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Effects of crushed wood ash on soil chemistry in young Norway spruce stands
Forest Ecology and Management 176 (2003) 121±132
Effects of crushed wood ash on soil chemistry in young Norway spruce stands Helen Arvidsson*, HeleÂne Lundkvist Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, SE-750 07 Uppsala, Sweden Received 18 July 2001; received in revised form 5 February 2002; accepted 10 May 2002
Abstract The use of logging residues as a fuel in district heating plants has led to regular wood ash recycling to forest soil to prevent soil nutrient depletion. Wood ash with a low content of unburnt matter reacts with water and air in a so-called self-hardening process. Hardening of the ash is a way to reduce its reactivity and thus increase the time for its dissolution. In four ®eld experiments, changes in soil chemistry were analyzed 6 years after application of hardened crushed wood ash to 8±10-year-old Norway spruce (Picea abies (L.) Karst.) stands. The 0±5, 5±10 and 10±20 cm layers of the soil were sampled, including the disturbed humus layer. Logging residues were collected at the preceding harvest. At each site, hardened crushed wood ash of two types, NymoÈlla and Perstorp, was applied in a randomized block design n 4. The dose applied was 3 Mg ha 1. Exchangeable Ca, Mg, K and effective cation exchange capacity (CECeff) on a per hectare basis in the 0±20 cm soil layers were signi®cantly higher in wood ash-treated plots than in the control plots in analyses across all study sites. Total exchangeable acidity was signi®cantly lower after wood ash application. There was a signi®cant effect on pH in the 0±5 cm layer of the soil in three of the sites, where pH increased on average by 0.5 units in wood ash Perstorp-treated plots and by 0.7 units in wood ash NymoÈlla-treated plots compared to control plots. Further down in the soil pro®le, no differences were detected at any site. Wood ash application resulted in a higher level of base saturation (BS), especially in the 0±5 cm layer. BS increased on an average by 39 and 31% units in the 0±5 cm soil layer, and by 13 and 10% units in the 5±10 cm soil layer, in wood ash NymoÈlla- and Perstorptreated plots, respectively, compared with the control. The results show that hardened wood ash recycling can compensate for base cations lost at whole-tree harvesting. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Acidity; Base cations; pH; Soil; Wood ash
1. Introduction At present, 17% of the energy supply in Sweden originates from forestry (Anon., 1999). The largest potential source of additional biofuels is logging residues from tree fellings. There is an increasing demand *
Corresponding author. Tel.: 46-1867-2434; fax: 46-1867-3430. E-mail address: [email protected] (H. Arvidsson).
for logging residues in Sweden. Burning of felling residues for heating does not give any net contribution to the carbon dioxide level of the atmosphere provided that forests are replanted after fellings. However, soil nutrient depletion and soil acidi®cation are the major concerns associated with removal of logging residues (c.f. Olsson et al., 1996). The depletion of soil nutrients can be counteracted by returning thewood ash to the soil. The effects of wood ash application on forest soil have been studied previously, but the majority of these
0378-1127/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 2 ) 0 0 2 7 8 - 5
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studies deal with untreated loose wood ash and only a few investigate ash that has been stabilized in some way. Kahl et al. (1996) conducted a ®eld experiment on the effects of application of loose wood ash in doses of 6, 13 and 20 Mg ha 1 on soil and soil solution chemistry. Ash application increased soil pH, base saturation (BS) and exchangeable base cations in both the O and B horizons. After 25 months, irrespective of the dose, pH had increased in the O horizon by approximately 2 pH units. Bramryd and Fransman (1995) reported an increase of approximately 1 pH unit in the mor layer 10 years after application of loose ash in a dose of 2 Mg ha 1. Loose ash taken directly from the burner is highly alkaline. There have been some concerns that loose ash may damage the plants and soil organisms. In order to avoid this, stabilization of the ash should be done. Wood ash with a low content of unburnt matter reacts with water and air in a so-called self-hardening process. In order to accomplish self-hardening, the ash is wetted, packed in a large pile, stored and then crushed into particles of suitable sizes (Steenari and Lindqvist, 1997). Pellets or granules of ash are an alternative to crushed hardened ash and also reduce the reactivity of the ash. Compared to loose, untreated ash, granulated ash has been shown to cause a less drastic pH effect on the soil (Eriksson, 1998a). The present paper reports on chemical changes in the soil in ®eld experiments in young stands of Norway spruce (Picea abies (L.) Karst.) after application of self-hardened wood ash. The soil chemistry study is part of a larger investigation, including studies on the impact of wood ash on leaching of nitrate and other elements and on changes in ®eld and bottom vegetation and tree nutrient status. We hypothesized that effects of ash application would be dependent on the climatic situation. More speci®cally, we anticipated the effects to be faster and more pronounced in southern than in northern Sweden. Therefore, the ®eld experiments were established in four climatic zones. We analyzed the following soil chemistry parameters 6 years after application of crushed hardened wood ash: exchangeable Ca, Mg, K, Na and Cd, cation exchange capacity (CECeff), pH, electrical conductivity, exchangeable acidity, BS, extractable NH4 , NO3 and total C and N. The ash dose applied, 3 Mg ha 1, is recommended by the National Forestry Board in Sweden in order to compensate for base cation losses at whole-tree (above ground) harvesting.
2. Materials and methods 2.1. Site descriptions The four ®eld experiments used in our investigation were established in a climatic gradient of sites with forest type Vaccinium myrtillus (HaÈgglund and Lundmark, 1977). Forest type V. myrtillus represents about 30% of the total forest area in Sweden. The sites were chosen to represent different climate conditions and the following four generalized climatic zones as they can be found in the National Atlas of Sweden (Anon., 1990): The south west (site name Flybacken) and the southern highlands (Ljungby) with high and fairly high acidifying deposition, respectively; the south east (Simtuna) with less acidifying deposition; and the northern coastal area (Malungs¯uggen) where deposition is low (Table 1). The northern coastal area has dry summers and a slightly humid climate in a broad belt along the coast of Norrland. The south east has a favorable temperature climate but dry summers and is slightly humid to a lesser degree. The south west has high precipitation and a markedly humid climate and southern highlands area has a humid climate. The spruce stands differed in stand age and were 2±4year-old when the wood ash was applied in 1993. All sites had been whole-tree harvested and planted with Norway spruce (P. abies (L.) Karst.). Soil scari®cation was carried out before planting at all sites except at Simtuna. Patch scari®cation was done on the Flybacken and Ljungby sites and harrowing on the Malungs¯uggen site. Both patch scari®cation and harrowing caused a slight disturbance of the forest ¯oor. 2.2. Experimental design and treatments The experiments had a randomized block design, with three treatments and four blocks at each site (one replicate per block, n 4, i.e. 12 plots per site). Each 3 m 3 m plot was surrounded by a 0.5 m border strip. Within a plot there were four planted Norway spruce trees. The treatments were control, application of wood ash NymoÈlla (WAN) and application of wood ash Perstorp (WAP). The ashes were from district heating plants, at NymoÈlla and Perstorp, Sweden. The WAN originated from a cyclone furnace ®red mainly with bark, whereas WAP originated
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Table 1 Characteristics of the experimental sitesa Site
Climate zone Forest typeb Location Altitude (m a.s.l.) Precipitation (mm per year) Length of growing season (days >5 8C) Wet deposition of nitrogen (kg ha 1 per year) Planting year Site index (H100)c Soil type Soil texture Clay content (%) Bulk density of mineral soil (<2 mm, g l 1) 0±5 cm 5±10 and 10±20 cm
Flybacken
Ljungby
Simtuna
Malungsfluggen
South west V. myrtillus 568450 N, 138230 E 170 800 240 12±14 1990 G28 Podsol Sandy loam 7.8
Southern highlands V. myrtillus 568500 N, 148000 E 165 650 240 10±12 1990 G28 Podsol Sandy loam 5.5
South east V. myrtillus 598420 N, 168500 E 30 540 210 6±8 1989 No data Podsol Sandy loam 10.5
Northern coastal area V. myrtillus 628100 N, 168530 E 380 570 180 2±4 1991 G24 Podsol Loamy sand 8.9
722 742
630 817
232 689
540 713
a
All sites were planted with Norway spruce (P. abies (L.) Karst.). Climate zones are from the National Atlas of Sweden (Anon., 1990). Forest type according to HaÈgglund and Lundmark (1977). c Height of dominant spruce at 100 years of age (HaÈgglund and Lundmark, 1977). b
from a circulating ¯uidized bed boiler ®red with 90% wood chips and 10% peat. After combustion, the ashes were stabilized by addition of water and allowed to harden before being crushed. The chemical composition, as determined by a LiBO2 melting technique, differed between the ashes (Table 2). A single dose of 3 Mg ha 1 (dry mass) of crushed wood ash was applied by hand as uniformly as possible to each ash-treated plot in August±October 1993. The dose applied was recommended by the National Forestry Board in Sweden in order to compensate for base cation losses at whole-tree (above ground) harvesting (Anon., 1998). The WAN contributed 44 kmolc ha 1 of Ca, 6 kmolc ha 1 of Mg and 0.8 kmolc ha 1 of K. The WAP contributed 24 kmolc ha 1 of Ca, 5 kmolc ha 1 of Mg and 1.5 kmolc ha 1 of K at application.
2.3. Soil sampling and chemical analyses Soil sampling was carried out in June 1999. From each plot, soil cores with a diameter of 25 mm were collected at 10 spots. The litter layer was removed from the samples in the ®eld. If wood ash particles could be seen, they were removed from the samples. Each core was divided into subsamples representing the layers 0±5, 5±10 and 10±20 cm below the soil surface. The 0±5 cm layer consisted of a mixture of humus and mineral soil, due to soil scari®cation. The soil samples of each layer were pooled to produce one sample per plot. The soil was sifted through a 2 mm mesh net prior to analysis. Soil dry weights were determined after the samples had been dried overnight at 105 8C. Calculations of nutrient amounts in the 0±5 cm layer were based on
Table 2 Chemical composition of the WAN and the WAP used in the present study
WAN WAP a
Ca (%)
Si (%)
Al (%)
K (%)
Mg (%)
Na (%)
P (%)
S (%)
LOIa
Cd (ppm)
29.7 16.2
9.5 10.7
3.2 4.9
1.0 2.0
2.4 2.0
0.6 1.6
0.4 0.4
1.4 2.9
19.4 13.8
5.4 10.4
Loss on ignition.
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bulk densities of the sifted soil fraction (<2 mm) (Table 1). Mean values n 12 for each site were used for the calculations. The bulk densities of the ®ne soil fraction in the 5±10 and 10±20 cm layers were estimated for each site with 50±100 rod penetration tests according to Tamm and Popovic (1989). Soil pH (H2O) was measured with a glass electrode on suspensions of soil in distilled water. Soil suspensions were made by adding 50 ml of distilled water to 7 g (0±5 cm layer) or 22 g (5±10 and 10±20 cm layers) of fresh, sifted soil. The suspensions were revolved on a reciprocal shaker for 2 h, and pH and conductivity were measured at room temperature after sedimentation overnight. Soil extracts for NH4 and NO3 analyses were prepared by adding 10 g (0±5 cm layer) or 20 g (5±10 and 10±20 cm layers) of fresh soil samples in 250 ml polyethylene bottle and adding 100 ml 1 M KCl. The ¯asks were revolved for 1 h. Chemical analyses of NH4 and NO3 in the ®ltered extracts were performed by using a ¯ow injection analysis (FIA) system. Exchangeable amounts of Na, K, Ca, Mg, Al and Cd in the soil were determined by using 1 M NH4Cl as extract. Chemical analyses of the ®ltered extracts were performed by using an inductively coupled plasmaÐ atomic emission spectrophotometer (Jobin Yvon JY-70 Plus). The soil extracts were prepared by adding 10 g (0±5 cm layer) or 20 g (5±10 and 10±20 cm layers) of fresh soil sample to a 250 ml polyethylene bottle and adding 100 ml 1 M NH4Cl. The ¯asks were revolved for 1 h, and then pH in the extracts was measured. Total nitrogen (N) and carbon (C) were analyzed with a dry oxidation procedure at about 1000 8C using a CarloErba elementary analyzer, model NA 1500.
Altot Al3 Al OH2 Al OH2
2.4. Data treatment
Table 3 General treatment effect on pools of exchangeable Ca, Mg, K, Na, effective CECeff and total acidity (kmolc ha 1) in the 0±20 cm soil layera
Exchangeable acidity was de®ned as the equivalent sum of exchangeable H and Al. Exchangeable base cations were de®ned as the equivalent sum of Na, K, Ca and Mg. Effective CECeff was de®ned as the sum of exchangeable base cations and exchangeable acidity. BS was de®ned as (exchangeable base cations/ CECeff 100. Exchangeable H was determined according to the following equations (molar units): Exchangeable H 10
pH
0:79
1
2Al OH2
Al OH2
Al OH2 10
5:47
Al OH2 10
10:3
Al3 H Al3 H
1 2
Altot and pH (H) refer to the measured concentrations in the extract. The equilibrium constants (10 5.47 and 10 10.3) and the H activity factor (0.79) were obtained from Baes and Mesmer (1976). For analysis of treatment effects on investigated soil chemical variables within sites, an analysis of variance (ANOVA) for randomized block design and signi®cance tests was carried out using the programme Super-Anova Abacus Concepts. Least signi®cant difference tests used the Tukey±Kramer test to detect differences between treatment means. In addition, a nested model was used to examine general treatment effects across all sites. The total pool of exchangeable Ca, Mg, K, Na and CECeff and total acidity were tested. Sites, treatments and blocks (blocks nested within sites), including the interaction between sites and treatments were then used as sources of variation. No transformation of data was considered necessary, since the variances were fairly homogeneous. 3. Results In general, the total pool of exchangeable Ca, Mg, K and the effective CECeff per hectare were signi®cantly higher in wood ash-treated plots than in the control plots (Table 3 and Fig. 1). Total exchangeable acidity was signi®cantly lower after wood ash application
Dependent variable
Treatment (2 d.f.)
Site (3 d.f.)
Treatment site (6 d.f.)
Ca Mg K Na CECeff Total acidity
0.0001 0.0018 0.0268 ns 0.02 0.0002
ns ns 0.0001 0.0003 0.0078 ns
ns ns 0.049 0.0437 ns ns
a p-Values are shown when p < 0:05 for treatment, site and the interaction between site and treatment.
Fig. 1. Amounts of exchangeable Ca (A), Mg (B) and K (C) in the soil after wood ash application (kmolc ha 1). Mean values for each site and treatment are given. Each bar is subdivided into 0±5, 5±10 and 10±20 cm layers of the soil from top to bottom. The treatments n 4 were WAN, WAP and control (C). S.D. bars refer to the total amounts. Bars with the same or no letter are not signi®cantly different p < 0:05 according to Tukey±Kramer test.
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Table 4 Concentrations of exchangeable base cations, acidity, CECeff and BS in soil layers 6 years after treatmenta Site Flybacken
Ljungby
Simtuna
Soil layer (cm)
Treatment
C a Mg K Na Acidity CECeff BSb (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (%)
0±5
WAN WAP C p
5.05b 4.26b 0.79a 0.001
0.82b 0.82b 0.46a 0.02
0.16 0.21 0.15 0.15
0.09 0.11 0.08 0.18
1.22b 1.89b 3.40a <0.001
7.34b 7.29b 4.89a 0.01
83.1b 73.3b 30.0a <0.001
5±10
WAN WAP C p
0.52b 0.48b 0.14a 0.002
0.17b 0.13ab 0.09a 0.04
0.06 0.06 0.06 0.87
0.04 0.04 0.05 0.70
2.55 2.57 2.80 0.06
3.34 3.28 3.13 0.52
23.6b 21.5b 10.5a 0.002
10±20
WAN WAP C p
0.14b 0.14b 0.05a 0.02
0.05 0.05 0.03 0.10
0.03 0.03 0.02 0.09
0.03ab 0.04a 0.03b 0.03
1.77 1.80 1.59 0.22
2.02 2.06 1.72 0.13
12.0b 12.5b 7.6 a 0.009
0±5
WAN WAP C p
9.99b 5.92ab 1.99a 0.02
2.02 0.95 0.67 0.05
0.41 0.22 0.20 0.067
0.16 0.09 0.09 0.083
1.26b 1.61b 4.30a 0.0001
13.57b 8.79ab 7.24 a 0.047
86.0b 81.2b 39.9a 0.0001
5±10
WAN WAP C p
0.67b 0.40ab 0.14a 0.028
0.22b 0.11b 0.06a 0.004
0.07 0.05 0.04 0.064
0.03 0.03 0.02 0.23
2.57 2.43 2.64 0.65
3.56 3.01 2.90 0.054
27.4b 19.1ab 8.8 a 0.017
10±20
WAN WAP C p
0.13 0.10 0.05 0.06
0.06b 0.04ab 0.03a 0.035
0.03b 0.02ab 0.02a 0.038
0.02 0.02 0.02 0.67
2.21 1.84 1.72 0.07
2.45 2.01 1.83 0.056
9.4b 8.6ab 5.9 a 0.024
0±5
WAN WAP C p
14.07 12.30 9.04 0.32
1.78 1.80 1.82 0.99
0.38 0.44 0.48 0.42
0.14 0.17 0.14 0.80
1.47b 3.03b 5.67a 0.003
17.83 17.74 17.16 0.97
5±10
WAN WAP C p
1.61 1.95 1.10 0.53
0.28 0.33 0.26 0.80
0.12 0.10 0.10 0.79
0.02 0.03 0.03 0.29
3.36 4.19 4.82 0.07
5.40 6.61 6.31 0.61
34.8 35.7 23.4 0.28
10±20
WAN WAP C p
0.43 0.51 0.22 0.17
0.09 0.10 0.07 0.51
0.07 0.05 0.04 0.10
0.01 0.01 0.02 0.16
2.19 2.27 2.65 0.35
2.79 3.25 3.00 0.62
20.4 20.7 11.7 0.044
WAN WAP C p
6.86b 4.73b 2.02a 0.0035
0.81b 0.69ab 0.39a 0.0135
0.32 0.27 0.26 0.29
0.09 0.06 0.04 0.17
1.28 1.76 2.58 0.13
9.37b 7.52ab 5.28a 0.0255
86.0b 77.1b 51.3a 0.0026
WAN WAP C p
0.90 1.09 0.78 0.48
0.16 0.22 0.16 0.22
0.12 0.15 0.14 0.18
0.03 0.03 0.03 0.85
2.77b 3.71ab 4.22a 0.034
3.98 5.20 5.34 0.08
29.5 29.0 20.7 0.21
Malungsfluggen 0±5
5±10
88.8b 82.6ab 66.8a 0.0255
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
127
Table 4 (Continued ) Site
Soil layer (cm)
Treatment
10±20
WAN WAP C p
Mg K Na Acidity CECeff BSb C a 1 1 1 1 1 1 (cmolc kg ) (cmolc kg ) (cmolc kg ) (cmolc kg ) (cmolc kg ) (cmolc kg ) (%) 0.34 0.42 0.30 0.32
0.08ab 0.08b 0.07a 0.0364
0.09 0.11 0.09 0.07
0.02 0.03 0.04 0.077
1.62 1.43 1.16 0.47
2.16 2.07 1.66 0.27
26.4 34.4 29.9 0.60
a The treatments n 4 were WAN, WAP and control (C). Signi®cantly different treatment means are indicated by different letters (Tukey±Kramer, p < 0:05). b Calculated as mean value of the replicates.
than in the control. Site and treatment interacted signi®cantly in their in¯uence on exchangeable pools of K and Na. Concentration of exchangeable Ca was greatly increased by the ash addition (Table 4). In the 0± 5 cm soil layer at Flybacken, concentrations of exchangeable Ca in WAN- and WAP-treated plots were six- and ®vefold higher, respectively, than in control plots. In the 5±10 and 10±20 cm layers, the Ca concentrations increased by a factor of 3 in both ash treatments compared with the control. In the 0±5 cm soil layer at Ljungby, exchangeable calcium concentrations were ®ve- and threefold higher in WAN and WAP, respectively, treatment than in the control. At Simtuna the increase was less pronounced, with 1.5 times as much Ca in the ash treatments as in the control. In the 0±5 cm soil layer at Malungs¯uggen, concentrations of exchangeable Ca in WAN- and WAP-treated plots were increased by three and two times, respectively, compared with the control. Total pools of exchangeable Ca also increased as a response to the ash addition (Fig. 1A). Compared with the control, the concentrations of Mg in the 0±5 cm layer were increased by a factor of 2 for both ash treatments at all sites except at Simtuna (Table 4). At Flybacken and Ljungby, an increase in Mg concentrations was also detected in the 5±10 and 10±20 cm layers of the ash treatments. On all sites except Simtuna, the total pools of exchangeable Mg increased as a response to the ash addition (Fig. 1B). Treatment effects on exchangeable K were only detected in the 10±20 cm layer at the Ljungby site, where the WAN treatment had a higher concentration of K than the control (Table 4). At the Malungs¯uggen site, the total pool of exchangeable K was higher in the WAP treatment than in the control (Fig. 1C).
At Flybacken, the exchangeable acidity in the upper 0±5 cm of the soil was 64 and 44% lower in WAN and WAP treatments, respectively, than in the control (Table 5). A decrease in acidity of the same order of magnitude was found in the 0±5 cm soil horizon for all sites. Further down, 5±10 and 10±20 cm in the soil pro®le, no differences were detected at any site except at Malungs¯uggen (5±10 cm) where treatment NymoÈlla wood ash decreased acidity by 34% compared with the control. In the 0±5 cm soil layer at Flybacken, in the treatments WAN and WAP, the BS was increased by 53 and 43% units, respectively, compared to the control. The increase was 13 and 11% units in the 5±10 cm and 4 and 5% units in the 10±20 cm soil layer. The increase in BS after ash treatment varied between the sites. BS increased on average by 39 and 31% units in the 0± 5 cm soil layer, in WAN- and WAP-treated plots compared with the control. At Flybacken, Ljungby and Simtuna, pH increased in the 0±5 cm layer on average by 0.7 pH units in WAN-treated plots and by 0.5 pH units in WAPtreated plots compared with control plots. At Malungs¯uggen, there was no signi®cant difference between the treatments. Further down in the soil pro®le, no differences were detected at any site (Table 5). No differences in electrical conductivity were found except at Malungs¯uggen, where the electrical conductivity was higher in the 10±20 cm soil layer in WAP-treated plots compared to control plots. No differences between treatments were found for NH4 or for total C and N concentrations (Table 5). At all sites except Simtuna there was a tendency for a higher C/N ratio in the WAN treatment than in the control in the upper 5 cm of the soil. All NO3 values were below the detection limit.
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Table 5 pH and electrical conductivity of soil extracts in distilled water, concentrations of salt extractable NH4 -N, Cd and concentrations (% of dry mass) of C and N and the C:N ratio in soil layers 6 years after treatmenta Site
Flybacken
Ljungby
Simtuna
Malungsfluggen
Treatment
pHH2 O
Electrical conductivity (mS cm 1)
NH4 -N (mg g 1)
Cd (mmolc kg 1)
0±5
WAN WAP C p
4.89b 4.74b 4.29a 0.001
23.0b 27.8ab 28.8a 0.041
3.2 6.1 4.9 0.046
1.7 2.2 1.6 0.046
5±10
WAN WAP C p
4.38 4.41 4.38 0.8
27.6 26.6 29.2 0.69
0.1 0.1 0.4 0.5
10±20
WAN WAP C p
4.74 4.66 4.73 0.18
21.2 21.1 17.4 0.20
0±5
WAN WAP C p
4.89b 4.80b 4.18a 0.002
5±10
WAN WAP C p
10±20
Soil layer (cm)
C
N
C:N
89 93 78 0.33
3.7 4.0 3.4 0.43
24 23 22 0.06
0.7b 0.6b 0.8a 0.002
35 33 34 0.85
1.6 1.6 1.6 0.99
21 20 20 0.33
0.6 1.5 1.1 0.19
1.0 0.8 0.9 0.23
27 25 26 0.75
1.4 1.3 1.3 0.79
20 20 20 0.86
33.4 22.7 30.1 0.13
1.4 0.6 2.5 0.16
3.7 2.9 2.7 0.29
197 103 122 0.06
6.6 3.7 4.5 0.07
29a 28ab 27b 0.05
4.19 4.35 4.28 0.07
35.7 27.8 26.9 0.05
0.2 0.3 0.2 0.9
0.6 0.5 0.5 0.65
38 30 31 0.18
1.4 1.2 1.2 0.53
27 26 25 0.22
WAN WAP C p
4.52 4.59 4.53 0.67
21.2 21.2 21.5 0.99
0.3 0.1 0.3 0.28
0.4 0.4 0.4 0.72
27 23 23 0.10
1.1 1.0 1.0 0.25
24 24 23 0.65
0±5
WAN WAP C p
4.71b 4.41b 4.02a 0.003
52.0 42.5 52.7 0.53
0.9 0 0.1 0.48
4.3 6.4 5.8 0.24
173 222 274 0.11
5.6 7.1 8.9 0.13
30 31 31 0.80
5±10
WAN WAP C p
4.41 4.19 4.13 0.22
32.9 51.8 48.2 0.21
2.6 2.3 0.1 0.69
1.1 1.4 1.1 0.75
49 62 54 0.70
1.6 1.9 1.8 0.80
31 32 31 0.28
10±20
WAN WAP C p
4.72 4.62 4.63 0.55
33.4 27.8 23.2 0.32
1.8 1.0 0.3 0.55
0.6 0.5 0.4 0.13
29 30 25 0.24
0.9 0.9 0.8 0.35
32 32 32 0.85
0±5
WAN WAP C p
5.26 5.06 4.93 0.31
29.7 26.4 24.3 0.48
8.5 3.3 8.8 0.043
2.3 2.5 1.6 0.19
77 49 44 0.06
2.8 1.7 1.7 0.06
28 29 26 0.14
5±10
WAN WAP C p
4.84 4.67 4.70 0.11
36.6 42.6 31.6 0.13
2.8 2.2 2.0 0.78
1.3 1.4 1.4 0.78
32 38 29 0.33
1.2 1.4 1.2 0.44
26 27 25 0.65
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
129
Table 5 (Continued ) Site
Soil layer (cm)
Treatment
pHH2 O
Electrical conductivity (mS cm 1)
NH4 -N (mg g 1)
Cd (mmolc kg 1)
10±20
WAN WAP C p
4.91 4.83 4.88 0.55
30.8b 46.8a 33.6b 0.01
4.4 4.2 3.1 0.35
1.3 1.6 1.7 0.32
C
38 55 49 0.44
N
C:N
1.5 2.0 1.9 0.36
26 26 25 0.82
a The treatments n 4 were WAN, WAP and control (C). Signi®cantly different treatment means are indicated by different letters (Tukey±Kramer, p < 0:05).
There was a tendency in the 0±5 cm soil layer for Cd concentrations to be higher in the WAP-treated plots compared with the control plots. In the 5±10 cm soil layer at Flybacken, exchangeable Cd was signi®cantly lower in the ash treatments than in the control. 4. Discussion Our most important ®nding was that hardened wood ash application in a dose of 3 Mg ha 1 generally resulted in modestly but signi®cantly increased soil pH, BS, concentrations of exchangeable Ca and Mg and CEC. The effects were most pronounced in the upper 0±5 cm layer. The increase in BS was mainly due to increased concentrations of Ca and Mg. BS increased in the whole soil pro®le. The four sites examined differ in their climatic conditions and deposition of nitrogen. We hypothesized that effects of ash application would be dependent on the climatic situation. However, regardless of differences in climate conditions, there were overall treatment effects detected for the pools of exchangeable Ca, Mg, K, for CEC and for the total pool of acidity as revealed by analysis across all sites. The Simtuna site, differed from the others in that only few variables showed signi®cant differences between the treatments. Stabilization of wood ash through self-hardening is a way to decrease the solubility of the mineral nutrients. After 6 years in the ®eld, most of the easily soluble salts (mainly K, Na, Cl and SO4 2 ) are most likely leached out from the ash. Soluble forms of Ca as calcium oxide (CaO) and portlandite (Ca(OH)2) and some Mg as MgO would also be lost from the ash (Steenari et al., 1998). It might be that some wood ash particles were included in the soil samples. However, the salt 1 M NH4Cl with which we extracted the soil
samples is a weak neutral salt and could probably not further dissolve any elements from the ash matrix (J. Eriksson, pers. commun.). The overall effect that application of wood ash increased the pool of Ca and Mg is an important ®nding. The results show that wood ash recycling may be a way to return base cations lost at wholetree harvesting. With WAN and WAP we applied 44 and 24 kmolc ha 1 Ca, respectively. According to our results, the pools of exchangeable Ca were on average 16 and 11 kmolc ha 1 higher after WAN and WAP addition, respectively, compared to the control (Fig. 1A). After a weathering time of 2.5 years in the ®eld in southwest Sweden, WAN (named CF ash by Steenari et al., 1998) had lost about 5% of the Ca and WAP (named CFB B ash by Steenari et al., 1998) 40% of the Ca. It is possible that WAP had a higher proportion of Ca present in easily dissolved forms such as portlandite (Ca(OH)2). The hardening process was probably not completed for WAP and only a part of the portlandite Ca(OH)2 had formed calcite (CaCO3). WAP originated from ®ring of wood chips but also some peat. Peat ash has been shown to form gypsum instead of slow releasing ettringite (Ca6Al2(SO4)3(OH)1226H2O) during the hardening process (Steenari et al., 1999). Results from modeling of the solid phase in wood ash particles suggest that after a weathering time of 2 years, Ca in the ash is present in the form of calcite (CaCO3) and the release rate is slowed down (Steenari et al., 1998). It is likely that WAN had lost 5% of its Ca after 2.5 years in the ®eld but after 6 years in the ®eld the loss had to be about 35% to match the difference in the pools of Ca that were 16 kmolc ha 1 higher in WAN-treated plots compared to the control. Modeling the stability of some Ca minerals during weathering of hardened wood ash suggests that 40% of the Ca content would
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have been lost after 2 years (Steenari et al., 1998). This is in agreement with column leaching tests at the laboratory (Steenari et al., 1998; Eriksson, 1998b). The Ca released from the WAN and WAP ashes seems to be mobilized and bound in an exchangeable form within the soil. Two years after application of a granulated wood ash in a dose of 3 t ha 1, Eriksson (1998a) reported an increase of 2.5±5 kmolc ha 1 of exchangeable Ca compared to the control and concluded that more of the Ca had yet to dissolve. The solubility of Ca from hardened wood ashes seems to be quicker than from granulated wood ash (Steenari et al., 1998). Application of the hardened WAN and WAP used in our study in a dose of 3 Mg ha 1 gave positive effects in terms of increased pools of Ca. Thus, wood ash application can compensate for losses of base cations after whole-tree harvesting. The concern about wholetree harvesting has been about nutrient removal and how to sustain long-term nutrient budgets. At four whole-tree harvested sites that were investigated 15 years after clearfelling, Olsson et al. (1996) found that the soil pools of exchangeable Ca were 0±6 kmolc ha 1 lower in whole-tree harvested plots compared to those in conventionally harvested plots. Thus, the ash dose used in our study increased the pool of exchangeable Ca more in absolute terms than it was reduced by whole-tree harvesting in the study by Olsson et al. (1996). The Mg pool increased by approximately 1± 3 kmolc ha 1 after wood ash addition (Fig. 1B). With WAN and WAP, we applied 6 and 5 kmolc ha 1 Mg, respectively. Steenari et al. (1998) reported losses of Mg between 10 and 30% after a weathering time of 2.5 years. Similar results were found in a column leaching test simulating a weathering period of 5 years (Eriksson, 1998b). Mg has been observed as MgO and Mg silicates in ashes (Steenari and Lindqvist, 1997). The low chemical solubility of Mg was probably due to the high pH. Steenari et al. (1998) noticed a slight increase in leaching of Mg towards the end of a simulated leaching period. The low recovery of Mg in our study suggests that more Mg will be leached from the ashes with time. We found that after 5 years, the exchangeable concentrations and the exchangeable pool of K were hardly affected by wood ash application. Two years after application of an untreated wood ash in a high
dose of 20 Mg ha 1, Kahl et al. (1996) found increased potassium concentrations in the mineral soil. Unger and Fernandez (1990) noticed an increase of K in the mineral soil with doses ranging from 4 to 20 Mg ha 1 of untreated wood ash. From a laboratory study using WAP, Eriksson (1998b) reported that approx. 50% of the original K was lost in a column leaching test, corresponding to approx. 5 years weathering in the ®eld. A similar release was found in samples collected from the ®eld after 2.5 years of weathering in the forest (Steenari et al., 1998). Since exchange sites on the soil particles attract Ca more strongly than they attract K, the low recovery of K on the exchange site could be due to greater leaching of K, but probably also to higher uptake by trees. In analyses of 1-year-old needles we found that 5 years after ash application, K concentration and K:N ratio were in general higher in wood ash-treated plots compared with a control (Arvidsson and Lundkvist, 2002). Furthermore, consecutive sampling for 5 years after ash application of the soil water at 50 cm depth with suction lysimeters indicated higher leaching of K from ash-treated plots compared to control plots for 2 years and thereafter it decreased to control levels (Arvidsson and Lundkvist, 2001). In the upper 5 cm of the soil, hardened wood ash application increased the pH by 0.7 pH units in WANtreated plots and 0.5 pH units in WAP-treated plots compared to control plots. The effects on soil pH were less than after application of loose wood ash in similar doses, but higher than after application of granulated wood ash (Kahl et al., 1996; Eriksson, 1998a; Levula et al., 2000). Levula et al. (2000) noted an increase of one pH unit and Kahl et al. (1996) noted an increase of two units one year after application of a loose wood ash in doses of 2.5 and 6 Mg ha 1, respectively. After application of a granulated wood ash, pH increased by 0.45 and 0.1 pH units after a dose of 3 Mg ha 1 to a forest soil in the north and south of Sweden, respectively (Eriksson, 1998a). During the hardening process, formation of less soluble Ca occurs but also reduction in the alkalinity. Both self-hardened wood ash products, such as those used in our study, and granulated wood ashes create more moderate pH effects in the soil than does loose wood ash. The concern about high pH effects is that it might lead to damage to the vegetation and/or soil fauna. We found no effects on the cover of different moss species 5 years after ash application of
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
WAP and WAN (Arvidsson et al., 2002). However, a previous study has shown initial damage on mosses caused by loose wood ash and WAP at a dose of 2 Mg ha 1, but the mosses recovered the year after application (Kellner and Weibull, 1998). One of the concerns regarding the negative effects of wood ash application is that it might lead to increased concentrations of Cd levels in the soil. For the WAP treatment, there was a tendency for higher concentrations of exchangeable Cd in the 0± 5 cm layer compared to control plots. In a column leaching study corresponding to a weathering time of 5 years, almost the whole of the initial amount of Cd in WAP remained in the ashes after a simulated 5 years of leaching (Eriksson, 1998b). Eriksson (1998b) suggested that a mobilization of exchangeable Cd from the mor layer occurred rather than leaching from the ash itself. Application of a granulated wood ash at a dose of 3.2 Mg ha 1 increased Cd content in enchytraeids, potworms, during the year after application, but it decreased the following 2 years back to control levels (Lundkvist, 1998). Lundkvist (1998) concluded that this was probably due to an increased mobility of exchangeable Cd rather than an actual release from the ash. Present research is aimed at trying to ®nd new methods to separate Cd from the ash prior to application in the ®eld (Sundqvist, 1999). The concern about direct leaching of Cd from the added ash could then be excluded. 5. Conclusions Application of hardened WAN and WAP used in our study in a dose of 3 Mg ha 1 gave positive effects in terms of increased pools of Ca, Mg and K. Wood ash application can compensate for losses of base cations after whole-tree harvesting. This is an important aspect for the potential to maintain long-term forest production under sustainable nutrient conditions even with intensive forest management. Acknowledgements We would like to thank Ege ToÈrnvall, Davor Djedovic, Erik Andersson, Berit Solbreck and Tomas GroÈnqvist for their assistance in the ®eld and labora-
131
tory. We also thank Dr. Bengt Olsson for providing valuable comments on the manuscript and Dr. Mary McAfee for correcting the English. The study was ®nancially supported by grant 8477-4 from the Swedish National Energy Administration. References Anon., 1990. The National Atlas of Sweden. The Forest. SNA Publishing. Stockholm. Anon., 1998. Skogsstyrelsen foÈreskrifter och allmaÈnna raÊd om skador paÊ mark och vatten. SKSFS 1998:5. Skogsstyrelsens foÈrfattningssamling. ISSN 0347-5212 (in Swedish). Anon., 1999. Energy in Sweden. ET 82:1999. Swedish National Energy Administration, Stockholm, Sweden. Arvidsson, H., Lundkvist, H., 2001. Wood Ash Application in Spruce Stands. Appendix IV in thesis by Arvidssor, H. 2001. Wood Ash Application in Spruce Stands. Effects on Ground Vegetation, Tree Nutrient Status and Soil Chemistry. Acta Universitatis Agriculturae Sueciae, Sylvestria 221. Doctoral dissertation. ISSN 1401-6230, ISBN 91-576-6305-X. Arvidsson, H., Lundkvist, H., 2002. Needle chemistry in young Norway spruce stands after application of crushed wood ash. Plant Soil 238, 159±174. Arvidsson, H., Vestin, T., Lundkvist, H., 2002. Effects of crushed wood ash application on ground vegetation in young Norway spruce stands. For. Ecol. Manage. 161, 75±87. Baes, C.F., Mesmer, R.E., 1976. The Hydrolysis of Cations. Wiley, New York, pp. 112±123. Bramryd, T., Fransman, B., 1995. Silvicultural use of wood ashesÐeffects on the nutrient and heavy metal balance in a pine (Pinus sylvestris L.) forest soil. Water Air Soil Poll. 85, 1039±1044. Eriksson, H.M., 1998a. Short-term effects of granulated wood ash on forest soil chemistry in SW and NE Sweden. Scand. J. For. Res. (Suppl. 2) 43±55. Eriksson, J., 1998b. Dissolution of hardened wood ashes in forest soils: Studies in a column experiment. Scand. J. For. Res. (Suppl. 2) 23±32. HaÈgglund, B., Lundmark, J.-E., 1977. Site index estimation by means of site properties. Scots pine and Norway spruce in Sweden. Stud. For. Suec. 138, 1±38. Kahl, J.S., Fernandez, I.J., Rustad, L.E., Peckenham, J., 1996. Soil processes and chemical transport. Threshold application rates of wood ash to an acidic forest soil. J. Environ. Qual. 25, 220± 227. Kellner, O., Weibull, H., 1998. Effects of wood ash on bryophytes and lichens. Scand. J. For. Res. (Suppl. 2) 76±85. Levula, T., Saarsalmi, A., Rantavaara, A., 2000. Effects of ash fertilization and prescribed burning on macronutrient, heavy metal, sulphur and 137 Cs concentrations in lingonberries (Vaccinium vitis-idea). For. Ecol. Manage. 126, 269±279. Lundkvist, H., 1998. Wood ash effects on enchytraeid and earthworm abundance and enchytraeid cadmium content. Scand. J. For. Res. (Suppl. 2) 86±95.
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Olsson, B.A., Bengtsson, J., Lundkvist, H., 1996. Effects of different forest harvest intensities on the pools of exchangeable cations in coniferous forest soils. For. Ecol. Manage. 84, 135± 147. Steenari, B.-M., Lindqvist, O., 1997. Stabilisation of biofuel ashes for recycling to forest soil. Biomass Bioenergy 13 (1±2), 39±50. Steenari, B.-M., Marsic, N., Karlsson, L.-G., Tomsic, A., Lindqvist, O., 1998. Long-term leaching of stabilized wood ash. Scand. J. For. Res. (Suppl. 2) 3±16. Steenari, B.-M., Schelander, S., Lindqvist, O., 1999. Chemical and leaching characteristics of ash from combustion of coal, peat
and wood in a 12 MW CFBÐa comparative study. Fuel 78, 249±258. Sundqvist, T., 1999. A high temperature granulation process for ecological ash recirculation. Licentiate Thesis. 1999:14. Division of Energy Engineering, Department of Mechanical Engineering, LuleaÊ University of Technology. ISSN 1402-1757. Tamm, C.O., Popovic, B., 1989. Acidi®cation experiments in pine forests. Swedish Environmental Protection Agency. Report 3589. 131 pp. ISSN 0282-7298. Unger, Y.L., Fernandez, I.J., 1990. The short-term effects of woodash amendment on forest soils. Water Air Soil Poll. 49, 299±314.
Effects of crushed wood ash on soil chemistry in young Norway spruce stands Helen Arvidsson*, HeleÂne Lundkvist Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, SE-750 07 Uppsala, Sweden Received 18 July 2001; received in revised form 5 February 2002; accepted 10 May 2002
Abstract The use of logging residues as a fuel in district heating plants has led to regular wood ash recycling to forest soil to prevent soil nutrient depletion. Wood ash with a low content of unburnt matter reacts with water and air in a so-called self-hardening process. Hardening of the ash is a way to reduce its reactivity and thus increase the time for its dissolution. In four ®eld experiments, changes in soil chemistry were analyzed 6 years after application of hardened crushed wood ash to 8±10-year-old Norway spruce (Picea abies (L.) Karst.) stands. The 0±5, 5±10 and 10±20 cm layers of the soil were sampled, including the disturbed humus layer. Logging residues were collected at the preceding harvest. At each site, hardened crushed wood ash of two types, NymoÈlla and Perstorp, was applied in a randomized block design n 4. The dose applied was 3 Mg ha 1. Exchangeable Ca, Mg, K and effective cation exchange capacity (CECeff) on a per hectare basis in the 0±20 cm soil layers were signi®cantly higher in wood ash-treated plots than in the control plots in analyses across all study sites. Total exchangeable acidity was signi®cantly lower after wood ash application. There was a signi®cant effect on pH in the 0±5 cm layer of the soil in three of the sites, where pH increased on average by 0.5 units in wood ash Perstorp-treated plots and by 0.7 units in wood ash NymoÈlla-treated plots compared to control plots. Further down in the soil pro®le, no differences were detected at any site. Wood ash application resulted in a higher level of base saturation (BS), especially in the 0±5 cm layer. BS increased on an average by 39 and 31% units in the 0±5 cm soil layer, and by 13 and 10% units in the 5±10 cm soil layer, in wood ash NymoÈlla- and Perstorptreated plots, respectively, compared with the control. The results show that hardened wood ash recycling can compensate for base cations lost at whole-tree harvesting. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Acidity; Base cations; pH; Soil; Wood ash
1. Introduction At present, 17% of the energy supply in Sweden originates from forestry (Anon., 1999). The largest potential source of additional biofuels is logging residues from tree fellings. There is an increasing demand *
Corresponding author. Tel.: 46-1867-2434; fax: 46-1867-3430. E-mail address: [email protected] (H. Arvidsson).
for logging residues in Sweden. Burning of felling residues for heating does not give any net contribution to the carbon dioxide level of the atmosphere provided that forests are replanted after fellings. However, soil nutrient depletion and soil acidi®cation are the major concerns associated with removal of logging residues (c.f. Olsson et al., 1996). The depletion of soil nutrients can be counteracted by returning thewood ash to the soil. The effects of wood ash application on forest soil have been studied previously, but the majority of these
0378-1127/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 2 ) 0 0 2 7 8 - 5
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studies deal with untreated loose wood ash and only a few investigate ash that has been stabilized in some way. Kahl et al. (1996) conducted a ®eld experiment on the effects of application of loose wood ash in doses of 6, 13 and 20 Mg ha 1 on soil and soil solution chemistry. Ash application increased soil pH, base saturation (BS) and exchangeable base cations in both the O and B horizons. After 25 months, irrespective of the dose, pH had increased in the O horizon by approximately 2 pH units. Bramryd and Fransman (1995) reported an increase of approximately 1 pH unit in the mor layer 10 years after application of loose ash in a dose of 2 Mg ha 1. Loose ash taken directly from the burner is highly alkaline. There have been some concerns that loose ash may damage the plants and soil organisms. In order to avoid this, stabilization of the ash should be done. Wood ash with a low content of unburnt matter reacts with water and air in a so-called self-hardening process. In order to accomplish self-hardening, the ash is wetted, packed in a large pile, stored and then crushed into particles of suitable sizes (Steenari and Lindqvist, 1997). Pellets or granules of ash are an alternative to crushed hardened ash and also reduce the reactivity of the ash. Compared to loose, untreated ash, granulated ash has been shown to cause a less drastic pH effect on the soil (Eriksson, 1998a). The present paper reports on chemical changes in the soil in ®eld experiments in young stands of Norway spruce (Picea abies (L.) Karst.) after application of self-hardened wood ash. The soil chemistry study is part of a larger investigation, including studies on the impact of wood ash on leaching of nitrate and other elements and on changes in ®eld and bottom vegetation and tree nutrient status. We hypothesized that effects of ash application would be dependent on the climatic situation. More speci®cally, we anticipated the effects to be faster and more pronounced in southern than in northern Sweden. Therefore, the ®eld experiments were established in four climatic zones. We analyzed the following soil chemistry parameters 6 years after application of crushed hardened wood ash: exchangeable Ca, Mg, K, Na and Cd, cation exchange capacity (CECeff), pH, electrical conductivity, exchangeable acidity, BS, extractable NH4 , NO3 and total C and N. The ash dose applied, 3 Mg ha 1, is recommended by the National Forestry Board in Sweden in order to compensate for base cation losses at whole-tree (above ground) harvesting.
2. Materials and methods 2.1. Site descriptions The four ®eld experiments used in our investigation were established in a climatic gradient of sites with forest type Vaccinium myrtillus (HaÈgglund and Lundmark, 1977). Forest type V. myrtillus represents about 30% of the total forest area in Sweden. The sites were chosen to represent different climate conditions and the following four generalized climatic zones as they can be found in the National Atlas of Sweden (Anon., 1990): The south west (site name Flybacken) and the southern highlands (Ljungby) with high and fairly high acidifying deposition, respectively; the south east (Simtuna) with less acidifying deposition; and the northern coastal area (Malungs¯uggen) where deposition is low (Table 1). The northern coastal area has dry summers and a slightly humid climate in a broad belt along the coast of Norrland. The south east has a favorable temperature climate but dry summers and is slightly humid to a lesser degree. The south west has high precipitation and a markedly humid climate and southern highlands area has a humid climate. The spruce stands differed in stand age and were 2±4year-old when the wood ash was applied in 1993. All sites had been whole-tree harvested and planted with Norway spruce (P. abies (L.) Karst.). Soil scari®cation was carried out before planting at all sites except at Simtuna. Patch scari®cation was done on the Flybacken and Ljungby sites and harrowing on the Malungs¯uggen site. Both patch scari®cation and harrowing caused a slight disturbance of the forest ¯oor. 2.2. Experimental design and treatments The experiments had a randomized block design, with three treatments and four blocks at each site (one replicate per block, n 4, i.e. 12 plots per site). Each 3 m 3 m plot was surrounded by a 0.5 m border strip. Within a plot there were four planted Norway spruce trees. The treatments were control, application of wood ash NymoÈlla (WAN) and application of wood ash Perstorp (WAP). The ashes were from district heating plants, at NymoÈlla and Perstorp, Sweden. The WAN originated from a cyclone furnace ®red mainly with bark, whereas WAP originated
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123
Table 1 Characteristics of the experimental sitesa Site
Climate zone Forest typeb Location Altitude (m a.s.l.) Precipitation (mm per year) Length of growing season (days >5 8C) Wet deposition of nitrogen (kg ha 1 per year) Planting year Site index (H100)c Soil type Soil texture Clay content (%) Bulk density of mineral soil (<2 mm, g l 1) 0±5 cm 5±10 and 10±20 cm
Flybacken
Ljungby
Simtuna
Malungsfluggen
South west V. myrtillus 568450 N, 138230 E 170 800 240 12±14 1990 G28 Podsol Sandy loam 7.8
Southern highlands V. myrtillus 568500 N, 148000 E 165 650 240 10±12 1990 G28 Podsol Sandy loam 5.5
South east V. myrtillus 598420 N, 168500 E 30 540 210 6±8 1989 No data Podsol Sandy loam 10.5
Northern coastal area V. myrtillus 628100 N, 168530 E 380 570 180 2±4 1991 G24 Podsol Loamy sand 8.9
722 742
630 817
232 689
540 713
a
All sites were planted with Norway spruce (P. abies (L.) Karst.). Climate zones are from the National Atlas of Sweden (Anon., 1990). Forest type according to HaÈgglund and Lundmark (1977). c Height of dominant spruce at 100 years of age (HaÈgglund and Lundmark, 1977). b
from a circulating ¯uidized bed boiler ®red with 90% wood chips and 10% peat. After combustion, the ashes were stabilized by addition of water and allowed to harden before being crushed. The chemical composition, as determined by a LiBO2 melting technique, differed between the ashes (Table 2). A single dose of 3 Mg ha 1 (dry mass) of crushed wood ash was applied by hand as uniformly as possible to each ash-treated plot in August±October 1993. The dose applied was recommended by the National Forestry Board in Sweden in order to compensate for base cation losses at whole-tree (above ground) harvesting (Anon., 1998). The WAN contributed 44 kmolc ha 1 of Ca, 6 kmolc ha 1 of Mg and 0.8 kmolc ha 1 of K. The WAP contributed 24 kmolc ha 1 of Ca, 5 kmolc ha 1 of Mg and 1.5 kmolc ha 1 of K at application.
2.3. Soil sampling and chemical analyses Soil sampling was carried out in June 1999. From each plot, soil cores with a diameter of 25 mm were collected at 10 spots. The litter layer was removed from the samples in the ®eld. If wood ash particles could be seen, they were removed from the samples. Each core was divided into subsamples representing the layers 0±5, 5±10 and 10±20 cm below the soil surface. The 0±5 cm layer consisted of a mixture of humus and mineral soil, due to soil scari®cation. The soil samples of each layer were pooled to produce one sample per plot. The soil was sifted through a 2 mm mesh net prior to analysis. Soil dry weights were determined after the samples had been dried overnight at 105 8C. Calculations of nutrient amounts in the 0±5 cm layer were based on
Table 2 Chemical composition of the WAN and the WAP used in the present study
WAN WAP a
Ca (%)
Si (%)
Al (%)
K (%)
Mg (%)
Na (%)
P (%)
S (%)
LOIa
Cd (ppm)
29.7 16.2
9.5 10.7
3.2 4.9
1.0 2.0
2.4 2.0
0.6 1.6
0.4 0.4
1.4 2.9
19.4 13.8
5.4 10.4
Loss on ignition.
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bulk densities of the sifted soil fraction (<2 mm) (Table 1). Mean values n 12 for each site were used for the calculations. The bulk densities of the ®ne soil fraction in the 5±10 and 10±20 cm layers were estimated for each site with 50±100 rod penetration tests according to Tamm and Popovic (1989). Soil pH (H2O) was measured with a glass electrode on suspensions of soil in distilled water. Soil suspensions were made by adding 50 ml of distilled water to 7 g (0±5 cm layer) or 22 g (5±10 and 10±20 cm layers) of fresh, sifted soil. The suspensions were revolved on a reciprocal shaker for 2 h, and pH and conductivity were measured at room temperature after sedimentation overnight. Soil extracts for NH4 and NO3 analyses were prepared by adding 10 g (0±5 cm layer) or 20 g (5±10 and 10±20 cm layers) of fresh soil samples in 250 ml polyethylene bottle and adding 100 ml 1 M KCl. The ¯asks were revolved for 1 h. Chemical analyses of NH4 and NO3 in the ®ltered extracts were performed by using a ¯ow injection analysis (FIA) system. Exchangeable amounts of Na, K, Ca, Mg, Al and Cd in the soil were determined by using 1 M NH4Cl as extract. Chemical analyses of the ®ltered extracts were performed by using an inductively coupled plasmaÐ atomic emission spectrophotometer (Jobin Yvon JY-70 Plus). The soil extracts were prepared by adding 10 g (0±5 cm layer) or 20 g (5±10 and 10±20 cm layers) of fresh soil sample to a 250 ml polyethylene bottle and adding 100 ml 1 M NH4Cl. The ¯asks were revolved for 1 h, and then pH in the extracts was measured. Total nitrogen (N) and carbon (C) were analyzed with a dry oxidation procedure at about 1000 8C using a CarloErba elementary analyzer, model NA 1500.
Altot Al3 Al OH2 Al OH2
2.4. Data treatment
Table 3 General treatment effect on pools of exchangeable Ca, Mg, K, Na, effective CECeff and total acidity (kmolc ha 1) in the 0±20 cm soil layera
Exchangeable acidity was de®ned as the equivalent sum of exchangeable H and Al. Exchangeable base cations were de®ned as the equivalent sum of Na, K, Ca and Mg. Effective CECeff was de®ned as the sum of exchangeable base cations and exchangeable acidity. BS was de®ned as (exchangeable base cations/ CECeff 100. Exchangeable H was determined according to the following equations (molar units): Exchangeable H 10
pH
0:79
1
2Al OH2
Al OH2
Al OH2 10
5:47
Al OH2 10
10:3
Al3 H Al3 H
1 2
Altot and pH (H) refer to the measured concentrations in the extract. The equilibrium constants (10 5.47 and 10 10.3) and the H activity factor (0.79) were obtained from Baes and Mesmer (1976). For analysis of treatment effects on investigated soil chemical variables within sites, an analysis of variance (ANOVA) for randomized block design and signi®cance tests was carried out using the programme Super-Anova Abacus Concepts. Least signi®cant difference tests used the Tukey±Kramer test to detect differences between treatment means. In addition, a nested model was used to examine general treatment effects across all sites. The total pool of exchangeable Ca, Mg, K, Na and CECeff and total acidity were tested. Sites, treatments and blocks (blocks nested within sites), including the interaction between sites and treatments were then used as sources of variation. No transformation of data was considered necessary, since the variances were fairly homogeneous. 3. Results In general, the total pool of exchangeable Ca, Mg, K and the effective CECeff per hectare were signi®cantly higher in wood ash-treated plots than in the control plots (Table 3 and Fig. 1). Total exchangeable acidity was signi®cantly lower after wood ash application
Dependent variable
Treatment (2 d.f.)
Site (3 d.f.)
Treatment site (6 d.f.)
Ca Mg K Na CECeff Total acidity
0.0001 0.0018 0.0268 ns 0.02 0.0002
ns ns 0.0001 0.0003 0.0078 ns
ns ns 0.049 0.0437 ns ns
a p-Values are shown when p < 0:05 for treatment, site and the interaction between site and treatment.
Fig. 1. Amounts of exchangeable Ca (A), Mg (B) and K (C) in the soil after wood ash application (kmolc ha 1). Mean values for each site and treatment are given. Each bar is subdivided into 0±5, 5±10 and 10±20 cm layers of the soil from top to bottom. The treatments n 4 were WAN, WAP and control (C). S.D. bars refer to the total amounts. Bars with the same or no letter are not signi®cantly different p < 0:05 according to Tukey±Kramer test.
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Table 4 Concentrations of exchangeable base cations, acidity, CECeff and BS in soil layers 6 years after treatmenta Site Flybacken
Ljungby
Simtuna
Soil layer (cm)
Treatment
C a Mg K Na Acidity CECeff BSb (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (cmolc kg 1) (%)
0±5
WAN WAP C p
5.05b 4.26b 0.79a 0.001
0.82b 0.82b 0.46a 0.02
0.16 0.21 0.15 0.15
0.09 0.11 0.08 0.18
1.22b 1.89b 3.40a <0.001
7.34b 7.29b 4.89a 0.01
83.1b 73.3b 30.0a <0.001
5±10
WAN WAP C p
0.52b 0.48b 0.14a 0.002
0.17b 0.13ab 0.09a 0.04
0.06 0.06 0.06 0.87
0.04 0.04 0.05 0.70
2.55 2.57 2.80 0.06
3.34 3.28 3.13 0.52
23.6b 21.5b 10.5a 0.002
10±20
WAN WAP C p
0.14b 0.14b 0.05a 0.02
0.05 0.05 0.03 0.10
0.03 0.03 0.02 0.09
0.03ab 0.04a 0.03b 0.03
1.77 1.80 1.59 0.22
2.02 2.06 1.72 0.13
12.0b 12.5b 7.6 a 0.009
0±5
WAN WAP C p
9.99b 5.92ab 1.99a 0.02
2.02 0.95 0.67 0.05
0.41 0.22 0.20 0.067
0.16 0.09 0.09 0.083
1.26b 1.61b 4.30a 0.0001
13.57b 8.79ab 7.24 a 0.047
86.0b 81.2b 39.9a 0.0001
5±10
WAN WAP C p
0.67b 0.40ab 0.14a 0.028
0.22b 0.11b 0.06a 0.004
0.07 0.05 0.04 0.064
0.03 0.03 0.02 0.23
2.57 2.43 2.64 0.65
3.56 3.01 2.90 0.054
27.4b 19.1ab 8.8 a 0.017
10±20
WAN WAP C p
0.13 0.10 0.05 0.06
0.06b 0.04ab 0.03a 0.035
0.03b 0.02ab 0.02a 0.038
0.02 0.02 0.02 0.67
2.21 1.84 1.72 0.07
2.45 2.01 1.83 0.056
9.4b 8.6ab 5.9 a 0.024
0±5
WAN WAP C p
14.07 12.30 9.04 0.32
1.78 1.80 1.82 0.99
0.38 0.44 0.48 0.42
0.14 0.17 0.14 0.80
1.47b 3.03b 5.67a 0.003
17.83 17.74 17.16 0.97
5±10
WAN WAP C p
1.61 1.95 1.10 0.53
0.28 0.33 0.26 0.80
0.12 0.10 0.10 0.79
0.02 0.03 0.03 0.29
3.36 4.19 4.82 0.07
5.40 6.61 6.31 0.61
34.8 35.7 23.4 0.28
10±20
WAN WAP C p
0.43 0.51 0.22 0.17
0.09 0.10 0.07 0.51
0.07 0.05 0.04 0.10
0.01 0.01 0.02 0.16
2.19 2.27 2.65 0.35
2.79 3.25 3.00 0.62
20.4 20.7 11.7 0.044
WAN WAP C p
6.86b 4.73b 2.02a 0.0035
0.81b 0.69ab 0.39a 0.0135
0.32 0.27 0.26 0.29
0.09 0.06 0.04 0.17
1.28 1.76 2.58 0.13
9.37b 7.52ab 5.28a 0.0255
86.0b 77.1b 51.3a 0.0026
WAN WAP C p
0.90 1.09 0.78 0.48
0.16 0.22 0.16 0.22
0.12 0.15 0.14 0.18
0.03 0.03 0.03 0.85
2.77b 3.71ab 4.22a 0.034
3.98 5.20 5.34 0.08
29.5 29.0 20.7 0.21
Malungsfluggen 0±5
5±10
88.8b 82.6ab 66.8a 0.0255
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
127
Table 4 (Continued ) Site
Soil layer (cm)
Treatment
10±20
WAN WAP C p
Mg K Na Acidity CECeff BSb C a 1 1 1 1 1 1 (cmolc kg ) (cmolc kg ) (cmolc kg ) (cmolc kg ) (cmolc kg ) (cmolc kg ) (%) 0.34 0.42 0.30 0.32
0.08ab 0.08b 0.07a 0.0364
0.09 0.11 0.09 0.07
0.02 0.03 0.04 0.077
1.62 1.43 1.16 0.47
2.16 2.07 1.66 0.27
26.4 34.4 29.9 0.60
a The treatments n 4 were WAN, WAP and control (C). Signi®cantly different treatment means are indicated by different letters (Tukey±Kramer, p < 0:05). b Calculated as mean value of the replicates.
than in the control. Site and treatment interacted signi®cantly in their in¯uence on exchangeable pools of K and Na. Concentration of exchangeable Ca was greatly increased by the ash addition (Table 4). In the 0± 5 cm soil layer at Flybacken, concentrations of exchangeable Ca in WAN- and WAP-treated plots were six- and ®vefold higher, respectively, than in control plots. In the 5±10 and 10±20 cm layers, the Ca concentrations increased by a factor of 3 in both ash treatments compared with the control. In the 0±5 cm soil layer at Ljungby, exchangeable calcium concentrations were ®ve- and threefold higher in WAN and WAP, respectively, treatment than in the control. At Simtuna the increase was less pronounced, with 1.5 times as much Ca in the ash treatments as in the control. In the 0±5 cm soil layer at Malungs¯uggen, concentrations of exchangeable Ca in WAN- and WAP-treated plots were increased by three and two times, respectively, compared with the control. Total pools of exchangeable Ca also increased as a response to the ash addition (Fig. 1A). Compared with the control, the concentrations of Mg in the 0±5 cm layer were increased by a factor of 2 for both ash treatments at all sites except at Simtuna (Table 4). At Flybacken and Ljungby, an increase in Mg concentrations was also detected in the 5±10 and 10±20 cm layers of the ash treatments. On all sites except Simtuna, the total pools of exchangeable Mg increased as a response to the ash addition (Fig. 1B). Treatment effects on exchangeable K were only detected in the 10±20 cm layer at the Ljungby site, where the WAN treatment had a higher concentration of K than the control (Table 4). At the Malungs¯uggen site, the total pool of exchangeable K was higher in the WAP treatment than in the control (Fig. 1C).
At Flybacken, the exchangeable acidity in the upper 0±5 cm of the soil was 64 and 44% lower in WAN and WAP treatments, respectively, than in the control (Table 5). A decrease in acidity of the same order of magnitude was found in the 0±5 cm soil horizon for all sites. Further down, 5±10 and 10±20 cm in the soil pro®le, no differences were detected at any site except at Malungs¯uggen (5±10 cm) where treatment NymoÈlla wood ash decreased acidity by 34% compared with the control. In the 0±5 cm soil layer at Flybacken, in the treatments WAN and WAP, the BS was increased by 53 and 43% units, respectively, compared to the control. The increase was 13 and 11% units in the 5±10 cm and 4 and 5% units in the 10±20 cm soil layer. The increase in BS after ash treatment varied between the sites. BS increased on average by 39 and 31% units in the 0± 5 cm soil layer, in WAN- and WAP-treated plots compared with the control. At Flybacken, Ljungby and Simtuna, pH increased in the 0±5 cm layer on average by 0.7 pH units in WAN-treated plots and by 0.5 pH units in WAPtreated plots compared with control plots. At Malungs¯uggen, there was no signi®cant difference between the treatments. Further down in the soil pro®le, no differences were detected at any site (Table 5). No differences in electrical conductivity were found except at Malungs¯uggen, where the electrical conductivity was higher in the 10±20 cm soil layer in WAP-treated plots compared to control plots. No differences between treatments were found for NH4 or for total C and N concentrations (Table 5). At all sites except Simtuna there was a tendency for a higher C/N ratio in the WAN treatment than in the control in the upper 5 cm of the soil. All NO3 values were below the detection limit.
128
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
Table 5 pH and electrical conductivity of soil extracts in distilled water, concentrations of salt extractable NH4 -N, Cd and concentrations (% of dry mass) of C and N and the C:N ratio in soil layers 6 years after treatmenta Site
Flybacken
Ljungby
Simtuna
Malungsfluggen
Treatment
pHH2 O
Electrical conductivity (mS cm 1)
NH4 -N (mg g 1)
Cd (mmolc kg 1)
0±5
WAN WAP C p
4.89b 4.74b 4.29a 0.001
23.0b 27.8ab 28.8a 0.041
3.2 6.1 4.9 0.046
1.7 2.2 1.6 0.046
5±10
WAN WAP C p
4.38 4.41 4.38 0.8
27.6 26.6 29.2 0.69
0.1 0.1 0.4 0.5
10±20
WAN WAP C p
4.74 4.66 4.73 0.18
21.2 21.1 17.4 0.20
0±5
WAN WAP C p
4.89b 4.80b 4.18a 0.002
5±10
WAN WAP C p
10±20
Soil layer (cm)
C
N
C:N
89 93 78 0.33
3.7 4.0 3.4 0.43
24 23 22 0.06
0.7b 0.6b 0.8a 0.002
35 33 34 0.85
1.6 1.6 1.6 0.99
21 20 20 0.33
0.6 1.5 1.1 0.19
1.0 0.8 0.9 0.23
27 25 26 0.75
1.4 1.3 1.3 0.79
20 20 20 0.86
33.4 22.7 30.1 0.13
1.4 0.6 2.5 0.16
3.7 2.9 2.7 0.29
197 103 122 0.06
6.6 3.7 4.5 0.07
29a 28ab 27b 0.05
4.19 4.35 4.28 0.07
35.7 27.8 26.9 0.05
0.2 0.3 0.2 0.9
0.6 0.5 0.5 0.65
38 30 31 0.18
1.4 1.2 1.2 0.53
27 26 25 0.22
WAN WAP C p
4.52 4.59 4.53 0.67
21.2 21.2 21.5 0.99
0.3 0.1 0.3 0.28
0.4 0.4 0.4 0.72
27 23 23 0.10
1.1 1.0 1.0 0.25
24 24 23 0.65
0±5
WAN WAP C p
4.71b 4.41b 4.02a 0.003
52.0 42.5 52.7 0.53
0.9 0 0.1 0.48
4.3 6.4 5.8 0.24
173 222 274 0.11
5.6 7.1 8.9 0.13
30 31 31 0.80
5±10
WAN WAP C p
4.41 4.19 4.13 0.22
32.9 51.8 48.2 0.21
2.6 2.3 0.1 0.69
1.1 1.4 1.1 0.75
49 62 54 0.70
1.6 1.9 1.8 0.80
31 32 31 0.28
10±20
WAN WAP C p
4.72 4.62 4.63 0.55
33.4 27.8 23.2 0.32
1.8 1.0 0.3 0.55
0.6 0.5 0.4 0.13
29 30 25 0.24
0.9 0.9 0.8 0.35
32 32 32 0.85
0±5
WAN WAP C p
5.26 5.06 4.93 0.31
29.7 26.4 24.3 0.48
8.5 3.3 8.8 0.043
2.3 2.5 1.6 0.19
77 49 44 0.06
2.8 1.7 1.7 0.06
28 29 26 0.14
5±10
WAN WAP C p
4.84 4.67 4.70 0.11
36.6 42.6 31.6 0.13
2.8 2.2 2.0 0.78
1.3 1.4 1.4 0.78
32 38 29 0.33
1.2 1.4 1.2 0.44
26 27 25 0.65
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
129
Table 5 (Continued ) Site
Soil layer (cm)
Treatment
pHH2 O
Electrical conductivity (mS cm 1)
NH4 -N (mg g 1)
Cd (mmolc kg 1)
10±20
WAN WAP C p
4.91 4.83 4.88 0.55
30.8b 46.8a 33.6b 0.01
4.4 4.2 3.1 0.35
1.3 1.6 1.7 0.32
C
38 55 49 0.44
N
C:N
1.5 2.0 1.9 0.36
26 26 25 0.82
a The treatments n 4 were WAN, WAP and control (C). Signi®cantly different treatment means are indicated by different letters (Tukey±Kramer, p < 0:05).
There was a tendency in the 0±5 cm soil layer for Cd concentrations to be higher in the WAP-treated plots compared with the control plots. In the 5±10 cm soil layer at Flybacken, exchangeable Cd was signi®cantly lower in the ash treatments than in the control. 4. Discussion Our most important ®nding was that hardened wood ash application in a dose of 3 Mg ha 1 generally resulted in modestly but signi®cantly increased soil pH, BS, concentrations of exchangeable Ca and Mg and CEC. The effects were most pronounced in the upper 0±5 cm layer. The increase in BS was mainly due to increased concentrations of Ca and Mg. BS increased in the whole soil pro®le. The four sites examined differ in their climatic conditions and deposition of nitrogen. We hypothesized that effects of ash application would be dependent on the climatic situation. However, regardless of differences in climate conditions, there were overall treatment effects detected for the pools of exchangeable Ca, Mg, K, for CEC and for the total pool of acidity as revealed by analysis across all sites. The Simtuna site, differed from the others in that only few variables showed signi®cant differences between the treatments. Stabilization of wood ash through self-hardening is a way to decrease the solubility of the mineral nutrients. After 6 years in the ®eld, most of the easily soluble salts (mainly K, Na, Cl and SO4 2 ) are most likely leached out from the ash. Soluble forms of Ca as calcium oxide (CaO) and portlandite (Ca(OH)2) and some Mg as MgO would also be lost from the ash (Steenari et al., 1998). It might be that some wood ash particles were included in the soil samples. However, the salt 1 M NH4Cl with which we extracted the soil
samples is a weak neutral salt and could probably not further dissolve any elements from the ash matrix (J. Eriksson, pers. commun.). The overall effect that application of wood ash increased the pool of Ca and Mg is an important ®nding. The results show that wood ash recycling may be a way to return base cations lost at wholetree harvesting. With WAN and WAP we applied 44 and 24 kmolc ha 1 Ca, respectively. According to our results, the pools of exchangeable Ca were on average 16 and 11 kmolc ha 1 higher after WAN and WAP addition, respectively, compared to the control (Fig. 1A). After a weathering time of 2.5 years in the ®eld in southwest Sweden, WAN (named CF ash by Steenari et al., 1998) had lost about 5% of the Ca and WAP (named CFB B ash by Steenari et al., 1998) 40% of the Ca. It is possible that WAP had a higher proportion of Ca present in easily dissolved forms such as portlandite (Ca(OH)2). The hardening process was probably not completed for WAP and only a part of the portlandite Ca(OH)2 had formed calcite (CaCO3). WAP originated from ®ring of wood chips but also some peat. Peat ash has been shown to form gypsum instead of slow releasing ettringite (Ca6Al2(SO4)3(OH)1226H2O) during the hardening process (Steenari et al., 1999). Results from modeling of the solid phase in wood ash particles suggest that after a weathering time of 2 years, Ca in the ash is present in the form of calcite (CaCO3) and the release rate is slowed down (Steenari et al., 1998). It is likely that WAN had lost 5% of its Ca after 2.5 years in the ®eld but after 6 years in the ®eld the loss had to be about 35% to match the difference in the pools of Ca that were 16 kmolc ha 1 higher in WAN-treated plots compared to the control. Modeling the stability of some Ca minerals during weathering of hardened wood ash suggests that 40% of the Ca content would
130
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
have been lost after 2 years (Steenari et al., 1998). This is in agreement with column leaching tests at the laboratory (Steenari et al., 1998; Eriksson, 1998b). The Ca released from the WAN and WAP ashes seems to be mobilized and bound in an exchangeable form within the soil. Two years after application of a granulated wood ash in a dose of 3 t ha 1, Eriksson (1998a) reported an increase of 2.5±5 kmolc ha 1 of exchangeable Ca compared to the control and concluded that more of the Ca had yet to dissolve. The solubility of Ca from hardened wood ashes seems to be quicker than from granulated wood ash (Steenari et al., 1998). Application of the hardened WAN and WAP used in our study in a dose of 3 Mg ha 1 gave positive effects in terms of increased pools of Ca. Thus, wood ash application can compensate for losses of base cations after whole-tree harvesting. The concern about wholetree harvesting has been about nutrient removal and how to sustain long-term nutrient budgets. At four whole-tree harvested sites that were investigated 15 years after clearfelling, Olsson et al. (1996) found that the soil pools of exchangeable Ca were 0±6 kmolc ha 1 lower in whole-tree harvested plots compared to those in conventionally harvested plots. Thus, the ash dose used in our study increased the pool of exchangeable Ca more in absolute terms than it was reduced by whole-tree harvesting in the study by Olsson et al. (1996). The Mg pool increased by approximately 1± 3 kmolc ha 1 after wood ash addition (Fig. 1B). With WAN and WAP, we applied 6 and 5 kmolc ha 1 Mg, respectively. Steenari et al. (1998) reported losses of Mg between 10 and 30% after a weathering time of 2.5 years. Similar results were found in a column leaching test simulating a weathering period of 5 years (Eriksson, 1998b). Mg has been observed as MgO and Mg silicates in ashes (Steenari and Lindqvist, 1997). The low chemical solubility of Mg was probably due to the high pH. Steenari et al. (1998) noticed a slight increase in leaching of Mg towards the end of a simulated leaching period. The low recovery of Mg in our study suggests that more Mg will be leached from the ashes with time. We found that after 5 years, the exchangeable concentrations and the exchangeable pool of K were hardly affected by wood ash application. Two years after application of an untreated wood ash in a high
dose of 20 Mg ha 1, Kahl et al. (1996) found increased potassium concentrations in the mineral soil. Unger and Fernandez (1990) noticed an increase of K in the mineral soil with doses ranging from 4 to 20 Mg ha 1 of untreated wood ash. From a laboratory study using WAP, Eriksson (1998b) reported that approx. 50% of the original K was lost in a column leaching test, corresponding to approx. 5 years weathering in the ®eld. A similar release was found in samples collected from the ®eld after 2.5 years of weathering in the forest (Steenari et al., 1998). Since exchange sites on the soil particles attract Ca more strongly than they attract K, the low recovery of K on the exchange site could be due to greater leaching of K, but probably also to higher uptake by trees. In analyses of 1-year-old needles we found that 5 years after ash application, K concentration and K:N ratio were in general higher in wood ash-treated plots compared with a control (Arvidsson and Lundkvist, 2002). Furthermore, consecutive sampling for 5 years after ash application of the soil water at 50 cm depth with suction lysimeters indicated higher leaching of K from ash-treated plots compared to control plots for 2 years and thereafter it decreased to control levels (Arvidsson and Lundkvist, 2001). In the upper 5 cm of the soil, hardened wood ash application increased the pH by 0.7 pH units in WANtreated plots and 0.5 pH units in WAP-treated plots compared to control plots. The effects on soil pH were less than after application of loose wood ash in similar doses, but higher than after application of granulated wood ash (Kahl et al., 1996; Eriksson, 1998a; Levula et al., 2000). Levula et al. (2000) noted an increase of one pH unit and Kahl et al. (1996) noted an increase of two units one year after application of a loose wood ash in doses of 2.5 and 6 Mg ha 1, respectively. After application of a granulated wood ash, pH increased by 0.45 and 0.1 pH units after a dose of 3 Mg ha 1 to a forest soil in the north and south of Sweden, respectively (Eriksson, 1998a). During the hardening process, formation of less soluble Ca occurs but also reduction in the alkalinity. Both self-hardened wood ash products, such as those used in our study, and granulated wood ashes create more moderate pH effects in the soil than does loose wood ash. The concern about high pH effects is that it might lead to damage to the vegetation and/or soil fauna. We found no effects on the cover of different moss species 5 years after ash application of
H. Arvidsson, H. Lundkvist / Forest Ecology and Management 176 (2003) 121±132
WAP and WAN (Arvidsson et al., 2002). However, a previous study has shown initial damage on mosses caused by loose wood ash and WAP at a dose of 2 Mg ha 1, but the mosses recovered the year after application (Kellner and Weibull, 1998). One of the concerns regarding the negative effects of wood ash application is that it might lead to increased concentrations of Cd levels in the soil. For the WAP treatment, there was a tendency for higher concentrations of exchangeable Cd in the 0± 5 cm layer compared to control plots. In a column leaching study corresponding to a weathering time of 5 years, almost the whole of the initial amount of Cd in WAP remained in the ashes after a simulated 5 years of leaching (Eriksson, 1998b). Eriksson (1998b) suggested that a mobilization of exchangeable Cd from the mor layer occurred rather than leaching from the ash itself. Application of a granulated wood ash at a dose of 3.2 Mg ha 1 increased Cd content in enchytraeids, potworms, during the year after application, but it decreased the following 2 years back to control levels (Lundkvist, 1998). Lundkvist (1998) concluded that this was probably due to an increased mobility of exchangeable Cd rather than an actual release from the ash. Present research is aimed at trying to ®nd new methods to separate Cd from the ash prior to application in the ®eld (Sundqvist, 1999). The concern about direct leaching of Cd from the added ash could then be excluded. 5. Conclusions Application of hardened WAN and WAP used in our study in a dose of 3 Mg ha 1 gave positive effects in terms of increased pools of Ca, Mg and K. Wood ash application can compensate for losses of base cations after whole-tree harvesting. This is an important aspect for the potential to maintain long-term forest production under sustainable nutrient conditions even with intensive forest management. Acknowledgements We would like to thank Ege ToÈrnvall, Davor Djedovic, Erik Andersson, Berit Solbreck and Tomas GroÈnqvist for their assistance in the ®eld and labora-
131
tory. We also thank Dr. Bengt Olsson for providing valuable comments on the manuscript and Dr. Mary McAfee for correcting the English. The study was ®nancially supported by grant 8477-4 from the Swedish National Energy Administration. References Anon., 1990. The National Atlas of Sweden. The Forest. SNA Publishing. Stockholm. Anon., 1998. Skogsstyrelsen foÈreskrifter och allmaÈnna raÊd om skador paÊ mark och vatten. SKSFS 1998:5. Skogsstyrelsens foÈrfattningssamling. ISSN 0347-5212 (in Swedish). Anon., 1999. Energy in Sweden. ET 82:1999. Swedish National Energy Administration, Stockholm, Sweden. Arvidsson, H., Lundkvist, H., 2001. Wood Ash Application in Spruce Stands. Appendix IV in thesis by Arvidssor, H. 2001. Wood Ash Application in Spruce Stands. Effects on Ground Vegetation, Tree Nutrient Status and Soil Chemistry. Acta Universitatis Agriculturae Sueciae, Sylvestria 221. Doctoral dissertation. ISSN 1401-6230, ISBN 91-576-6305-X. Arvidsson, H., Lundkvist, H., 2002. Needle chemistry in young Norway spruce stands after application of crushed wood ash. Plant Soil 238, 159±174. Arvidsson, H., Vestin, T., Lundkvist, H., 2002. Effects of crushed wood ash application on ground vegetation in young Norway spruce stands. For. Ecol. Manage. 161, 75±87. Baes, C.F., Mesmer, R.E., 1976. The Hydrolysis of Cations. Wiley, New York, pp. 112±123. Bramryd, T., Fransman, B., 1995. Silvicultural use of wood ashesÐeffects on the nutrient and heavy metal balance in a pine (Pinus sylvestris L.) forest soil. Water Air Soil Poll. 85, 1039±1044. Eriksson, H.M., 1998a. Short-term effects of granulated wood ash on forest soil chemistry in SW and NE Sweden. Scand. J. For. Res. (Suppl. 2) 43±55. Eriksson, J., 1998b. Dissolution of hardened wood ashes in forest soils: Studies in a column experiment. Scand. J. For. Res. (Suppl. 2) 23±32. HaÈgglund, B., Lundmark, J.-E., 1977. Site index estimation by means of site properties. Scots pine and Norway spruce in Sweden. Stud. For. Suec. 138, 1±38. Kahl, J.S., Fernandez, I.J., Rustad, L.E., Peckenham, J., 1996. Soil processes and chemical transport. Threshold application rates of wood ash to an acidic forest soil. J. Environ. Qual. 25, 220± 227. Kellner, O., Weibull, H., 1998. Effects of wood ash on bryophytes and lichens. Scand. J. For. Res. (Suppl. 2) 76±85. Levula, T., Saarsalmi, A., Rantavaara, A., 2000. Effects of ash fertilization and prescribed burning on macronutrient, heavy metal, sulphur and 137 Cs concentrations in lingonberries (Vaccinium vitis-idea). For. Ecol. Manage. 126, 269±279. Lundkvist, H., 1998. Wood ash effects on enchytraeid and earthworm abundance and enchytraeid cadmium content. Scand. J. For. Res. (Suppl. 2) 86±95.
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