Master Thesis In order to obtain the academic degree Master of Science

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Technische Universität Berlin Faculty III Process Science

Institute of Environmental Technology Chair of Circular Economy

and Recycling Technology

(Head of Chair Dr.-Ing. Vera Susanne Rotter)

Master Thesis

In order to obtain the academic degree Master of Science

Comparison of vermicomposts and thermophilic composts regarding

fertilizing potential and mycorrhization in a pot experiment with lettuce

Submitted by Corinna Sarah Schröder Matriculation No. 320582

First reviewer: Prof. Dr.-Ing. Vera Susanne Rotter, TU Berlin

Second reviewer: Prof. Dr. habil. Eckhard George, Leibniz Institute of Vege- table and Ornamental Crops (IGZ)

Scientific supervision: Dipl.-Ing. Oliver Larsen, TU Berlin

Date of Submission: February 19, 2020

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Eidesstattliche Erklärung

Hiermit erkläre ich, dass ich die vorliegende Arbeit selbstständig und eigenhändig sowie ohne unerlaubte fremde Hilfe und ausschließlich unter Verwendung der aufgeführten Quellen und Hilfsmittel angefertigt habe. Alle Ausführungen, die anderen veröffentlichten oder nicht ver- öffentlichten Schriften wörtlich oder sinngemäß entnommen wurden, habe ich kenntlich ge- macht.

Die Arbeit hat in gleicher oder ähnlicher Fassung noch keiner anderen Prüfungsbehörde vor- gelegen.

Berlin, den

……… Unterschrift

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Acknowledgements

I want to thank Olli for the great supervision and for introducing this beautiful topic to me.

Thanks to Prof. Rotter and to Prof. George for making it possible to write this thesis at the CERT department and at IGZ.

I would like to thank Ari and Franzi for all the support and help, for all the advice and the coffee and for strengthening my belief in saving the world through faeces.

A very special thanks goes to Anja, without whom this experiment and thesis would have probably failed right at the start, who was rescuing the lettuces several times and who taught me so many things.

Thanks to Birgit Fischer and to Kerstin Schmidt for all the help with the lab work and to the gardeners of IGZ for watering the lettuces on the weekends.

I want to thank Esther and Paula for producing the vermicomposts.

Thanks to Oscar and Aladdin for washing lettuce roots with me for hours, while listening to trash music.

Thanks to all my other colleagues from IGZ, Katia, Susanne, Sarah, Farina, Luisa and all the others for making these last months a fun time.

Thanks to Ine for cross-reading the thesis.

Thanks to my flatmates for supporting me and cheering me up when I was down. Thanks to Luisa for telling me every day that I am the best, to Chris for the formatting help and to Moritz for his PC screen.

I want to thank Giulio for having a lot of patience with me, for his unlimited support and for all the little things he did to help me.

Thanks to Luisa, Pia, Merle, Fabi, Saschi, Malte, Fine, Clemens and Lars for being the best friends that one can have and thanks to the blue beaver for helping me finish my studies.

Thanks to my family for always believing in me, no matter what, for always being there and for pushing me a little when I needed it.

Thanks to all my friends and all the other people who I did not mention

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Abstract

The present thesis aims to evaluate the fertilizing potential of composts and vermicomposts from urban wastes and their potential to supply mycorrhizal fungi for a colonization of plant roots. For this purpose, a pot experiment with lettuce under greenhouse conditions was conducted. Two vermicomposts from fruit and vegetable waste mixed with (1) coconut fibre or (2) fibreboard + soil, and two thermophilic composts from green waste and human faeces, respectively, were examined. 100 g dry matter compost per pot in a quartz sand substrate were applied (n = 5). Nitrogen and micronutrients were added as mineral fertilizers and the shoot uptake of N, P, K, Mg, Ca and Na was investigated. The highest total uptake of Ca and Mg as well as the highest yield was measured in the coconut vermicompost. Faecal compost and coconut vermicompost achieved the highest P and K contents. The uptake of Ca and Mg from the faecal compost was inhibited compared to the other treatments, probably due to pH effects and antagonist effect between different cations. None of the variants delivered N beyond the amount of mineral fertilization. To investigate mycorrhiza colonization, a second set of sterilized treatments was set up and root samples of original and sterilized treatments examined. Colonization was scarcely found and a limited supply of mycorrhizal fungal spores by all composts concluded.

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Kurzfassung

Ziel der vorliegenden Arbeit ist die Bewertung des Düngepotentials von Komposten und Wurmkomposten verschiedene städtischer Abfälle sowie ihr Potential zur Versorgung mit Mykorrhizapilzen für eine Besiedlung von Pflanzenwurzeln. Zu diesem Zweck wurde ein Topfexperiment mit Salatpflanzen unter Gewächshausbedingungen durchgeführt. Zwei Wurmkomposte aus Obst- und Gemüseabfällen, gemischt mit (1) Coir (Kokosnussfaser) oder (2) Wellpappe + Erde sowie zwei thermophile Komposte aus Grünschnitt bzw. aus menschli- chen Fäkalien wurden untersucht. 100 g Trockenmasse Kompost wurden je Topf in einem Quarzsandsubstrat appliziert (n = 5). Stickstoff sowie Mikronährstoffe wurden mineralisch zugedüngt und die Aufnahmen von N, P, K, Mg, Ca sowie Na im Spross untersucht. Die höchs- ten Gesamtaufnahmen von Ca und Mg, sowie der höchste Ertrag wurden im Coir-Wurmkom- post gemessen. Fäkalkompost und Coir-Wurmkompost erzielten die höchsten P- und K-Ge- halte. Die Aufnahme von Ca und Mg aus dem Fäkalkompost war gehemmt, wahrscheinlich aufgrund des hohen pH-Wertes und antagonistischer Effekte zwischen verschiedenen Katio- nen. Keine der Varianten lieferte N über die Menge der mineralischen Düngung hinaus. Zur Untersuchung der Mykorrhiza-Kolonisation wurde ein zweiter Satz sterilisierter Behandlun- gen angelegt und Wurzelproben der originalen und sterilisierten Behandlungen auf Mykor- rhiza untersucht. Eine Besiedlung wurde kaum gefunden und eine begrenzte Versorgung mit Mykorrhiza durch alle Komposte festgestellt.

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List of figures

Figure 1. Experimental setup of the conducted pot experiment. ... 28

Figure 2: N shoot concentration for all treatments. ... 38

Figure 3: P shoot concentration for all treatments. ... 40

Figure 4: K shoot concentration for all treatments. ... 41

Figure 5: Lettuce shoot of SC treatment with necrotic tissue in the older leaves... 42

Figure 6: Mg shoot concentration for all treatments. ... 43

Figure 7: Ca shoot concentration for all treatments. ... 44 Figure 8: correlation between available Mg supply [g] and Mg content [g per plant] in the lettuce shoot tissue ... B Figure 9: Correlation between Na concentration in the composts [mg kg^-1] and Na content [mg] in the lettuce shoot tissue ... B Figure 10: Correlation of pH value in the composts to the P content of the lettuce shoots per plant ... C Figure 11: Evapotranspiration per day and plant [g] in relation to the maximum daily temperature [°C] in the greenhouse. Measured and interpolated data. ... C Figure 12: correlation between total Nmin supply (compost + mineral fertilization) of the treatments [mg] and the N content in the lettuce shoots [mg] ... E

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List of tables

Table 1: Separate collection and theoretical potential of different organic waste streams in Germany ... 18 Table 2: Quantity of nutrient elements applied per pot via nutrient solution ... 29 Table 3: Shoot dry and fresh matter, root dry matter and root:shoot ratio of lettuce plants (mean ± standard deviation). ... 36 Table 4: Diameter of lettuce shoots ... 37 Table 5. Nutrient contents (mean ± standard deviation) of lettuce shoots for macronutrients ... 39 Table 6: Nutrient concentration in the lettuce shoots (mean ± standard deviation) for the different treatments and optimum nutrient levels for lettuce leaves according to Bergmann (1993). ... A Table 7: Electric conductivity, pH values, organic matter and concentration of nutrients and heavy metals ... D

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List of abbreviations

General abbreviations

AbfKlärV German Sewage Sludge Ordinance (Klärschlammverordnung)

BSR Berliner Stadtreinigung

CE Circular Economy

DüMV German fertilizer Ordinance ( Düngemittelverordnung)

EU European Union

GHG Greenhouse gases

IGZ Leibniz Institute of Vegetable and Ornamental Crops KrWG German Circular Economy Act (Kreislaufwirtschaftsgesetz)

ANOVA Analysis of variance

n number

mio million

p Person

𝞢 sum

Physical units

kg kilogram

g gram

mg milligram

t ton

Mt megaton

Gt gigaton

cm centimetre

mm millimetre

µm micrometre

nm nanometre

Vol. Volume

ml millilitre

l litre

min minute

h hour

a year

pH Negative decimal logarithm of the reciprocal of the hydrogen ion activity

EC Electric conductivity

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µS cm^-1 Micro Siemens per cm, EC unit

hPa Hectopascal, pressure unit

MJ Megajoule, energy unit

λ Wavelength lambda

°C degree Celsius, temperature Unit

Treatment related abbreviations

FIAS flow injection analysis

ICP-OES inductively coupled plasma optical emission spectrometry CAL calciumacetate + calciumlactate + acetic acid solution

VC Vermicompost

TC Thermophilic compost

VC-C Vermicompost from coir and kitchen waste

VC-P Vermicompost from fibreboard, soil and kitchen waste

TC-F Faecal compost from human excreta

TC-G Green waste compost

TC-G2, TC-G3 Green waste compost treatments with higher mineral N fertilization

SC Sand control treatment

VC-C-A Autoclaved vermicompost from coir and kitchen waste

VC-P-A Autoclaved vermicompost from fibreboard, soil and kitchen waste TC-F-A Autoclaved faecal compost from human excreta

TC-G-A Autoclaved green waste compost

DM Dry mass

FM Fresh mass

OM Organic matter

AMF Arbuscular mycorrhizal fungi

+AM Treatment inoculated with AMF Rhizoglomus irregularis high spore density

-AM Mock inoculum treatment

+AM/Inoq Treatment inoculated with AMF Rhizoglomus irregularis low spore density

Chemical abbreviations

As Arsenic

B Boron

C Carbon

C10H12N2NaFeO8 Ethylenediaminetetraacetic Acid Ferric Sodium Salt (EDTA)

Ca Calcium

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CaCl2 Calcium chloride

Ca5(PO4)3OH Fluorine apatite Ca5(PO4)3F hydroxyapatite Ca(SO4)2 Calcium sulfate

Cd Cadmium

CO2 Carbon dioxide

Cr Chrome

Cu Copper

CuSO4 Copper sulfate

Fe Iron

H3BO4 Boric Acid

HCl Hydrochloric acid

H2PO4- Dihydrogen phosphate H2PO42- Hydrogen phosphate

He Helium

K Potassium

K2SO4 Potassium sulfate

KH2PO4 Potassium dihydrogen phosphate

Mg Magnesium

MgSO4 Magnesiumsulfate

Mn Manganese

MnSO4 Manganese(II) sulfate

Mo Molybdenum

MoO3 Molybdenum trioxide

N Nitrogen

NO3 Nitrate

NH3 Ammonia

NH4 Ammonium

(NH4)Mg[PO4]·6H2O Struvite

N2O Nitrous oxide (laughing gas)

Na Sodium

Ni Nickel

OH Hydroxide

P Phosphorous

PO4 Phosphate

Pb Lead

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S Sulfur

W Wolfram

Xmin Chemical element X in mineral form Xorg Chemical element X in organic form Xtot Total concentration of chemical element X

Zn Zinc

ZnSO4 Zinc sulfate

mol Mole

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1. Introduction

1.1 Status quo of agricultural production

1.1.1 Resource consumption

Since the green revolution, agricultural practice is primarily based on the intensive cultivation of field crops in monocultures. Moreover, synthetic fertilizers, containing in particular nitrogen (N), phosphate (P) and potassium (K), have been used to increase yields, as these can easily supply plants with readily available nutrients. In 2010, 104 Mt N and 18 Mt P were used for global agricultural fertilization (Springmann et al, 2010). The production of these fertilizers, however, contributes strongly to environmental pollution. The extraction of ammonia (NH3) from air using the Haber-Bosch process alone accounts for about 2 % of the global energy consumption (Pfromm, 2017). According to Bellarby et al (2008) the production of 1 kg N fertilizer requires 65 - 101 MJ, which is equivalent to the energy contained in 1.5 – 2.5 kg of crude oil. Furthermore, food production contributes almost one third to the global anthro- pogenic greenhouse gas (GHG) emissions (Vermeulen et al., 2012), which corresponds to a carbon dioxide (CO2) equivalent of 5.2 Gt a^-1 (Springmann et al. 2010). Of these, 5 - 11 % can be attributed alone to the production of synthetic mineral fertilizers (Bellarby et al 2008).

The exploitation of resources to produce synthetic K- and P-fertilizers, on the other hand, is resource-intensive and causes landscape changes and erosion through removal of the topsoil and vegetation, as well as water contamination and air pollution by leaching of toxic minerals, exhaust gases and dust (UNEP 2001). The remaining geogenic sources of rock phosphate are becoming increasingly complex to exploit and therefore it is becoming more difficult to clean them from impurities such as naturally existing heavy metals. According to Reta et al.

(2018) radioactive and heavy metal elements are the main contaminants of surface- and groundwater, associated with P mining. Moreover, P is considered a critical resource and should therefore be conserved. In 2013, the total production of phosphate was around 200 Mt and global reserves were calculated to 65 Gt (BGR, 2014). Kiliches (2013) argues, that at a constant production rate, reserves will last for another 320 years. On the other hand, P consumption has risen significantly in recent decades, globally by 30 % from 1980 to 2010 (ibid.), especially in Asian countries (Gellings and Parmenter, 2004). According to Kiliches (2013), consumption of P in European countries is currently stagnating, but will increase again in the future. Moreover, P reserves are concentrated in a few regions, resulting in a

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dependency on P imports in most countries (BGR, 2014). The production of synthetic P-fertilizers for the European Union (EU) is based on the extraction and transport of Rock Phosphate from distant mining sites outside of Europe. Therefore, recycling of P gained importance from both an economic and an environmental point of view.

1.1.2 Land degradation

The excessive use of synthetic mineral fertilizers in recent decades, in addition to the use of pesticides, low irrigation and non-compliance with crop rotation systems or fallow periods, has led to severe soil degradation of cultivated areas (Tilahun et al 2018, p.24). According to McIntyre et al. (2009), in 2009 38% of arable land worldwide was affected by degradation.

GIZ (2015) reports, that the soil of 52 % of global agricultural land is moderately or severely degraded. As a consequence, increasingly higher quantities of fertilizers have to be used to achieve similar yields, further worsening degradation symptoms. According to McIn- tyre et al. (2009), the amount of N applied per quantity of crop produced increased dramat- ically between 1961 and 1996.

The downside of easily available synthetic mineral fertilizers is that they do not supply the soil with organic matter (OM), which, however, also needs to be restored in order to maintain soil fertility. Soil OM is a main component in the formation of soil aggregates. It acts as an exchange site for ions and has the ability to binds nutrients in the soil. Furthermore, it sup- plies energy and carbon (C) to soil organisms and is therefore indispensable for a healthy soil.

The depletion of OM in the soils thus leads to a decay of stabilizing soil aggregates, while degraded soils have a poor water and nutrient retention capacity and are less aerated.

(Blume et al, 2010)

Agricultural practices that predominantly focus on the use of synthetic fertilizers thus ultimately lead to a decrease of soil fertility in the long run. A sustainable agricultural practice should therefore preserve and restore soil OM through the use of organic amendments.

To sum up, the agricultural practices that are being conducted worldwide harm aquatic and terrestrial ecosystems and are main drivers for climate change. Thus, it is crucial for future food production, to mitigate these effects by focusing on circular economy (CE) approaches, to cycle regionally available resources and close nutrient loops. Cycling of nutrients from organic wastes can contribute to a large extend to a more sustainable form of agriculture.

Moreover, a sustainable agricultural practice should preserve and restore soil OM through the use of organic amendments.

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1.2 Potential of organic matter recycling in urban areas

The potential for nutrient and OM recycling is particularly high in cities, since, following the global trend of urbanization, most people of today live in urban environments. In 2018, 55%

of the global population, i.e. 4.2 billion people, were living in cities. By 2050, this figure will be nearly 70%, (Birch and Wachter, 2011). Each year, about 1.0 to 1.9 Gt of municipal waste is produced in cities globally (GIZ, 2016), consisting of 20 – 80 % organic material (Vergara and Tchobanoglous, 2012). On the other hand, only 4% of urban N and P fluxes are recycled (figures from 2000) (Morée et al, 2013). Even though recycling numbers are usually higher in industrialized countries compared to other countries, there is a high potential to improve the existing systems. As this thesis is settled in the German context, the following section will focus on the situation in Germany.

1.2.1 Fate & treatment of organic wastes for nutrient cycling

The German Circular Economy Act (Kreislaufwirtschaftsgesetz - KrWG, 2012) defines organic waste as biodegradable waste from households, parks, gardens and landscape management (§3 (7), KrWG). In Germany, the waste is usually collected by disposal companies and treated depending on its structure. Easily degradable OM like food waste is fermented in biogas plants and used for energy production. The resulting digestate can be directly used as fertilizer or further composted and used as soil amendment. Green waste from gardens, parks and landscape management is processed in composting plants and the product is sold as green waste compost. According to the Circular Economy Act, all private households are obliged to collect the organic waste they produce separately from other waste streams (§11 (1) KrWG, effective since 01.01.2015) and to transfer it to the local disposal companies (§17 KrWG). Exemptions are possible if a minimum of 25 m² garden area per person (Ernst and Worlitzer, 2019) are given to establish own recycling processes. In 2017, 53.8 kg per person of organic food waste and 71.3 kg per person of garden waste was collected separately (Table 1), equalling only 48.4 % of the theoretical potential (Destatis, 2019, Krause et al., 2014). This means, that even though §11 (1) KrWG came into effect already five years ago, the share of organic waste collected by German disposal companies is still insufficient.

Reasons for this include private composting of many households in sparsely populated areas as well as a lack of economic feasibility for disposal companies (Krause et al., 2014). But also in cities and metropolitan areas not all households have access to an organic waste bin. In Berlin the connection rate in 2016 was 80 % in inner city districts and 20 - 25 % in suburban areas (Abgeordnetenhaus Berlin, 2017). A large amount of organic waste still ends up in the

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residual waste, which then undergoes mechanical-biological treatment and disposal or thermal utilization in a waste-to-energy plant. The potential of this waste stream for nutrient recycling is thus not sufficiently utilized.

Table 1: Separate collection and theoretical potential of different organic waste streams in Ger- many

in 2017 for 83 Mio. Inhabitants (Statistisches Bundesamt (2017)), [1] (Destatis 2019), [2] (Krause et al., 2014). Numbers for separate collection [kg a^-1 per person (p)] and potential used [%] calculated from [1] and [2]

Separate collection [1000 t]^[1]

Separate collection [kg a^-1 per p]

Theoretical potential [kg a^-1 per p]^[2]

Potential used in [%] of collection

Food waste 4,466 53.8 81 66.4

Garden waste 5,920 71.3 177 40.3

𝞢 10,386 125 258 48.4

Centralized collection systems also face several drawbacks: (i) the organic waste needs to be collected and transported for several kilometres, requiring money and energy, (ii) it is often contaminated with plastic and heavy metals, caused by wrong sorting and usage of plastic bags for disposal, and (iii) one heavily contaminated influent can cause the pollution of a whole batch. Additionally, centralized systems are not able to react quickly to influx changes with a capacity adjustment, since existing plants are built for a long-term usage. Expanding central organic waste collection to 100% would probably have more costs than benefits, since bins are often not provided when the risk of wrong sorting is high, and collection via the organic waste bin would therefore lead to contamination of the final product.

1.2.2 Possible pathways to utilization of urban waste potential

To finally sum up, there is a large potential of urban organic waste streams, which are not optimally used at the moment. At the same time citizens and municipalities of many cities and metropolitan areas around the world take steps towards a regional food production and urban agriculture. In Germany this includes primarily community gardens, balcony and roof- top farming as well as allotment gardens, with the latter already existing since the beginning of the 20th century but now experiencing a comeback. An improved cycling of urban organic wastes in a local, circular economy approach could help restore organic matter and nutrients in agricultural soils. At the same time, it could help reduce energy consumption as well as environmental impacts of production and usage of synthetic mineral fertilizers. Decentral- ized organic waste recycling could therefore serve as a good alternative or supplement for the existing centralized systems in urban areas, and help supplying urban food production

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with locally produced fertilizers of controlled quality. One technology suitable for this purpose could be small-scale vermicomposting.

Vermicomposting is the managed processing of organic wastes to achieve a stabilized product using different types of earthworms (E. eugeniae, E. fetida, E. andrei, P. excavatus) for acceleration and promotion of microbial decomposition (Dominguez, 2004). It was already described as an artificial process for the production of soil fertilizers at the beginning of the 1940s by Oliver (1941) and is based on the natural function of earthworms in the soil. It was not long before the first small-scale vermicomposting systems were invented by Hopp (1954) and Crowe and Bowen (1954), with the intention to provide an alternative to thermophilic composting of household wastes. This approach became more and more popular in the following decades, as small-scale vermicomposting is a low-odour and space-saving process, which requires little effort and can therefore be carried out indoors by residents lacking an own garden (Sherman and Appelhof, 2011). Vermicomposting can produce a nutrient-rich organic fertilizer which contains more available nutrients and plant growth hormones than conventional compost (ibid.).

1.2.3 Fate & treatment of human excreta for nutrient cycling

Another urban waste water streams which is seen as key sources for “urban mining”, are human excreta (Chowdhury et al., 2014). A significant proportion of the nutrients applied in plant cultivation is finally consumed by humans through agri-food products and these nutrients inevitably enter the sewage system via human excreta. Although human urine, for ex- ample, accounts for less than 1 % of the waste water volume, it comprises 70 to 80 % of the N and about 45 to 60 % of the P in urban municipal waste water (Simha and Ganesapil- lai, 2017; Herrmann and Klaus, 1997). According to the characteristic composition of food, other nutrients such as K, sulphur (S) or micronutrients are contained in urine and thus ultimately in municipal waste water. These elements, which have previously been taken from the soil during plant production, should ultimately be replaced in order to maintain soil fertility. The currently most common technical processes for the recovery of nutrients from waste water mainly concern individual elements, e.g. the recovery of P from waste water by struvite ((NH4)Mg[PO4]·6H2O) precipitation or P extraction from sewage sludge ash. On the other hand, conversion and removal of N from waste water via the combination of nitrifica- tion and denitrification requires most of the energy consumed by waste water treatment plants. Such waste water treatment further leads to significant gaseous N losses due to nitrous oxide (N2O) emissions from activated sludge processes. Most of the nutrients (P, K, S)

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remain in the sewage sludge, where cross-contamination with pharmaceuticals, heavy metals and microplastic coming from other sources than toilets, can be observed. Due to this cross-contamination, field-fertilisation with sewage sludge has been restricted or banned by many national governments (e.g. Germany, cf. German Sewage Sludge Ordinance (Klä- rschlammverordnung AbfKlärV)). In Germany, currently 65% of the sewage sludge produced is dried, incinerated and then deposited in landfills (Roskosch and Heidecke, 2018).

1.2.4 Possible pathways to utilization of human excreta potential

First approaches for novel, recycling-oriented sanitation service include the usage of dry toilets. Dry toilets are increasingly replacing chemical toilets at several German festivals and are becoming increasingly popular with campers. The collected excreta are thermophilically composted with toilet paper, sawdust and sometimes other additives. The existing systems either recycle urine and faeces together or separate them and treat them separately. However, the legal framework for the use of these composts is not yet in place. In principle, the EU’s “end- of-life”-criterion (CE marked fertilizing products and amending Regulations (EC No 1069/2009 and EC No 1107/2009) promotes the production of bio-based recycling fertilisers but does not explicitly mention (processed) human excreta, neither urine nor faeces. Also in many European countries, the agricultural use of excreta is not yet covered by the legal framework. Political work and a paradigm shift are thus needed to integrate this resource into waste water or solid waste management and fertilizer legislations at European and national level.

1.3 Goals and Hypotheses

Small-scale vermicomposting for urban organic waste and composting for human excreta are promising approaches to closing urban nutrient cycles on a local level and providing valuable organic fertilizers for urban and peri-urban cropland. The objective of this thesis is to examine and assess the physicochemical properties and fertilization potential of organic fertilizers from different urban sources, to gain knowledge about the value of these sources for agricultural practices and to detect potential drawbacks of these new approaches. Two small- scale vermicomposts (VC) and two thermophilic composts (TC) of different urban waste streams, namely two different VC from kitchen waste, a TC from human excreta and a thermophilic green waste compost were examined. For this purpose, a pot experiment with lettuce was conducted, and yield and nutrient composition of the plants evaluated. As N from organic fertilizers is released more slowly than other nutrients, additional mineral N fertilization was applied, and nutrient release potential for K, P, Mg, and Ca under sufficient N supply

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was determined. Yield response and nutrient composition of the lettuce shoot tissue was regarded as fertilizing potential of the composts.

Additionally, the effect of the different VC and TC (from here on referred to as "composts", when summarizing both VC and TC) on the colonization of the lettuce roots by symbiotic arbuscular mycorrhizal fungi (AMF) was examined. This was based on the idea, that mesophilic composting does not destroy as many fungal spores as thermophilic composting, since fungi are less thermotolerant than bacteria (Insam and de Bertoldi, 2007) and spores of AMF are likely to survive passage through the intestines of earthworms (Redell and Spain, 1991).

It is therefore more likely that root colonisation with spores of AMF occurs after application of VC compared to TC. Based on this background, the following hypotheses were set up:

Hypothesis 1: Fertilization of lettuce with vermicompost or faecal compost leads to a significantly higher biomass and significantly higher concentrations and contents of the macronutrients P, K, Mg and Ca in the lettuce shoot tissue, compared to thermophilic garden waste compost.

Hypothesis 2: Application of mesophilic vermicompost leads to a colonization of lettuce roots by compost-derived arbuscular mycorrhiza in contrast to application of thermophilic composts.

1.4 Introduction manuscript

A part of this thesis is supposed to serve as the basis for a scientific manuscript and to be published as a research article after further editing. Thus, it was aimed to follow the style of writing of scientific publications in the respective chapters. An introduction for the manuscript is not included here, as it will follow the same argumentation as the introduction for this thesis, though in a more condensed way. It will focus on the energy consumption and environmental pollution caused by the production and application of synthetic fertilizer production and the potential of nutrient recycling from urban areas. A short literature review will focus on the current state of VC as organic fertilizers and the knowledge gap about less well researched soil amendments like human excreta.

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2. Background

2.1 Composting

Composting is a controlled aerobic biodegradation process for the stabilization and sanitation of solid organic wastes. Microbial degradation processes transform the organic sub- stance to minerals and stabilized OM under the release of CO2, water and heat. Due to the production of heat energy by the microbial activity, the composting process undergoes a thermophilic phase. In this phase, temperatures of maximum 80 °C can be reached, and sanitation of the composted material through pathogen elimination takes place. (Insam and de Bertoldi, 2007)

Composting is a well-established process for a wide range of organic wastes. It is one method for the stabilization and sanitation of human excreta which is successfully applied (Vin- nerås et al., 2003; Ogwang et al., 2012). Compost from faecal matter has already been tested as a soil amendment and was effectively improving crop productivity (Krause et al., 2016).

However, research on the potentials of faecal composts in crop production is still scarce.

Comparison to other urban organic fertilizers can help to estimate the potential of faecal composts for the integration into a more sustainable and regional nutrient cycling economy.

2.2 Vermicomposting

2.2.1 Process of vermicomposting

Vermicomposting is a managed stabilization process for organic wastes using earthworms (Dominguez, 2004). The worms increase the surface area of the original material by ingesting and fragmenting it, simultaneously aerating and mixing it by moving through the substrate.

Hence, they optimally prepare it for decomposition by microorganisms, thus enhancing microbial decomposition rate of the waste (Lim et al., 2016). Since a large share of the waste passes through the digestive tract of the earthworms during the process of vermicomposting, the resulting VC is a fine-textured product (Arancon et al., 2004).

2.2.2 Microbiology of vermicomposting and Potential for AMF supply

Part of the degradation process of organic material is carried out by endosymbiotic bacteria in the intestines of the worms. Enzymes produced by these endosymbiotic bacteria, readily available OM and mucus are released together by the worms as vermicast and serve as cat- alysts for decay of OM or nutrients for the growth of microorganisms. At the same time, the

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earthworms feed on microorganisms colonizing the waste material, thus having a strong in- fluence on the composition of the microbial community in the material. Overall, the total biomass of bacteria and fungi is reduced during vermicomposting. Bacterial growth rates are decreased, whereas fungal growth rates are not affected. (Dominguez, 2011)

Brown et al., (2000) showed, that earthworms are able to digest a range of microorganisms, such as bacteria, fungi, but also protozoa and nematodes. Fungal spores, on the other hand, can only partly be degraded, depending on the spore characteristics and the earthworm species (Reddell and Spain, 1991; Brown, 1995). It was examined for several fungal species (e.g.

fusarium lateritium, a plant parasite), that their spores were not able to germinate after pas- sage through earthworm intestines (Moody et al., 1996). In a study about earthworms as vectors for mycorrhiza in the soil, on the other hand, it was found, that the majority of AMF spores remained intact and able to germinate after the passage through earthworms of different species (Reddell and Spain, 1991). In the same study, sorghum (sorghum bicolour) was successfully infected with AMF by the examined earthworm casts (ibid.).

2.2.3 Sanitation of vermicomposts and removal of human pathogens

Vermicomposting is a mesophilic process, usually taking place in a temperature range of 10 - 35 °C, with an optimum of 15 - 25 °C, depending on the species (Dominguez, 2004). Out- side this range of tolerable temperatures, the feeding and reproduction activity of the earthworms decreases or even ceases completely (Edwards and Bohlen, 1996). The movement of the earthworms through the waste material aerates and mixes the substrate, thus preventing the process of self-heating, which is induced by microbial activity in thermophilic composting systems. Therefore, in contrast to thermophilic composting, there is no thermophilic phase, in which temperatures of minimum 55 - 70 °C are reached over a period of at least three days (Edwards and Subler, 2011).

Studies on the reduction of human pathogens during vermicomposting showed contradicting results. In many cases, however, a considerable reduction of various microbes, such as E. coli and Salmonella (Edwards and Subler, 2011), or Salmonella and Pseudomonas (Finola et al., 1995) was achieved. Riggle (1996) found that after two months the levels of Salmonella, enteric viruses and viable helminth eggs fell below the detection limit, while faecal bacteria were still found, yet in notably reduced numbers. Thus, input material like human excreta should undergo further treatment steps, to ensure elimination of human pathogens, before used as a soil amendment in food crops (Lalander et al., 2013).

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2.2.4 Vermicompost for fertilizer application

For the production of VC, a broad variety of organic wastes is utilized, such as different animal manures, food and paper wastes, biogas slurry and crop residues. The type of input material has an effect on the fertilizing qualities of the VC product (Aynehband et al., 2017). However, independent from the type of organic waste used, 84 % of the studies on VC effects on plant growth published until 2018, showed yield increasing effects on plants (Hussain and Ab- basi, 2018). Reasons stated for the growth stimulation of plants are an improved nutrient supply (Tognetti et al., 2005), as well as the presence of growth promoting substances in the vermicast, e.g auxin and cytokinin (Krishnamoorthy and Vajranabhaiah, 1986) or humic acids (Canellas et al. 2002). Hernandez et al. (2015) found that application of humates extracted from VC reduced the time until harvest maturity in lettuce by two to three weeks and Arancon et al. (2004) related the stimulating effect of VC on plant growth to plant growth regulators and enhancement of microbial activity in the soil. Furthermore, VC was found to suppress the populations of plant pests (Arancon et al., 2005; Simsek-Ersahin, 2010), an effect also known from other organic fertilizers (Culliney and Pimentel, 1986). In addition to its plant growth promoting qualities, VC can improve soil properties, e.g. by increasing soil po- rosity and water holding capacity (Goswami et al., 2017).

The application of very high quantities of VC as an amendment for soils or substrates, can on the other hand reduce the growth of plants (Ali et al., 2007) or even lead to their death (Lazcano and Dominguez, 2010). Non-degraded phytotoxic compounds from the organic waste and an increased salinity can be reasons for this effect (Singh et al., 2013).

Compared to thermophilic composts, VC from the same input material were found to achieve a finer and more homogeneous product (Hanc and Dreslova, 2016) and to have a higher concentration of nutrients (Pattnaik and Reddy, 2010). Thermophilic compost, which was post- treated by vermicomposting was found to have higher nutrient concentrations and improved fertilizing properties compared with the original TC (Tognetti et al., 2005).

2.3 Mycorrhiza

The term mycorrhiza (from Greek ‘mycos’ = fungus and ‘rhiza’ = root) refers to a mutualistic symbiosis between fungi and plant roots, which can be found in the majority of terrestrial plant species (Smith and Read, 2008). Mycorrhiza comprises, among others, the two important types i) ectomycorrhiza, which grows mainly on tree roots and whose hyphal network

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is formed outside and in the intercellular spaces of the outer root layers, and ii) the endomy- corrhizal fungi, which grow between and in the cells of the root epidermis of their host plant (Parniske, 2008).

Endomycorrhiza are the arbuscular mycorrhizal fungi (AMF), which are named after tree- shaped structures (arbuscules), that many of the AMF (Division Glomeromycota) form within the plant root cells. A key function of AMF for the host plant is the supply with a number of nutrients, most of all P, and also N, Zn and Cu, through uptake by fungal hyphae. The hyphal network spreads and thus extends the range of nutrient access for the plant beyond the rhi- zosphere. Furthermore, fungal hyphae are thinner than plant roots and are therefore able to penetrate smaller pores, which are not accessible to the plant roots themselves. Hence, at the same root length, the efficacy of AMF colonized roots in nutrient uptake is higher than in non-colonized roots. (Smith and Read, 2008)

In return, the Glomeromycota fungi are supplied with organic C assimilated by the plant. The fungi are dependent on the C supply of the associated plant to complete their life cycle and are thus obligate biotroph (Parniske, 2008). The supply of C to the fungi can make up 4 - 20 % of the net assimilated C of the plant (Smith and Read, 2008). In addition to the nutrient exchange between the symbiotic partners, AMF increase the resistance of the plants to root pathogens and improve their drought stress tolerance (Marschner, 2012).

2.4 Lettuce

Lettuce (lactuca sativa var. capitata L.) is an important vegetable plant belonging to the family of Asteraceae. It can be cultivated in many different soils and prefers temperatures of 10 - 20 °C and a pH of 6 - 8 (Rubatzky and Yamaguchi, 1997). Lettuce is sensitive to acidic pH values and can be inhibited in growth and head formation at temperatures over 30 °C (ibid.).

Germination temperature should be controlled, as temperatures under 20 °C stimulate and accelerate germination and improve germination rates (Borthwick and Robbins, 1928). Let- tuce plants have a comparably shallow root system and are therefore prone to moisture stress (Rubatzky and Yamaguchi, 1997).

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3. Material and Methods

The following sections will present the materials and methods used for this thesis, which are thought to be used as a scientific manuscript. They will include the part of the experiment, which was focussing on the compost characteristics and their plant fertilization properties.

3.1 Composts

Four different composts were examined in this study, including (i) two composts from vermicomposting (VC) and (ii) two composts from thermophilic composting (TC). The vermicomposts were produced at Technische Universität (TU) Berlin in a ten-week process from Janu- ary to March 2019 in household sized batch systems made of 10-litre buckets using Eisenia fetida earthworms. The bedding material selected was 1.5 kg of wet coir (coconut fibre) for the first vermicompost (VC-C) or a mixture of 1 kg of soil (“Einheitserde” by Einheitserde Werkverband e.V. Typ Classic) and 110 g of corrugated fiberboard for the second vermicompost (VC-P), respectively (Braun, 2019). Twice a week, kitchen waste consisting of 16.5 % coffee grounds and 83.5 % fruit and vegetable peels and residues from a university canteen were fed to the earthworms to a total quantity of 1140 g per bucket (ibid.). The faecal compost (TC-F) was provided by the compost producer Birkenhof in Lindendorf, Libbenichen (Bran- denburg, Germany). The TC-F was produced in a three-month thermophilic composting process using a mix of human faeces, toilet paper and saw dust, which was collected at > 15 different festivals in Northern Germany by three start-ups that rent and operate dry toilets for public events. The toilets use a drainage system for separating urine and faeces, meaning that also some urine is mixed with the faecal matter. The thermophilic green waste compost (TC-G) was a commercially available product from the local waste disposal company Berliner Stadtreinigung (BSR).

3.2 Analysis of compost samples

Chemical analysis of the two vermicomposts and the green waste compost were carried out at TU Berlin. In preparation, the samples were sieved to < 11.2 mm to remove non-degraded plant parts (wood) and subsamples were taken with a ripple divider Type RT for analysis and storage. The pH of the composts was measured in a suspension of 5 ml material in 25 ml of a 0.01 mol l^-1 CaCl2-solution (DIN EN 15933:2010) and electric conductivity (EC) (modified DIN CEN/TS 15937:2013) was measured in the fresh samples in a 1:25 (mDM/Vol.) extraction with double distilled water. Gravimetric water content was determined after oven drying for 24 h at 105 °C and organic matter (OM) was determined through loss on ignition of the dry sample

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at 550°C (DIN EN 15935). Soluble Nitrate (NO3), Ammonium (NH4) and Magnesium (Mg) were extracted for 60 minutes in a solution of 1:25 (mDM/Vol.) using a 0.0125 mol l^-1CaCl2-solution (modified VDLUFA, 2012a Ch. A6.1.4.1 and Ch. A6.2.4.1). Extractions were analysed using ion chromatography (DX-500, Dionex Corporation Sunnyvale, California, USA), flow injection for atomic spectroscopy (FIAS) (FIAStar 5000 System by Foss GmbH, Hamburg/Hilleroed, Den- mark) and inductively coupled plasma optical emission spectrometry (ICP-OES) (iCAP 6000 Series, Thermo Fisher) (NO3, NH4, Mg), respectively. Calcium acetate lactate (CAL)-extracta- ble P and K were measured in the material using a 1:25 (mDM/Vol.) CAL-solution (modified VDLUFA, 2012a, Ch. A6.2.1.1) and analysed via ICP-OES. For the elemental analysis, the composts were dried at 105 °C and ground to a particle size of < 250 µm with a planetary ball mill (PM 400 by Retsch, Haan, Germany). The samples were subjected to aqua regia digestion and microwave pressure digestion (DIN EN 16174:2012-11) in a MARS 5 microwave (CEM GmbH Kamp-Lintfort, Germany) followed by ICP-OES measurement to determine the contents of the macronutrients Catot, Ktot, Mgtot and Ptot, micronutrients Cutot, Fetot, Mntot, Zntot and Natot

and heavy metals Astot, Cdtot, Crtot, Nitot and Pbtot. For the measurement of Ktot and Mgtot in the faecal compost, the samples were digested as described above but analysed by flame atomic absorption spectrometry (AAS 400, Perkin Elmer). Concentrations of Ctot and Ntot for all four composts were measured using a Vario EL III CHNS Elemental Analyser (Elementar GmbH Langenselbold, Germany). The analysis of EC, Ptot andCatot, in thefaecal compost was carried out according to DIN EN 13038 (2012-01), DIN EN ISO 11885 (E22) (2009-09) and DIN EN ISO 11885 (2009-09), respectively.

According to Blume et al., (2010) 30 % of Norg from organic fertilizers is available in the first vegetation period after application. Since growth period was only 5 weeks, a lower availability of 10 % was estimated for this experiment. The availability can thus be calculated as:

𝑁_𝑚𝑖𝑛+𝑁_𝑡𝑜𝑡− 𝑁_𝑚𝑖𝑛 10

3.3 Experimental setup

From June to July 2019, a five-week pot experiment with lettuce under glasshouse conditions was carried out at the Leibniz Institute of Vegetable and Ornamental Crops (IGZ) in Großbeeren, Germany. The experimental setup is shown in Figure 1.

The pot substrate was a mixture of quartz sand and compost, prepared as described in the following paragraph. The amount of compost applied was calculated in a way that the plants received sufficient P and K from the compost to produce a per head yield of 15 g dry weight (DM) or 250 g fresh weight (FM) with an average of 6% dry matter content (the minimum

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weight per head is 100 g FM [according to EU Regulation (EC) No 1580/2007]) and with a target concentration of 0.45% P and 4.2 % K in the shoot DM (see Bergmann, 1993). Based on the minimum total P and K content measured in the composts (see Fehler! Verweisquelle konnte nicht gefunden werden.), 100 g compost per pot were applied resulting in at least 0.07 g total P and 0.63 g total K. To obtain comparable physical conditions in the substrate, the same amount of compost was added in all respective treatments. As plant N demand would not be covered by the applied quantity of compost, additional N was supplied so that the plant uptake of the other macro elements was not limited. To compare individual nutrient contributions, an additional treatment with purely mineral fertilization without compost (SC) as well as two green waste compost treatments with two higher levels of N fertilization (TC-G2, TC-G3) were set up. Before planting, 3.5-litre plastic pots (Teku-Tainer; Pöppelmann, Germany) were filled with a homogenous mixture of 100 g (DM) compost and 1.67 kg (DM) of washed quartz sand (0.5 - 1.2 mm grain size) for the treatments VC-C, VC-P, TC-F, TC-G and TC-G2, TC-G3. The treatment SC with mineral fertilization received a pot filling of 1.93 kg (DM) sand. Each treatment was replicated five times (n = 5).

Figure 1. Experimental setup of the conducted pot experiment. Green boxes refer to the different compost treatments, blue, red and yellow boxes to the mineral fertilization solution added per pot.

The maximum water holding capacity was determined for all pot substrates used in the respective treatments (modified according to Alef, 1994). For this purpose, 0.5-litre plastic pots were filled with one of the substrates (n = 3), saturated in a water bath and then placed on a

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sand bed for 1 h for draining. Afterwards, the water content of the pot contents was determined on the basis of the difference in weight before and after drying at 105 °C. The resulting water mass corresponds to the maximum water absorption capacity.

Seeds of lettuce (Lactuca sativa var. capitate) cultivar "Lucinde" (Bingenheimer Saatgut AG, Echzell, Germany) were germinated in quartz sand, and kept at 7 °C for the first 24 h to accelerate germination. At the three-leave stadium, the seedlings were pricked into a peat- filled cultivation tray and received a mineral fertilization of 16 mg N, 4 mg P, 13 mg K and 1 mg Mg per plant, using a solution of 3 g l^-1 MANNA LIN M Spezial (Wilhelm Haug GmbH &

Co KG, Germany). After 10 days, seedlings were planted into the prepared pots. The planting date was regarded as day no 1. The pots were set-up completely randomized on a table.

For the basic supply of essential macro and micronutrients, the plants received a nutrient solution (as shown in Table 2) with the exception of P and K in the compost treatments during the first two days of the experiment. The compost-free sand control treatment (SC) received a complete mineral fertilization. A proportion of 188 mg N of the Ntot given (see Table 2) was applied to all treatments on day 21 after planting.

Table 2: Quantity of nutrient elements applied per pot via nutrient solution at day 1, 2 and 21 of the growth period.

Treatments: VC-C (coir + kitchen waste vermicompost), VC-P (fibreboard, soil + kitchen waste vermicompost), TC-F (faecal compost), TC-G (green waste compost), TC-G2 and TC-G3 (green waste compost with additional N fertilization), SC (Sand Control without compost addition)

Element Supplied form VC-C, VC-P, TC-F, TC-G

TC-G2 TC-G3 SC

[mg pot^-1] [mg pot^-1] [mg pot^-1] [mg pot^-1]

NH4-N NH4NO3 188 283 378 188

NO3-N NH4NO3 188 281 377 187

∑ NH4NO3 376 564 755 376

K KH2PO4

K2SO4

- - - 114

191

P KH2PO4 - - - 90.1

Mg MgSO4 80.9 80.9 80.9 161

Ca Ca(SO4)2 30.2 30.2 30.2 130

Fe C10H12N2NaFeO8 10.4 10.4 10.4 10.4

Mn MnSO4 5.04 5.04 5.04 5.04

Zn ZnSO4 5.06 5.06 5.06 5.06

B H3BO4 5.07 5.07 5.07 5.07

Cu CuSO4 2.04 2.04 2.04 2.04

Mo MoO3 2.07 2.07 2.07 2.07

S s.a. 131 130.8 131 356

Na C10H12N2NaFeO8 4.0 4.0 4.0 4.0

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The plants were irrigated with deionized water during the whole growth period, maintaining a substrate water content of 60% of the maximum water holding capacity. Water was added each day according to the daily water loss due to evapotranspiration, which was determined gravimetrically on a weekly basis. The irrigated volume applied ranged from 50 to 350 ml per day supplied either one time or split in several doses, depending on the size of the plants and the temperature. At very high temperatures in the greenhouse, the evapotranspiration rate was greatly increased (Figure 11, Appendix) and hence, irrigation was carried out close to the maximum water holding capacity of the substrate to avoid phases of drought stress between the irrigation units.

The shoot diameter was measured using the maximum distance of two opposite leaves tips, and the visual evaluation for potential deficiencies was carried out at days no. 16, 25 and 35 of the growth phase. The climate data in the greenhouse cabin was recorded continuously throughout the experiment. The average air temperature was 26.6°C at day and 20.7 °C at night and the average relative humidity was 57.9 %.

3.4 Plant analysis

3.4.1 Harvest and biomass analysis

After a 37-day growth period, the shoots (including the stem) were harvested, roots were washed manually from the substrate and the fresh weight of both root and shoot was measured. Root and shoot samples were oven-dried at 60 °C until a constant weight was reached and dry weight was recorded and regarded as total biomass. Subsequently, samples were ground to < 250 µm in a centrifugal mill (ZM 200, Retsch, Haan, Germany) and homogenised for further analysis.

3.4.2 Nutrient analysis in the plant tissue

Subsamples of the ground plant material of about 250 mg each were digested using 5 ml nitric acid and 3 ml hydrogen peroxide (VDLUFA, 2012b, Ch. 10.8.1.2.) and subjected to microwave pressure digestion (MARS 5 Xpress by CEM GmbH Kamp-Lintfort). P, K, Ca, Mg and Na concentrations were determined using ICP-OES in iCAP7400 (Thermo Fisher Scientific GmbH, Dreieich) and a wavelength of λ = 178.284 nm (P), 766.490 nm (K), 315.877 nm (Ca), 279.553 nm (Mg) and 589.592 nm (Na). For N and C analysis the samples were digested by DUMAS dry oxidation at 950 °C in an oxygen-enriched He-atmosphere in a combustion tube filled with W(VI)oxide in a vario el cube (Elementar Analysensysteme GmbH, Langenselbold)), using a thermal conductivity detector (VDLUFA, 2012a, Ch. 2.2.5.).

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3.5 Statistics

The measured nutrient concentrations and DM and FM of roots and shoots were statistically analysed. For this purpose, the mean and standard deviation were calculated. Provided that data met the condition of normal distribution (Shapiro-Wilk-Test), the data was subjected to an analysis of variance (one-way ANOVA; P < 0.05) to calculate significant factor effects. The levels of significance between the groups was determined using the Tukey-Test (P < 0.05). All statistical methods were conducted with the software STATISTICA version 13 (StatSoft Inc., Tulsa, Oklahoma, USA).

3.6 Mycorrhiza colonization

Additional to the methods mentioned above, the following procedures were carried out.

They were not included in the first material and methods part, since they are considered as a separate part of the conducted pot experiment that did not yield publishable results.

3.6.1 Experimental setup

To examine a possible colonization of lettuce roots with compost-derived AMF, a portion of each compost was either left untreated or sterilized by autoclavation (VX-150 by Systec GmbH, Linden, Germany) at 134 °C for 20 min. The pots were filled and prepared for the experiment as described in Chapter 3.3 (treatments: VC-C-A = autoclaved coconut fibre vermicompost, VC-P-A = autoclaved cardboard vermicompost, TC-F-A = autoclaved faecal compost, TC-G-A = autoclaved green waste compost) with five replicates each (n = 5). To avoid contamination with AMF among the treatments, all used equipment was disinfected with ethanol between working with the different treatments. The lettuce shoots were harvested together with those from the other treatments and treated in the same way (see Chapter 3.4.1). During harvest subsamples were taken from the fresh roots of all eleven different treatments to test AMF colonization. For this purpose, samples of 1 cm length (about 1 g FM in total) were cut off from the root system, i.e. from the middle part and root tips, and stored as a mixed sample in a 15 % ethanol solution at 7 °C until examination.

Additionally, a control pot experiment with lettuce was conducted from the end of July until mid-August in cooperation with Anja Müller (IGZ), to examine whether a colonization of lettuce with AMF under the given greenhouse conditions was theoretically possible. Eight pots were filled with 2.1 kg of washed silica sand. The first four pots (+AM) were each inoculated with 30 g inoculum comprising the AMF Rhizoglomus irregularis with a minimum of 50 spores cm^-3 on loess soil as carrier material. Two pots (-AM) received 30 g of the same inoculum pre-treated as follows: the inoculum was suspended in deionised water and filtered

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through a filter paper with pore size <4 µm (Whatman® grade 589/3). Bacterial cells were able to pass the filter, whereas the fungal spores and carrier material were retained. The retentate was afterwards autoclaved and both filtrate and retentate added to the other four pots as mycorrhiza-free "mock inoculum". The last two pots (+AM/Inoq) received a second inoculum ("Inoq Advantage" with hyphae fragments and spores of Rhizoglomus irregularis without carrier material) containing less spores than the inoculum described above, i.e. the applied quantity of spores for (+AM/Inoc) was around 60 spores in total per pot. After 6 weeks the lettuce plants were harvested and root samples taken as described above.

3.6.2 Root staining and examination for AM colonization

The root samples were analyzed for AMF colonization via root staining and examination under a dissection microscope. For this purpose, the samples were stained with ink modified according to Vierheilig et al., (1998). In this procedure the root pieces were first covered in 10 mol l^-1 potassium hydroxide (KOH) solution and incubated for 45 min at 60 °C to make the cell walls permeable for the staining reagent. Afterwards they were acidified in 2 mol l^-1 hydrochloric acid (HCl) for 2 min and then stained with a solution of ink in 5 % acetic acid for 45 min at 60 °C. As a last step, they were placed in lactic acid for destaining and storage. The rate of root length colonization was measured using a dissection microscope with 50x mag- nification and mycorrhiza were counted using a modified gridline intersection method (Ten- nant, 1975; Kormanik and McGraw, 1982).

Plant care, root staining and microscopic examination for the control pot experiment were carried out by Anja Müller (IGZ).

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4. Results and Discussion

The following chapter will present and discuss the findings from the first part of the experimental setup, which will be used as a scientific manuscript. It will focus on the physicochemical characteristics of the composts and the nutritional status and yield response of the grown lettuce plants.

4.1 Chemical and physical properties of the composts

4.1.1 Nutrient composition

Fehler! Verweisquelle konnte nicht gefunden werden. presents the nutrient composition of t he tested composts. The faecal compost TC-F showed the highest concentration of N (19.4 g kg^-1), P (3.98 g kg^-1), Mg (3.88 g kg^-1) and Ca (21.2 g kg^-1) and contained high concentrations of K (12.8 g kg^-1), which was only slightly exceeded by the vermicompost VC-C (14.7 g kg^-1 K).

The concentrations of K, P, Mg and Ca found in TC-F correspond well to concentrations found by Krause et al. (2015) for a faecal compost enriched with biochar. The nutrient composition in the thermophilic green waste compost TC-G is comparable to that found in the vermicompost VC-P with the exception of having a higher P concentration and reduced Na concentration.

Concentrations of N, P, K, Mg and Na differed widely in both vermicomposts. They were higher in VC-C than in VC-P, in the cases of P, K and Na even about twice as high (Table 7), whereas Ca was significantly higher in paperboard-based vermicompost VC-P. This finding indicates an impact of the bedding material on the product quality in terms of differences in nutrient concentrations.

Total N concentrations in the composts of 10 to 19 g kg^-1 fit the 12 g kg^-1 typically found in composts according to Blume et al. (2010) and were similar to concentrations found by Her- nández et al. (2010) for thermophilic composts and vermicomposts (14-16 g kg^-1) and to concentrations found by Arancon et al. (2003) for different vermicomposts (10 - 19 g kg^-1). Min- eral nitrogen levels were highest in VC-C (0.7 g kg^-1) compared to TC-F (0.47 g kg^-1) or VC-P (9.85 mg kg^-1 or 0.009 g kg^-1) and TC-G (7.87 mg kg^-1 or 0.008 g kg^-1), showing the lowest concentrations. As composting and vermicomposting are aerobic processes, Nmin was mainly present in the form of nitrate (NO3-), with only very low concentrations of ammonium (NH4+).

The NO3- concentrations in VC-C and TC-F are comparable to results of Hernández et

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al. (2010) (0.35 g kg^-1). According to the estimated N availability (see Chapter 3.2) approxi- mately 230 mg of N from VC-C and TC-F and 100 mg from VC-P and TC-G were available per plant from the applied compost amounts, in addition to the mineral fertilization.

During the progressing composting process, the C:N ratio in the metabolized matter decreases until a stabilized compost product is obtained. To minimize priming effects when compost is applied to the soil or added to potting substrate, the C:N ratio should be below 18 for standard compost (Kehres and Vogtmann, 1988) and below 22 for vermicompost (Ed- wards et al., 2011). Three of the tested composts comply with these recommendations with C:N ratios of 22, 15 and 18, respectively, found in VC-P, TC-F and TC-G. Only the VC-C treatment slightly exceeds the requirements with a C:N ratio of 27.

4.1.2 Organic Matter and pH value

The pH values and concentrations of OM of the composts are shown in Table 7. The pH values are close to neutral for VC-P (7.2) and TC-G (7.6), while VC-C is slightly acidic with pH 6.1. All three composts are within the range of 5.5 - 8.0, which is considered adequate for plant growth when using potting media or soils (Edwards et al., 2011). The faecal compost TC-F, however, had an alkaline pH value of 8.8, which is comparable to pH values for vermicomposts and composts produced from farmyard or cattle manure in other studies (Durak et al., 2017; Hernández et al., 2010). Soils used for cropping should generally have a pH between 5.0 and 6.8, as many nutrients are well soluble in this range (Blume et al., 2010; Pe- terson, 1982). Compared to sandy soils, the quartz sand used in the present experiment is a mineral substrate, and thus has no pH-buffering capacity (Zoltán, 2010). In soils, carbonates and clay minerals, as well as humic substances from the soil buffer the pH value of any amendment, reducing its pH influencing effect (Blume et al. 2010). Therefore, our tested compost additions would have a higher pH-changing effect in the sand substrate, than they would have had in soil. The pH values in the pot substrates are thus most likely close to the original pH values of the respective compost.

OM in mature composts varies from 25 - 40 % of DM, and should not fall below 25 % (Kehres and Vogtmann, 1988). This condition was reached by all four composts. Noteworthy was the exceptionally high share of OM in VC-C with over 80 %.

4.1.3 Electric conductivity, salt and sodium content

The values for the EC and Na concentration are shown in Table 7. According to Rich- ards (1954), a soil is considered saline at an EC > 4000 µS cm^-1. High soluble salt concentrations in soil amendments can induce salt stress in plants and should, according to Edwards