contro, Plasma Con S 35, Eching,
Munich, Germany). The H + concentration of each sample was calculated according to the program described by Prenzel (1982).
Measurements of biomass-N
Biomass-N was measured by the chloroform-fumigation extraction
method (Brookes et al. 1985b) and calculated from the relationship
B N = EN/0.54 where BN is biomas N and E N is total (inorganic and organic) N extracted by 0.5 M K2SO4from soil (immediately after fumigation) minus the amount extracted from a non-fumigated soil at the time
the fumigation commenced. For the biomass N determinations, fieldmoist samples of 50 g (Ah horizon), 25 g (Oh horizon), or 12.5 g (Olf l,
Of 2 horizons) oven-dry soil were fumigated with ethanol-free chloroform in desiccators (101itres). Each desiccator contained a beaker
(50 ml) with 50 ml alcohol-free CHC13 with a few (four) antibumping
granules and three beakers (500 ml) with soil (50 g, 25 g, or 12.5 g, respectively). The desiccator was evacuated until the CHC13 boiled vigorously (after 5 - 10 min). The tap was closed and the desiccator left in the
dark for 24 h. The soil was then extracted immediately with 0.5 M
K2SO4 (soil : solution, 1 : 4) for 30 min and filtered (Whatmann no. 42).
Unfumigated (control) soils were routinely extracted during the fumiga-
tion period. The extracts were frozen at - 2 0 ~ until analysis. A white
precipitate (probably CaSO 4) was recorded in some of the soil extracts
after thawing. This precipitate did not interfere with the N determination and no attempt was made to remove it. Total N in the K2SO4 extracts was measured after Kjeldahl digestion as described by Brookes et
al. (1985a). All results are means of seven replicate determinations expressed on an oven-dry soil basis (105 ~ 24 h). The statistical significance of differences was tested by analyses of variance and the Bonferroni t-test (Sachs 1984).
Results
Effects on chemcial an physical soil properties
Table 1 shows the effects of the different treatments on
the soil chemical and physical properties measured at the
end of the experiment (September 15, 1986). Only liming
increased the pH in the Olft and Ofz layers. A very small
pH decrease was observed after acid precipitation in the
Olfl layer in comparison with the irrigated plot. The cation exchange capacity generally increased after liming in
the Olfl, Of 2, and Oh layers (by about 190%, 170~ and
350/0, respectively). This increase may be attributed to an
increase in mineralization and humification. No changes
in cation exchange capacity were observed in the irrigated
plot. Acid precipitation decreased the cation exchange capacity in the Olfl layer by about 30~ and in the Ot'2 layer by approximately 20%. These decreases are hard to explain but they suggest that unfavorable changes took
place in the organic matter fractions over a relatively
short period.
Total C ranged between 40% (upper horizons) and
5% (deeper horizons). Water-soluble organic C also decreased continuously (to 50% in the Ah layer) within increasing soil depth. Except for the irrigated plot, the
highest values of water-soluble organic C were measured
Table 1. Effect of different treatments on soil physicochemical properties in different organic horizons of a Parabrown earth (orthic luvisol) under
Picea abies L. at the end of one growing season (autumn 1986)
Treatment
Control
Lime
Tap water
Acid
Horizon
Olf 1
Of 2
Oh
Ah
Olf 1
Of 2
Oh
Ah
Olf 1
Of2
Oh
Ah
Olf 1
Of2
Oh
Ah
HzO
(~
70.4
65.8
46.6
28.4
69.4
69.4
56.1
27.6
70.2
78.0
60.6
34.6
68.6
71.0
59.5
32.4
pH
(H20)
4.1
3.6
3.6
3.5
6.4
4.4
3.9
3.8
4.6
3.8
3.6
3.5
4.2
3.7
3.5
3.5
C
N
Ct
(%)
WS
(mgkg -1)
Nt
(%)
Nmin
(mgkg ~)
NO~(mgkg-')
NH~(mgkg -~)
42.7
36.2
17.4
5.6
36.5
36.0
12.4
3.8
45.0
34.2
I6.5
4.2
44.8
42.9
23.3
4.8
1020
1150
845
738
2420
2640
994
549
1079
1280
765
630
1276
1239
613
618
1.4
1.3
0.7
0.4
1.4
1.4
0.6
0.3
1.6
1.3
0.7
0.3
1.5
1.4
1.0
0.3
12.4
9.4
10.8
11.9
8.4
7.5
15.3
14.5
13.3
5.3
6.9
5.0
16.5
10.0
10.4
13.3
4.3
6.7
8.6
10.5
2.7
5.2
12.6
12.9
4.1
2.3
3.1
2.2
2.3
1.4
4.8
10.5
8.1
2.7
2.2
1.4
5.7
2.3
2.7
1.6
9.2
3.0
3.8
2.8
14.2
8.6
5.6
2.8
Ct, total C; WS, water-soluble; Nt, total N; Nmin, mineral N (NO~--N+ NH~--N); CEC, cation exchange capacity
C:N
CEC
(mEq 100 g - ~)
29.1
28.7
24.2
14.4
26.9
26.4
23.3
15.2
28.3
26.9
21.4
14.5
30.1
30.2
23.8
19.2
22
21
17
9
65
56
22
8
23
21
16
8
15
18
16
9
132
1000 ]
9
Olfl
C1 -A1
Spring
[ ] of 2
6OO
t
[ ] Oh
500
600 1
[ ] Ah
8oo /
"T
400 1
z
300
E
v
200
(:33
200 -
Z
~; lOO
~
0
'7
-
z
400
E
Z
200 -
,~
0
E
o
Summer
x~
._
o
~
tO
/
./
o/
_A
u ~ . ......
0""
-100
-200
-300 -
Autumn
- -
Olfl
----- Of 2
9 Spring
9 Summer
- - - Oh
.......... Ah
9 Autumn
\
\
9
Fig. 2. Increase or decrease in biomass N (mg N kg- l dry weight) of
various horizons as affected by different treatments (A1, control plot;
A2, limed plot; C1, plot irrigated with tap water, B1, plot treated with
acid precipitation) under a spruce forest (Picea abies L.) near Augsburg.
C1-A1, effect of irrigation; C1-B1, effect of proton input; A2-A1, effect of liming
8O0fl
600
/.
0
k~ -400 -
oE 1000
A2-A1
./
400
q
C1 -B1
-
400"
200-
Table 2. Biomass N as a percentage of total N in various horizons in
relation to soil treatment
0
A1
A2
Cl
B1
Fig. 1. Effect of different treatments on biomass N (mg Nkg -1 dry
weight) in different horizons of a Parabrown earth under spruce forest
(Picea abies L.) near Augsburg, measured in spring, summer, and autumn, 1986. The standard variation was smaller than 10%0in the Olfl,
Of2, and Oh horizons and smaller than 20% in the Ah layer
in the Of 2 layer, perhaps reflecting the more constant
moisture conditions compared with the O f t layer. Liming increased the water-soluble organic C in the upper
horizons (Olf l, Of 2) by about 130~ Total C decreased
weakly after liming in the Olfl layer. Irrigation and acid
precipitation had no clear effects on total C or water-soluble organic C.
Total N decreased with depth, from 1.4~ (Olf 1, O f 2)
to 0.7O/o (Oh) and 0.4O/o (Ah). No differences were observed a m o n g the four treatments. In deeper horizons.
NH~--N decreased and NO~--N increased. The mineral-N soil fraction (NH~--N + NO~--N) was mainly nitrate
after liming and increased in the deeper horizons (Oh,
40~
Ah, 20O7o) but decreased in the upper horizons
(Olfl, 47o7o; O f 2, 25O/o) in comparison with the control
plot. The irrigated plots had lower mineral-N contents
(50o7o) in the Of 2, Oh, and Ah horizons, perhaps due to
leaching of NO~- by irrigation. The acid precipitation
caused a small increase in mineral N in the Olf t layer
(33O7o). The acid-irrigated plot had slightly increased
C : N ratios.
E f f e c t s on b i o m a s s N
Figure 1 shows the effects of different treatments on biomass N in various horizons and seasons. Biomass N decreased significantly (P = 0.01) with soil depth. In comparison with Olfl, O f 2 contained about 50~ (all treat-
Horizon
Control
Lime
Irrigated
(tap water)
Acid
Olf1
o~
Oh
Ah
1.7
1.0
0.7
0.7
6.8
2.0
0.8
0.7
4.8
2.0
0.9
0.8
1.8
0.5
0.8
0.8
Measurements taken on 15 September 1986
ments), the Oh 30% and the Ah 20O/o of biomass N. The
overall seasonal effect as shown in the upper horizons
(Olfl, O f 2) was characterized by a decrease (not significant) in biomass N from April to July. However, a considerable increase was apparent after liming or irrigation,
particularly in September for the Olf I and O f 2 horizons.
A sharp decrease in biomass N was obvious in the plot
treated with acid precipitation in September (P = 0.05)
compared with the irrigated but not the control soil. The
Oh and Ah horizons had fairly uniform biomass N levels
for most of the year, but clear differences a m o n g the soil
treatments were recorded in the upper horizons
(P = 0.01) at the end of the year (autumn). Compared to
the control plot, biomass N increased in the limed plot by
about 200% in the Olf 1 layer and about 160% in the O f 2
horizon. Irrigation also increased biomass N compared
with the control plot, by about 150~ in the Olfi layer,
100~ in the Of 2 layer, and 50% in the Oh layer. Acid
precipitation increased biomass N slightly in comparison
with the control plot, but decreased it compared with the
irrigated horizons Olf I and Ot'2, by about 50O7o and 30o70,
respectively. Figure 2 summarizes the differences between
treatments.
Table 2 shows the relationship between biomass N and
total N in the various horizons and treatments. There
133
were significant changes by treatment and by horizon.
Liming increased biomass N from 1.7% to 6.8% of total
N in the Olfl layer and from 1% to 2~ in the Of 2 layer
whilew, irrigation increased it from 1.7% to 4.8~ in the
Olfl layer and from 1% to 2% in the Of 2 layer. In contrast acid irrigation decreased biomass N as a percentage
of total N, form 4.8% to 1.8% in the Olfl layer and
from 2% to 0.5% in the Of 2 layer.
Table 3 shows the relationship between biomass-N
and the soil physicochemical properties. Biomass N was
significantly and positively correlated with pH, water
content, cation exchange capacity, water-soluble organic
matter and the C : N ratio. The highest correlation coefficient was found for the relationship with pH.
Discussion
The proportion of N fixed in the microbial biomass ranged from 0.7% to 6.8% in the Olfl horizon of the limed
plot. A similar range of between 2% and 8% has been reported for other soils including forest soils (Anderson
and Domsch 1980; Azam et al. 1986). In the present
study, the biomass was significantly affected by liming,
irrigation and, eventually, acid precipitation.
Lime applied in 1984 resulted in a significant increase
in biomass N, but only in the Olfl (200%) and Of 2 layers
(160%). Cation exchange capacity clearly increased, even
at the depth of the Oh layer. A decrease in easily decomposable organic material may have been responsible for
this result. These findings are in agreement with results
reported by Mai and Fiedler (1979) and Lang and Beese
(1985). In contrast, Baath et al. (1980) reported a decrease in the biomass after liming, in spite of a strong increase in soil pH. The increase in water-soluble organic
matter found in the upper horizons of the limed plot in
the present study suggests that liming increased C mineralization. The weak reduction in total C in the Olfl
horizon of this plot may also have been a result of increased C mineralization, with an increase in the rate of
CO2 release and leaching of water-soluble organic matter. Accelerated C mineralization after liming has been reported previously (NOmmik 1978; Lohm et at. t984). The
mineral N fraction was mainly N O ; and the proportion
increased in the deeper horizons. This may indicate that
nitrification was stimulated (Baath et al. 1980; Lang and
Beese 1985). NH~--N decreased weakly in the upper horizons, perhaps due to a greater immobilization of N by
Table 3. Pearson's correlation coefficient between biomass N and soil
properties
pH (H20)
H20 (o70)
CEC (mEq 100 g - 1)
WSOM (mg k g - 1)
Total N (%)
Total C (%)
C:N
r
r
r
r
r
r
r
=
=
=
=
=
=
=
0.919'**
0.593 *** (n = 44)
0.721 ***
0.668 **
0.665 **
0.629**
0.510"
* P < 0 . 0 5 , * * P < 0 . 0 1 , ***P
Biology and Fertility
~
Q Springer-Verlag 1992
Seasonal effects of liming, irrigation, and acid precipitation
on microbial biomass N in a spruce (Picea abies L.) forest soil
M. von Liitzow 1'2, L. Zeiles a, I. Scheunert 1, and J.C.G. Ottow 2
1GSF - Institut ftir r
Chemie, Ingolst~idter Landstr. 1, W-8042 Neuherberg, Federal Republic of Germany
Zlnstitut for Mikrobiologie und Landeskultur, Justus-Liebig-Universit~it Giessen, Senckenbergstr. 3, W-6300 Giessen, Federal Republic of Germany
Received September 29, 1991
Summary. Seasonal effects of liming, irrigation, and acid
precipitation on microbial biomass N and some physicochemical properties of different topsoil horizons in a
spruce forest (Picea abies L.) were measured throughout
one growing season. The highest biomass N was recorded
in autumn and spring in the upper soil horizons, while
the lowest values were obtained in summer and in deeper
horizons. The clearest differences between the different
soil treatments were apparent in autumn and in the upper
horizons. Liming increased the microbial biomass N
from 1.7~ of the total N content to 6.8% (Olfl layer)
and from 1% to 2~ of the total N content in the Of 2
layer. The main inorganic-N fraction in the deeper horizons was NO 3 . An increase in cation exchange capacity
was observed down to the Oh layer, while soil pH was only slightly higher in the Olft and Of 2 layers after liming.
The effects of irrigation were less marked. The microbial
biomass N increased from 1.7~ of total N to 4.8% in the
Olfl layer and from 1070 to 2% of total N in the Of 2 layer. In the Olfl layer an increase in C mineralization was
observed. Acid precipitation decreased the microbial biomass N in the upper horizons from 4.8% of total N to
1.8O7o in the Olft layer and from 2o70 to 0.5~ in the Of 2
layer. No significant changes in soil pH were observed,
but the decrease in cation exchange capacity may result
in a decrease in the proton buffering capacity in the near
future.
Key words: Microbial biomass N - Spruce forest - Acid
deposition - Irrigation - Liming - Carbon mineralization - Picea abies
Acid "rain" (precipitation and deposition by interception) may affect unfertilized terrestrial ecosystems by increasing the total proton acidity in the long term. Since
soil microorganisms have a major effect on the decomposition of organic matter and provide an important
Offprint requests to: M. von LtRzow
sink/source ("pool") for plant nutrients in soil, changes
in this biomass following acid deposition may have important feedback effects on biogeochemical features, particularly in topsoils. Since microbial cells undergo a rapid
turnover, the soil microbial biomass may be regarded as
a relatively sensitive and labile fraction of the total soil
organic matter. Thus, changes in the biomass within a relatively short period should reflect ecological stresses long
before they can be detected by chemical analysis
(Powlson and Brookes 1987). In the present work, we
studied the effects of anthropogenic treatments, such as
liming, irrigation, and acid precipitation, on microbial
biomass N and on major chemical and physical properties of the soil under a 76-year-old spruce forest (Picea
abies L.) over one growing season (1986).
Materials and methods
Site and sampling
The spruce forest selected (76-year-old Picea abies L.) was located in the
state forest district Aichach, "H6glwald" (540 m above sea level), near
Augsburg, Germany (Kreutzer and Bittersohl 1986). The climate is characterized by a mean annual precipitation of 800ram (May-July
290 ram) and a mean annual temperature of 7.3 ~ (May-July, 14~
The soil was classified as a weakly acid (pH 4) Parabrown earth (orthic
luvisol). The parent material was derived from fine sediment of the upper Miocene (Molasse) and is covered by thin loamy loess deposits of
Quaternary origin. The acid humus (moder) is about 5 cm thick. The
litter (1) horizon, 4 - 5 cm thick, contains less than 10070 fine humus. The
subhorizons Olf 1 and Of 2 contain partially decomposed litter residues
of moderately matted structure. The Oh horizon (about 0 - 1 cm) comprises very dark brown to black, well humified organic material, containing more than 70~ fine organic matter with a gradual smooth
boundary. The Ah horizon (5 - 10 cm) has a subangular structure with
very few roots. Four different plots, each of 2500 m 2, were designed: (1)
Control plot; (2) limed plot, with 4 t ha -1 of dolomite powder (5507o
CaCO3, 40~ MgCO3) distributed by hand on the surface of the litter
2 years (April 1984) before the measurements started; (3) plot irrigated
with tap water (pH -5.5) at the rate of 180 mm.ha -1 year -1 in 15 portions (12 mm per event) during the growing season (May-October), using a sprinkler system (Perrot, ZA 30); (4) plot with acid irrigation,
treated as for plot 3 except that the tap water adjusted to pH 2.7-2.8
with sulphuric acid.
131
At regular intervals (April 9, July 14 and September 15, 1986) seven
samples were collected from different points in plot, from the Olf~,
Of 2, Oh, and Ah horizons. The seven subsamples were carefully mixed,
homogenized, sieved (2 mm), and used in a fresh state for biomass N
determinations. Living roots, organic particles, and other fragments
were removed by hand-sorting.
Physicochemical characterization
Air-dried samples were analyzed by standard methods in most cases
(Schlichting and Blume 1966). Water-soluble organic C was determined
as described by Burford and Bremner (1975). To determine NH2-N
and NO3-N, 10 g of the air-dried material was extracted with 100 ml
1070 K2SO4 solution (Navone 1964). Total C and N were measured by
heat conduction, as described by Ehrenberger and Gorbach (1973). Airdried mixed samples were ground to a fine powder in a steel burr mill
(Retsch, Haan, Germany) and analyses performed on a Carlo Erba
(ELA 1106, Rodana, Milano, Italy) auto-analyser. To measure exchangeable cations 3 g (Olf t, Of 2 Oh horizons) of 5 g (Ah horizon) of
the air-dried material was shaken with 75 ml 1 M NH4C1 for 1 h and
the soil extract was analysed with an inductively coupled plasma atom
emission spectrometer (ICP-AES; Contro, Plasma Con S 35, Eching,
Munich, Germany). The H + concentration of each sample was calculated according to the program described by Prenzel (1982).
Measurements of biomass-N
Biomass-N was measured by the chloroform-fumigation extraction
method (Brookes et al. 1985b) and calculated from the relationship
B N = EN/0.54 where BN is biomas N and E N is total (inorganic and organic) N extracted by 0.5 M K2SO4from soil (immediately after fumigation) minus the amount extracted from a non-fumigated soil at the time
the fumigation commenced. For the biomass N determinations, fieldmoist samples of 50 g (Ah horizon), 25 g (Oh horizon), or 12.5 g (Olf l,
Of 2 horizons) oven-dry soil were fumigated with ethanol-free chloroform in desiccators (101itres). Each desiccator contained a beaker
(50 ml) with 50 ml alcohol-free CHC13 with a few (four) antibumping
granules and three beakers (500 ml) with soil (50 g, 25 g, or 12.5 g, respectively). The desiccator was evacuated until the CHC13 boiled vigorously (after 5 - 10 min). The tap was closed and the desiccator left in the
dark for 24 h. The soil was then extracted immediately with 0.5 M
K2SO4 (soil : solution, 1 : 4) for 30 min and filtered (Whatmann no. 42).
Unfumigated (control) soils were routinely extracted during the fumiga-
tion period. The extracts were frozen at - 2 0 ~ until analysis. A white
precipitate (probably CaSO 4) was recorded in some of the soil extracts
after thawing. This precipitate did not interfere with the N determination and no attempt was made to remove it. Total N in the K2SO4 extracts was measured after Kjeldahl digestion as described by Brookes et
al. (1985a). All results are means of seven replicate determinations expressed on an oven-dry soil basis (105 ~ 24 h). The statistical significance of differences was tested by analyses of variance and the Bonferroni t-test (Sachs 1984).
Results
Effects on chemcial an physical soil properties
Table 1 shows the effects of the different treatments on
the soil chemical and physical properties measured at the
end of the experiment (September 15, 1986). Only liming
increased the pH in the Olft and Ofz layers. A very small
pH decrease was observed after acid precipitation in the
Olfl layer in comparison with the irrigated plot. The cation exchange capacity generally increased after liming in
the Olfl, Of 2, and Oh layers (by about 190%, 170~ and
350/0, respectively). This increase may be attributed to an
increase in mineralization and humification. No changes
in cation exchange capacity were observed in the irrigated
plot. Acid precipitation decreased the cation exchange capacity in the Olfl layer by about 30~ and in the Ot'2 layer by approximately 20%. These decreases are hard to explain but they suggest that unfavorable changes took
place in the organic matter fractions over a relatively
short period.
Total C ranged between 40% (upper horizons) and
5% (deeper horizons). Water-soluble organic C also decreased continuously (to 50% in the Ah layer) within increasing soil depth. Except for the irrigated plot, the
highest values of water-soluble organic C were measured
Table 1. Effect of different treatments on soil physicochemical properties in different organic horizons of a Parabrown earth (orthic luvisol) under
Picea abies L. at the end of one growing season (autumn 1986)
Treatment
Control
Lime
Tap water
Acid
Horizon
Olf 1
Of 2
Oh
Ah
Olf 1
Of 2
Oh
Ah
Olf 1
Of2
Oh
Ah
Olf 1
Of2
Oh
Ah
HzO
(~
70.4
65.8
46.6
28.4
69.4
69.4
56.1
27.6
70.2
78.0
60.6
34.6
68.6
71.0
59.5
32.4
pH
(H20)
4.1
3.6
3.6
3.5
6.4
4.4
3.9
3.8
4.6
3.8
3.6
3.5
4.2
3.7
3.5
3.5
C
N
Ct
(%)
WS
(mgkg -1)
Nt
(%)
Nmin
(mgkg ~)
NO~(mgkg-')
NH~(mgkg -~)
42.7
36.2
17.4
5.6
36.5
36.0
12.4
3.8
45.0
34.2
I6.5
4.2
44.8
42.9
23.3
4.8
1020
1150
845
738
2420
2640
994
549
1079
1280
765
630
1276
1239
613
618
1.4
1.3
0.7
0.4
1.4
1.4
0.6
0.3
1.6
1.3
0.7
0.3
1.5
1.4
1.0
0.3
12.4
9.4
10.8
11.9
8.4
7.5
15.3
14.5
13.3
5.3
6.9
5.0
16.5
10.0
10.4
13.3
4.3
6.7
8.6
10.5
2.7
5.2
12.6
12.9
4.1
2.3
3.1
2.2
2.3
1.4
4.8
10.5
8.1
2.7
2.2
1.4
5.7
2.3
2.7
1.6
9.2
3.0
3.8
2.8
14.2
8.6
5.6
2.8
Ct, total C; WS, water-soluble; Nt, total N; Nmin, mineral N (NO~--N+ NH~--N); CEC, cation exchange capacity
C:N
CEC
(mEq 100 g - ~)
29.1
28.7
24.2
14.4
26.9
26.4
23.3
15.2
28.3
26.9
21.4
14.5
30.1
30.2
23.8
19.2
22
21
17
9
65
56
22
8
23
21
16
8
15
18
16
9
132
1000 ]
9
Olfl
C1 -A1
Spring
[ ] of 2
6OO
t
[ ] Oh
500
600 1
[ ] Ah
8oo /
"T
400 1
z
300
E
v
200
(:33
200 -
Z
~; lOO
~
0
'7
-
z
400
E
Z
200 -
,~
0
E
o
Summer
x~
._
o
~
tO
/
./
o/
_A
u ~ . ......
0""
-100
-200
-300 -
Autumn
- -
Olfl
----- Of 2
9 Spring
9 Summer
- - - Oh
.......... Ah
9 Autumn
\
\
9
Fig. 2. Increase or decrease in biomass N (mg N kg- l dry weight) of
various horizons as affected by different treatments (A1, control plot;
A2, limed plot; C1, plot irrigated with tap water, B1, plot treated with
acid precipitation) under a spruce forest (Picea abies L.) near Augsburg.
C1-A1, effect of irrigation; C1-B1, effect of proton input; A2-A1, effect of liming
8O0fl
600
/.
0
k~ -400 -
oE 1000
A2-A1
./
400
q
C1 -B1
-
400"
200-
Table 2. Biomass N as a percentage of total N in various horizons in
relation to soil treatment
0
A1
A2
Cl
B1
Fig. 1. Effect of different treatments on biomass N (mg Nkg -1 dry
weight) in different horizons of a Parabrown earth under spruce forest
(Picea abies L.) near Augsburg, measured in spring, summer, and autumn, 1986. The standard variation was smaller than 10%0in the Olfl,
Of2, and Oh horizons and smaller than 20% in the Ah layer
in the Of 2 layer, perhaps reflecting the more constant
moisture conditions compared with the O f t layer. Liming increased the water-soluble organic C in the upper
horizons (Olf l, Of 2) by about 130~ Total C decreased
weakly after liming in the Olfl layer. Irrigation and acid
precipitation had no clear effects on total C or water-soluble organic C.
Total N decreased with depth, from 1.4~ (Olf 1, O f 2)
to 0.7O/o (Oh) and 0.4O/o (Ah). No differences were observed a m o n g the four treatments. In deeper horizons.
NH~--N decreased and NO~--N increased. The mineral-N soil fraction (NH~--N + NO~--N) was mainly nitrate
after liming and increased in the deeper horizons (Oh,
40~
Ah, 20O7o) but decreased in the upper horizons
(Olfl, 47o7o; O f 2, 25O/o) in comparison with the control
plot. The irrigated plots had lower mineral-N contents
(50o7o) in the Of 2, Oh, and Ah horizons, perhaps due to
leaching of NO~- by irrigation. The acid precipitation
caused a small increase in mineral N in the Olf t layer
(33O7o). The acid-irrigated plot had slightly increased
C : N ratios.
E f f e c t s on b i o m a s s N
Figure 1 shows the effects of different treatments on biomass N in various horizons and seasons. Biomass N decreased significantly (P = 0.01) with soil depth. In comparison with Olfl, O f 2 contained about 50~ (all treat-
Horizon
Control
Lime
Irrigated
(tap water)
Acid
Olf1
o~
Oh
Ah
1.7
1.0
0.7
0.7
6.8
2.0
0.8
0.7
4.8
2.0
0.9
0.8
1.8
0.5
0.8
0.8
Measurements taken on 15 September 1986
ments), the Oh 30% and the Ah 20O/o of biomass N. The
overall seasonal effect as shown in the upper horizons
(Olfl, O f 2) was characterized by a decrease (not significant) in biomass N from April to July. However, a considerable increase was apparent after liming or irrigation,
particularly in September for the Olf I and O f 2 horizons.
A sharp decrease in biomass N was obvious in the plot
treated with acid precipitation in September (P = 0.05)
compared with the irrigated but not the control soil. The
Oh and Ah horizons had fairly uniform biomass N levels
for most of the year, but clear differences a m o n g the soil
treatments were recorded in the upper horizons
(P = 0.01) at the end of the year (autumn). Compared to
the control plot, biomass N increased in the limed plot by
about 200% in the Olf 1 layer and about 160% in the O f 2
horizon. Irrigation also increased biomass N compared
with the control plot, by about 150~ in the Olfi layer,
100~ in the Of 2 layer, and 50% in the Oh layer. Acid
precipitation increased biomass N slightly in comparison
with the control plot, but decreased it compared with the
irrigated horizons Olf I and Ot'2, by about 50O7o and 30o70,
respectively. Figure 2 summarizes the differences between
treatments.
Table 2 shows the relationship between biomass N and
total N in the various horizons and treatments. There
133
were significant changes by treatment and by horizon.
Liming increased biomass N from 1.7% to 6.8% of total
N in the Olfl layer and from 1% to 2~ in the Of 2 layer
whilew, irrigation increased it from 1.7% to 4.8~ in the
Olfl layer and from 1% to 2% in the Of 2 layer. In contrast acid irrigation decreased biomass N as a percentage
of total N, form 4.8% to 1.8% in the Olfl layer and
from 2% to 0.5% in the Of 2 layer.
Table 3 shows the relationship between biomass-N
and the soil physicochemical properties. Biomass N was
significantly and positively correlated with pH, water
content, cation exchange capacity, water-soluble organic
matter and the C : N ratio. The highest correlation coefficient was found for the relationship with pH.
Discussion
The proportion of N fixed in the microbial biomass ranged from 0.7% to 6.8% in the Olfl horizon of the limed
plot. A similar range of between 2% and 8% has been reported for other soils including forest soils (Anderson
and Domsch 1980; Azam et al. 1986). In the present
study, the biomass was significantly affected by liming,
irrigation and, eventually, acid precipitation.
Lime applied in 1984 resulted in a significant increase
in biomass N, but only in the Olfl (200%) and Of 2 layers
(160%). Cation exchange capacity clearly increased, even
at the depth of the Oh layer. A decrease in easily decomposable organic material may have been responsible for
this result. These findings are in agreement with results
reported by Mai and Fiedler (1979) and Lang and Beese
(1985). In contrast, Baath et al. (1980) reported a decrease in the biomass after liming, in spite of a strong increase in soil pH. The increase in water-soluble organic
matter found in the upper horizons of the limed plot in
the present study suggests that liming increased C mineralization. The weak reduction in total C in the Olfl
horizon of this plot may also have been a result of increased C mineralization, with an increase in the rate of
CO2 release and leaching of water-soluble organic matter. Accelerated C mineralization after liming has been reported previously (NOmmik 1978; Lohm et at. t984). The
mineral N fraction was mainly N O ; and the proportion
increased in the deeper horizons. This may indicate that
nitrification was stimulated (Baath et al. 1980; Lang and
Beese 1985). NH~--N decreased weakly in the upper horizons, perhaps due to a greater immobilization of N by
Table 3. Pearson's correlation coefficient between biomass N and soil
properties
pH (H20)
H20 (o70)
CEC (mEq 100 g - 1)
WSOM (mg k g - 1)
Total N (%)
Total C (%)
C:N
r
r
r
r
r
r
r
=
=
=
=
=
=
=
0.919'**
0.593 *** (n = 44)
0.721 ***
0.668 **
0.665 **
0.629**
0.510"
* P < 0 . 0 5 , * * P < 0 . 0 1 , ***P