Harvested shoots were dried at 60°C, weighed, ground with a plant mill, and stored for further investigations. The P content in plant tissue was measured after dry ashing using the molybdovanadate method (Page et al. 1982). Plant P uptake was calculated by multiplying the P content of the shoots and shoot biomass.

The soil samples were air-dried and sieved (2 mm) before analysis. Soil pH was measured in 0.01 M CaCl2 using a 1:2.5 soil-to-solution ratio. For characterization of soil P pools, different methods were used. The method described by Van der Paauw (1971) was used to determine water-extractable P (Pw) with a soil-to-water ratio of 1:25. The P concentrations in the extracts were measured by the phosphomolybdate blue method via flow-injection analysis. The content of double-lactate-soluble P (Pdl) (photometric method) was quantified according to Blume et al. (2000). By means of the ammonium oxalate method (Schwertmann 1964) the extractable amount of P (Pox) allows the estimation of the amount of inorganic P being adsorbed on amor­phous iron and aluminium oxides in the soil. Pox and the oxalate-soluble aluminium and iron contents (Alox, Feox) in soil were extracted and their concentrations were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES; JY 238, Jobin Yvon, France). With use of these data, the P-sorption capacity [PSC (mmol kg-1) = (Alox + Feox)/2] and the degree of P saturation [DPS (%) = Pox/ PSC x 100] could be calculated according to Lookman et al. (1995) and Schoumans (2000). Total P was analysed after aqua regia dissolution in a microwave oven (Mars Xpress, CEM, Kamp-Lintfort, Germany) followed by ICP-OES.

Furthermore, the sequential P fractionation method developed by Hedley et al. (1982) was used. Different P fractions of decreasing bioavailability (resin-P, NaHCO3-P, NaOH-P, H2SO4-P) were extracted step by step by using stronger extracting agents. The remaining P in the soil sample after the extraction steps is considered as residual P. The residual P content was determined by subtracting the amount of extracted P from the total P content [residual P = total P — (resin-P + NaHCO3-P + NaOH-P + H2SO4-P)] as described by Schlichting et al. (2002). Total P was determined by aqua regia digestion in a microwave oven.

2.2.2 Statistics

Soil and plant data corresponding to four spatial replications were subjected to two- and one-factorial analysis of variance (general linear model). The results are reported as main effects and interactions. The means of soil and plant parameters were compared by the Duncan test. Significances were determined at p < 0.05. Significantly different means were indicated by using different characters. The statistical analysis was carried out using SPSS 15.0.

Two recent studies (Nieminen 2008b, 2009) focused on the interaction between wood ash and carbohydrate supply in microcosms. The enchytraeid C. sphagne — torum was chosen as the target organism because of its importance in boreal forest soil, and because studies have consistently shown that it is sensitive to wood ash. The abundance of microbial-feeding nematodes provided information on microbial production.

Nieminen (2008b) studied the interactive effects of sucrose and loose wood ash on enchytraeids and nematodes in organic Norway spruce forest soil from which enchytraeids had been extracted using the Baermann wet funnel technique (O’Con­nor 1957). After extraction, the humus was sieved, weighed into 20 cotton-plugged glass jars and 20 individuals of the enchytraeid C. sphagnetorum were returned and each microcosm was inoculated with microflora and microfauna. Nieminen (2008b) treated the microcosms with loose wood ash (480 mg per microcosm,

1,0 kg ha-1) and sucrose (1.6 g per microcosm, 1.3 Mg C ha-1) in a full factorial design.

After a 3-month incubation at constant temperature, the dry matter content of organic soil was 22 ± 0.5% (mean ± standard error, n = 20) irrespective of treat­ment (Nieminen 2008b). Addition of wood ash increased the soil pH from

5.2 ± 0.1 to 6.9 ± 0.2 in both sucrose-amended and non-amended soil. Sucrose addition increased and wood ash addition reduced enchytraeid length. Sucrose addition increased nematode abundance by more than 100% on average. Wood ash addition alone decreased enchytraeid abundance compared with the control (Fig. 4.1).

Nieminen (2009) studied the interactive effects of three levels of solid sucrose (0, 0.88 or 8.8 g, equalling 0, 100 and 1,000 kg C ha-1; the intermediate treatment was omitted in the original article) and two levels of birch ash (0 or 1.175 g per microcosm, equalling 500 kg ha-1) in pots containing a layer of organic Norway spruce forest soil on mineral soil. In addition to one Norway spruce (Picea abies (L.) H. Karst. ssp. abies) seedling, these pots also contained the grasses Deschamp — sia flexuosa (L.) Trin. and Calamagrostis epigejos (L.) Roth and the experiment was continued in a greenhouse for one growing season (Nieminen 2009).

Wood ash increased the soil pH from 5.4 ± 0.06 to 5.7 ± 0.06 irrespective of carbon addition (Nieminen 2009). Sucrose increased the moisture of organic soil from 40 ± 0.02% to 57 ± 0.11% fresh mass in C1000 (analysis of variance, sucrose x ash F224 = 4.9, p = 0.017; control: simple effect of sucrose F2,24 = 11.4, p < 0.001), but this was partially counteracted by wood ash (mois­ture percentage 46 ± 0.05% in AC1000; F124 = 7.5, p = 0.011). Enchytraeids went close to extinction in control pots, but in C1000 treatments reached 1.8 times the initial density regardless of wood ash (sucrose F2,24 = 10.5, p < 0.001).

Enchytraeid length varied from 3.66 ± 0.28 mm in C1000 to 5.07 ± 1.46 mm in AC1000 ash-treated pots and the wood ash effect was significant. Wood ash increased nematode abundance (ash F124 = 5.6, p = 0.027). The nematode com­munity in control pots consisted mainly of bacterial feeders (50% of individuals; in particular, Rhabditis sp.) and predators (Mononchus sp.), and all others amounted to less than 25% of individuals.

Wood ash is applied to forest soils to alleviate nutrient depletion and soil acidifica­tion, either alone or in combination with N fertiliser. Wood ash is also applied as lime replacement, providing base cations to increase soil pH (Steenari et al. 1999; Meiwes 1995; Brunner et al. 2004). This liming effect can be attributed to Ca and Mg carbonates in the ash as well as to its fine structure (Pitman 2006). Arvidsson and Lundkvist (2003) observed an increased soil pH after 3 Mg ha-1 wood ash application in young Norway spruce (Picea abies) stands. Moreover, concentra­tions of exchangeable Ca and Mg as well as the effective cation-exchange capacity were elevated compared with the control. As salts contained in the ash started to dissolve after application, high K, Na and SO4 concentrations were also found in the soil (Augusto et al. 2008). Jacobson et al. (2004) reported an increased soil pH and base-cation content 5 years after amendment with self-hardened and crushed ash (3, 6 or 9 t ha-1) or pelleted ash (3 t ha-1) on two different coniferous sites in Sweden, whereby the ash formulation did not have an effect on soil chemistry despite differences in solubility. Basic substances used to amend soil may, however, foster nitrification and nitrate leaching in soil ecosystems and hence enhance soil acidity, counteracting the positive effects of wood ash application (Meiwes 1995). Since ash components bind to organic substances in the humus layer of forest soils, fertilisation effects of wood ash amendments on soil acidity and extractable Ca and Mg were found to last for many years (Bramryd and Fransman 1995; Saarsalmi et al. 2001, 2004, 2005; Mandre et al. 2006). The impact of wood ash applications (9 and 18 Mg ha-1) on soil properties in different tree stands (European larch, aspen and poplar) was evaluated in a 7-year experiment in Michigan, revealing that wood ash was able to foster long-term productivity and repeated applications may even have the potential to make up for biomass-C losses due to plantation management operations (Sartori et al. 2007).

2.3.1 Effect of Biomass Ashes on P Uptake and Shoot Biomass

In the field experiments positive results of ash supply were found in Rostock on the loamy sand (Table 2.6), but not in Trenthorst on the sandy loam (Table 2.7). In Rostock in 2007 higher barley yields (significant) and higher P uptakes (by trend) were found after SA and RMA application in comparison with the control. For maize in 2008 the best effects were found again after SA supply but also after CA supply (Table 2.6).

The missing effects in the Trenthorst experiment concerning yield and P uptake (Table 2.7) were most probably related to the soil conditions, mainly to the higher pH of this soil (Tables 2.2, 2.10, 2.11). Therefore, the liming effect of biomass ashes did not result in a further adv antage regarding the availability of nutrients, like we expected for sandy soils with lower pH. Furthermore, the soil P content in the Trenthorst soil was higher, which may have masked the P fertilizing effects of the ashes.

Owing to the lower soil volume, the fertilizing effects were higher in the pot experiments than in the field experiments. Significant effects were found for both soils in the 2007 and 2008 experiments.

The crop P uptake increased when P was supplied, independently of whether ash or TSP was added. In 2007, maize showed the highest P uptake of all main crops, with a mean value of 91.3 mg pot-1. In comparison with the control, the maize P uptake rose owing to P supply. The highest increasing rates were found for CA (about 34%) and TSP (about 44%) (Table 2.8). These results are in coherence with the biomass yield of maize (data not shown).

In 2008 on sandy loam, barley, which generated the highest biomass, also had the highest P uptake (especially after RMA supply: 94.6 mg pot-1) (Table 2.9).

Maize and lupin showed notable positive reactions on CA fertilization, with up to 74% more P uptake than in the control. For the catch crops, the highest P uptakes were found for phacelia and buckwheat in both pot experiments in 2007 and 2008.

Crop-specific P utilizations from the P sources were also relevant. In 2007, usually the highest effects were found for TSP and RMA, whereas the effects of RMA were a little smaller than those of TSP. The opposite was found for lupin and

phacelia, with slightly better results due to RMA. In consequence of the lower P concentration, SA application usually resulted in a lower crop P uptake than the other ashes. For oil radish after SA supply, even lower values were found than in the control without P. However, the P uptake of phacelia in the SA treatment was 36% higher than in the control. The SA effect on the P uptake of phacelia was even comparable to the RMA effect (Table 2.8). Differences in P uptake were also found after CA application, with high values for maize and rather low values for barley and lupin.

These effects underline the crop-specific mechanisms (see also Fig. 2.1) which should be considered when planning ash application within the crop rotation. Plant — specific adaptation mechanisms may warrant a sufficient P supply also under conditions of P deficiency in soil. For example, rape may excrete organic acids in the root zone, which is an effective strategy to increase P uptake mainly on soil with higher pH (Hoffland 1992). Buckwheat has been shown to have different P uptake efficiencies depending on soil conditions (Zhu et al. 2002). According to Van Ray and Van Diest (1979), different plant species differ in their behaviour with respect to uptake of cations. Excessive accumulation of cations within the plant can result in net excretion of H+, and in a lowering of pH values in soil, as was found in our experiments after cultivation of phacelia and buckwheat. Besides such kinds of chemical modifications in the rhizosphere, morphological root adaptations of plants may also help to supply plants with P (Fig. 2.1).

High P uptake of catch crops used as green manure provides a high potential for P supply of succeeding crops, when the decomposing catch crop releases P. According to our results, buckwheat and phacelia, which had high P uptake rates when fertilized with ashes, could be suitable in this sense. Furthermore, a combi­nation of green manure crops and ash application can also provide the soil with organic material, which ashes do not contain.

physiological enhanced chemical availability:

• changes in rhizosphere chemistry (pH; redox potential)

•

release of organic acids and enzymes

The most dramatic effects of wood ash and lime on enchytraeids have been reported in laboratory microcosms containing only a small tree seedling as a primary producer (Liiri et al. 2002c, 2007) or no plants (Pokarzhevskii and Persson 1995). It has long been realized that ash effects on decomposers are stronger in laboratory experiments than in the field, but the reason for this has been unknown (Huhta et al. 1986). In a recent experiment by Nieminen (2008b) the negative effects of wood ash on enchytraeid size and abundance were offset by sucrose addition without any change in pH, supporting the hypothesis that wood ash effects can be alleviated by relaxing carbon limitation to microbes.

Huhta et al. (1983) used quite large pieces (40 cm x 60 cm) of Scots pine forest soil. Nematode populations started to decline in control microcosms 3 weeks after the start of the experiments, and later collembolan and enchytraeid populations declined as well. A mixture of birch ash and superphosphate reduced the populations of enchytraeids, mites and later also collembolans as much as lime. Nematode populations were initially stimulated by the treatments, but the effect turned nega­tive towards the end of the experiment. The experiment of Liiri et al. (2007) lasted for 1 year, and enchytraeids went close to extinction in untreated control pots as well as in ash-treated systems. In the experiment of Liiri et al. (2002c) enchytraeid biomass as well as the abundance of fungal-feeding nematodes declined even in unamended microcosms despite sufficient moisture, suggesting that the experimen­tal ecosystems were severely resource limited. In the same way, the enchytraeid population declined in control microcosms in the experiment of Pokarzhevskii and Persson (1995). Nieminen and Setala (2001) demonstrated carbon limitation in experimental microcosms: fungal-feeding nematodes propagated rapidly after cel­lulose addition to pine microcosms. Thus, carbon availability to microbes seems to be limiting decomposer activity in most laboratory microcosms, and consequently, resource limitation may have emphasized the effects of disturbances such as wood ash and lime observed in laboratory microcosms.

Carbon additions not only provide resources for microbes, they can also increase soil moisture (Szili-Kovacs et al. 2007). Using a simple carbohydrate such as sucrose as the only carbon source has the advantage that it is easier to distinguish nutritional effects from other effects. The heterotrophic microcosms reported in Nieminen (2008b) were maintained relatively moist and because no carbon effect on moisture was detected at the end of the experiment, the carbon effects were probably nutritional in that study. In contrast, the topsoil in the greenhouse experi­ment (Nieminen 2009) was much drier at the end of the experiment. Since quite a large amount of solid sucrose was used (Nieminen 2009), a mulching effect was initially possible. In addition, sucrose is hygroscopic, but other mechanisms are also possible. In any case, the increased moisture in the C1000 sucrose treatment was critical for the persistence of enchytraeids (Nieminen 2009). Since enchytraeids are sensitive to drought, and consequently likely to suffer locally from the increasing frequency of extreme conditions such as drought (Lindberg et al. 2002), it can be suggested that more attention should be paid to the interaction of soil carbon and moisture.

The hierarchical nature of the soil food web is also worth noting. Even though low molecular weight carbon compounds are taken up and utilized on timescales ranging from seconds (Hill et al. 2008) to days (van Hees et al. 2002), the effects of labile carbon additions at higher trophic positions were still evident after one growing season.

When looking at the effect of wood ash amendments on tree growth in Nordic countries, Augusto et al. (2008) revealed a considerable site dependency using a meta-analysis approach. Whereas wood ash was not able to improve tree growth on mineral soils, it had a significant effect on trees planted on organic soils. Reviewing different studies from Finland, Sweden and Switzerland with regard to the impact of wood ash applications on tree growth and vitality, Lundstrom et al. (2003) reported neutral or even negative effects of ash fertilisation. Investigating the effect of hardened wood ash application (up to 3 Mg ha-1) on ground vegetation in young Norway spruce stands on mineral soils, Arvidsson et al. (2002) found that biodiver­sity and plant biomass were not affected. In a Swiss forest, fine roots of spruce were influenced by ash application (4 t ha-1) on mineral soil, whereby ash fertilisation enhanced the number of root tips, forks and the root length, but resulted in decreased root diameters (Genenger et al. 2003). In a set of field experiments applying wood ash (1-9 Mg ha-1) on 30-60-year-old Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands on mineral soil in Sweden, stem growth was only promoted when N (150 kg ha-1) was added, whereas wood ash amendments without N did not lead to significant responses (Jacobson 2003). The same was true for combined wood ash and N applications on a Scots pine (Pinus sylvestris) stand on a low-productivity mineral soil, where wood ash plus N positively influenced tree growth even 20 years after application. Nitrogen fertilisation alone only led to a short-term effect (Saarsalmi et al. 2006). Whereas wood ash or sludge application alone did not have any influence on the structure of a commercial willow plantation in central Sweden in a 3-year experiment, harvestable shoot biomass was increased by a combined sludge (2.6 t ha-1) and ash (5.5 t ha-1) treatment and thus gave results comparable to fertilisation with mineral fertiliser corresponding to 14.5 kg P ha-1 year-1, 48 kg K ha-1 year-1 and 100 kg N ha-1 year-1 (Adler et al. 2008). However, this treatment showed negative effects on wood fuel quality concerning P, K and heavy metal concentrations in the bark and wood. Plant growth or biomass production was also not influenced by wood ash fertilisation (10 and 20 Mg ha-1 for 3 years) in a willow plantation on a silt loam soil in the state of New York (Park et al. 2005). In this experiment, wood ash did not have an impact on nutrient concentrations of foliar, litter and stem tissue, whereas the concentrations of soil-extractable P, K, Ca and Mg were significantly higher than in control plots. In contrast, Moilanen et al. (2002) observed a positive effect of ash fertilisation (8 and 16 t ha-1) on tree volume growth even 50 years after amendment on a drained peat mire, being accompanied by elevated nutrient concentrations in the peat.

The results presented are attributed to the fact that ash is low in N, which is the main limiting element for plant growth on mineral soils in boreal forests. In contrast, ash fertilisation was considered to be more suitable for peatland forests displaying higher N contents (Hanell and Magnusson 2005) and was found to promote tree growth (height, diameter and biomass) of a young Pseudotsuga menziesii plantation and a Pinus radiata plantation on N-rich mineral soil in

Spain (Solla-GullcSn et al. 2006, 2008). Besides enhanced stem-wood growth of Norway spruce, Rosenberg et al. (2010) also observed increased CO2 evolution rates even 12 years after wood ash applications (6 Mg ha-1) on a N-rich soil, indicating that ash amendments of N-rich sites have to be evaluated carefully regarding their effect on C and N cycling.

In the field experiment in Rostock the bioavailable Pw and Pdl contents in soil (0-30 cm) were slightly increased following P supply (Table 2.10). Owing to a high standard deviation, these differences were not significant. The effects of the three ashes were similar. On average, slightly higher P values were measured for the CA treatment.

In Trenthorst the ashes also resulted in higher bioavailable P contents in soil (the differences were significant in spring 2008). Again, the highest increasing effect was found for the CA treatment (Table 2.11).

Like for the plant characteristics, the effects on the soil P pool were also found to be higher in the pot experiments than in the field experiments. Significant increases of high available P contents in the soil due to P application were measured at the end of the pot experiments.

In the pot experiments in 2007 with loamy sand the cultivated crops and interactions between crop and fertilization had also an effect. Cultivation of lupin resulted in the highest P values (Table 2.12). This can be partly explained by the

low P uptake of this species (Table 2.8). Furthermore, in many studies P mobiliza­tion effects were found for lupin, albeit mainly for white lupin (Shen et al. 2003; Kania 2005) owing to special root morphology (cluster roots) and root-induced chemical changes in the rhizosphere. According to results of Egle et al. (2003) and Pearse et al. (2007), blue lupin, which was used in the pot experiments, does not generate such “cluster roots”, but can enhance nutrient availability by means of carboxylate excretion into the soil and uptake of cations.

The decrease of the readily available P directly after phacelia harvest is probably only a temporary process. In a long-time field experiment with various catch crops, phacelia cultivation resulted in high levels of bioavailable P in the soil (Eichler — Lobermann et al. 2008a).

In the pot experiments with sandy loam (2008) the Pw and Pdl contents in the soil were also influenced by fertilization. The highest values were found after RMA, CA, and TSP application (Table 2.13).

Remarkably, in the experiments in 2007 and 2008 there were no differences in Pw contents of the soil between the P fertilizing treatments (TSP and ashes), even though commercial TSP fertilizer contains 80-93% water-soluble P (Mullins and Sikora 1995) and the water solubility of P in crop ashes is usually lower than 1% (Eichler-Lobermann et al. 2008b).

The P contents in soil were also related to the crop P uptake, namely high P uptakes usually resulted in P exhaustion in soil and in lower soil P contents. Thus, the relatively low P uptake of oil radish (Table 2.9) was related to rather high Pw and Pdl values (Table 2.13). Phacelia, which had the highest P uptake of all crops, showed comparably lower Pw and Pdl values. In contrast, high soil P contents were

found after buckwheat cultivation in the ash and TSP treatments (Table 2.13), despite the high P uptakes (Table 2.9).

The P fractionation method can provide additional information about the path­way of remaining ash P in the soil and helps to predict its presumable availability. In the pot experiments the highest soluble P fractions (resin P and NaHCO3P) were increased by the ashes as well as by TSP, as was shown, for example, for the loamy sand (see Fig. 2.2). The less available P fractions (NaOH P, H2SO4 P, and residual P) however, were not affected (data not shown). In comparison with the control, the total P content increased when P was supplied (Fig. 2.2).

2.4 Conclusions

According to our results, a high fertilization effect of biomass ashes can be expected. In the pot experiments and in the field experiment in Rostock, biomass ashes led to raised P uptakes of the crops and increased contents of the more easily available P pools in soil (Pw, Pdl, resin P, NaHCO3 P). Interactions of biomass ashes and cultivated crops had an additional effect on the utilization of P in ashes and should be considered for practical fertilization decisions. Provided that the ashes do not contain harmful substances, the utilization of biomass ashes in crop production is an important method for the recirculation of nutrients in agriculture and may save nutrient resources.

Acknowledgements This project was supported by the Federal Ministry of Food, Agriculture and Consumer Protection (BMELV), Germany (support code 22016206) (2007-2009). The project execution organization was the Agency for Renewable Resources (FNR), Germany. The project was accomplished in cooperation with the following project partners: the Institute of Organic Farming of the Johann Heinrich von Thunen-Institute (vTI)/Federal Research Institute for Rural Areas, Forestry and Fisheries, and the Leibniz Institute for Agricultural Engineering Potsdam — Bornim, Germany.

The hypothesis that carbon amendment increased the ability of C. sphagnetorum to resist wood ash disturbance because of enhanced microbial production is supported by the large increase in the abundance of microbial-feeding nematodes (Nieminen 2008b), which is in accordance with the results of earlier field experiments. Baath et al. (1995) found that wood ash application reduced the ratio of fungi to bacteria in pine forest soil. In a field study the ratio of fungal to bacterial phospholipid fatty acids was lower in forests treated with loose ash than in forests treated with hardened ash, although the difference from the control was not significant (Perkiomaki and Fritze 2002). Further, ash treatment was shown to alter the carbon utilization pattern of bacteria in a microcosm study, indicating changes in the bacterial community structure (Fritze et al. 2000). Although wood ash increases CO2 evolution rates (Perkiomaki and Fritze 2002), Jokinen et al. (2006) concluded that not all microbial groups are equally stimulated by wood ash. In other words, by increasing the soil pH, wood ash application can favour fast-growing microbial species (Zimmermann and Frey 2002), which are not necessarily preferred food sources for dominant animals in forest soil (e. g. bacteria over fungi). An increase in microbial activity can also result from the bacterial decomposition of microbial residues. In particular, because the dominant enchytraeid species C. sphagnetorum is a litter feeder dependent on fungal activity, it is plausible that a shift towards the dominance of r-strategist bacteria has a negative influence on it. In accordance with this reasoning, Nieminen (2009) observed a tendency towards a lower proportion of bacterial-feeding nematodes in the sucrose treatment. We do not know whether sucrose increased the numbers of the same microbes that were negatively affected by wood ash, or if it increased other possible food sources for enchytraeids. On the basis of these and the present results, it seems that loose wood ash affects enchytraeids to some extent through a change in microbial community structure, and that sucrose counteracts this effect.

A moderate wood ash disturbance in the autotrophic experiment (Nieminen 2009) had little direct effect on decomposer animals. Since enchytraeids only persisted in sucrose-amended pots, the interaction of wood ash and carbon avail­ability could not be tested. Although wood ash did not affect enchytraeid biomass, it did increase the size of individual worms, indicating that there were fewer but larger enchytraeids in the ash-treated microcosms. Because C. sphagnetorum reproduces asexually by fragmentation, a large individual size may be indicative of delayed reproduction. On the other hand, a higher wood ash application rate led to significantly smaller enchytraeid body size in the heterotrophic experiment (Nieminen 2008b), suggesting that when these organisms reproduce, they produce smaller offspring. This reasoning is supported by the data obtained by Nieminen and Haimi (2010), who found that enchytraeid populations originating from an ash — treated plot had a lower propagation rate (smaller fragmentation frequency) than populations from adjacent untreated control forest even when the animals were transferred to laboratory microcosms containing untreated organic soil. Also, the body size dynamics differed between populations with different disturbance his­tories. The overall length variation of the disturbed populations was smaller than that of the control populations, and, hence, the mean enchytraeid length could be either smaller or greater than that of control, depending on the sampling date (Nieminen and Haimi 2010).

Fertilisation of coniferous forest soil with wood ash (5 t ha-1) was demonstrated to affect microbial biomass (on the basis of phospholipid fatty acid analysis). Fungi reacted more sensitively to wood ash treatment than bacteria, which was reflected by decreasing fungal-to-bacterial phospholipid fatty acid ratios (Baath et al. 1995). Because ectomycorrhizal fungi are known to play an important role in the nutrient supply of trees, Hagerberg and Wallander (2002) investigated the effect of wood ash amendment on a Norway spruce forest floor and revealed an increase in ectomycor — rhizal biomass. The ectomycorrhizal fungus Piloderma sp. was found to frequently colonise granulated wood ash in a wood-ash-fertilised spruce forest, suggesting a direct impact on nutrient mobilisation (Mahmood et al. 2001, 2002). Piloderma sp. was moreover assumed to affect short-term storage of Ca derived from wood ash granules, whereas no effect on P storage or release was discovered (Hagerberg et al. 2005). Gaitnieks et al. (2005) reported a positive effect of wood ash (6 t ha-1) on Suillus sp. when it was applied prior to planting of Scots pine seedlings; this was accompanied by increased root and needle biomass of the seedlings.

In a long-term study on different forest sites, wood ash fertilisation (5-8 t ha-1) led to increased CO2 production caused by enhanced microbial activity but did not influence N2O emissions, although nitrification and denitrification may have been affected by wood ash application (Maljanen et al. 2006a, b). This effect was shown by Ozolincius et al. (2006) in a Pinus sylvestris stand in Lithuania, revealing an increase of ammonifying, nitrifying and denitrifying microorganisms after wood ash application (1.25-5 t ha-1). In contrast, Saarsalmi et al. (2010) did not find changes in net nitrification when investigating the effect of wood ash (3 t ha-1) combined with N (0.15 t ha-1) on soil microbial processes in two coniferous stands in Finland 15 years after application.

Trond Knapp Haraldsen, Per Anker Pedersen, and Arne Gr0nlund

Abstract Bottom wood ash (BWA) contains high concentrations of Ca, Mg, K and P, whereas meat and bone meal (MBM) has been found to be a good N and P fertilizer. In a pot experiment on soils with low contents of readily available K and P, the effects of a mixture of MBM and BWA were compared with those of mineral NPK (21-4-10), MBM, MBM plus K and Mg mineral fertilizer, and MBM and different types of crushed K — or Mg-rich rock.

The mixture of MBM and BWA gave the highest yield of barley, at the same level as mineral for NPK, and significantly higher than for MBM alone. For the yield of spring wheat there was no significant difference between the treatments with BWA or other K-rich additives to MBM, MBM used alone and mineral NPK. Compared with the other treatments, the MBM and BWA mixture significantly increased the pH of the soils by 0.5 units. MBM plus BWA represents an interesting concept for development of recycled NPK fertilizer of organic origin.

3.1 Introduction

Many by-products from the food industry and waste products from industry and bioenergy plants contain high concentrations of plant nutrients. The degree of recycling of these plant nutrients differs, but there is an untapped potential for use of by-products and waste products as fertilizers. The bottlenecks for use are partly lack of knowledge of fertilization and liming effects, logistic problems, relatively cheap disposal of ash at landfills, heavy metal content and restrictions due to governmental regulations (see Chap. 1, Knapp and Insam 2011; Chap. 8,

T. K. Haraldsen (H) and A. Gr0nlund

Soil and Environment Division, Norwegian Institute for Agricultural and Environmental Research, Frederik A. Dahls vei 20, 1432 As, Norway e-mail: trond. haraldsen@bioforsk. no

P. A. Pedersen

Department of Plant and Environmental Science, Norwegian University of Life Sciences, P. O. Box 5003, 1432 As, Norway

H. Insam and B. A. Knapp (eds.), Recycling of Biomass Ashes,

DOI 10.1007/978-3-642-19354-5_3, © Springer-Verlag Berlin Heidelberg 2011

Saraber et al. 2011). In Norway the regulations for use of organic fertilizers and related material also apply for ash materials (Norwegian Ministry of Food and Agriculture 2003). These regulations are based on quality classes of heavy metals on a dry matter basis. Ash has increased concentrations of metals on a dry matter basis compared with the original organic material, and the regulations therefore strongly limit use of ash. In Norway most of the bioenergy plants collect bottom and fly ash in one container, giving a blend ash with higher concentrations of heavy metals than are allowed to be used on agricultural land.

Ash from bioenergy plants has mainly been considered as liming material because of its high content of Ca, although the Mg, K and P content may also be of importance. Owing to the strict regulations, ash has hardly been used in agriculture in Norway in recent years. Risse (2002) reviewed use of wood ash in agriculture in the USA, and referred to several investigations where liming with wood ash gave better growth than use of traditional limestone. The liming effects of ashes vary between 8 and 90% of the total neutralizing power of lime. Etiegni et al. (1991a, b) found that wood ash had positive effects as K fertilizer and as a liming agent, but the amounts should be restricted in accordance with the plants’ need for K, and should not elevate the pH of the soil too much. The pH was the most important rate-limiting component. Saarelaa (1991) found that high application rates of wood ash supplied K in excess, and consequently decreased the Ca contents of plants. Mozaraffi et al. (2000) found that ash significantly increased K and decreased Mg concentrations in corn, and concluded that ash was a potentially good K source and a potential liming agent for acid soils. Different investigations on ash used as K or P fertilizer have shown different effects: almost the same of effect as wood ash as mineral K fertilizer (Erich 1991; Ohno 1992), whereas the P effects were better correlated with the citrate P than the total P in comparison with mineral P fertilizer (Erich 1991; Hansen 2004). Clapman and Zibelske (1992) found that plant uptake of Mg, K, Mn and P increased as the wood ash amendment increased. Meyers and Kopecky (1998) found land application of wood ash to be an environmentally safe alternative to landfilling, which may replace conventional limestone and K fertilizer for forage crop production.

Meat and bone meal (MBM) contains appreciable amounts of N, P and Ca, making it interesting as fertilizer for various crops. MBM has good effects as N fertilizer (Salomonsson et al. 1994,1995; Jeng et al. 2004), and has a positive effect on baking performance of wheat (Fredriksson et al. 1997, 1998). Jeng et al. (2006) showed that the relative P efficiency of MBM was 40-50% compared with P in superphosphate (YARA P8) in experiments with cereals and rye grass, and Ylivainio et al. (2008) found MBM suitable as a long term P supply to perennial crops. Because use of MBM as feed to produce animals is banned in the European Union, the meat industry has focused on an alternative use of MBM. The interest in the use of MBM as fertilizer will increase if MBM is included in an organic mineral fertilizer which has a predictable NPK effect similar to a compound mineral NPK fertilizer. The annual production of MBM of category 3 material is about 30,000 t. MBM of category 3 material is allowed for use as fertilizer in Norway for all crops, except grassland which is used for grazing or mowing, but can also be used for grassland if it is mixed with other fertilizer materials (Norwegian Ministry of Food and Agriculture 2007). Combining animal bones, feathers and wood ash to make mineral NPK fertilizers was described by Chojnacka et al. (2006), but the fertilizers had high P content relative to N content.

The aim of this investigation was to test different mixtures of MBM and additives of mineral K, crushed K-rich or Mg-rich rock and bottom wood ash (BWA), and to compare the effects with those from the use of compound mineral NPK fertilizer (Yara Fullgjpdsel® NPK 21-4-10) and an unfertilized control. The results should be used for development of organic mineral fertilizers based on MBM and BWA or other suitable K-rich material, which give a predictable NPK effect similar to that of mineral NPK. The investigation also aimed to find suitable types of BWA with low concentrations of heavy metals and high concentrations of K and Mg which satisfy the quality requirements for use on agricultural land in Norway (Norwegian Ministry of Food and Agriculture 2003).