Changes in microbial and soil properties

Soil Biology & Biochemistry 34 (2002) 403±412
www.elsevier.com/locate/soilbio

Changes in microbial and soil properties following compost treatment of
degraded temperate forest soils
W. Borken*, A. Muhs, F. Beese
Institute of Soil Science and Forest Nutrition, University of GoÈttingen, BuÈsgenweg 2, 37077 GoÈttingen, Germany
Received 13 March 2001; received in revised form 3 September 2001; accepted 25 September 2001

Abstract
The long-term effect of compost treatment on soil microbial respiration, microbial biomass carbon (Cmic) and biomass nitrogen (Nmic), soil
organic carbon (SOC), and soil total nitrogen (STN) was studied in six degraded forests, Lower Saxony, Germany. The study was conducted
in mature beech (Fagus sylvatica L.), pine (Pinus sylvestris L.) and spruce (Picea abies Karst.) forests on silty soils at Solling and on sandy
soils at UnterluÈû. Mature compost from separately collected organic household waste was applied for soil amelioration at an amount of
6.3 kg m 22 on the soil surface. After 2 years, soil samples were taken from the control and compost plots and were separated into .2 and
,2 mm fractions of the O-horizon and into mineral soil intervals from 0±5, 5±10, and 10±20 cm depths. The original compost had a pH of
7.5, high inorganic salt content, low organic C content, narrow C-to-N ratio, and low microbial activity and biomass. Compost signi®cantly
reduced the microbial respiration per mass unit in the O-horizons .2 mm by 17% and in the O-horizons ,2 mm by 25%. Cmic and Nmic
decreased signi®cantly by 22 and 23% in the O-horizons ,2 mm and by 35 and 28% in the O-horizons .2 mm, respectively. Our estimates
suggest that the reduction in microbial respiration and biomass in the O-horizons resulted partly from the mixture of compost and the Ohorizons. The average loss of 1.2 kg m 22 organic matter may have also contributed to the reduction in microbial biomass and respiration in
the O-horizons of the compost plots. However, it is not clear whether the decomposition of the original organic matter in the O-horizons was

increased by the compost application. In the mineral soils, the compost treatment caused signi®cant increases in microbial respiration, Cmic
and Nmic by 14±21% at 0±5 cm and by 14±23% at 10±20 cm depth. Although not signi®cant, a similar trend was found for the 5±10 cm
depth. Increased release of nutrients and dissolved organic matter (DOM) could have promoted microbial growth and activity in the mineral
soils. The signi®cant increase in STN and the narrowing C-to-N ratio indicate that the investigated forest soils were not N-saturated. This
®eld study suggests that super®cial application of compost from separately collected organic household waste increase microbial activity and
biomass in the mineral soil by release of nutrients from the O-horizon to the mineral soil. q 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Amelioration; Compost; Microbial biomass; Microbial respiration; Temperate forests

1. Introduction
Excessive removal of biomass in past centuries and high
atmospheric proton and N loads in recent decades caused a
strong degradation and nutrient imbalance in many forest
soils in Central Europe (Ulrich, 1994). During this longterm degradation, the incorporation of organic matter by
soil burrowing organisms has been reduced in the upper
mineral soil. Moreover, acid precipitation decreased the
microbial biomass and C mineralization in the O-horizon
of beech forests (Wolters, 1991), pine forests (Baath et al.,
1980) and spruce forests (Zelles et al., 1987; von LuÈtzow et
* Corresponding author. Address: The Woods Hole Research Center,
P.O. Box 296, Woods Hole, MA 02543, USA. Tel.: 11-508-540-9375152; fax: 11-508-548-5633.

E-mail address: wborken@whrc.org (W. Borken).

al., 1992). Thus, soil acidi®cation has probably contributed
to the accumulation of organic matter and nutrients in the
forest ¯oor.
To counteract soil acidi®cation and nutrient imbalances
various treatments such as liming, wood ash application,
phosphorus and potassium fertilization have been performed in many degraded forests of Central Europe. Liming
and wood ash application to the soil surface raise the soil pH
of the forest ¯oor, improve base saturation, and decrease the
amount of Al 31 in soil solution. Besides the chemical
improvements, these practices generally increase the microbial biomass and activity in the O-horizon of degraded
forest soils (Zelles et al., 1990; Baath and Arnebrant,
1994; Smolander et al., 1994).
Little is known about the effect of organic fertilizers,
such as compost, on microbial biomass and activity in
degraded forest soils. In recent years, the separation of

0038-0717/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0038-071 7(01)00201-2

404

81
16
4
7.5
837
8.4

54

74
23
3
8.6
837
8.4

90

77
16
8
12.7
837
8.4

131

39
46
15
12.4
900
7.5

103

14

58
28
10.1
1038
7.2

115

27
54
19
9.0
1038
7.2

150

Mean annual
rainfall (l m 22)
Mean annual

temperature (8C)

organic household waste and the use of new composting
technologies have improved the compost quality (Ammar,
1996) and increased the amount of compost in some
European countries. Therefore compost may be used not
only in agriculture, horticulture, landscape conservation
and reclamation of mining areas but also for amelioration
of degraded forest soils (Borken and Beese, 2000). Guerrero
et al. (2000) found increased bacteria and fungal populations and improved stability of soil aggregates when
municipal solid waste compost was applied to burnt forest
soils. The authors pointed out that compost addition is a
suitable technique for accelerating the natural recovery
process of burnt soils. However, the release of nutrients
and the effect on the autochthon microbial community of
forest soils may vary with the maturity, chemical composition and amount of compost. Certainly, the microbial
community of compost and forest soils is different and,
therefore, the competition between species may affect the
decomposition of organic matter.
To study the application of mature compost from organic

household waste in degraded forest soils, a long-term
experiment was set up at six forest sites. We chose beech,
pine and spruce stands on silty soils at Solling and on sandy
soils at UnterluÈû. In the present study we focus on the investigation of microbial respiration, Cmic and Nmic in the Ohorizons and in the upper mineral soil 2 years after compost
was applied to the soil surface. Additionally, changes in soil
organic carbon (SOC) and soil total nitrogen (STN) were
related to microbial properties. We hypothesized that the
application of compost would increase the microbial
respiration, Cmic and Nmic in the upper mineral soil due to
increase of pH in soil solution and the release of nutrients
and dissolved organic carbon from the compost in the long
term. Limited nutrients such as phosphorus may stimulate
the growth and activity of microorganisms.

2. Materials and methods

Elevation
(m)

504

508

270

117

115

110

Geographical
location

51846 0 N, 9835 0 E

51846 0 N, 9834 0 E

51834 0 N, 9840 0 E

52850 0 N, 10818 0 E

52850 0 N, 10817 0 E

52850 0 N, 10816 0 E

SB Solling
beech
SS Solling
spruce
SP Solling
pine
UB UnterluÈb
beech
US UnterluÈb
spruce
UP UnterluÈb
pine

2.1. Sites

Site

Table 1
Some characteristics of the study sites

Stand age
(year)

O-horizon
(kg m 22)

Clay content
(%)

Silt content
(%)

Sand content
(%)

W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412

The experiment was carried out in beech (Fagus sylvatica), spruce (Picea abies) and pine stands (Pinus sylvestris)
at Solling and at UnterluÈû in Lower Saxony, Germany
(Table 1). All sites are characterized by strong soil acidi®cation with a base saturation of less than 10% in the soil
pro®le from 5 cm down to 100 cm depth. Aluminum is the
dominating exchangeable cation of the soil matrix. Recently
lime applications were used to alter the pH in the O-horizon,
and increased the base saturation of the mineral soil at 0±
5 cm depth. Further chemical properties of the O-horizons
and the mineral soils are given in Tables 2 and 3, respectively.
The 150-year beech stand (SB) and the 115-year spruce
stand (SS) at the Solling plateau above 500 m elevation have
a mean annual air temperature of 7.2 8C and an annual
precipitation of 1038 mm, evenly distributed throughout

405

W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412
Table 2
Properties of the amended compost and the O-horizon layers from the control plots in 1997
Horizon

Site

Compost

pH (KCl)

Organic C (mg g 21)

N (mg g 21)

P (mg g 21)

S (mg g 21)

Na (mg g 21)

K (mg g 21)

M (mg g 21)

Ca (mg g 21)

7.5

217

22.8

4.0

2.9

3.6

10.7

4.8

27.6

L

SB
SS
SP
UB
US
UP

±
±
±
±
±
±

507
503
470
461
497
510

14.6
15.2
14.3
12.1
13.0
17.5

0.8
0.8
0.6
0.7
0.6
1.2

1.2
1.2
1.5
1.1
1.1
1.2

0.1
0.1
0.1
0.1
0.1
0.1

1.1
1.7
1.1
1.1
0.9
3.2

1.0
0.6
2.3
1.5
0.5
0.9

10.0
3.9
12.4
12.0
4.7
3.7

F

SB
SS
SP
UB
US
UP

±
±
±
±
±
±

417
387
363
447
446
458

16.1
15.2
14.5
15.1
16.7
18.4

0.8
0.8
0.8
0.8
0.8
0.7

1.7
2.1
2.1
1.5
2.0
2.2

0.1
0.2
0.2
0.1
0.1
0.1

1.3
1.3
1.6
1.0
0.9
0.8

16.2
29.6
5.6
2.2
2.2
1.2

34.0
55.3
13.9
11.9
8.5
3.9

H

SB
SS
SP
UB
US
UP

4.5
3.6
±
3.3
2.9
2.6

226
341
±
344
358
324

10.3
13.3
±
14.3
12.2
12.3

0.7
0.8
±
0.6
0.5
0.5

1.7
1.9
±
1.8
1.5
1.6

0.2
0.2
±
0.1
0.1
0.1

2.5
3.6
±
0.8
0.9
0.6

32.0
8.7
±
1.9
1.1
0.4

56.0
16.2
±
4.1
4.0
1.9

the year. The 103-year pine stand at Solling (SP) was
located at an elevation of 270 m and has a mean annual
temperature of 7.5 8C and an annual precipitation of
900 mm. The soils of these sites developed on 30±80 cm
thick soli¯uction deposits, overlaying weathered Triassic
Sandstone. Texture of the soils at 0±20 cm depth was
dominated by the silt fraction (46±58%) with varying clay
and sand contents. According to the FAO classi®cation
(FAO, 1998), the soils of the stands were classi®ed as
well-drained (SP) to poorly-drained (SS) dystric Cambisols
with a moder-type O-horizon. Considerable amounts of

organic matter in the range of 9.0±12.4 kg m 22 are stored
in the 5±8 cm thick O-horizon in the stands at Solling
(Table 1).
The 131-year beech (UB), the 90-year spruce (US) and
the 54-year pine stand (UP) at UnterluÈû were located close
to each other at an elevation above 110 m (Table 1). The
long-term average of mean annual air temperature is 8.4 8C
and the mean annual precipitation is 837 mm. The soils are
developed from ¯uvio-glacial sand and gravel deposited
beyond a terminal moraine during the Warthe-stadium of
the Saale/Riss ice age. The soils contain about 74±81%

Table 3
Physical and chemical properties of the mineral soils from the control plots in 1997
Depth (cm)

Site

Bulk density (g cm 23)

pH (CaCl2)

CEC (mmol kg 21)

0±5

SB
SS
SP
UB
US
UP

1.16
1.00
1.17
1.32
1.42
1.19

3.75
3.34
3.27
3.20
3.05
2.79

104
180
86
49
57
60

5±10

SB
SS
SP
UB
US
UP

1.30
1.17
1.40
1.35
1.59
1.32

3.81
3.25
3.68
3.61
3.44
2.91

76
140
52
48
33
44

10±20

SB
SS
SP
UB
US
UP

1.31
1.20
1.24
1.41
1.60
1.23

4.01
3.70
4.05
4.03
4.15
4.32

58
101
34
34
18
45

406

W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412

sand, 16±23% silt and 3±8% clay at 0±20 cm depth. The
soils have been classi®ed as well-drained dystric Cambisol
(FAO, 1998) with moder-type O-horizons. The beech stand
(UB) had no ground vegetation and stored 12.7 kg m 22
organic matter in the 6±9 cm thick O-horizon (Table 1).
The spruce stand (US) and the pine stand (UP) stored 8.6
and 7.5 kg m 22 organic matter in the O-horizon, respectively. The pine stand had a dense cover of grass and
Vaccinium species.
2.2. Experimental design and sampling
At all study sites, three control and treatment plots, each
of 27 m 2, were established within a fenced area of 500 m 2.
At each compost plot 6.3 kg m 22 of sieved (,10 mm)
mature compost (Fertigkompost, Umweltschutz Nord,
Ganderkesee, Germany) was applied to the soil surface in
the summer of 1997. The compost was produced from
separately collected organic household waste consisting
mainly of plant residues, wood shavings and to a lesser
extent of leftovers. The compost had a bulk density of
0.42 g cm 3, with 83% being ,2 mm. The thickness of the
compost layer applied to the soil surface was 1.5 cm.
Because of the maturation during the composting process
the compost had a low C content of 217 g kg 21 (Table 2)
and a narrow C-to-N ratio of 9.5. The compost provided
higher N, P, S, Na, K, Mg and Ca contents than the Ohorizons of the study sites. At the time of application, the
compost contained a large inorganic salt fraction of
13 g kg 21. After 2 years the compost was partly mixed
with the O-horizon due to soil organisms such as epigeic
earthworms. In May 1999, two soil cores of 10 cm in
diameter were taken from each control and compost plot
to a depth of 30 cm and were separated into the O-horizon,
0±5, 5±10, and 10±20 cm soil depth, for analysis of chemical and microbial properties.
2.3. Chemical and microbial analysis
The O-horizons from the control and compost plots were
separated into two fractions of .2 and ,2 mm by handpicking and sieving. The fraction ,2 mm amounted to 54±92%
(control plots) and 68±96% (compost plots) of the total Ohorizon. Both fractions from the compost plots included
compost particles but the portion is unknown and may
have varied within and among the plots. The mineral soil
cores were passed through a 2 mm sieve. Subsamples were
dried and homogenized for analysis of organic C and total N
which were measured after combustion with an Carlo Erba
C/N analyzer. For microbial analysis, the soil samples were
adjusted to 50 ^ 5% of water-holding capacity and were
stored for over 4 weeks at 4 8C. Water-holding capacity
ranged from 150 to 450% in the O-horizon material and
from 20 to 90% in the mineral soils. All samples were
incubated for 24 h at 22 8C before microbiological measurements. Microbial respiration of soil samples was determined
as CO2 production at 22 8C using air-tight jars, which were

connected to an automated gaschromatograph equipped
with an electron capture detector (Loft®eld et al., 1997).
CO2 concentration was measured after closure of jars and
after 6 h of incubation.
Cmic and Nmic were measured by fumigation±extraction
(Brookes et al., 1985; Vance et al., 1987). One part of soil
samples, i.e. 5 g of O-horizon material and 25 g of mineral
soil, were extracted with 60 ml 0.5 M K2SO4 for 30 min
on an oscillating shaker at 250 rev min 21 and ®ltered
(Schleicher & Schuell 595 1/2, Dassel, Germany). The
other part was fumigated with methanol-free CHCl3
(Merck, Darmstadt, Germany) for 24 h at 25 8C. The fumigant was removed and the soil then extracted as described
before. Organic carbon was measured after ultravioletpersulphate oxidation to CO2 by infrared detection using a
Dohrman DC 80 automated system (Wu et al., 1990). Cmic
was estimated from the relationship EC/kEC, where EC is
[(organic C extracted from fumigated soil) minus (organic
C extracted from non-fumigated soil)] and kEC ˆ 0:45 (Wu
et al., 1990; Joergensen, 1996). The N contents of the
extracts were determined by a digesting process with UV
radiation in a continuous ¯ow system (Skalar, Erkelenz).
Nmic was estimated from the relationship EN/kEN, where EN
is [(organic N extracted from fumigated soil) minus (organic
N extracted from non-fumigated soil)] and kEN ˆ 0:54
(Brookes et al., 1985; Joergensen and Mueller, 1996). Initial
microbial respiration and microbial biomass C of original
compost samples …n ˆ 6† were measured in August 1997 by
the same the methods as described before.
2.4. Statistics
Data were analyzed using SAS statistical software (SAS
Institute, 1996). A 2-way ANOVA was performed to test the
signi®cance of effects (sites and compost treatment) on
microbial respiration, Cmic, Nmic, SOC, STN, and C-to-Nratio using means of three replications from each site.
Linear and non-linear regressions were used to test for
correlation between microbial properties, SOC and STN
contents of soil samples. Students-t-tests were performed
to compare linear regression equations from the control
and compost plots. Values of microbial properties from
the O-horizons were log-transformed for testing statistical differences of exponential regression equations. The
numbers presented in the tables are arithmetic means and
are given on an oven dry basis (105 8C, 24 h).
3. Results
3.1. Microbial properties
The 2-way ANOVA results revealed highly signi®cant
effects …p , 0:0001† of forest sites on microbial respiration,
Cmic and Nmic of the O-horizon .2 and ,2 mm and all
mineral soil depths (Table 4). With a few exceptions, the
beech stands at Solling and UnterluÈû showed higher values

Table 4
Amount of soil organic matter (SOM), contents of soil organic carbon (SOC) and soil total nitrogen (STN), C-to-N ratio, microbial respiration, contents of Cmic and Nmic in the fractionated O-horizons and the
mineral soils from the control (2) and the compost plots (1). CV stands for coef®cient of variation of all samples per depth …n ˆ 36†
Fraction

Site

SOM (kg m 22)

SOC (mg g 21)

STN (mg g 21)

C-to-N ratio (g g 21)

Respiration (mg C g 21 h 21)

Cmic (mg g 21)

Nmic (mg g 21)

2

1

2

1

2

1

2

1

2

1

2

1

2

1

SB
SS
SP
UB
US
UP
CV%

1.8
2.4
2.2
1.0
3.7
4.3
46

1.8
3.3
2.4
0.6
1.7
4.6
58

462
481
432
429
439
435
10

400
323
365
296
394
328
20

17
17
15
17
15
15
13

17
18
14
14
17
16
15

27
29
28
25
30
29
6

24
18
25
21
23
21
11

40.4
25.7
38.0
41.4
29.1
23.4
39

28.6
22.5
34.8
33.8
28.8
16.6
34

7.25
4.82
6.90
15.68
7.58
6.98
48

6.51
3.63
3.67
11.81
6.58
4.23
53

1015
423
589
1844
668
644
58

701
326
427
1332
820
402
57

O-horizon, ,2 mm

SB
SS
SP
UB
US
UP
CV%

7.9
7.9
8.0
11.3
4.8
5.0
32

11.1
12.6
13.8
15.2
13.7
10.0
15

285
402
361
268
316
334
22

198
248
214
262
242
263
26

15
17
16
12
12
11
23

14
15
12
13
13
12
15

19
24
23
23
25
29
14

14
17
17
20
18
22
15

8.8
10.1
9.7
10.0
11.3
8.8
17

6.1
5.7
5.7
9.6
10.7
4.9
38

2.91
3.52
3.05
2.70
2.58
2.23
19

1.97
1.68
1.81
1.89
2.17
1.51
21

349
346
254
334
174
180
31

250
122
185
263
233
127
36

Soil depth (cm)

Site

SOC (mg C g 21)

STN (mg N g 21)

C-to-N ratio (g g 21)

Respiration (mg C g 21 h 21)

Cmic (mg C g 21)

2

1

2

1

2

1

2

1

2

1

2

1

Nmic (mg N g 21)

0±5

SB
SS
SP
UB
US
UP
CV%

51.9
45.8
34.9
26.8
24.2
39.5
34

50.7
49.7
44.5
31.0
22.6
45.3
31

2.7
2.3
1.3
0.8
0.7
1.1
56

2.7
2.8
1.8
1.2
0.9
1.6
43

20
20
28
32
34
34
23

19
18
24
26
25
28
17

0.40
0.46
0.37
0.37
0.24
0.23
37

0.42
0.47
0.46
0.37
0.28
0.36
25

0.49
0.29
0.25
0.22
0.15
0.19
88

0.43
0.35
0.29
0.26
0.23
0.35
26

38.1
23.3
20.2
24.8
16.6
15.2
79

33.2
25.2
28.4
28.2
25.3
26.5
22

5±10

SB
SS
SP
UB
US
UP
CV%

33.8
27.2
20.3
18.1
10.3
26.5
37

30.6
24.4
17.4
18.9
9.2
29.5
38

1.7
1.4
0.8
0.6
0.4
0.8
50

1.6
1.7
0.8
0.7
0.4
1.0
49

20
19
25
31
27
33
22

19
15
22
28
23
30
24

0.19
0.22
0.14
0.21
0.11
0.12
34

0.22
0.20
0.17
0.19
0.14
0.15
25

0.28
0.19
0.06
0.13
0.07
0.10
58

0.29
0.18
0.07
0.13
0.07
0.14
56

24.2
15.6
6.6
13.6
6.6
10.1
52

22.9
14.5
10.2
12.8
6.8
9.7
45

10±20

SB
SS
SP
UB
US
UP
CV%

28.6
20.8
11.6
12.9
6.6
19.7
46

25.0
15.3
10.7
14.4
7.5
26.6
44

1.4
1.3
0.6
0.5
0.2
0.7
57

1.5
1.2
0.6
0.6
0.3
0.9
49

20
17
20
28
27
30
22

17
13
19
26
23
30
29

0.16
0.10
0.11
0.17
0.07
0.12
30

0.17
0.12
0.16
0.16
0.09
0.14
28

0.24
0.09
0.02
0.07
0.04
0.07
44

0.25
0.10
0.05
0.08
0.06
0.11
68

19.0
6.1
2.5
7.0
3.4
6.3
37

18.5
7.9
5.8
7.1
4.5
6.9
61

W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412

O-horizon, .2 mm

407

408

W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412

Fig. 1. Effect of compost addition on microbial respiration, Cmic and Nmic of the total O-horizons based on unit area in six forest soils. All values are calculated
from the total amount of organic matter and the microbial properties of the O-horizons .2 and ,2 mm (Table 4). All values are expressed as proportional
deviation from the compost plots to the respective control plots.

for microbial properties than the respective spruce and pine
stands of these study areas. However, there was no clear
distinction for these properties between the spruce and
pine stands in the O-horizon and mineral soil. Microbial
properties at all sites followed a sharp gradient from both
fractionated O-horizons down to the mineral soil at 10±
20 cm depth.
The compost treatment had a signi®cant effect on all
microbial properties in the .2 mm …p , 0:02† and
,2 mm fraction of the O-horizons …p , 0:0001†; in the
mineral soils at 0±5 cm depth …p , 0:01† and at 10±20 cm
depth …p , 0:04† (Table 4). However, the in¯uence of
compost treatment was different for the O-horizons and
the mineral soils. Cmic decreased in the O-horizons by 22
(.2 mm) and by 35% (,2 mm). Also, Nmic decreased by 23
and 28% in the O-horizons .2 and ,2 mm. Microbial
respiration was reduced by 17% in the O-horizons .2 mm
and by 25% in the O-horizons ,2 mm. In contrast to the Ohorizons, microbial respiration, Cmic and Nmic increased by
14±21% in the mineral soil at 0±5 cm depth and by 14±
23% at 10±20 cm depth. Although the compost treatment
was not signi®cant at 5±10 cm depth, the microbial respiration and microbial biomass tended also to increase.
Total Cmic and Nmic of the O-horizons generally decreased
by 6±30% (Fig. 1) although the total amount of organic
matter increased by 28±82% due to the compost addition
(Table 4). The only exceptions were the pine stand at
Solling with an increase of 8% in Nmic and the spruce
stand at UnterluÈû with increases of 17% in Cmic and 40%
in Nmic (Fig. 1). Compared to the other compost plots, there
was no or only little loss in total amount of organic matter at
SP and US. On average, total Cmic and Nmic were, respec-

tively, 10 and 4% lower in the compost plots. Total microbial respiration showed a distinct pattern: it increased at SP,
SS, UB, and US by 1±29% and decreased at UP by 13% and
at SB by 15%, but on average, there was no difference
between compost and control plots.
Initial microbial respiration and microbial biomass C
of compost were 6.0 mg C g 21 h 21 and 1.1 mg g 21 (not
shown). Based on these values, the compost addition of
6.3 kg m 22 increased the total microbial respiration and
Cmic of the O-horizons by 38 mg m 22 h 21 and 6.9 g m 22 in
the summer of 1997. Taking initial values into account, total
microbial respiration and Cmic decreased on average by 23
and 27% in the compost plots during 2 years.
Cmic and Nmic were linearly correlated for the O-horizon in
the control (R2 ˆ 0:81; p , 0:001) and compost plots
(R2 ˆ 0:85; p , 0:001). The C-to-N ratio of the microbial
biomass was 9.5 for the control plots and 9.4 for the compost plots. Linear regressions for Cmic and Nmic of the
mineral soils resulted in R2 ˆ 0:82 …p , 0:001† for the
control and R2 ˆ 0:74 …p , 0:001† for the compost plots.
The average Cmic-to-Nmic ratios were 11.3 and 12.0 for the
control and compost plots, respectively.
3.2. SOC and STN content
The results of the ANOVA indicate that the site effects on
SOC and STN were not signi®cant for the fractionated Ohorizons. There was only a site effect on STN …p , 0:007† in
the O-horizon .2 mm. By contrast, a very large part of the
variance in SOC …p , 0:0001†; STN …p , 0:0001† and C-toN ratio …p , 0:0001† were explained by site effects in all
mineral soil depths. The highest SOC and STN contents

409

W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412

Table 5
Correlation matrix of microbial respiration, Cmic and Nmic with soil organic carbon (SOC) and soil total nitrogen (STN) of the O-horizons …n ˆ 72† and mineral
soils …n ˆ 108† from the control and compost plots
Fraction

Parameter

Control plots

Compost plots

Regression ®t

R2

Regression ®t

R2

O-horizons

Microbial respiration by SOC
Cmic by SOC
Nmic by STN

y ˆ 2:15 e0:0054x
y ˆ 0:82 e0:0044x
y ˆ 0:08 e0:11x

0.48
0.39
0.22

y ˆ 1:54 e0:0072x
y ˆ 0:68 e0:005x
y ˆ 0:05 e0:13x

0.65
0.46
0.22

Mineral soils

Microbial respiration by SOC
Cmic by SOC
Nmic by STN

y ˆ 0:007x 1 0:02
y ˆ 0:007x 1 0:02
y ˆ 9:6x 1 4:1

0.60
0.56
0.45

y ˆ 0:006x 1 0:06
y ˆ 0:007x 1 0:01
y ˆ 9:7 1 3:2

0.53
0.64
0.58

occurred in the mineral soil of the beech and spruce stand at
Solling (Table 4). These soils also had high silt contents
(Table 1). Although variation in soil texture at UnterluÈû
was negligible, the pine stand showed relatively high SOC
and STN contents compared to the beech and spruce stands.
The C-to-N ratios decreased down the mineral soil pro®le in
all sites but were narrower in the silty soils from Solling
than in the sandy soils from UnterluÈû.
Compost treatment had highly signi®cant effects on SOC
content and C-to-N-ratio in the O-horizons .2 mm …p ,
0:0001† and ,2 mm …p , 0:0001†: SOC contents were
reduced by 21% in the .2 mm and by 27% in the ,2 mm
fraction (Table 4). In contrast, STN content was not signi®cantly affected by compost treatment. However, STN
content in the O-horizons ,2 mm increased by 10% in the
sandy soils from UnterluÈû and decreased by 13% in the silty
soils from Solling. No signi®cant differences were detected
for the SOC contents in the mineral soils between the
control and compost plots. STN contents were signi®cantly
altered in the mineral soils by 24, 8.4 and 7.6% at 0±5 …p ,
0:001†; 5±10 …p , 0:06† and 10±20 cm depths …p , 0:02†;
respectively. The C-to-N ratios were signi®cantly reduced
…p , 0:0001† by compost treatment in all mineral soil
depths.

3.3. Relationships between microbial and soil properties
All relationships between microbial and soil properties
were highly signi®cant …p , 0:001† for the O-horizons
and mineral soils. However, the ®tted slopes from the
control and compost plots were not signi®cantly different
(Table 5). Thus, the compost treatment had no effect on the
relationship between microbial and soil properties. For the
O-horizons, microbial respiration and Cmic increased exponentially with increasing SOC. The SOC content explained
48 (control plots) and 65% (compost plots) of variance in
microbial respiration, 39 (control plots) and 46% (compost
plots) of the variance in Cmic. The increase of microbial
respiration per unit SOC was stronger than the increase of
Cmic as indicated by the steeper slopes. An exponential trend
was also found for the relationship of Nmic and STN but the

relationships were weak for both the control plots …R2 ˆ
0:22† and the compost plots …R2 ˆ 0:22†:
For the relationships between microbial and soil properties of the mineral soils, best results were obtained by
performing linear regressions. SOC explained 60 and 53%
of variance in microbial respiration, 56 and 64% of variance
in Cmic in samples from the control and compost plots,
respectively. STN content and Nmic of the mineral soil had
a higher correlation for the control …R2 ˆ 0:45† and compost
plots …R2 ˆ 0:58† than in the O-horizons.

4. Discussion
Microbial respiration (0.07±0.46 mg C g 21 h 21), Cmic
(0.02±0.49 mg C g 21 soil) and Nmic contents (3±38 mg N g 21
soil) in the mineral soils from our study sites were low
compared to undisturbed or less degraded temperate forest
soils (e.g. Ross and Tate, 1993; Joergensen et al., 1995;
Joergensen and Scheu, 1999). According to Raubuch and
Beese (1995), soil microbial properties may re¯ect differences in environmental conditions such as base saturation of
mineral soils. For instance, the silty soils from Solling
generally showed higher base saturation (Table 3), microbial biomass and respiration than the sandy soils at UnterluÈû
(Table 4). Additionally, tree species and litter quality affect
C and nutrient availability and thus control soil microbial
properties. The higher microbial biomass and respiration in
the mineral soil of the beech stands indicate higher C availability than the respective spruce and pine stands at Solling
and UnterluÈû. The overall low microbial biomass of our
forest soils has been subjected to energy (C) and nutrient
limitations (Scheu and Schaefer, 1998) but also to soil acidi®cation (Wolters, 1991; von LuÈtzow et al., 1992). However,
environmental stress may increase microbial respiration due
to higher energy requirements for maintenance of active soil
microorganisms as indicated by altered metabolic quotients
(Anderson and Domsch, 1993).
The super®cial addition of large amounts of mature
compost resulted in a signi®cant decrease in microbial
biomass and respiration in the O-horizons .2 and ,2 mm
of our study sites. Accordingly, SOC contents of the

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W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412

O-horizons were signi®cantly reduced by the compost treatment while STN content was not affected. The amount of
added compost was in the same range as the amount of
organic matter in the O-horizons.
It is likely that microbial respiration and biomass of the
O-horizons were partly reduced due to mixing with the
compost. The initial microbial respiration rate and Cmic of
the applied compost were only 6.0 mg C g 21 h 21 and
1.1 mg C g 21, respectively. These values are considerably
lower than those of the O-horizons from the control and
compost plots. Moreover, from a laboratory study it may
be deduced that the original microbial respiration rate of the
compost decreased during 2 years after addition to the Ohorizon. Chodak et al. (2001) found a decrease of more than
50% in CO2 evolution for similar mature compost at a
temperature range from 5±25 8C during a 120-day incubation.
From the microbial properties, based on dry weight, it is
not clear whether the decrease in microbial respiration and
biomass resulted only from the mixture of the O-horizons
with compost or by additional processes. Therefore, we
calculated proportional deviations in microbial properties
of total O-horizons per unit area. Surprisingly, average
total Cmic (210%) and Nmic (24%) decreased while the
total microbial respiration in the compost plots was not
different from the control plots (Fig. 1). In fact, total microbial respiration and microbial biomass of the O-horizons
initially increased by 38 mg m 22 h 21 and 6.9 g m 22 when
the compost was added. The reduction in microbial biomass
may be partly explained by the strong loss of 1.2 kg m 22
organic matter in the O-horizon from the compost plots
during 2 years. Although the sample size (78.5 cm 2) and
the number of replications …n ˆ 6† include a large error, it
is likely that the amount of compost was reduced by decomposition (Chodak et al., 2001) and leaching of salts and
dissolved organic matter (DOM).
Additionally, our results suggest that the original microbial community in the O-horizons was reduced by the
compost treatment in two ways. On the one hand, the microbial community of the compost was probably different from
the O-horizon. Guerrero et al. (2000) found high fungi population in municipal solid waste compost and pointed out that
compost fungi are more tolerant to sodium chloride and
sulfates than soil fungi. Competition between microorganisms and changes in microbial populations could have also
affected the activity and biomass of key organisms such as
lignin decomposing fungi. Scheu and Parkinson (1994)
pointed out that fungi generally dominate the microbial
biomass in the O-horizon. A reduction in the lignin breakdown following compost application could affect growth of
other microorganisms by decreasing contents of cellulose
and hemicellulose protected by lignin structure. However,
the constant C-to-N ratio of the microbial biomass indicates
that there was no shift from fungal to bacterial population in
the compost plots. Generally, bacteria have a low biomass
C-to-N ratio in the range of 3±5 while that of fungi can vary
between 4 and 15 (Paul and Clark, 1996).

On the other hand, elevated concentrations of mineral N
could suppress the production of lignin-degrading enzymes
by fungi (Fog, 1988; Tien and Myer, 1990). Changes in
the species composition of micro-fungi have been found
in forest soils treated with ammonium nitrate-fertilizer
(Arnebrant et al., 1990). The amended mature compost
contained considerable amounts of inorganic salts, particularly rich in nitrate, and thus may have diminished the autochthonous microbial community of the O-horizon in the
long term. Our ®eld measurements of soil matric potential
and seepage water at 10 cm depth (data not shown) reveal
that inorganic salts from the compost remained for approximately 3 months in the O-horizon. Several authors reported
suppression of soil microbial biomass and respiration
when high doses of inorganic salts were added (Martikainen
et al., 1989; Smolander et al., 1994; Thirukkumaran and
Parkinson, 2000).
According to previous ®ndings (SoÈderstroÈm et al., 1983),
dissolved salts may have become toxic for some soil microorganism due to increased osmotic potential in the Ohorizons. Moreover, some soil microorganisms or microbial
processes may be suppressed or diminished at critical
concentrations of speci®c ions in soil solution. For instance,
an inhibition of nitri®cation was observed when ammonium
sulfate or ammonium chloride was applied in high dose
(Lang et al., 1993). Our results suggest that the initial salt
content of the compost could have contributed to the decline
in the original microbial biomass of the O-horizons.
In contrast to the O-horizons, signi®cant increases in Cmic,
Nmic and microbial respiration were found in the mineral
soils at 0±5 and 10±20 cm depth. A trend towards higher
Cmic, Nmic and microbial respiration rate was also measured
in the 5±10 cm depth. These changes could be related to the
improved supply of nutrients in soil solution. We observed
increased concentrations of dissolved organic carbon
(DOC), nitrate, phosphate and potassium in the soil solution
over the long term (data not shown). Super®cial application
of lime and wood ash increase microbial biomass and
respiration in the O-horizon (Zelles et al., 1990; Baath and
Arnebrant, 1994; Smolander et al., 1994) but generally did
not affect the mineral soil of forests.
During the ®rst 30±60 days, the population of bacteria
and fungi decreased when a burnt forest soil was amended
with municipal solid waste compost (Guerrero et al., 2000).
However, the microbial population of the burnt soil
increased only after the high salt content of compost was
reduced by intense rainfall. It is obvious that reported effects
of fertilizer treatments on microorganisms strongly related
to salt concentration in soil solution and on type of fertilizer.
As a result of improved phosphorous supply, SOM in the
mineral soils may have become more available to microorganisms. Phosphorous is known as a limiting nutrient in
many German forests. Gallardo and Schlesinger (1994)
found increased microbial biomass in the mineral soil of a
warm temperate forest following phosphorous fertilization.
By contrast, no phosphorous fertilization effect on microbial

W. Borken et al. / Soil Biology & Biochemistry 34 (2002) 403±412

biomass and activity was observed in the O-horizon of a
Norway spruce stand (Smolander et al., 1994).
The release of DOC from the compost may have also
promoted the growth of autochthonous microorganisms in
the mineral soils. In a laboratory study, the release of DOC
from mature compost decreased with increasing temperature and exceeded the CO2 release at temperatures below
11 8C (Chodak et al., 2001). The rather high DOC release
described by Chodak et al. (2001) may indicate that DOC
from mature compost was an important C source for soil
microorganisms in our forest sites. However, DOC is
generally a small carbon resource for microorganisms in
forest soils. Borken et al. (1999) found a net release of 60±
83 kg DOC-C ha 21 yr 21 from the O-horizon and upper
10 cm of the mineral soil in an adjacent Norway spruce
stand at Solling.
Zech et al. (1994) stated that the absorption of DOC by
sesquioxides contributes to the storage of organic matter in
mineral soils. The SOC contents in the mineral soils of our
sites were not affected by the compost treatment. However,
the observed increase in STN indicates transport of N from
the compost to the mineral soil and retention in the mineral
soil, perhaps by adsorption of DOM with a relatively low Cto-N ratio. Microorganisms could have modi®ed DOM by
using it as a C source, thereby reducing the C-to-N ratio. An
adsorption of DOM with a lower C-to-N ratio than SOM
would have increased the STN content more than the SOC
content. Transformation of inorganic N into organic N by
microbial decomposition of plant residues (Barber, 1995)
could also have increased the STN content. In accordance
to our results, repeated additions of inorganic N fertilizers
led to long-term retention of N in soils of pine and hardwood
forests (Aber et al., 1998). Although the forest sites in the
study of Aber et al. received moderately increased amounts
of N by atmospheric deposition, 85±99% of additional N
was accumulated in soils.
The Cmic-to-Nmic ratios of 11.3 for the control plots and of
12.0 for the compost plots are wider than the mean of 7.7
reported for a large number of beech forest soils but within
the wide range of 5.4±17.3 (Joergensen et al., 1995).
According to Paul and Clark (1996) fungi would be
expected to dominate the decomposition of SOM in the
mineral soil of both plots. Moreover, the Cmic-to-Nmic ratios
indicate that the increased STN content and altered supply
of nitrate did not affect the fungi±bacteria ratio in the
compost plots.
The Cmic-to-Nmic ratio of forest soils is not related to C and
N availability, however, microbial N incorporation is
affected by C and N availability (Joergensen et al., 1995).
Our results suggest limited C availability in the control and
compost plots. Availability of N to soil microorganisms is
probably not limited due to high atmospheric N deposition
in our forests. Furthermore, the increased N availability by
the application of compost did not narrow the Cmic-to-Nmic
ratios. The weaker relationships between Nmic and STN
content compared to relationships between Cmic and SOC

411

content for the control and compost plots may also indicate
suf®cient N is available for microorganisms.
In conclusion, the results of our study suggest that the
addition of mature compost to the soil surface increase the
microbial biomass and respiration of degraded mineral
forest soils by altering the release of nutrients and DOM
from the organic horizon in the long term. High inorganic
salt contents and/or the microbial community of compost
can reduce speci®c microbial transformations by diminishing the original biomass of O-horizons. Consequently,
application of compost with low salt content is desired for
better soil amelioration. The increase in STN content and
the narrowing of the C-to-N ratio indicate that the forest
soils were not N-saturated and have the capacity to accumulate additional amounts of N.
Acknowledgements
We thank E. Davidson and K. Savage for their comments
on the manuscript. This study was ®nanced by Deutsche
Bundesstiftung Umwelt. We wish to thank Umweltschutz
Nord, Ganderkesee, Germany for delivering compost for the
®eld experiment. W. Borken acknowledges the ®nancial
support received by the Deutsche Forschungsgemeinschaft.
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