In accordance with earlier studies, wood ash increased nematode abundance (Hyvonen and Huhta 1989) in the autotrophic experiment (Nieminen 2009) but not in the heterotrophic experiment (Nieminen 2008b). Although nematodes were not identified, it is probable that their diversity was less in the simpler heterotrophic experiment, and this could partly explain their different response. Another major difference between the two experiments was that in the experiment without plants, soil moisture was kept optimal throughout the experiment, whereas in the pot experiment with plants, the organic soil dried considerably after grass harvest.

The increase of nematode numbers after loose wood ash application in field lysimeters with pine seedlings was mostly due to increased abundance of bacterial feeders, in other words, the ratio of bacterial feeders to fungal feeders increased (Liiri et al. 2002b). Liiri et al. (2007) found that loose wood ash reduced the abundance of fungal-feeding nematodes, but no effect on nematodes was evident in another microcosm study by Liiri et al. (2002c). The results are in broad accordance with an increased ratio of bacteria to fungi after ash application reported elsewhere (Baath et al. 1995; Perkiomaki and Fritze 2002), although Liiri et al. (2002b) did not detect ash effects on the ratio of bacteria to fungi. This illustrates that given sufficient response time, microbe-feeding nematodes can reliably indi­cate ash effects on soil microbes. It remains unclear why nematodes are not always responsive to wood ash. One possible reason for this is the initial community composition. For example, in Liiri et al. (2002c), the abundance of fungal-feeding nematodes was low and highly variable at the beginning of the experiment, which obviously made it difficult to observe changes in the ratio of bacterial feeders to fungal feeders.

4.2 Conclusion

In summary, laboratory experiments have shown that wood ash effects on dominant enchytraeids depend on labile carbon availability to the decomposer food web. The fact that increased carbon availability alleviated wood ash effects on enchytraeids without changing the pH supports a view that wood ash effects on soil animals are partly indirect consequences of altered food resources. In other words, food limita­tion magnifies negative wood ash effects. Although the effects of loose wood ash are well known, knowledge of the effects of granulated ash and ashes amended with organic materials on soil organisms in boreal coniferous forests is still incomplete.

Acknowledgements The study was financially supported by the Runar Backstram Foundation and the Maj and Tor Nessling Foundation. I appreciate the cooperation of the Jyvaskyla Soil Ecology Group, help with Table 4.1 from J. Haimi, V. Huhta, M. Liiri and H. Setala, and con­structive comments on the manuscript by two anonymous reviewers.

Wood ash application at rates of 1 and 5 t ha-1 in a Scots pine stand in central Finland decreased numbers of the enchytraeid worm Cognettia sphagnetorum, and slightly changed the soil microarthropod community. Soil chemical parameters were also influenced by these treatments, whereas microbial communities were only affected by the higher ash concentration (Haimi et al. 2000). Enchytraeid size and abundance were found to be reduced in microcosms containing 30 g humus from a Norway spruce forest and amended with 480 mg wood ash, but the negative effect could be offset by sucrose, indicating that the impact of wood ash on soil animals in forest ecosystems is mainly linked to C input rates. Negative effects may thus be avoided by minimising C limitations for decomposers (Nieminen 2008; see Chap. 4, Nieminen 2011).

3.2.1 Chemical Analysis

Total metals, P and S in crushed rock, bottom ash and plant material were extracted by 7 M KHNO3 and determined by inductively coupled plasma optical emission spectrometry according to ISO 11885 (ISO 2007). The pH of the soil was deter­mined in a solid-water suspension (1:2.5, v/v). Readily available P, K, Mg, and Ca in soil were determined by extraction with 0.1 M ammonium lactate and 0.4 M acetic acid (pH 3.75) in a solid-to-solution ratio of 1:20 (w/v) (Egner et al. 1960). Nonexchangeable K was extracted by 1 M HNO3 according to Pratt (1965). The particle size distribution of the soils was determined according to Elonen (1971). Total N was determined as Kjeldahl N as described by Bremner (1960).

Rogelio Nogales, Gabriel Delgado, Mar Quirantes, Manuel Romero, Esperanza Romero, and Eduarda Molina-Alcaide

Abstract Wet and dry olive cakes are the most important wastes generated when olive oil is produced. In recent years, both olive wastes have been incinerated to produce electricity, and thereby large amounts of fly and bottom ash are generated. In this study, physical, physicochemical, and chemical characteristics of olive waste ashes produced in Andalusian biomass power plants were analyzed to evaluate their suitability for agriculture. High variability among fly and bottom ashes may be ascribed to the origin of the olive waste and the combustion temperature. Waste olive ashes, which contained all particle sizes, showed high values of pH, salinity, water holding capacity, calcium carbonate equivalent, and P, K, Cu, and B contents. In contrast, moderate values were recorded for Ca, Mg, Zn, and Ni. Nitrogen is scarce in olive waste ashes; they thus can only be part of any fertilization strategy.

5.1 Introduction

The renewable energy consumption in the EU will increase from 11.6% in 2009 to 20% by 2020. Biomass is the main (61%) resource for the renewable energy consumed (10th EurObserv’ER 2010). In Spain, the contribution of renewable energy tp total gross domestic consumption in 2008 was 7.6%, of which biomass up 5.1 Mt (47% of total renewable energy, INE 2010).

Olive oil production is one of the most important industries in Mediterranean countries. In Spain, olive tree cultivation mainly occurs in Andalusia. In 2008, 600 x 103-900 x 103 t olive oil was produced in this region, using the two-phase centrifugation systems as common (90%) extraction technology (Fig. 5.1). This system generates huge amounts (between 2.5 and 3.5 Mt/year in Andalusia) of a

R. Nogales (H), M. Quirantes, M. Romero, E. Romero, and E. Molina-Alcaide Estacion Experimental del Zaidin (CSIC), Profesor Albareda, 1, 18008 Granada, Spain e-mail: rogelio. nogales@eez. csic. es

G. Delgado

Department of Edaphology, University of Granada, Campus Universitario de la Cartuja, 18071 Granada, Spain

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

DOI 10.1007/978-3-642-19354-5_5, © Springer-Verlag Berlin Heidelberg 2011

waste called crude wet olive cake, or alperujo, which is composed of olive pulp, stones, and skins together with residual oil, and water added during the oil extrac­tion process. Alperujo is an acidic, semihumid waste, rich in organic matter and potassium. After drying (less than 1% moisture), its low heating values ranges from 15 to18 MJ kg-1. Part of this waste is dried and treated with solvents to obtain olive-cake oil and a waste called dry olive cake, or orujillo. The orujillo (0.6-0.9 Mt/year in Andalusia) has recalcitrant organic matter, high potassium content, and low heating values between 14.5 and 20 MJ kg-1 (Agencia Andaluza de Energia 1999; Alburquerque et al. 2004; Caputo et al. 2003; Nogales et al. 1998).

In recent years, both olive wastes are being used as fuel for electrical energy production. In Andalusia, ten biomass power plants have been established and produced 0.81 TWh (80% of the total renewable electricity generation in this region) in 2009. In general, the previously mentioned olive wastes, alone or mixed with other wastes, are burned in conventional boilers at 450°C. The heat released is used to heat water to turn a steam turbine, which generates green electric energy. In some biomass power plants, fluidized-bed combustors at 850°C are used as boilers. The combustion of olive wastes for energy production generates great amounts of fly ash and bottom ash (between 4 and 8% of the total burned olive wastes) as end waste. In general, this end waste is landfilled in sites adjacent to the biomass power plants. However, the use of landfills for ash disposal is expensive and is being discouraged by more stringent regulations and public opposition.

Numerous studies focused on chemical characteristics of ash produced by coal combustion or gasification (Ahmaruzzarman 2010; Hytonen 1998; Jala and Goyal 2006). In contrast, ash generated from biomass has received less attention and most of the research has focused on ash from woody biomass combustion (Demeyer et al. 2001; Kuba et al. 2008; Someshwar 1996; Vance 1996; see Chap. 6, Omil et al. 2011). Other ashes have been characterized, such as those from the pulp and paper industry (Naylor and Schmidt 1989; Muse and Mitchell 1995) and those produced
by the incineration of municipal solid waste (Zhang et al. 2002) and biosolids (Benitez et al. 2001; Merino et al. 2005) or other agricultural wastes (Mozaffari et al. 2000). However, information is not available concerning the characteristics of ashes from olive waste combustion.

The aim of this study was to analyze the physical, physicochemical, and chemi­cal characteristics of fly ash and bottom ash produced in Andalusian biomass power plants, which use olive wastes (wet and dry olive cakes) as fuel, to evaluate their suitability for use in agriculture.

Heavy metal concentrations have to be considered when wood ash is recycled to forests; thus, the quality of the applied ash is of great concern to avoid accumulation of heavy metals in the environment (Stupak et al. 2008). In a microcosm experiment performed by Fritze et al. (2000), Cd derived from wood ash application on forest soils did not show any harmful effects on the microbial activity or fungal and bacterial community structure. In the same experiment, ash treatments were found to induce a shift in archaeal community patterns, whereas Cd alone or with ash did not have an influence (Yrjala et al. 2004). When looking at the heavy metal contents of forest berries (Rubus chamaemorus, Vaccinium vitis-idaea, Vaccinium uligino — sum) or mushrooms (Russula paludosa, Lactarius rufus, Lactarius trivialis, Suillus variegates, Paxillus involutus) on different Finish forest sites after wood ash fertilisation (4-14 t ha-1), Moilanen et al. (2006) observed no accumulation of heavy metals or even a decrease in the long term. Similar results were found in six Pinus radiata plantations repeatedly fertilised with 4.5 t wood ash per hectare in northwestern Spain, leading to a decrease of Zn, Cu and Cd levels in some mushroom species, which was attributed to an increase in soil pH. Only Mn concentrations were elevated in all mushroom species investigated (Amanita mus — caria, Russula sardonia, Tricholomapessundatum, Laccaria laccata, Micenapura, Suillus bovinus, Xerocomus badius). Heavy metals did not accumulate in tree needles or ground vegetation (Omil et al. 2007). Another aspect of recycling ashes back to the soil is the accumulation of 137Cs (Hedvall et al. 1996). However, application of wood ash at a level of 3.0 and 4.2 kg ha-1 contaminated with 30-4,800 Bq 137Cs per kilogram on different coniferous forest sites in Sweden did not significantly increase radioactivity in the biological system (soil, field vegetation, tree parts) when measured 5-8 years after ash amendment, which was partly attributed to the antagonistic effects of wood ash K on 137Cs (Hogbom and Nohrstedt 2001). This finding was confirmed in a 100-year-old Scots pine (Pinus sylvestris L.) stand on Fe podsol in central Finland, on which ash fertilisation (1,2.5 and 5 t ha-1) led to a reduction of 137Cs concentrations in lingonberries (Vaccinium vitis-idaea L.) analysed 2 and 7 years after application of ash (Levula et al. 2000).

A pot experiment in a greenhouse was performed. Two soils were used; a sand (Elverum) and a sandy loam (0ksna) (Table 3.1). The soils were selected for this experiment because of the low content of readily available K, Mg and P which was found by Jeng et al. (2006). Although the soils were sampled at the same locations as the soils used in the experiments of Jeng et al. (2006), assuming low concentra­tions of readily available P and K, analyses of the soils selected for this experiment showed higher concentrations of readily available K (Table 3.2) than were found in the previous investigation [Elverum 7.6 mg readily available K (100 cm3)-1, 0ksna 8.6 mg readily available K (100 cm3)-1]. According to 0gaard et al. (2002), no yield response to applied K can be expected if the concentration of readily available K exceeds 10 mg (100 cm3)-1 (8 mg 100 g-1 and bulk density 1.25 mg m-3).

The experiment was designed to supply NPK similar to that supplied by use of the compound mineral NPK fertilizer Yara Fullgj0dsel® 21-4-10. On the basis of the contents of N and P in MBM, and of K in different crushed rock powders and BWA (Table 3.3), the amounts of different components in the experimental design (Table 3.4) were calculated using the following assumptions for calculation of effective amounts of NPK:

1. The N effect of MBM was estimated as 80% of Kjeldahl N as equal to mineral N based on Jeng et al. (2004).

2. The P effect of MBM was estimated as 50% of total P equal to the effect of mineral P (Jeng et al. 2006).

3. The amount of K extracted by 1 M HNO3 from crushed rock powder and by 7 M HNO3 from BWA was estimated as plant available and equal to mineral K.

Although the total amount of NPK applied differed between the treatments, based on the assumptions for effective amounts of N, P and K, it was intended to obtain almost the same effect of NPK as mineral NPK (treatments 3-12).

The pot size was 7.5 l, and the height of the soil in the pots was 20 cm. The fertilizer level was based on normal fertilization recommendations for cereals in Norway (120 kg N ha-1), and the concentration of plant nutrients in the pots should be at the same level as in a 20-cm-deep plough layer. All amounts of added fertilizer were calculated on a hectare to pot basis. There were three replicates. The crops used in the experiment were spring barley (Hordeum vulgare cv Kinnan) and spring wheat (Triticum aestivum), and the amounts of K applied (60 kg K ha-1) were in line with normal fertilization recommendations for cereals in Norway. Seeding was performed in May with 30 seeds in each pot. After germination the weakest plants were removed, leaving 20 plants per pot. Unfortunately, barley seeds from two different batches were used, and uneven germination of barley was recorded owing to poor germination of the seeds from one batch. However, in the pots with fewer than 20 plants, the lack of plants was partly compensated for by an increased number of tillers. A mean of 19 ears per pot was found at harvest for both barley and wheat. Therefore, the effect of uneven germination was found not to have a significant influence on the yield.

The intended temperature in the greenhouse was 15°C at night and 20°C during the day, but on warm days with outdoor temperature above 20°C the temperature inside the greenhouse was somewhat higher than the outdoor temperature, reaching 30°C during some summer days. The pots were initially irrigated 3 days a week, but in

warm periods irrigation was carried out almost daily to prevent drought. The irrigation caused no leaching of plant nutrients from the pots during the experiment.

The nutrient balances were calculated on the basis of effective amounts of P and K applied and uptake of P and K in wheat grain. In the experiment straw was not harvested and nutrient uptake in the straw is therefore not included in the calcu­lations of nutrient balance. After the experiment had finished, soil samples from all treatments from both the wheat and the barley experiments with both soils were taken (0-20 cm), 48 samples in total. The samples consisted of nine subsamples, three from each pot. The results for the soil samples in Table 3.7 represent means for both soils and both crops.

3.2.2 Statistical Analysis

One-way analysis of variance was carried out. For multiple comparisons the Ryan- Einot-Gabriel-Welch (REGWQ) multiple range test was applied with a signifi­cance level of P = 0.05, and the means presented followed by the same letter are not statistically different.

The calcium carbonate equivalent (CCE) content was determined by analyzing the evolution of CO2, after reaction with dilute hydrochloric acid, in a Bernard calci — meter (MAPA 1986). The total organic carbon content was determined by dichro­mate oxidation of the samples and subsequent titration with ferrous ammonium sulfate (Yeomans and Bremner 1989). The total Kjeldahl N was determined by semimicro-Kjeldahl digestion (Bremner and Mulvaney 1982). The total concentra­tions of P, K, Ca, Mg, Na, Fe, Mn, Cu, Zn, Cd, Ni, Pb, and B were analyzed by inductively coupled plasma mass spectrometry after digestion of samples in con­centrated aqua regia (McGrath and Cunliffe 1985).

5.2.3 Statistical Analysis

Statistical analyses were carried out using the Statistical Package for Social Science (SPSS® Windows version 13.0) and Excel Statistics 2003 for Windows.

Wood ash is not only a valuable fertiliser in forest ecosystems, it can also benefit agricultural soils, especially acid soil types.

Analysing the impact of wood ash (5 and 201 ha-1) on an Italian agricultural soil regarding its physicochemical, microbiological and biochemical properties, Perucci et al. (2008) observed increasing pH values and electrical conductivity as well as decreasing microbial biomass C in the first months after application, but no long­term effects of ash amendments were found. Enhanced crop production for barley (Hordeum vulgare L.) and canola oil seed (Brassica rapa L.) was monitored when Boralf soils in central Alberta were supplemented with wood ash (12.5 or 25 t ha-1) in combination with N fertiliser (Patterson et al. 2004a). Although wood ash was, moreover, found to positively influence canola seed oil content, it may impair oil quality owing to an increase in the concentration of glucosinolate (Patterson et al. 2004b).

Combining wood ash with N sources is an interesting option for designer com­posts or fertilisers. Admixture of 8 and 16% wood ash and organic wastes prior to composting did have positive effects on the composting process (temperature, microbial activity) and the quality of the final product (no increase in heavy metal concentrations, improved nutrient balance) (Kuba et al. 2008). In comparison with mineral and organic fertilisers, wood-ash-amended compost was superior for the recultivation of a Tyrolean ski run, increasing plant cover and soil microbial biomass and respiration (Kuba et al. 2008) (Fig. 1.2). Composts produced with 8% wood ash admixture fostered utilisation of C sources (polymers, carboxylic and amino acids, alcohol, and carbohydrates) in a MicroResp™ assay and led to a change in microbial community structure, whereas compost with 16% ash altered bacterial and fungal community composition, but did not enhance C utilisation (Bougnom and Insam 2009). Bougnom et al. (2009, 2010) demonstrated that compost produced with wood ash supplement (8 and 16%) may be a cheap alternative to liming in tropical areas, where many soils are characterised by a low pH. Wood ash alone also significantly increased pH and electrical conductivity in a tropical soil in Cameroon and was found to supply nutrients to the soil (Voundi Nkana et al. 2002). Besides raising soil pH, wood ash amendments (4 and 6 t ha-1)

on an acid soil in Nigeria improved maize grain yield (Mbah et al. 2010). As lime or artificial fertilisers are unaffordable for resource-poor farmers, wood ash may be an alternative for improving soil fertility in agricultural soils in the tropics (Voundi Nkana et al. 1998; Bougnom et al. 2010; see Chap. 7, Bougnom et al. 2011). Wood ash application of up to 41 ha-1 on tropical soil in Uganda was observed to enhance bean (Phaseolus vulgaris) and soybean (Glycine max. L) biomass, but led to higher Cu, Zn, Cd and Pb concentrations in edible plant parts (Mbaherekire et al. 2003). Analysing the effect of wood ash application as well as combined wood ash and compost amendments on soil microorganisms, Odlare and Pell (2009) revealed toxic effects of wood ash on potential denitrification in an arable soil on a short­term and a long-term basis. Compost was, however, able to mitigate these heavy — metal-related negative effects of the ash.