Wood Ash Recycling Research Articles

Assessing the carbonation potential of wood ash for CO2 sequestration

Wood ash, a byproduct of wood combustion, poses environmental challenges when disposed of in landfills. This study explores a sustainable alternative by investigating the carbonation of wood ash, a process converting CO2 into stable carbonate minerals. With increasing concerns about waste management, this research aims to identify optimal carbonation conditions by varying relative humidity, liquid-to-solid ratio (L/S), and temperature. Results demonstrate that the ideal conditions for wood ash carbonation involve a moderate relative humidity of 55%, room temperature at 25 °C, and a lower L/S ratio. Thermogravimetric analysis (TGA) indicates that extended curing times increase CaCO3 formation. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirm the presence of carbonate phases. Mechanical strength tests reveal that samples with lower porosity and higher carbonation products exhibit superior strength. This study contributes to the understanding of wood ash carbonation but also emphasizes its potential practical applications in construction materials as light aggregates in cement concrete. The research explores the implications for sustainable waste management, offering insights into environmentally and economically viable solutions for wood ash recycling.

Cadmium accumulation in organisms from a spruce plantation amended with wood ash - an environmental risk?

Recycling of wood ash from power plants to forest plantations returns plant nutrients lost at harvest. However, wood ash contains a considerable amount of cadmium (Cd) that may accumulate in the forest food web, and eventually threaten environment and human health. We examined the short-term (6–24 months) uptake of Cd in a range of organisms from different trophic levels in the forest food web. We amended twelve field plots in a Norway spruce plantation with wood ash in different concentrations (0, 3, 4.5 and 6 t ha−1), and subsequently measured Cd concentration in three vascular plant species, three metazoan groups, a lichen, and fruiting bodies of four ectomycorrhizal fungal species. Cd content varied significantly between the major taxonomic groups; metazoans contained most and vascular plants least, but also within the groups, most pronouncedly for ectomycorrhizal basidiomycetes. In vascular plants, metazoans as well as fungi, we found some examples that Cd content correlated significantly with wood ash amendment, however most organisms were unaffected, and no group of organisms contained more Cd than allowed for comparable food items. We therefore conclude that with the wood ash dosages used here, the environmental risk of Cd accumulation is slight, at least in the forest system that we examined.

Response of soil and vegetation in a warm-temperate Pine forest to intensive biomass harvests, phosphorus fertilisation, and wood ash application

The objective of this study was to assess the effects of different intensities of biomass harvesting, and the possible effects of compensation methods, on forest functioning. To do so, we carried out a split-plot experiment (SW France) crossing four different intensities of biomass harvesting (Stem-Only Harvest [SOH], Aboveground Additional Harvest [AAH], Belowground Additional Harvest [BAH], and Whole-Tree Harvest [WTH]) and three compensation methods (control [C], wood ash application [A] and phosphorus fertilisation [P]). The experimental treatments were followed by the plantation of pines (Pinus pinaster). The environmental consequences of treatments on soil and vegetation were evaluated 11 years after the tree plantation.Despite their low additional biomass exports (+10 % for AAH to +34 % for WTH), the non-conventional harvest practices exported much higher quantities of nutrients than the conventional SOH technique (+145 % of exported N in WTH). Additional biomass harvests impacted the soil organic matter content, with negative effects on P-organic, soil cation exchange capacity, exchangeable Ca, and most extractible nutrients. However, tree nutritional status was improved by P-fertiliser or wood ash. We observed a positive effect of wood ash application on soil pH and nutrient content but, like additional harvests, wood ash application decreased the pool of soil organic carbon (~10 %).Overall, the experiment showed that exporting more forest biomass due to the additional harvesting of biomass had negative consequences on the ecosystem biogeochemistry. Additional harvests have impoverished the soil, and decreased the soil organic carbon content. Importantly, applying nutrients as fertiliser or wood ash did not compensate for all the negative impacts of biomass exports and the method of wood ash recycling in forests could even decrease the soil organic carbon.

A Combined Measurement and Modelling Approach to Assess the Sustainability of Whole-Tree Harvesting—A Swedish Case Study

The demand of renewable energy has increased the interest in whole-tree harvesting. The sustainability of whole-tree harvesting after clear-cutting, from an acidification point of view, depends on two factors: the present acidification status and the further loss of buffering capacity at harvesting. The aims of this study were to investigate the relationship between these two factors at 26 sites along an acidification gradient in Sweden, to divide the sites into risk classes, and to examine the geographical distribution of them in order to provide policy-relevant insights. The present status was represented by the acid neutralizing capacity (ANC) in soil solution, and the loss of buffering capacity was represented by the estimated exceedance of critical biomass harvesting (CBH). The sites were divided into three risk classes combining ANC and exceedance of CBH. ANC and exceedance of CBH were negatively correlated, and most sites had either ANC < 0 and exceedance (high risk) or ANC > 0 and no exceedance (low risk). There was a geographical pattern, with the high risk class concentrated to southern Sweden, which was mainly explained by higher historical sulfur deposition and site productivity in the south. The risk classes can be used in the formulation of policies on whole-tree harvesting and wood ash recycling.

Effect of High Concentrations of Wood Ash on Soil Properties and Development of Young Norway Spruce (Picea abies (L.) Karst) and Scots Pine (Pinus sylvestris L.)

Wood ash recycling can be a reasonable method for energy producers to decrease waste problems. Using wood ash as a fertilizer or liming material could improve soil macro and micronutrient content in peat soils. Therefore, the effect of wood ash on Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.) juvenile growth and nutrient content in the soil after spreading wood ash in medium to high doses before and after planting seedlings was investigated in peat forests in the Eastern part of Latvia. The aim of the study was to evaluate the effect of high doses of wood ash on soil properties and the growth of planted Norway spruce and Scots pine seedlings up to 10 years after experiment establishment. Wood ash was applied a year before planting seedlings in doses of 5 and 10 t ha−1 and right after planting in concentrations of 5, 10, 15, and 20 t ha−1. Changes in macronutrient content (i.e., phosphorus [P], and potassium [K]) and tree height and diameter at breast height were measured at one and 10 years after establishing the experiment. Fertilization one year prior to planting the seedlings exhibited a positive response on tree height and diameter growth compared to fertilization after the seedlings were planted. Soil samples from fertilized plots one year after establishment contained more P and K in the soil than the control plots. Wood ash application of the highest doses did not reach the overdose limit, as the tree growth (height and diameter at breast height) results of fertilized plots were similar to those of the control fields; therefore, no significant negative effect on tree growth was discovered.

Recycling of ash from co-incineration of waste wood and forest fuels: An overlooked challenge in a circular bioenergy system

Wood ash recycling to forests after logging residues harvest is important to ensure long-term sustainable forest management, however, it is not recycled in Sweden at the level required to compensate for current logging residue out-take. A problem in this context is wood ash contamination through co-incineration of waste wood with forest fuels, a practice driven by the political goal of a circular bioenergy system. We performed a case study of co-incineration at a typical Swedish district heating (DH) plant, which showed that the forest fuel ash alone could be recycled to forests due to high nutrient levels. Co-incineration with waste wood resulted however in such high levels of contaminants that the ash was landfilled as hazardous waste. Our assessment of the Swedish DH sector showed that wood ash contamination through co-incineration is common, and that only a minor proportion of the ash from forest fuels is recycled to the forest. It also revealed a lack of reliable data regarding ash production and management, making implementation and evaluation of effective countermeasures difficult. Practical measures to enable wood ash recycling, such as removal of waste wood from the fuel mix, incineration of separate fuels, and ash after-treatment, are hampered by technical and economic barriers. Furthermore, no comprehensive policy tools currently exist on either a national or EU level that facilitate wood ash recycling. Thus, we conclude that comprehensive and efficient policy tools are urgently needed to overcome current barriers, and stimulate large-scale recycling of wood ash for long-term sustainable forest fuel utilisation.

Nudging Acceptability for Wood Ash Recycling in Forests: A Choice Experiment

In this paper, our objective is to assess the general French population's acceptability of application of wood ash in forests, a measure currently not allowed but under consideration by the government. The main originality of our approach is that we test how a nudge can be used as an instrument to increase social acceptability, conveying objective information regarding ash recycling. Furthermore, although we do not consider it as a welfare measure, we show how the estimation of the willingness-to-pay can be considered as a complement to the more traditional social acceptability measure. Three nudges were introduced as three treatments in a discrete choice experiment. In the first treatment, the options with wood ash application were highlighted to indicate to the respondents that they corresponded to pro-environmental measures (positive framing). In the second treatment, we changed the wording of the two non-status quo options to highlight the recycling aspect of wood ash application. In the last treatment, we adopted a productive wording to highlight the fact that wood ash application increases wood production. Treatments, in particular positive framing and productive wording, influence the willingness-to-pay but depend on the attitudes of the respondents.

Determinants of forest owners attitudes towards wood ash recycling in Sweden - Can the nutrient cycle be closed?

The use of biomass, in particular wood, has increased this last decade as a result of the European Union's objectives to reduce the use of fossil energies. This has amplified the use of whole-tree harvesting and the exploitation of forest residues from traditional timber harvest. However, these practices have some ecological consequences because they remove nutrients from the forest, thus potentially reducing soil fertility. To compensate for this nutrient loss, it has been proposed to recycle wood ash to reintroduce the exported nutrients. In this paper, we assess private forest owners' willingness to pay to spread ash in Västmanland, Sweden, where ash recycling is not widely adopted, though an increasing supply of wood ash. In particular, we take into account behavioural motives that may explain forest owners' willingness to pay (Theory of Planned Behaviour and environmental sensitivity). We conclude that Swedish forest owners generally have a positive willingness-to-pay for wood ash application in their forests, but that this measure is highly dependent on their attitudes. We also show that a forest owner's decision to apply ash to all or a portion of his/her forest is explained by two different characteristics: the landowner's environmental sensitivity and his/her perceived control of wood ash recycling.

Could a residential wood ash recycling programme be part of the solution to calcium decline in lakes and forests in Muskoka (Ontario, Canada)?

One possible solution to the recent decline of calcium (Ca) concentrations in Canadian Shield forests and lakes in eastern North America is the addition of Ca-rich wood ash to watersheds. We investigated the feasibility of using small, mainly residential sources of non-industrial wood ash (NIWA) for this purpose by quantifying concentrations of its major nutrients and metals, its toxicity to Daphnia in aqueous extracts, and estimating the amount of NIWA available in the District of Muskoka in central Ontario. Locally collected NIWA averaged 30% Ca, and also contained smaller but significant amounts of K, Mg, Na, and P. Of these, K was so soluble that it was toxic to Daphnia over 48 h in the concentrate and 10-fold dilution; however, sedimented ash was not toxic over 15 d. Most metal levels in NIWA were below targets permitting unrestricted land application. However, Cu and Zn were just above these targets, but well below those for conditional use. Muskoka residents generate about 235 000 kg of NIWA annually, not enough to treat all central Ontario areas affected; however, a NIWA recycling programme implemented across southern Ontario could generate enough ash to solve the Ca decline problem in Muskoka’s forests and lakes.

Wood ash decreases cadmium toxicity to the soil nematode Caenorhabditis elegans

Wood ash is a beneficial fertilizer and liming agent in nutrient depleted soils, but it also contains considerable amounts of cadmium (Cd), which can be toxic to organisms in the environment. Therefore, risk assessments regarding utilization of wood ash is required. Here, we studied how wood ash (applied in doses equivalent to 0, 3 and 6 t ha−1) and Cd (applied in doses of 0, 10, 150, 300, 600, 1200 and 2000 mg kg−1) affected growth of the soil nematode Caenorhabditis elegans. The treatments were combined in a full factorial design. Wood ash alone greatly stimulated both soil respiration and growth of C. elegans, whereas Cd alone had a toxic effect. However, unrealistically high Cd levels were needed to severely affect growth of C. elegans and soil respiration, especially soil respiration was very resilient to Cd amendment. Ash addition decreased Cd toxicity to C. elegans, with an EC50 value of 390 mg Cd kg−1 in the 3 t ash ha−1 treatment, and an increase of EC50 to 1894 mg Cd kg−1 in the 6 t ash ha−1 treatment. This is probably because ash increases the Cd sorption capacity of the soil, and thereby decreases the bio-availability of Cd. The results suggest that there is no acute toxic effect of Cd to nematodes associated with wood ash recycling; in fact, our results suggest that ash actually decrease Cd toxicity.

Critical biomass harvesting – Applying a new concept for Swedish forest soils

Abstract The contribution of forest harvesting to base cation losses and soil acidification has increased in recent years in Sweden, as the demand for bioenergy has increased and the sulphur deposition has decreased. Thus, new policy tools are required to evaluate the progress of the recovery from acidification, and as a basis for forest management recommendations. In this study we introduce and test a concept, “Critical biomass harvesting”. The concept builds on the concept “Critical loads”, which has been used world-wide for several decades as a bridge between science and policies related to transboundary air pollution and acidification. The basis for the concept is an acidity mass balance, with sources and sinks of acidity. A critical limit defines the highest acceptable acidification status of the water leaving the root zone. Based on the critical limit, the highest allowed biomass harvesting can be calculated, keeping the other parameters constant. In this study the critical limit was set to ANC (Acid Neutralizing Capacity) = 0. Nitrogen was assumed to be affecting acidity only if it leaches from the root zone. The critical biomass harvesting was calculated for almost 12 000 National Forest Inventory sites with spruce and pine forest, using the best available data on deposition, weathering and nitrogen leaching. The exceedance of critical biomass harvesting was calculated as the difference between the estimated harvest losses and the critical biomass harvesting. The results were presented as median values in merged catchments in a catchment database, with totally 2079 merged catchments in Sweden. According to the calculations, critical biomass harvesting was exceeded in the southern half of Sweden already at stem harvesting in spruce forests. Whole-tree harvesting expanded the exceedance area, and increased the exceedance levels in southern Sweden. The exceedance in pine forest was lower and affected smaller areas. It was concluded that the concept of critical biomass harvesting can be successfully applied on the same database that has been used for critical load calculations in Sweden, using basically the same approach as has been extensively applied, evaluated and discussed in a critical load context. The results from the calculations in Sweden indicate that whole-tree harvesting, without wood ash recycling, can be expected to further slow down recovery, especially in the most acidified parts of the country, in the southwest.

바이오매스 나무재를 활용한 친환경 보강토의 특성 연구

세계적으로 많은 양의 바이오매스가 농업, 산림 및 에너지 자원으로 사용되고 있으나, 사용된 바이오매스의 많은 양은 여전히 단순 소각 후 폐기하고 있는 실정이다. 이는 자원의 낭비와 폐기 공간 부족 등의 문제를 초래하게 되며, 이에 따라 바이오매스 재의 처리 및 활용에 대한 방안은 시급하다고 하겠다. 따라서 바이오매스 재의 가장 큰 양을 차지하는 나무재를 건설재료로 활용할 수 있다면, 이는 자연자원의 보존과 쓰레기 저감에 크게 기여할 수 있을 것으로 판단한다. 본 논문은 바이오매스 재의 한 종류인 나무재의 건설재료로서의 적용 가능성을 타진하기 위하여, 나무재의 미세구조를 관찰하고, 나무재 및 보강토의 투수계수와 압밀특성을 분석하였다. 본 연구의 결과로부터 나무재의 함량을 소량으로 제한하는 경우에 지반재료의 압축성에는 큰 영향을 미치지 않으며 투수성을 크게 감소시키는 효과가 있음을 확인하였다. Biomass has been used as agriculture, forest and energy resources. The combustion of biomass matter becomes biomass ash that is dumped without control or disposed in landfills. Thus, the recycling or treatment of biomass ash is required. Wood ash is one of largest portion of biomass ash. Therefore, the recycling of wood ash in construction area will provide both new types of renewable energy sources and an environmental solution reducing the waste. The main objective of this study is to explore the physical, mechanical properties of Ottawa 20/30 sand, wood ash and mixture of them including Scanning Electron Microscope (SEM), hydraulic conductivity, and consolidation. It was observed that, small addition of wood ash to Ottawa 20/30 sand reduced the permeability significantly without increasing compressibility much.

Responses of bryophytes to wood-ash recycling are related to their phylogeny and pH ecology

Ash generated by the combustion of solid biofuels is increasingly being returned to the fuel’s place of origin (mostly forests). In this way, nutrient depletion and acidification caused by biofuel ...

Ground vegetation has a major role in element dynamics in an ash-fertilized cut-away peatland

In Finland, recycling of wood-ash as a fertilizer has been widely studied in recent decades in peatlands drained for forestry. Wood-ash is reported to promote tree growth without any significant negative impacts on the environment and could, therefore, be a suitable option on cut-away peatlands, which are estimated to increase by 30,000 ha over the next ten years. However, the environmental effects of ash-fertilization on cut-away peatlands or on ground vegetation are not well known. We studied the effects of wood- and peat-ash application on the nutrient content in soil and plants and on the heavy metal content in the vegetation of a cut-away peatland. Six treatments of different quantities and mixtures of wood-ash, peat-ash, biotite, or Forest PK-fertilizer were replicated in three plots. Both wood- and peat-ash fertilization ensured an adequate level of nutrients for the early establishment and growth of ground vegetation and birch seedlings in a cut-away peatland. Dense pioneer moss cover was important in trapping the heavy metals, such as cadmium, which are present in the ash. Ground vegetation of mosses and herbaceous plants also had a major role in the retention of the nutrients that could otherwise have leached from the open cut-away peatland area during the early stages of afforestation. Both wood- and peat-ash proved to be suitable for the initial fertilization of afforested cut-away peatlands, but in order to guarantee a sufficient long-term potassium supply for tree growth, an application of biotite with the peat-ash is recommended.

Wood ash dilemma-reduced quality due to poor combustion performance

Recycling of wood ash is based on the presumption that moderate concentrations of environmentally harmful elements are a part of the nutrient cycle and do not increase in net concentrations in the forest soil. It is assumed that the same quantities of harmful elements are harvested from the forest and recycled back. This principle does not apply to polycyclic aromatic hydrocarbons (PAHs) since these pollutants are formed during the combustion process, especially when the combustion performance is poor. Additionally, industrial combustors are adjusted in order to reduce NOx-emissions, indirectly causing formation of PAHs. This study examined fly ash from combustion of pulverized wood for its elemental and PAH concentrations during a period of 9 weeks. The 16 EPA-PAH concentrations range between 40 and 300 mg kg−1. Re-burning of the ash reduces the PAH concentrations to 0.24 mg kg−1 and organic carbon concentration from 40% to 5%, enhancing its composition significantly. It is important to determine the amount and fate of PAHs spread on forest soils with wood ash to ensure the improvement of the health of the forest ecosystem. Maximized energy efficiency of industrial boilers is the key to reducing anthropogenic emissions of greenhouse gases and enabling a sustainable nutrient recycling system.

Environmental assessment of incinerator residue utilisation

Incineration ashes may be treated either as a waste to be dumped in landfill, or as a resource that is suitable for re-use. In order to choose the best management scenario, knowledge is needed on the potential environmental impact that may be expected, including not only local, but also regional and global impact. In this study, A life cycle assessment (LCA) based approach was outlined for environmental assessment of incinerator residue utilisation, in which leaching of trace elements as well as other emissions to air and water and the use of resources were regarded as constituting the potential environmental impact from the system studied. Case studies were performed for two selected ash types, bottom ash from municipal solid waste incineration (MSWI) and wood fly ash. The MSWI bottom ash was assumed to be suitable for road construction or as drainage material in landfill, whereas the wood fly ash was assumed to be suitable for road construction or as a nutrient resource to be recycled on forest land after biofuel harvesting. Different types of potential environmental impact predominated in the activities of the system and the use of natural resources and the trace element leaching were identified as being relatively important for the scenarios compared. The scenarios differed in use of resources and energy, whereas there is a potential for trace element leaching regardless of how the material is managed. Utilising MSWI bottom ash in road construction and recycling of wood ash on forest land saved more natural resources and energy than when these materials were managed according to the other scenarios investigated, including dumping in landfill.

The influence of N load and harvest intensity on the risk of P limitation in Swedish forest soils

Nitrogen (N) is often considered to be the major factor limiting tree growth in northern forest ecosystems. An increased N availability, however, increases the demand for other nutrients such as base cations and phosphorous (P) which in turn may change which nutrient is the limiting factor. If P or base cations become limiting, N will start to leach which means a risk of increased eutrophication of surface waters. As many studies focus on base cations, this study instead aims at estimating P budgets on a regional scale for different harvesting scenarios relevant for Swedish conditions. P budget calculations were carried out for 14,550 coniferous sites from the Swedish National Forest Inventory, as weathering+deposition–harvesting–leaching. Three scenarios with different harvest intensities were used: 1) no harvesting, 2) stem harvesting and 3) whole-tree harvesting. The input data were derived from measurements and model results. The P budget estimates indicate that harvesting, especially whole-tree harvesting, result in net losses of P in large parts of Sweden. The highest losses were found in southern Sweden due to high growth rate in this area. In the whole-tree harvesting scenario the losses exceeded 1 kg ha − 1 y − 1 on many sites. N budget calculations on the same sites indicate that N generally accumulates in the whole country and especially in the southern parts. Consequently, the N and P budget calculations indicate that the forests in southern Sweden are in a transition phase from N-to P-limitation to growth. This transition will proceed as long as the accumulation of N continues. These results are important in a sustainable forestry context, as a basis for assessing the risk of future N leaching, and in designing recommendations for abatement strategies of N deposition and for application of wood ash recycling and N fertilization.

Wood-ash recycling affects forest soil and tree fine-root chemistry and reverses soil acidification

Wood ash was applied to a forest ecosystem with the aim to recycle nutrients taken from the forest and to mitigate the negative effects of intensive harvesting. After two years, the application of 8,000 kg ha−1 of wood ash increased soil exchangeable Ca and Mg. Similarly, an increase in Ca and Mg in the Norway spruce fine roots was recorded, leading to significant linear correlations between soil and root Ca and soil and root Mg. In contrast to these macronutrients, the micronutrients Fe and Zn and the toxic element Al decreased in the soil exchangeable fraction with the addition of wood ash, but not in the fine roots. Only Mn decreased in soil and in fine roots leading to a significant linear correlation between soil and root Mn. In soil, as well as in fine roots, strong positive correlations were found between the elements Ca and Mg and between Fe and Al. This indicates that the uptake of Mg resembles that of Ca and that of Al that of Fe. With the wood ash application, the pH increased from 3.2 to 4.8, the base saturation from 30% to 86%, the molar basic cations/Al ratio (BC/Al) of the soil solution from 1.5 to 5.5, and the molar Ca/Al ratio of the fine roots from 1.3 to 3.7. Overall, all below-ground indicators of soil acidification responded positively to the wood ash application within two years. Nitrate concentrations increased only slightly in the soil solution at a soil depth of 75–80 cm, and no signs of increased heavy metal concentrations in the soils or in the fine roots were apparent. This suggests that the recycling of wood ash could be an integral part of sustainable forest management because it closes the nutrient cycle and reverses soil acidification.

Effects of crushed wood ash on soil chemistry in young Norway spruce stands

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 field 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, Nymölla 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 (CEC eff) on a per hectare basis in the 0–20 cm soil layers were significantly higher in wood ash-treated plots than in the control plots in analyses across all study sites. Total exchangeable acidity was significantly lower after wood ash application. There was a significant 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 Nymölla-treated plots compared to control plots. Further down in the soil profile, 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 Nymölla- and Perstorp-treated plots, respectively, compared with the control. The results show that hardened wood ash recycling can compensate for base cations lost at whole-tree harvesting.

Needle chemistry in young Norway spruce stands after application of crushed wood ash

Nutrient concentrations in current and 1-year-old needles were analyzed annually for 5 years after application of hardened wood ash in 1–4-year-old Norway spruce (Picea abies (L.) Karst.) stands within a range of climate and fertility gradients. At each site, 3000 kg ha−1 hardened wood ash of two types, Nymolla and Perstorp, was applied in a randomized block design. Wood ash Nymolla contained 12 kg ha−1 P, 30 kg ha−1 K, 891 kg ha−1 Ca, 72 kg ha−1 Mg and wood ash Perstorp contained 12 kg ha−1 P, 60 kg ha−1 K, 486 kg ha−1 Ca, and 60 kg ha−1 Mg. The ash was intended to compensate for nutrients removed at the preceding harvest when logging residues were collected and removed from the site (whole-tree harvesting). The climate gradient included four climate zones throughout Sweden and each of these included a fertility gradient of three sites classified according to their ground vegetation type. There were no effects on nutrient concentrations in the needles 1 year after the application of wood ash. Five years after ash application, the concentrations of P, K and Ca in current and 1-year-old needles were higher than in the control plots. The results were consistent over all stands, irrespective of climate zone and fertility status. P and K concentrations were higher in spruce needles from plots treated with Perstorp wood ash, whereas Ca concentrations were higher in those of Nymolla treated plots. Analyses across all study sites revealed a treatment effect in terms of increased ratios of P:N, K:N and Ca:N in 1-year-old needles. The ratio P:N tended to increase with time in the Perstorp wood ash treatment compared with the control. The needle concentrations of Mg and S were not affected by the ash applications. The increase in needle nutrient concentrations after application of hardened wood ash suggests that wood ash recycling could be used in order to replace nutrients removed at whole-tree harvesting.