Granulated Wood Ash Research Articles

Soil change and broadleaf tree growth 10 years after wood ash and brash co-application to a clearfelled lowland conifer site in Britain

Abstract Wood ash use, to raise pH and replace nutrients lost through forest harvesting, is well regulated in Scandinavia and Canada, but not yet in the UK. This experiment applied granulated wood ash from mixed tree thinnings to a lowland clay mineral soil at ~2.3 t ha−1 dose rate, after clearfell of western hemlock (Tsuga heterophylla (Raf.) Sarg.). With brash (~56 t ha−1 dry weight) as N resource, a 4 × 4 matrix of ash only, ash + brash, brash only and control treatments were planted with oak seedlings (Quercus robur L.). Soil survey was undertaken before ash application and followed over 10 years. By year 2, self-sown grass was dominant in the control and ash plots, and birch (Betula pendula, Roth.) was present across all treatments by year 4. In year 10, oak height was 25–29 per cent greater in brash and ash + brash plots, with DBH increased >20 per cent over the controls. Birch DBH was greater by 30 per cent in brash plots but was over 50 per cent in the ash + brash plots. Foliar concentrations of Ca, K and P significantly increased with ash addition in both oak and birch, as Al, Mn, Fe and Cr decreased. Soil pH (CaCl2) was reduced in all treatments in year 2 likely due to nitrification, during organic matter and needle breakdown, but recovered 8 years later to be significantly highest in ash and ash + brash plots. Mg, K, Ca, Na, Ba and S concentrations were higher in ash plot soils, but soil organic matter, total carbon and total nitrogen declined due to mineralization and uptake by grass and trees. Wood ash addition did not significantly increase heavy metal concentrations in either soil or foliage. In the long term, wood ash aided soil recovery and promoted tree growth in combination with the brash – it could be beneficial for tree growth after thinning/coppicing on heavy mineral soils, with the prerequisite of an existing ground cover. Aim To quantify the effects of wood ash and brash addition over time to soils and tree growth after conifer clearfelling on a lowland clay soil site.

Effects of different nutrient compensation treatments following forest fuel extraction on biomass of young Norway spruce (Picea abies (L.) Karst.)

Whole tree harvesting of forests may require compensation for losses of nutrients and alkalinity. The effects of three different practical ameliorative methods on spruce allometry, total biomass, and nutrient uptake were studied in an experiment in a 3-year-old Norway spruce ( Picea abies (L.) Karst.) stand in south-west Sweden. The treatments were one application of the fine fraction of logging residues, one application of granulated wood ash, two applications of an N-free vitality fertiliser, and untreated control. Analysis of covariance showed that spruce needle and stem allometry depended on treatment. Spruce fine root allometry was very variable, showing no discernible effect of treatment. Fine root distribution was shallower in treatments with higher graminoid biomass (vitality and wood ash). Vitality treatment increased average concentrations of Ca, Mg, and Zn in spruce total biomass. Ash treatment only increased the Zn concentration. The average N concentration was similar between treatments. Spruce total biomass per unit area was inversely correlated with graminoid biomass. Measurements of N uptake in spruce and graminoid biomass indicated that there was competition for N between spruce and graminoids. Thus, the effect of nutrient compensation on competition needs to be considered when predicting the effect on the growth of the target species.

Effects of wood ash, green residues and N-free fertiliser on naturally regenerated birch and field vegetation in a young Norway spruce stand in SW Sweden

ABSTRACT Treatments added to young conifer stands aiming to compensate for the loss of nutrients and alkalinity associated with whole-tree harvesting for bioenergy purposes have the potential to affect the growth of competitors to the conifers. Three different nutrient compensation treatments were applied to a young Picea abies (L.) Karst. stand in south-west Sweden, 2 or 3 years following final felling. The treatments were; fine fraction of harvest residues (15 Mg dw ha−1); granulated wood ash (4.1 Mg dw ha−1); nitrogen-free vitality fertiliser (twice 1.5 Mg ha−1); untreated control. Root biomass and total biomass of graminoids (mainly Deschampsia flexuosa (L.) Trin) were significantly greater in the wood ash and vitality fertiliser treatments than in the residues and control treatments. The aboveground and coarse root biomass of naturally regenerated birch (Betula spp.) and the aboveground biomass of dwarf shrubs (mainly Calluna vulgaris (L.) Hull.) and bottom layer were not affected by the treatments. Calcium and magnesium concentrations in the aboveground biomass of graminoids and phosphorus concentration in the biomass of bottom layer were significantly the highest in the vitality fertiliser treatment. Thus, nutrient compensation with vitality fertiliser or granulated wood ash may increase competition from graminoids in the establishment phase.

Why granulated wood ash decreases N2O production in boreal acidic peat soil?

Increased use of bioenergy has increased the production of wood ash in power plants. Wood ash is used as a fertilizer to improve tree stand growth in nitrogen-rich peatland forests. Nutrients removed during tree harvest are recycled back to the forest by wood ash fertilization. However, there is a risk that ash enhances microbial processes and associated nitrous oxide (N2O) production in peat. Because there are difficulties in spreading loose ash, ash is nowadays granulated or hardened in other ways before it is applied as fertilizer. Granulation process changes not only the physical but also the chemical properties of ash. In previous studies wood ash has showed variable effects on N2O emissions. Nevertheless, there are indications that in laboratory conditions granulated wood ash decreases N2O production. We conducted laboratory experiments to investigate the capability of granulated wood ash to decrease N2O production in peat soils and the role of nitrification and denitrification in N2O production. Acetylene inhibition experiments showed that N2O production was dominated by nitrification over denitrification. The rate of nitrification as well as N2O production from nitrification and denitrification decreased by the addition of granulated wood ash. Wood ash addition increased peat electrical conductivity while peat pH remained unchanged. The inhibitory effect of ash was associated to ion content because isolated ion addition experiments produced a similar decline in N2O production. The inhibition of ions was more evident in acidic conditions because when peat pH was increased by addition of lime, the ions or granulated ash inhibited N2O production significantly less than they did at natural peat pH. Our results show that manipulation of ion strength could offer a new tool to slow nitrification and denitrification processes and decrease the associated N2O emissions in acidic soils.

Spot mounding and granulated wood ash increase inorganic N availability and alter key components of the soil food web in clear-cut Norway spruce forests

The interactive effects of site preparation (spot mounding) and fertilization (granulated wood ash) on soil properties, soil micro- and mesofauna and ground vegetation were studied in two Norway spruce plantations established in clear-cut forests in Central Finland. Half of the seedlings were planted on mounds created by the planting machine, and the rest on intact forest floor. Half of the seedlings on mounded and intact forest floor were fertilized by adding granulated wood ash to circular plots surrounding the seedlings. Initial samples were taken from mounded and intact soil immediately after planting in June. Samples were taken from all treated plots in the autumn in the first and the second year after the treatments. Wood ash increased soil moisture percentage, the abundances of collembolans and mites, the biomass of enchytraeid populations, the pool size of water-extractable NH 4-N in soil and the N concentration of spruce needles. Spot mounding had little immediate effects, but increased the proportion and abundance of bacterial-feeding nematodes later on. In the second year, spot mounding increased NH 4-N in organic soil and N concentration of the spruce needles, and reduced pH irrespective of wood ash addition. In accordance with general disturbance theories, our plots, particularly those disturbed by spot mounding, were characterized by bacterial-based food chains, and increased availability of inorganic N. The ash effects on soil organisms and nitrogen availability were better explained by increased soil moisture than by pH and conductivity, suggesting that the ash granules acted as inorganic mulch. Both wood ash and, in particular, spot mounding have the potential to increase N leaching locally. However, spot mounding may be preferable to other site preparation methods, because this method disturbs a smaller area of soil.

The costs and profitability of using granulated wood ash as a forest fertilizer in drained peatland forests

Abstract Increasing and more intensive energy wood harvesting from forests necessitate efforts to ensure that adequate amounts of nutrients are recycled back onto the site. Recycling nutrients back to the forest in the form of wood ash is a natural means to correct the nutrient imbalance and acidity of forest soils that can occur from intensive management, as well as to solve the problem of disposing of wood combustion wastes. Methods of refining and spreading have been developed to improve the logistics and cost competitiveness of recycling wood ash back into the forest as fertilizer. In this study, the costs of spreading granulated wood ash in the forest were calculated under Finnish conditions. The profitability of recycling wood ash to drained peatland forests as a fertilizer was also analyzed, from the forest owner’s point of view. For this analysis, wood ash was compared with chemical fertilizer in terms of effect, cost and profitability. Wood ash fertilization using the ground-based forwarder system was two to three times cheaper than using the aerial helicopter-loader system. From the forest owner’s point of view, the fertilization of peatland forest with wood ash proved to be a very profitable silvicultural investment (IRR 3–12 percent). To improve the economics of wood ash recycling to forests, ground-based spreading of granulated ash should be emphasized. Furthermore, in order to create large enough operational units for the cost-efficient spreading of ash, there needs to be comprehensive planning of spreading sites.

Short-term effects of nutrient compensation following whole-tree harvesting on soil and soil water chemistry in a young Norway spruce stand

A growing demand for bioenergy from conventional forestry in Sweden will increase the need of nutrient compensation, that preferably should be made relatively shortly after harvesting and have no undesired side-effects. This study compared the effects of granulated wood ash (Ash), N-free, dolomite-based fertiliser (Vitality) and the green fraction of harvest residues (Residues) on the podsolic soil and soil solution of a young Norway spruce (Picea abies (L.) Karst) stand in SW Sweden. The treatments were applied three years after clear-felling and whole-tree harvesting. The soil solution was repeatedly sampled in the rooting zone 2–5 years after treatment. The soil study was performed 4 years after the Ash treatment and 3 years after Residues treatment and the last Vitality treatment (the Vitality treatment was applied on two occasions over 2 years). The Vitality treatment increased base saturation and effective CEC in the humus layer in relation to the other treatments, and also increased Ca and K concentrations in the soil solution. The Ash treatment resulted in higher exchangeable K concentration than Vitality in the litter layer, and Residues increased K concentrations in the soil water. No treatment influenced the KCl-exchangeable nitrate concentrations in the soil or the nitrate levels in the soil water. The results indicate that granulated wood ash could be used for long-term nutrient compensation without undesired short-term side-effects.

Effects of wood-ash application on potential carbon and nitrogen mineralisation at two forest sites with different tree species, climate and N status

In the future it may become common practice to return wood-ash to forest ecosystems in order to replenish nutrients removed when brash has been extracted as a source of bioenergy. Wood-ash contains most of the nutrients that are present in the brash before its removal and burning, with the important exception of nitrogen (N). In the present paper we report measurements of CO 2 emissions and net N mineralisation in the humus layer and the upper 5 cm of mineral soil 12 years after the application of wood-ash to two study sites, representing different tree species, climatic conditions and N deposition histories. We hypothesized that application of wood-ash would increase both carbon (C) and net N mineralisation rates at Torup, an N-rich site with Norway spruce ( Picea abies (L.) Karst.) in the south, whereas the net N mineralisation rates would not be affected at Vindeln, an N-poor site with Scots pine ( Pinus sylvestris L.) in the north, where a possible N-limitation would restrict any N mineralisation. The treatments, comprising additions of 0, 1, 3 or 6 Mg of granulated wood-ash ha −1, were applied in a randomised block design, replicated three times. Wood-ash from the same batch was used for all treatments at both sites. All factors were measured under laboratory conditions with controlled temperature and moisture levels. The potential CO 2 emissions (kg ha −1 year −1 of CO 2–C) at Torup were significantly higher in the 3 and 6 Mg ha −1 treatments than in the control treatment, and the highest application resulted in an extra loss of 0.5 Mg ha −1 of soil C annually as compared to the control. No such differences were detected at Vindeln. The results suggest that wood-ash application can deplete soil organic C at locations with similar characteristics (N-rich soil, spruce dominated, warm climate) as at Torup in this study.

Dissolution of granulated wood ash examined by in situ incubation: Effects of tree species and soil type

Wood ash recycling to forests may counteract nutrient losses caused by biomass harvest, since most nutrients except nitrogen are largely retained in the ash. Raw wood ash has an alkaline reaction with water and contains easily soluble as well as resistant compounds. Ash can be treated to ease handling and to avoid undesired effects on vegetation and leaching of nutrients. Forest ecosystems with different tree species and soils provide variable conditions for mineral dissolution with respect to pH, amount of organic ligands and humidity in the forest floor and the top soil. To study the effects of tree species and soil type on wood ash dissolution, granulated wood ash with particle size 2–4 mm was incubated in situ for 7 years in polyamide mesh bags. The bags were placed under the organic horizon of beech, oak, Norway spruce and Douglas-fir on a nutrient poor soil (typic Haplorthod ) and a nutrient-rich soil (oxyaquic Hapludalf )i n Denmark. After 7 years of incubation, the weight loss of the wood ash granulates was 20% in both soil types. Nutrient losses determined by total element analysis were about 35% for calcium, magnesium and potassium and 19% for phosphorus, regardless of tree species or soil type. Incubation for 7 years could not demonstrate possible effects of tree species and soil type on the dissolution of granulated wood ash incubated in mesh bags. The missing effect of tree species and soil type is suggested to be an effect of the incubation method and the pre-treatment of the ash tested here using cement as a binder. Across this broad range in chemical weathering environment the granulated wood ash dissolved at a rather slow rate, suggesting that this ash will have a negligible impact on the soil environment. r 2007 Elsevier Ltd. All rights reserved.

Effects of wood ash, vitality fertilizer and logging residues on needle and root chemistry in a young Norway spruce stand

The nutrient status of a 6-year-old Norway spruce stand in south-west Sweden was examined 4 and 5 years after application of soil ameliorative treatments. In addition to control plots, three treatments were tested: granulated wood ash at 4150 kg dry weight (dw) ha−1, a nitrogen-free, dolomite-based vitality fertilizer (SkogVital) at 2×1500 kg ha−1 and the fine fraction of harvest residues (mostly needles) at 15,050 kg dw ha−1. The treatments had no short-term effect on height increment. Nitrogen (N) was probably the growth-limiting element, but phosphorus (P) and potassium (K) were also in suboptimum supply. The vitality fertilizer increased the foliar concentration (or the element/N ratio) of P, calcium (Ca) and zinc, while ash application increased the foliar Ca/N ratio. The vitality fertilizer also increased magnesium and Ca concentrations in roots and decreased aluminium concentrations, whereas logging residues and wood ash only increased manganese concentrations in roots. Thus, the vitality fertilizer had a more marked effect on tree nutrient status than the granulated wood ash.

Fine-root distribution and morphology in an acidic Norway spruce ( Picea abies (L.) Karst.) stand in SW Sweden in relation to granulated wood ash application

Wood ash is recommended as a compensatory fertiliser to counteract the effects of acidic deposition on forest ecosystems. Spatial distribution of biomass, necromass and morphology parameters of the fine roots (diameter classes <1, 1–2, <2 mm) of Norway spruce ( Picea abies (L.) Karst.) were analysed in response to fertilisation with granulated wood ash (GWA) in a long-term field experiment in SW Sweden. GWA was applied as a single dose of 3200 kg ha −1 and the fine roots were sampled 9 years later by soil coring. Soil cores were divided into 1-cm strata within the top 0–2.5 cm humus limits, the lower humus below 2.5 cm (with varying thickness) and the mineral soil to 50 cm depth (from ground surface). Total fine-root biomass in the control (C) and GWA treatment, 256 ± 20 and 258 ± 25 g m −2, respectively, and length 2072 ± 182 and 1800 ± 198 m m −2, respectively, did not differ statistically from each other. Total fine-root necromass in the 1–2 mm fraction was significantly higher in C than in the GWA treatment, 130 ± 12 and 80 ± 10 g m −2, respectively. Fine-root biomass in the <1 mm fraction was significantly greater in the lower humus in the GWA treatment, but this did not affect the total biomass in the <1 mm fraction in the whole soil profile. The biomass-to-necromass ratio (1–2 mm) was significantly higher in the GWA treatment in the 0–30 cm soil layer than in the corresponding layer of the control. Specific root length (SRL) was lower in the GWA treatment than in the control in the 0–5 cm soil layer. The lower necromass and SRL were more clearly related to the GWA treatment, whereas the difference in the vertical distribution of biomass may have been related to the thicker humus layer in the GWA plots.

Ectomycorrhizal fungal biomass in roots and uptake of P from apatite by Pinus sylvestris seedlings growing in forest soil with and without wood ash amendment.

Forest soil from an experimental Norway spruce forest with four levels of wood ash addition (0, 1, 3 and 6 tonnes ha(-1)) was used to inoculate pine (Pinus sylvestris) seedlings with indigenous ectomycorrhizal (EM) fungi. Uptake of 32P and 86Rb in a root bioassay was used to estimate the demand for P and K by seedlings grown in the different soils. Utilisation of P from apatite was tested in a laboratory system where uptake by the ectomycorrhizal mycelium was separated from uptake by roots. The demand for P and K in the seedlings was similar regardless of the ash treatment. Variation in EM levels, estimated as fungal biomass (ergosterol) in roots, was large in the different soils, but not related to ash addition. Uptake of P from apatite was, on average, 23% of total seedling P and was not related to EM levels. It was concluded that the improved P uptake from apatite by EM fungi found in earlier studies is probably not a general phenomenon among EM fungi. The small effect of ash addition on EM levels and P uptake suggests that addition of granulated wood ash is a forest management treatment that will have only minor influence on ectomycorrhizal symbiosis.

04/00297 Drying of granulated wood ash by flue gas from saw dust and natural gas combustion: Holmberg, S. L. et al. Resources, Conservation and Recycling, 2003, 38, (4), 301–316

04/00297 Drying of granulated wood ash by flue gas from saw dust and natural gas combustion: Holmberg, S. L. et al. Resources, Conservation and Recycling, 2003, 38, (4), 301–316

Drying of granulated wood ash by flue gas from saw dust and natural gas combustion

At the district heating plant of Kalmar, Sweden an on-line unit for production of granulated wood ash for nutrient recycling on forest soils is being applied. Currently, the granules are dried by hot air from an oil-fired burner. The objective of this work was to investigate how drying by flue gas affects the hardening of granules, or impacts their chemical composition and properties. Ninety-six granule samples were treated by flue gas from natural gas combustion in a laboratory pilot scale flue gas generator. CO 2, CO, O 2, C 3H 8 and NO concentrations were varied during the experiment. Additionally, some samples were treated by flue gas from combustion of sawdust at the heating plant in Kalmar. Drying by flue gases did not affect the chemical composition of granules, but minor effects were seen in their mineralogy. The carbonate content was slightly higher in granules treated with flue gas from natural gas combustion compared to the granules dried by hot air only, when measured by wet chemical methods. Results from XRD analysis imply that the calcite content is higher and the portlandite and arcanite content slightly less in granules treated with flue gas from sawdust combustion compared to the granules dried by hot air only. The results from this investigation showed no negative effects on ash granule composition or physical structure by the use of a flue as a drying medium.

Ectomycorrhizal colonisation of roots and ash granules in a spruce forest treated with granulated wood ash

Granulated wood ash has been proposed as a slow release fertiliser suitable for forest soils. In this study ectomycorrhizal colonisation of roots and ash granules was studied in a 40-year-old spruce forest treated with 0, 3 or 6 t ha −1 granulated wood ash. We used PCR-RFLP methods for ITS-typing and identification of ectomycorrhizal fungi. In total 20 different ITS-types were recognised on roots in the organic soil horizon. Five of these were identified to species and two to genus. Six species, Tylospora fibrillosa Donk, Cortinarius sp. 3, Piloderma sp. 1, and three unidentified ITS-types (Ve-95-1, Tö-95-3 and Ve-95-9) each occurred on over 5% of the total root tips analysed. Together these comprised 55% of the ectomycorrhizal community on the screened roots. Ash granules collected from the fertilised plots were normally colonised by fungal mycelia. PCR-RFLP analysis of these mycelia revealed the presence of four ITS-types. Three of these ( Piloderma sp. 1, Ha-96-3 and Tor-97-1) were also present on the mycorrhizal roots. Piloderma sp. 1 was the most abundant species colonising roots. A possible role of ectomycorrhizal mycelia in the direct mobilisation of nutrients from ash granules is discussed.

Mineralogy of granulated wood ash from a heating plant in Kalmar, Sweden

The central heating plant of Kalmar, Sweden produces 200–300 tons wood ash every year. A stabilised material for nutrient recycling is produced by adding water and dolomite to the wood ash and granulating the mixture. Combined mineralogy and chemistry can be used to interpret the transformation processes that occur during hardening and weathering of the granules, thus leading to a possibility to refine the production process and final characteristics of the granules. Mineralogy was separately studied in the wood ash, dolomite, self-hardened wood ash and granules by X-ray diffraction. Magnesium- and calcium-containing minerals are most common in the ash materials in the present study. The amounts of portlandite and calcite present in self-hardened and granulated ash samples are clearly higher than those in the untreated ash, showing that these minerals are formed during the treatments. Additionally, one potassium-containing secondary mineral, syngenite, is formed during the self-hardening of wood ash. Quartz, dolomite and the Fe–K–Mg-silicate in the granules originate from dolomite. The secondary minerals gypsum and calcium silicate hydrate are present in the granules. Portlandite occurs only in control granules in the field study. This suggests that hardening of granules continues in the field and portlandite is transformed into calcite. After up to 3 years on forest soil, the crystalline compounds dolomite, calcite, quartz, ankerite, albite and alumohydrocalcite are present in granules, of which alumohydrocalcite is formed as a secondary mineral in the field. These results suggest that the dissolution of granulated wood ash is strongly delayed compared with untreated wood ash and self-hardened wood ash because of the formation of less soluble compounds during the granulation process.

Solubilisation and colonisation of wood ash by ectomycorrhizal fungi isolated from a wood ash fertilised spruce forest

In Sweden application of granulated wood ash has been suggested as a method to supplement nutrient loss resulting from harvesting of forest residues for bioenergy production. Mycelia of two ectomycorrhizal fungi Piloderma sp. 1 and Ha-96-3, were commonly found to colonise ash granules in a wood ash fertilised spruce forest. Thirty-eight fungal isolates were selected from 10 taxa to investigate the possible role of different ectomycorrhizal fungi in nutrient mobilisation from ash. The taxa were Cenococcum geophilum Fr., Piloderma croceum Erikss. and Hjortst., Piloderma sp. 1, Thelephora terrestris (Ehrenb.) Fr., Tylospora fibrillosa Donk, and five unidentified species, all originating from a wood ash fertilised spruce forest. The isolates were tested for their ability to solubilise tricalcium phosphate (TCP) or hardened wood ash (HWA) in vitro. Ha-96-3, P. croceum and Piloderma sp. 1 were the only taxa which solubilised TCP. Abundant calcium oxalate crystals were formed in TCP and HWA plates with Piloderma sp. 1. Ha-96-3 and two isolates of P. croceum produced intermediate amounts of crystals. Ha-96-1 and T. fibrillosa produced low amounts of crystal but no crystal formation was observed by any of the other isolates. Piloderma sp. 1 from HWA plates had significantly higher concentrations of P, compared to P. croceum or Ha-96-3. Piloderma sp. 1 and P. croceum were further tested for their ability to colonise wood ash in microcosms containing intact mycorrhizal associations. After 7 months Piloderma sp. 1 colonised ash amended patches with a dense, mat like mycelium, whereas P. croceum mycelia avoided the ash patches. Possible differences between these fungi in patterns of carbon allocation were investigated by labelling seedlings with 14CO 2. Piloderma sp. 1 mycelia allocated significantly more 14C to ash patches than P. croceum. P. croceum allocated relatively more 14C to control patches than to the ash patches. The possible role of ectomycorrhizal fungi in mobilisation of nutrients from wood ash is discussed.

Solubilisation and colonisation of wood ash by ectomycorrhizal fungi isolated from a wood ash fertilised spruce forest.

In Sweden application of granulated wood ash has been suggested as a method to supplement nutrient loss resulting from harvesting of forest residues for bioenergy production. Mycelia of two ectomycorrhizal fungi Piloderma sp. 1 and Ha-96-3, were commonly found to colonise ash granules in a wood ash fertilised spruce forest. Thirty-eight fungal isolates were selected from 10 taxa to investigate the possible role of different ectomycorrhizal fungi in nutrient mobilisation from ash. The taxa were Cenococcum geophilum Fr., Piloderma croceum Erikss. and Hjortst., Piloderma sp. 1, Thelephora terrestris (Ehrenb.) Fr., Tylospora fibrillosa Donk, and five unidentified species, all originating from a wood ash fertilised spruce forest. The isolates were tested for their ability to solubilise tricalcium phosphate (TCP) or hardened wood ash (HWA) in vitro. Ha-96-3, P. croceum and Piloderma sp. 1 were the only taxa which solubilised TCP. Abundant calcium oxalate crystals were formed in TCP and HWA plates with Piloderma sp. 1. Ha-96-3 and two isolates of P. croceum produced intermediate amounts of crystals. Ha-96-1 and T. fibrillosa produced low amounts of crystal but no crystal formation was observed by any of the other isolates. Piloderma sp. 1 from HWA plates had significantly higher concentrations of P, compared to P. croceum or Ha-96-3. Piloderma sp. 1 and P. croceum were further tested for their ability to colonise wood ash in microcosms containing intact mycorrhizal associations. After 7 months Piloderma sp. 1 colonised ash amended patches with a dense, mat like mycelium, whereas P. croceum mycelia avoided the ash patches. Possible differences between these fungi in patterns of carbon allocation were investigated by labelling seedlings with 14CO(2). Piloderma sp. 1 mycelia allocated significantly more 14C to ash patches than P. croceum. P. croceum allocated relatively more 14C to control patches than to the ash patches. The possible role of ectomycorrhizal fungi in mobilisation of nutrients from wood ash is discussed.

Assessment of the radiation field from radioactive elements in a wood-ash-treated coniferous forest in Southwest Sweden

The distribution of natural and antrophogenic radioactive elements in soil and wood was investigated in a 30-year-old forest stand of Norway spruce. Forest plots treated with a single dose of granulated wood ash in 1989 were compared with untreated control plots. It was observed that the retention of radiocesium and radiostrontium by the forest soil is rather strong in spite of the high annual precipitation (1100 mm a −1) and the relatively acidic conditions of the soil. Most of the deposited nuclear weapon fall-out of radiocesium and radiostrontium is still residing in the forest soil. Radiostrontium, but not radiocesium, was found in the intrasoil water collected with lysimeters at soil depths of 20 and 50 cm. Wood xylem radial distributions of radiostrontium indicated a decreased bioavailability with time after deposition of nuclear weapons fall-out, and no major differences could be observed on comparison of wood from ash-treated plots with wood from untreated plots. The activity concentration of radiocesium in tree rings formed prior to 1986 and grown at the ash-treated plot was about two to three times that found in wood from the untreated control plot. In order to make a dosimetric assessment, the spectroscopic change in the radiation field was investigated at the forest plots and at a deposit for industrial waste (southeast Sweden). A portable spectroscopic system employing a semiconductor-type detector (HPGe) and a scintillation detector (3″ × 3″ NaI(Tl)) was used in order to compare the radiation field from deposited ash of various dates of disposal and ash-treated forest plots to controls, respectively. From depth distribution data obtained by activity determination of cores from the ash deposit, theoretical calculations of the primary radiation field showed a reasonable agreement (±2–8%) with results obtained from the field-gamma measurements. The main contributions to absorbed dose in air (105–130 nSv h −1) on the ash and sludge deposit are 214B, 40K, 208Tl, 137Cs, 214Pb, 228Ac, 134Cs and 212Pb. In the ash-treated forest and the corresponding control plots 137Cs and 40K were the main contributors of absorbed dose rate in air. A set of biomass effective filtration factors and biomass effective linear attenuation factors was calculated in order to depict how the forest stand modifies the intensity of the primary radiation field from the ash application.

Phosphorus and nitrogen fertilization of a Norway spruce forest-effects on needle concentrations and acid phosphatase activity in the humus layer

Increased atmospheric deposition of N might eventually lead to P deficiency. The relation between needle P concentration and acid phosphatase activity in the humus layer was studied during 1990–93 in a Norway spruce stand where the water and N and P supplies had been experimentally manipulated since 1988. Treatments included control (C), yearly application of ammonium sulphate (NS), N-free fertilizer (V), granulated wood ash (A), irrigation (I), drought (D) and water plus nutrients in an “optimum” combination (IF). We found indications of a feed-back mechanism for P, where low concentrations in the needles were associated with increased acid phosphatase activity in the humus layer. Acid phosphatase estimations made during moist soil conditions were much more informative than those made during dry conditions. We further argue that a site-specific “base-line” exists for acid phosphatase activity in the soil, mainly originating from enzymes immobilized in the field, but active in the assay. Increased phosphatase activity, above the base line, was generally found in the A, I and NS treatments, but in some cases also in C. Although P and N concentrations were significantly higher in the IF treatment as compared to the C and the D treatments, the P as fraction of N was 0.10 and thus balanced in all cases. In the A and I treatment P:N was around 0.09, while it was only 0.07 in the NS treatment, mainly due to high N concentrations. The latter treatment thus created an imbalanced situation where P additions most likely would have increased tree growth.