Spatial Patterns of Characteristics and Soil Formation in the transitional landscape zone, central part of Bogowonto Catchment, Java, Indonesia

DISSERTATION

zur Erlangung des Akademischen Grades einer Doktorin der Naturwissenschaften am Institut für Geographie der Fakultät für Geo-und Atmosphärenwissenschaften der Leopold Franzens-Universität, Innsbruck

eingereicht von

Nur Ainun Harlin Pulungan

Betreuung: Univ. Prof. Johann Stötter (Institut für Geographie, Innsbruck) Assoz. Prof. Clemens Geitner (Institut für Geographie, Innsbruck) Prof. Junun Sartohadi (Fakultät für Geographie, UGM, Yogyakarta)

Innsbruck, 2016

Leopold-Franzens-Universität Innsbruck

Eidesstattliche Erklärung

Ich erkläre hiermit an Eides statt durch meine eigenhändige Unterschrift, dass ich die vorliegende Arbeit selbständig verfasst und keine anderen als die angegebenen Quellen und Hilfsmittel verwendet habe. Alle Stellen, die wörtlich oder inhaltlich den angegebenen Quellen entnommen wurden, sind als solche kenntlich gemacht.

Die vorliegende Arbeit wurde bisher in gleicher oder ähnlicher Form noch nicht als Magister- /Master-/Diplomarbeit/Dissertation eingereicht.

28.10.2016 Datum Unterschrift

ACKNOWLEDGEMENTS

I would like to thank to all those who supported the study and made this dissertation possible. Without their excellent guidance, encouragement, caring, patience, and effort, this study could have been never accomplished. To all persons who are mentioned or cannot be mentioned by name in this page, I am greatly indebted.

First of all, I express my sincere gratitude to my first supervisor, Professor Johann Stötter for his valuable guidance, taught, and ideas to my scientific work, also for providing me with very kind atmosphere for doing research from the beginning until the end of this study. I also would like to thank to Assoc.Professor Clemens Geitner for his valuable comments, enormous advises that improve the quality of this work a lot, and particularly for supporting me doing laboratory research. I would like to express my deepest gratitude to Professor Junun Sartohadi for his unceasing support, effort, guidance, and time which contributed a lot throughout this study.

I would like to thankful to OeAD and Technology Grant of Asea-Uninet for providing me the opportunity and the scholarship to pursue my study at Innsbruck University.

I would like to extend my grateful to Bogowonto Research Group members – Aries D. Wardana, Febrian Maritimo, Elok S Pratiwi, Rini Meiarti, Zuhara Candraningrum, Garri Kusuma, and Wayan Wisnu M – who helped me out to do fieldwork and several laboratory analyses in Geography, UGM. I also would like to thank to Pak Udin’ family in Margoyoso, Mas Dwi’ family in Loano for their kindness and helpful during my fieldwork. They have been becoming my new family.

I also deeply appreciate Mrs. Niken Sawitri, Prof. Dewi Galuh Condro Kirono, Dr. Evita Hanie Pangaribowo, Dr. Dyah Rahmawati Hisbaron, Wirastuti Widyatmanti, Ph.D – for their priceless time in proofreading my dissertation; Simone Sandholz, Ph.D – for helping in Zusammenfassung translation; Ilva Dolģe, M.Sc, Eva Kauk, M.Sc, and Novi Rahmawati, M.Sc – for language checking. Thanks to my room fellow in Geography Institute – Richard Hastik, Haida Christin, and Stefanie Palma. Also, thanks to all my Indonesian’ friends in Innsbruck – Nina Novira, Sarrah Ayuandari, Utia Suarma, Syamsul Bachri, Hermawan Trinugraha, Agung Dewanto, Rm. Stenly Viany, Rm. Subali, Rm. Sukristiono, Nuri Efiana, Arko Wicaksono, Widiyanto and Bu Jenny for their friendliness.

Also I am notably grateful to the persons who highly motivate my study - father and mother – their love, patience, and pray always strengthen me. Last but not least, thanks to Hariman Maulana who has been always supporting me during my study. Alhamdulillah...

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TABLE OF CONTENTS

ACKNOWLEDGEMENT i TABLE OF CONTENTS ii LIST OF FIGURES v LIST OF TABLES viii SUMMARY x ZUSAMMENFASSUNG xii

Chapter 1 Introduction 1.1 Scientific background 1 1.1.1 in Indonesia 1 1.1.2 Soils in Java 5 1.1.3 Focus and lack of soil research in Indonesia 7 1.2 Knowledge gaps 8 1.3 Research problems 9 1.4 Objectives and Research questions 12 1.5 State of the dissertation 13 1.6 Thesis outline 13

Chapter 2 Studies on relevant literature 2.1 Introduction 14 2.2 What is soil? 15 2.2.1 Soil definition 15 2.2.2 Soil systems 16 2.3 Soil genesis 20 2.3.1 Soil-forming factors 22 2.3.2 Soil-forming processes 23 2.3.3 Autochtonous vs Allochtonous 25 2.4 Soil in the tropics 27 2.5 Volcanic soils 29 2.6 Hydrothermal alteration 30 2.7 Human-induced soils 35 2.8 Soil 36 2.9 Soil redistribution 38 2.10 Conceptual Framework 39

Chapter 3 Research systems, Methods, and Terminology definition 3.1 System of the study 41 3.2 Data acquisitions 43 3.2.1 Soil sampling in the field 43

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3.2.2 Environmental data 48 3.3 Soil sample analysis 48 3.3.1 Soil sample preparation for laboratory analysis 48 3.3.2 Soil morphological properties 48 3.3.3 Soil physical properties 49 3.3.4 Soil chemical properties 49 3.3.5 Soil mineralogical properties 51 3.4 Results analysis 52 3.4.1 Profile development analysis 52 3.4.2 Descriptive-statistic analysis 52 3.4.3 Spatial analysis 52 3.5 Terminology definition 54

Chapter 4 Understanding the characteristics of study area 4.1 Geographical sites 55 4.2 Physical-Environmental Setting 57 4.2.1 Climatic and soil hydrologic condition 57 4.2.2 Parent rocks and soil parent materials 61 4.2.3 Land surface morphology 63 4.2.4 Vegetation cover 64 4.3 Socio-Culture-Economic Setting 67 4.3.1 Demographic condition 67 4.3.2 Cultural development 69 4.3.3 Economic and livelihood 71

Chapter 5 Results 5.1 Overview 74 5.2 Spatial variation of soils 76 5.3 Soil development 86 5.3.1 Analysis of soil properties 86 5.3.1.1 Residual soils 86 (i) Morphological and physical properties 86 (ii) Chemical properties 98 (iii) Mineralogical properties 103 (iv) Recapitulation of residual soil property results 110 5.3.1.2 Redistributed soil material 113 (i) Morphological properties 113  Landslide-redistributed soil material 113  Human-redistributed soil material 117 (ii) Physical properties 118  Landslide-redistributed soil material 118  Human-redistributed soil material 120 (iii) Chemical properties 123  Landslide-redistributed soil material 123

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 Human-redistributed soil material 127 5.3.1.3 Recapitulation of soil properties based on soil-scape concept 132 5.3.2 Assessment of soil profile development 138 5.3.2.1 Residual soils 139 (i) Ratio of SOM in A-horizon to SOM in B- or C-horizon 139 (ii) Ratio of percentage of in C-horizon to percentage of clay 140 in A/A+B horizon 5.3.2.2 Human redistributed-soil material 141 (i) Ratio of SOM in A-horizon to SOM in B- or C-horizon 141 (ii) Ratio of percentage of clay in C-horizon to percentage of clay 143 in A/A+B horizon 5.3.2.3 Landslides redistributed-soil material 144  Depletion zone of landslides 144  Accumulation zone of landslides 151 5.4 Genesis of soil parent material 154 5.4.1 Soil parent material from weathered parent rock 155 5.4.2 Soil parent material from volcanic ash deposit 157 5.4.3 Soil parent material from altered parent rock 158 5.4.4 Redistributed soil material 160 5.4.4.1 Landslide-redistributed soil material 160 5.4.4.2 Human-redistributed soil material 163 5.5 Variations of soil formation 166 5.5.1 Monogenetic soils 166 5.5.2 Polygenetic soils 168

Chapter 6 Discussion 6.1 Soil-scape relationships 172 6.2 Soil formation and soil development 178 6.3 Soil-Human interaction 184 6.3.1 Influences of soil properties to human activities 184 6.3.2 Impact of human activities on soils 188

Chapter 7 Conclusions and Outlook 7.1 Conclusions 193 7.2 Outlook 196

References 198

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LIST OF FIGURES

Fig.1.1 Rainfall type distribution in Indonesia 2 Fig.1.2 Volcanic arcs of Java 6 Fig.2.1 Soil pedon, polypedon, and other units related to a soil-scape 16 Fig.2.2 Soil system behavior in time 20 Fig.2.3.Tropical and non-tropical climate range of the world 28 Fig.2.4 Evolution of magmatic-hydrothermal system during a cooling process of a 31 porphyry intrusion Fig.2.5 Types of alteration as a function of temperature, K+ and H+ activities 32 Fig.2.6 Diagram of hydrothermal alteration in rocks containing: (A) dominant alkali- 33 feldspar; (B) dominant plagioclase Fig.2.7 Conceptual framework of the study 40 Fig.4.1 Location of the study area 57 Fig.4.2 Rainfall pattern based on nearby climatic stations 58 Fig.4.3 Heavy rainfall in the study area affecting high velocity of run-off 60 Fig.4.4 The presence of seepage in the study area found 30 cm below the surface 60 Fig.4.5 Physiographic units of Java Island and the study area located 61 Fig.4.6 Distribution of lithology in the study area 62 Fig.4.7 Geomorphic units of the study area 64 Fig.4.8 Types of land uses in the study area 65 Fig.4.9 map of the study area 66 Fig.4.10 Population in Central Java Province 67 Fig.4.11 Land uses percentage in Central Java Province 71 Fig.4.12 Sengon and Cinnamon as the wood commodity in the study area 72 Fig.5.1 Map of landscape systems of the study area 77 Fig.5.2 Map of landform segments of the study area and soil profile sites 79 Fig.5.3 Soil profile examples showing the variation due to different 87 soil parent materials Fig.5.4 Reddish coloration in altered material due to Fe oxidation and hematite 88 development during hydrothermal alteration Fig.5.5 White coloration of altered material due to Silica enrichment during 89 hydrothermal alteration Fig.5.6 Horizon-based distribution of grain size of fine earth (<2mm) of selected soil 97 profiles Fig.5.7 CEC and exchangeable base cations of various soil parent materials 98

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Fig.5.8 Exchangeable base cations per horizon of residual soils 99 Fig.5.9 XRD diagram showing the presence of halloysite and kaolinite in volcanic ash 104 soil from profile-1 horizon C Fig.5.10 XRD result of each soil parent material in the study area 105 Fig.5.11 Comparison of CEC with: (a) clay content & (b) SOM 127 Fig.5.12 Soil material redistribution by landslides 144 Fig.5.13 Landslides that remove the surface and/or sub-surface soils 145 Fig.5.14 Landslides that remove the soils up to regolith (saprolite-type) 146 Fig.5.15 Landslides that reveals the altered materials to the surface 147 Fig.5.16 Landslides that remove the soils up to regolith (colluvium-type) 148 Fig.5.17 Landslides that remove the soil material up to regolith (airfall deposit-type) 149 Fig.5.18 Landslides that remove the soils up to the underlying parent rocks 150 Fig.5.19 Distribution of soil parent material in the study area according to geological 154 formations Fig.5.20 Weathered parent rocks in the study area 155 Fig.5.21 Thick volcanic ash soils in the northern part of the study area 157 Fig.5.22 Presence of smectite type of clay (montmorillonite) in altered materials based 158 XRD analysis result Fig.5.23 The presence of altered material due to hydrothermal alteration in some parts 159 of the study area Fig.5.24 Types of landslides-redistributed material: (a) dominated by soil material; (b) 160 mixed of soil material and saprolite Fig.5.25 Distribution of landslides in the study area based on field survey 2007-2014 161 Fig.5.26: Landslide-redistributed material as new soil parent material in the study area: 162 (a) dominated by soil material; (b) mixed landslide-redistributed soil material Fig.5.27 Human activities on slope surface: (a) Human-tillage practice to overturn the 164 soils; (b) Mechanic tillage practice to overturn the soils; (c) terracing as one of soil redistributing management in slope areas; (d) crop rotation (paddy into ginger) Fig.5.28 Mixed soil material of human-redistributed material 165 Fig.5.29 Sketch of monogenetic soils illustrating the single soil formation cycle 166 Fig.5.30 Monogenetic soils in the study area 167 Fig.5.31 Sketches of polygenetic soil types in the study area 168 Fig.5.32 Polygenetic soils in the study area 169 Fig.5.33 Types of polygenetic soils in the study area 170 Fig.6.1 Altered parent rocks 179 Fig.6.2 Variation of agricultural plants based on soil parent material 185

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Fig.6.3 Cultivated landslide-redistributed soil material that may generate the next 186 landslides Fig.6.4 Traces of seepage within landslide-redistributed soil material 30 cm below the 187 surface Fig.6.5 Some effects of on soil development 189 Fig.7.1 Dynamic of Soil-Human System 195

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LIST OF TABLES

Table 1.1 Soil types in Indonesia 3 Table 1.2 Knowledge gap matrix 10 Table 1.3 Objectives and Research Questions 12 Table 2.1 Hierarchy of soil systems for modelling soil development 17 Table 2.2 Selected types of soil-forming processes mostly occurred in the study 24 area Table 2.3 Types of hydrothermal processes 34 Table 3.1 Characteristics of the catchment system in the study area 41 Table 3.2 Characteristics of the soil system in the study area 42 Table 3.3 Soil profiles for residual soil analyzing 44 Table 3.4 Soil profiles for landslide deposits analyzing 45 Table 3.5 Soil profiles for human-induced soils analyzing 46 Table 3.6 Relation of research questions, objectives, data, methods, and results 53 Table 4.1 Administration boundary of the study area 55 Table 4.2 Population statistic data of Central Java Province 68 Table 4.3 Agricultural land in the study area 71 Table 5.1 Characteristics of landform segments of the study area 78 Table 5.2 Landscape characteristics of soil profiles within the landform 81 segments Table 5.3 Morphological and physical properties of residual soils based on field 90 assessment Table 5.4 Physical properties of residual soils based on laboratory analysis 93 Table 5.5 Chemical properties of residual soils based on laboratory analysis 100 Table 5.6 XRF analysis of altered- and weathered soil parent material 108 Table 5.7 Recapitulation of residual soil property results 111 Table 5.8 Morphological and physical properties of soils based on field 114 assessment Table 5.9 Particle size distribution and COLE Index of landslide-redistributed 118 soil materials (L) and non-redistributed soils (NL) Table 5.10 Range and average of particle size distribution of landslide- 119 redistributed soil material (L) and non-landslide soils (NL) Table 5.11 Particle size distribution of human-redistributed soils 121 Table 5.12 Chemical properties of landslide-redistributed soil materials and non- 124 landslide soils

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Table 5.13 Range and average of chemical properties (CEC, Cation bases, and 125 pH) of landslide-redistributed soil material (L) and non-landslide soils (NL)

Table 5.14 Range and average of chemical properties (P2O5, SOM, C, N-total) 126 of landslide-redistributed soil material (L) and non-landslide soils (NL)

Table 5.15 N-total, P2O5, SOM, pH of human-redistributed soils 128 Table 5.16 Exchangeable base cations, Base saturation, and CEC of human- 130 redistributed soils Table 5.17 Recapitulation of soil properties based on soil-scape concept 133 Table 5.18 Soil profile development assessments of residual soils 139 Table 5.19 Soil profile development assessments of human-redistributed soils 142 Table 5.20 Landslide-soil material properties concerning landslide classification 152 in the study area Table 5.21 Mineralogical composition of parent rocks in the study area based on 156 X-ray powder diffraction (XRPD)analysis results

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Spatial Patterns of Soil Characteristics and Soil Formation in the transitional landscape zone, central part of Bogowonto Catchment, Java, Indonesia

Summary

This research focuses on evaluating the spatial patterns of soil characteristics and soil formation in the transitional zone of Sumbing Quaternary Volcanic, Menoreh Tertiary Volcanic, and Halang Tertiary Structural systems. The objectives of this research are: to identify the spatial pattern of soils in the study area, to characterize the soil parent materials and the soils in the study area, and to evaluate the soil formation and the soil development in the study area. The knowledge gaps raised in this research are: (i) the relationship between soil formation and landscape system; (ii) the influence of relief in soil profile development and in soil formation cycle; (iii) the influence of slope surface processes in soil profile development of hilly areas;(iv) the consideration of slope deposit as soil parent material; (v) the anthropogenic influence on surface soils and its consequences for soil redistribution.

We applied survey method supported with soil sampling. We analyzed the samples both qualitatively in the field and quantitatively in the laboratory. The sampling area is the central part of Bogowonto catchment. The catchment area was chosen because the area have various factors and processes which are significant to influence the soil formation and the soil development in the study area. The soil sampling method applied on this field investigation was purposive sampling according to soil-scape system. There were totally 43 pedons selected based on landform segmentations. There were 16 pedons sampled for residual soils analysis. There were 27 pedons sampled for redistributed soils analysis; contained by 11 pedons of landslide deposit and 16 pedons of human induced-soil. We conducted soil properties analyses i.e. morphological, physical, chemical, and mineralogical for data analysis, followed the standard of Laboratory Methods Manual (2004). We also conducted quantitative assessment of the degree of soil profile development. Two ways were applied on this assessment: (i) Ratio of (SOM); (ii) Ratio of percentage of clay. We used descriptive-statistic analysis to interprete the soil properties data. We applied spatial analysis to simplify the spatial patterns of phenomenon in the landforms.

The results show that the soil variation in the transitional landscape zone is not sufficient to be discussed through the catena concept of single slope. It is because the catena concept only provides two dimensional descriptions of soils along the slope transect. However, to explain the soil variation in the transitional landscape zone needs a concept which describes the configuration and arrangement of a landscape. The soil-scape concept is better applied on explaining the soil variation in a transitional landscape zone. As the transitional landscape zone, the study area spatially consists of short sequences of hill slopes with the possibility of various soil parent materials along the slopes, complex reliefs, as well as intensive slope surface processes. Consequently, there is no sequential pattern of soil characteristics along the upper, middle, and lower parts of the study area in the regional scale. This is due to the fact that relief condition in the transitional landscape zone is not laid sequentially from the upper to the lower parts. The soil variation in the study area is more influenced by the types of soil parent materials and relief condition, rather than the slope position.

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The other results show that the soil formation in this study does not only consider the weathering of parent rock to perform the soil parent materials. It also considers the other processes supporting the soil parent materials deposition such as hydrothermal alteration, burial process, and anthropogenic process. It is commonly found that the soil formation is always started by parent rock weathering. However, a contrary occurrence is found that in some location the soil formation is also controlled by the parent rock alteration due to hydrothermal effect. Overall, the residual soils may develop from various soil parent materials such as weathered parent rock materials, weathered volcanic ash materials, and altered parent rocks materials. The differences of weathered parent materials and altered parent materials are strongly described on the properties of color, texture, CEC, clay type, cation bases, base saturation and SOM. Soils developed on weathered parent rock materials have brownish to grayish color, whereas, soils developed on altered parent rock materials have reddish to orange color. Texture of soils developed on weathered parent rock materials show less than 30% of clay content, whereas, texture of soils developed on altered parent rock materials show much higher clay content, at most > 60%. Soils developed on weathered parent materials have medium to high CEC value that is 20- 70 me/100gr indicating the clay type of illite and montmorrillonite. The illite is dominated by partial substitution of aluminium and silicate due to weak K-bonding among the alumino-silicate layers. However, the montmorillonite has weak oxygen bonding that is easily substituted. In the formation of montmorillonite, the alumino (Al3+) is mostly substituted by Mg2+. Consequently, these clay types result in the excess negative charge, and thus cause the high capability of exchanging and binding cations leads to the high base saturation. In contrast, soils developed on altered parent materials have much lower CEC value that is < 10 me/100gr indicating the clay type of kaolinite. This low CEC is followed by a fewer amount of exchangeable cations because the kaolinite is dominated by hydrolysis that cause the replacement of cation bases by the ion H+. Consequently, this type of clay results in low capability of exchanging and binding cations causing low base saturation.

As the transitional landscape zone, landslides are also the influencing factor for soil formation and soil development. The effect of landsides in soil variation are focused on two zones i.e. depletion zone and accumulation zone. The soil development is cut off in the depletion zone of landslide. On the other side, the presence of landslide deposit on the slope surface is able to interrupt the influence of underlying weathered parent rock in soil development. The landslide deposit may bury the former soil profile in the deposition area, and bring about the new soil formation. Also, most of soils in the study area have been influenced by different types of human activities that generate different responses in soil development. Human activities are able to modify the soil characteristics both physically and chemically. The activities of human together with landslide are also able to redistribute the soils and interrupt the soil profile development.

Keywords: soil formation, soil characteristic, soil parent materials, weathered parent rock, altered parent rock, landslide-redistributed soils, human-redistributed soil

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Räumliche Muster von Bodeneigenschaften und Bodenbildung in der Landschaftübergangszone im zentralen Teil des Einzugsgebiets Bogowonto, Java, Indonesien

Zusammenfassung

Die vorliegende Forschungsarbeit fokussiert die Bodeneigenschaften und Bodenentwicklung in der Übergangszone des Sumbing Quartär-Vulkansystems, des Menoreh Tertiär-Vulkansystems und des tertiären Halang Systems. Die Forschungsziele bestehen in der Identifikation der räumlichen Muster von Böden, der Charakterisierung der Substrate der Böden und der Charakterisierung der Bodenentwicklung im Forschungsgebiet. Die Arbeit soll folgende Beiträge zur Überbrückung von Wissenslücken leisten: (i) eine Berücksichtigung der Beziehungen zwischen Bodenbildung und Landschaftssystem; (ii) Klärung des Einflusses des Reliefs auf die Entwicklung von Bodenprofilen und in der Bodenbildungszyklus; (iii) Charakterisierung des Einflusses von Hangoberflächenprozessen auf die Entwicklung von Bodenprofilen von hügeligen Gebieten; (iv) Berücksichtigung von Hangmaterial als Substrat der Bodenbildung; (v) der Einfluss von menschlicher Nutzung auf Boden eigenschaften und Bodenumlagerungen.

Die verwendete Erhebungsmethode wurde durch Bodenbeprobungen unterstützt. Die entnommenen Proben wurden sowohl qualitativ bereits im Feld als auch quantitativ im Bodenlabor untersucht. Die Probenentnahme erfolgte im zentralen Teil des Bogowonto Einzugsgebiets. Das Einzugsgebiet wurde ausgewählt, da es verschiedene Faktoren und Prozesse abbildet die signifikanten Einfluss auf die Bodenentwicklung im Untersuchungsgebiet haben. Als Methode der Bodenbeprobung wurden Zielstichproben gemäß soil-scape-system gewählt. Insgesamt wurden 43 Peda ausgewählt, basierend auf den Landschafts-Segmenten. 16 der Peda wurden für die Analyse von Verwitterungsböden herangezogen, 27 für eine Analyse umgelagerter Böden, unterteilt nach der Morphodynamik in 11 (durch Rutschung) und 16 (durch den Menschen). Die durchgeführten Analysen der Bodeneigenschaften umfassten morphologische, physikalische, chemische und mineralogische Analysen, dem Soil Survey Laboratory Methods Manual (2004) folgend. Daneben wurden auch Verfahren zur Abschätzung der Bodenprofilentwicklung angewendet: das Verhältnis der organischen Materie (SOM) und des prozentualen Anteils von Ton. Dabei wurden deskriptive statistische Analysen zur Beschreibung der Bodeneigenschaften verwendet. Die räumlichen Besonderheiten der Landform wurden vereinfacht dargestellt auf Basis einer Raumanalyse.

Die Ergebnisse zeigen dass die Bodenvariationen in der Landschafts-Übergangszone nicht ausreichend diskutiert werden kann nur auf der Grundlage des Catena-Konzepts auf einzelhang, was sich begründet in den nur zweidimensionalen Beschreibungen von Böden entlang des Hang- Transekts, die das Konzept anbietet. Um aber die Bodenvariationen im Untersuchungsgebiet zu erklären, bedarf es eines Konzepts, das die Landschaftskonfiguration einschließt. Hier ist das soil- scape Konzept besser geeignet. Das Untersuchungsgebietumfasst kurze Abschnitte von Hängen mit der Möglichkeit diverser Böden entlang der Neigung, aufgrund des komplexen Reliefs sowie der intensiven Hangoberflächenprozesse. Folglich gibt es keine sequentiellen Muster von Bodeneigenschaften entlang der oberen, mittleren und unteren Abschnitte des Studiengebiets auf regionaler. Ebene, begründet durch die nicht-sequentiell von den oberen zu den unteren Abschnitten gelegte Reliefkonditionen in der Landschafts-Übergangszone. Die Bodenvariationen im Studiengebiet sind mehr beeinflusst von den Typen der Substrate und der Reliefkonditionen als von den Hangpositionen.

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Die vorliegende Studie zeigt, dass es nicht ausreicht, für die Bodenbildung nur die Verwitterung des Ausgangsgesteins zu betrachten, sondern auch andere Prozesse wie Umlagerungen durch Rutschungen und den Menschen sowie hydrothermische Veränderungen im Ausgangsgesteins. Üblicherweise wird angenommen, dass Bodenbildung immer mit Verwitterung vom Ausgangsgestein beginnt. Es wurde allerdings herausgefunden, dass an einigen Stellen die Bodenbildung durch hydrothermale Effekte auf Ausgangsgestein kontrolliert wird. Insgesamt können sich Verwitterungsböden aus verschiedenen Materialien wie verwittertem Muttergestein, verwitterter Vulkanasche und verändertem Ausgangsgestein bilden. Die Unterschiede der verwitterten und der veränderten Ausgangsgestein werden ausführlich beschrieben anhand von Farbe, Textur, Kationen Austauschkapazität (CEC), Tonminerale, Basenkationen, Basensättigung und organischer Substanz (SOM). Böden, die auf verwittertem Ausgangsgestein entwickelt sind haben bräunliche bis gräuliche Farbe, während Böden aus verändertem Ausgangsmaterial rötlich bis orange sind. Erstere weisen weniger als 30% Tonanteil auf, während Letztere deutlich höhere Tonanteile haben bis maximal >60%. Böden auf verwittertem Substrate haben mittlere bis hohe CEC-Werte, 20-70 me/100gr und haben in der Feinfraktion Illit und Montmorillonit. Der Illit wird durch teilweise Substitution von Aluminium und Silikat durch schwache K-Bindung zwischen den Alumino-Silikatschichten dominiert. Der Montmorillonit hat schwache Sauerstoffbindung, die leicht zu ersetzen ist. Bei der Bildung von Montmorillonit wird das Aluminium (Al3+) meist durch Magnesium (Mg2+) ersetzt. Diese Tonminerale sind austauschstark und führen zur Bindung der Kationen und damit zu einer hohen Basensättigung. Im Gegensatz dazu haben die auf verändertem Ausgangsmaterialien entwickelten Böden viel niedrigere CEC-Werte <10 me/100 gr aufgrund der Dominanz von Kaolinit sowie geringere Basensättigungen.

In der untersuchten Landschaftsübergangszone sind beeinflussen Rutschungen die Bodenentwicklung maßgeblich, wobei hinsichtlich der Bodenvariabilität eine. Abtrags- und Akkumulationszone unterschieden werden kann. In der Abtragszone ist die Bodenentwicklung gestört, die Profile reduziert. In der Akkumulationszone wird die Bodenbildung ebenso gestört, jedoch durch die Überlagerung des ursprünglichen Ausgangsgesteins, so dass die Bodenbildung auf dem neuen Material wieder beginnt. Außerdem sind die meisten Böden im Untersuchungsgebiet durch verschiedene menschliche Aktivitäten beeinflusst, die zu unterschiedlichen Auswirkungen bei der Bodenentwicklung führen. Durch menschliche Aktivitäten, werden Bodeneigenschaften modifiziert, sowohl physisch als auch chemisch. Die Aktivitäten des Menschen zusammen mit denen der Rutschungen führen zu neuen räumlichen Verteilungen der Böden mit unterschiedlichen Profilentwicklungen.

Stichwort: Bodenbildung , Bodeneigenschaften , Bodenausgangsmaterialien, verwittertes Ausgangsgestein, veränderte Ausgangsgestein, durch Rutschungen-umverteilte Böden, durch Menschen-umverteilte Böden.

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1

CHAPTER 1 INTRODUCTION

1.1 Scientific background 1.1.1 Soils in Indonesia

Soils in Indonesia are typically influenced by humid tropical climatic setting; rainfall and temperature being the major factors affecting soil formation and soil development (Hardjowigeno, 2003). Both the intensity and the frequency of rainfall drive the vertical water movements within soil profiles (Fang et al., 2011), and may control fine soil materials and major bases translocation (Khomo et al., 2011). However, intensity and frequency of rainfall vary across areas having different rainfall types. There are three types of rainfall in Indonesia, i.e. equatorial type, tropical monsoon type, and local type (Tjasyono, 1999), with specific annual rainfall pattern (see Fig.1.1) which influence soil formation and soil development. The average annual rainfall in Indonesia varies between 2000-3000 mm (BPS, 2015). On the other side, temperature takes a significant role in tropical climatic setting with regard to weathering and evapotranspiration processes. High temperature, together with high rainfall frequency, controls the weathering of parent rocks, and thus has impact on formation of soils (Darmawijaya, 1990). Temperature also relates to evapotranspiration process, and thus controls the humidity which has significant influence on the soil development. In Indonesia, the humidity remains high, at most > 60% (e.g. Swarinoto and Sugiyono, 2011). As a consequent, this high humidity causes fast organic decomposition processes (van Wambeke, 1992), and generates humification faster than organic matter mineralisation (Nikita-Martzopoulou, 1981).

Soils in Indonesia are also controlled by active and passive morphostructures due to its location in active plate movements. The morphostructures associate with the endogenic processes that control the formation of landforms (Pannekoek, 1949). Tectonic and volcanic processes which actively control the formation of Indonesia (Verstappen, 2000) have created several landforms in the form of uplifted, subsidence, folding hills, volcanic slopes, and magmatic intrusion areas (Thornbury, 1958). Consequently, those processes have resulted in relief and lithology variations which are important for soil formation, and are essential to control the development of soil and the removal of surface soil due to geomorphic processes (Scarciglia

2 et al., 2005). Moreover, the tectonic and volcanic processes have produced the passive morphostructure i.e. lithologies as parent rocks in soil formation. The dominant parent rocks in Indonesia are derived from igneous rocks as well as sedimentary rocks that provide various rates in weathering, and thus determine the soil characteristics and soil development in certain areas.

Rainfall type boundary

Fig.1.1: Rainfall type distribution in Indonesia (source: BMKG, 2014)

In effect, high rainfall intensity and high humidity, as well as tectonic and volcanic processes, are attributed to soil formation and soil development in Indonesia. As a consequence, they forms the variation of soil types as mentioned in Table 1.1. It is in line with Jenny (1941) cited in Kirkpatrick et al. (2014) which stated that the soil formation concept not only deals with parent rocks but also deals with the interaction with other four factors i.e. climate, organism, relief, and time. According to the climate, lithology, and relief setting, the soil types in Indonesia can be categorized into 18 types based on the modified Dudal-Soepraptohardjo classification system which was simplified by PPT Classification System (1978/1982). The soil types are controlled by the variation of subsurface diagnostic horizon (Bockheim et al., 2014). Table 1.1 shows the characteristics and the distributions of each in Indonesia.

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Table 1.1: Soil types in Indonesia (source: Hardjowigeno, 2003)

No Based on Dudal- Based on Characteristics Distribution Soepraptohardjo PPT Based on recent concept of soil genesis Classification and classification System 1978/1982 1 Organosol Organosol Soil with histic horizon 50 cm or more East of Sumatra, West and low bulk density and South of Kalimantan, along west-coast of Papua 2 Litosol Litosol Shallow soil found on solid rock up to a Most of hilly and depth of 20 cm from the ground mountainous area 3 - Ranker Soil with A-umbric horizon with a Most of hilly and thickness less than 25 cm and no other mountainous area diagnostic horizon 4 Renzina Renzina Soil with A-mollic horizon on limestone, Along south-coast of and calcium carbonate content of more Java, West of Sumatra than 40% 5 Grumusol Grumusol Soil with more than 30% of clay content Most of Java, West of expanding when it is wet and cracking Sumatra, East Nusa when it is dry; has cracks with a width of Tenggara 1 cm and a depth of cracks up to 50 cm; has gilgai or wedge structure at depths between 25-125 cm 6 Gleisol, Gleisol Soil with hydromorfic characteristic at a Kalimantan and East of depth of 0-50cm; and has histic-, umbric- Sumatra Gleisol Humus, , molic-, calsic- or gipsic horizon Alluvial Hidromorf 7 Alluvial Alluvial Soil derives from recent , Along east-coast of layering, has irregular organic content, Sumatra, along north- and only have epipedon ochric, histic or coast of Java, and most sulfuric with content less than 60% of river valley area at the depth 25-100 cm from the ground 8 Regosol Coarse-textured soil of albic materials Most of Indonesia having no other horizon except ocric, histic or sulfuric with sand content more than 60% at a depth 25-100 cm from the ground 9 Andosol Soil with black to dark brown colour Area with old-active with high organic matter content; crumb, volcanoes i.e. most of porous, and slippery (smeary). In the Java, West- and North subsurface horizon, soil has brown to of Sumatra, Nusa yellowish brown, and sometimes has thin Tenggara silica sementation 10 Latosol Latosol Soil with clay content over 60%; crumb Most of Indonesia to blocky; loose; has a uniform colour boundaries within deep solum (over 150 cm); blurred horizon; base saturation of less than 50%; generally has epipedon of

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umbric and cambic. 11 Brown Forest Kambisol Soil with B-cambic horizon or A-umbric Most of Indonesia Soils, or A-mollic horizon; and no hydromorfic characteristics Brown 12 Red-yellow Podzolik Soil with B-argillic horizon; base Most of Indonesia Podzol, saturation <50%; no albic horizon. Grey-brown Podzol 13 Mediteran Mediteran Similar to Podsolic, soil with argillic Along south-coast of horizon but the base saturation is more Java, Nusa Tenggara than 50% 14 Planosol Soil with E-albic horizon located above Kalimantan argillic or natric horizon (horizon with the real texture changes, heavy clay or fragipan at the depth 125 cm from the ground, has hydromorfic characteristic in E-albic horizon 15 Podzol Podzol Soil with B-spodic horizon Most of Java, West Sumatra, Sulawesi

Soil types in Indonesia vary based on their location i.e. lowland, upland, or mountain areas. Soils in lowland areas are mainly formed by rapid and intensive weathering processes, called laterisation, under the influence of perennial tropical climatic setting (Tan, 2008). According to Tan (2008), the major soils formed in this area are latosols or reddish-colored soils as result of rapid weathering processes; red-yellow podzolic soils as the resulting from acidic parent materials; red-yellow mediterranean which are mainly formed in areas having monsoon- type climate; grumusol or dark-colored soils which are formed in marl with smectite clay formation; and organosol or soils which are mainly formed in coastal region.

In comparison to soils in the lowland areas, soils in the upland areas receive more influence of humification instead of rapid weathering due to a cooler climate (Tan, 2008). In addition, the upland areas are often considered as the transitional zone between lowland and mountain areas. As a consequence, these areas are characterized by both processes of laterization of lowland soils and podzolization of mountain soils. The major soils formed in these areas are red-yellow podzolic soils, similar to the lowland areas, but they are more likely due to the combined influence of laterization and podzolisation; brown forest soils which are mainly formed under the influence of deciduous forest; and are often found in high elevation of >600 m above sea level (Tan, 2008).

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Soils in the mountain areas are also shaped by slow weathering processes due to cooler climate, and are strongly formed by podzolisation process resulting in the depletion of alkali. These soils are solely found at an elevation of >1000 m above sea level or extend to the summit of volcanoes (Tan, 2008). The major soils formed in this area are as mainly developed on volcanic material containing allophane glass; brown podzolic soils as mainly formed in acid parent materials or with low content of carbonates; grey-brown podzolic soils as mainly develop on intermediate volcanic material and as the effect of deciduous and mixed forest of cool humid regions; podzol soils as mainly composed of illuvial accumulation of free sequioxide and humus accumulation which characterize the formation of spodic horizon (Tan, 2008).

1.1.2 Soils in Java Widely crossed by the volcano range (Karig, 1974; cited in Umar et al., 2014), most of areas in Java are subjected to the formation of volcanic soils. The volcano range is distributed along the island from West to East, as the result of the subduction of the Indo-Australia Plate beneath the Eurasian Plate along the Java Trench, a process that has been active for 45Ma (Hall, 2002). As a consequence, this volcano range makes Java as a volcanic island (Smyth, 2008). Among 129 active volcanoes in Indonesia, there are 44 volcanoes located in Java Volcanic Arc (PVMBG, 2013). According to Soeria-Atmadja et al. (1994), the Java Volcanic Arc is categorized into two sub-arcs (Fig.1.2): (i) Old Java Volcanic Arc (Late Eocene – Early Miocene) located in the southern part of Java Island with Tertiary volcanoes; (ii) Modern Java Volcanic Arc (Late Miocene – Pliocene) located in the central of Java Island with Quaternary volcanoes. Therefore, the activities of those volcanoes produce amount of volcanic material which is the dominant underlying parent rocks in soil formation in Java.

Volcanic soils in Java are underlaid by the old- and the recent volcanic materials (Smyth, 2005) which have different mineral composition. The old volcanic material is mainly found as old-Andesite. The mineral composition of this material is acid and tends to be composed by andesitic to rhyolithic (Smyth, 2008). On the other side, the recent volcanic material is mainly found as volcanic ash deposit which is the major cover material on the slope surfaces as it is the most recent volcanic product in Java. Volcanic ash soils in Java are mainly derived from recent Pleistocene to Holocene deposits (van Ranst et al., 2002). The mineral composition of these

6 materials is silica, and thus produces basaltic andesite (Nicholls et al., 1980; cited in Faure, 2013). Furthermore, volcanic ash is rapidly weathered (Fiantis, 2011) and often leads to perform typical thick volcanic ash soils. Overall, volcanic soils are usually formed in a wide range of altitude from 900 m upwards (Subagyo and Buurman, 1980), and can develop into andosol, litosol, podzol, or podzolik as they meet the conditions stated in Table 1.1.

Fig.1.2: Volcanic arcs of Java

Often, volcanic soils in Java form the multi layers of soils by the overlaying of old volcanic deposit by recent volcanic material on (Widodo, 2001). These multi layers of soils have caused soils with lithological discontinuity, in the sense of Lorz (2011). These specific conditions induces landslide occurrences in Java significantly (Mulyanto and Stoops, 2003), as changing consistency between the layers leads to slope instability.

On the other hand, volcanic soils in Java are influenced by alteration processes of volcanic parent rocks. This is because in some areas the activities of volcanoes are followed by the appearance of magmatic intrusion causing the alteration of parent rocks. This study is in line with the previous study by Verstappen (2000) which examined that some areas in Java where locates in the uplifted zones are encountered by volcanic activities, e.g. magmatic intrusion. As a consequence, not only weathering processes but also alteration processes of the underlying parent rocks must be taken into account in the formation of volcanic soils in Java, as will be explained in detail in the Chapters 5 and 6.

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These volcanic soils provide two sides impact on environment. Young volcanic soils contribute a high productivity for agriculture purposes (Hikmatullah, 2010), due to containing big amount of soil nutrients and having high porosity (Mulyanto and Stoops, 2003). Thus, most of young volcanic soils are usually cultivated for tea plantation and horticulture (Yatno and Zaujah, 2008), and also for paddy field, due to water abundance (Mulyanto, 1999). On the other side, the old volcanic soils are mainly composed by high clay content (Wada, 1987; Fiantis, 2011) and which makes them prone to structural failure causing landslides (Langmay et al., 2000).

The central part of Bogowonto catchment has been chosen as the study area since this area has been built by both recent and old volcanic materials, and thus representing a typical landform in Java. In addition, gently to rough relief as well as human influence on soil surface result in certain processes on the slopes which vary both soil formation and soil development in the study area. Therefore, the central part of Bogowonto catchment is an appropriate representative area to study the soil formation and soil development in volcanic areas.

1.1.3 Focus and lack of soil research in Indonesia According to Hardjowigeno (2003), soil research in Indonesia has been started since 1920. It was initiated by Dr. E. C. Jul. Mohr who conducted first soil research in Indonesia. He focused on soil climates and soil characteristics in mostly Indonesia. After Dr. Mohr, the other soil scientists were Prof. Dr. Ir. F.A. van Baren (focused on agrogeology and mineralogy) and Prof. Dr. H.J. Hardon (focused on soil genesis and ). They became the first lecturers in Landbouw Hageschool which is now known as Bogor Agricultural Institute - “Institut Pertanian Bogor”. Their works were continued by Dr. J. van Rummelen and Dr. J. van Schuylenborgh. After the Independence Day of Indonesia, some scientists interested in soils were Tan Kim Hong (focused on and soil mineralogy), Go Ban Hong (focused on soil fertility and ), Kang Biauw Tjwan (focused on soil fertility, agronomy, and agroforestry), Tejoyuwono Notohadiprawiro (focused on soil fertility), and Sarwono Hardjowigeno (focused on pedogeomorphology and ).

Recently, applied soil studies have become the main focus of soil research in Indonesia. Most of the recent studies are dealing with soil fertility and soil conservation. The researches are

8 intended to increase agricultural productivity in order to support national agriculture program: food sovereignty. Several soil researches have contributed to widen the understanding of applied soil study in Indonesia, e.g. the changes in agricultural practices in north Lampung (Imbernon, 1999), agroforestry system in Lampung (Hairiah et al., 2006), residual phosphor and organic matter in agriculture land in North Sumatra (Dalimunthe and Tanjung, 2006), the development of soil in paddy field, Central Sulawesi (Rajamuddin, 2009), changes in East Kalimantan (Kamp et al., 2009), erosion modeling for conservation (Sulistyo, 2009), soil characteristics and classification in paddy soil in Jombang (Rahayu et al., 2014).

In comparison, the increasing of applied research on soils leads to lacking of studies on soil genesis in Indonesia, especially volcanic soil genesis. On the other hand, volcanic soils research in Indonesia has actually been initiated since half a century ago (see Tan, 1965). Hereinafter, several studies on volcanic soils have been conducted to characterize volcanic soils in Indonesia in general. However, the extensive information regarding with genesis of volcanic soils remains limited (van Ranst et al., 2002).

1.2 Knowledge gaps Studying the genesis of soils involves the understanding of soil formation and soil development. The soil formation is always initiated by the deposition of soil parent materials. It is supported by geogenic process. The soil formation is important to determine the further soil development through pedogenic processes. There is an increasing interest in academia, in recent years, to investigate why different soil formation occurs and what the soil properties are resulted.

Numerous studies have answered several questions related to soil formation in many areas. They include but not limited to: (i) soil formation and its relation to the weathering process in Siberia (Vogt et al., 2010), (ii) soil formation and different topographic position effect (Durak and Surucu, 2005), (iii) the rate of soil forming process under different model of (Alexandrovskiy, 2007), (iv) pedogenic properties as the evidence for soil formation (Tsai et al., 2010).

In the case of Indonesia, soil formation related studies are mostly conducted as followed: (i) the development of soils based on its morphological, physical, chemical, and mineralogical characteristics (Mastur et al., 2000; Van Ranst, 2002; Alkusuma and Badayos, 2003; Fiantis et

9 al., 2011), (ii) the influence of different age of parent rocks in soil genesis (Mulyanto, 1999); (iii) the influence of elevation in soil genesis (Hikmatullah, 2003; Hikmatullah, 2010); (iv) the influence of different types of weathered parent rocks in soil formation (Yatno and Zaujah, 2008); (v) the influence of climates in soil formation (Hikmatullah and Nugroho, 2010). Table 1.2 provides a summary of these previous studies which conduct on the field of soil formation and soil development.

As outlined in Table 1.2, there are a number of knowledge gaps resulting from the previous research works. The gaps include: the influence of relief in soil profile development and in soil formation cycle, the relationship of soil formation and landscape systems, the influence of slope surface processes in soil profile development, the contribution of slope deposit as soil parent material, the anthropogenic influence on surface soils and its consequences for soil redistribution. In comparison to the previous research works, these gaps are arising for the areas where having various relief setting and frequent slope surface processes. The study of soils in such condition therefore needs broader knowledge with respect to the understanding of the dynamics of soil formation and soil development occurred. To the end, those gaps become the focus on this research work, and it reflects the novelty of this research.

1.3 Research problems Variations of soil formation and of soil development are the key problems in the study area. Both geomorphic and anthropogenic seems to be the significant processes towards the variations of soil formation and of soil development. Active slope surface processes and intensive human influence on soil redistribution have caused changes in soil formation and in soil development of particular area. In this case, the deposition of soil parent materials is observed as a more than one-period of deposition, and thus causes more than one cycle of soil formation. That becomes a problem because the multi-cycles of soil formation not only influence the following soil development but also disturb the existing soil profile. Therefore, the evaluation of multi formation of soils and multi development of soils within the profile is a challenging task in this soil research.

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Table 1.2: Knowledge gap matrix

No Authors Subject Areas Findings Knowledge gaps 1 Mulyanto Morphology, physical, Mt. Galunggung Stage of soil profile Relief effect in the soil (1999) and chemical development profile development characteristics of some and in the soil volcanic soils based on formation differences in the age of parent rocks and elevation Soil formation and 2 Hikmatullah et al. Volcanic soil properties Mt. Kelimutu Soil properties landscape systems (2003) based on elevation and Soils suitability based relationship their suitability for on elevation agricultural purposes differences 3 Hikmatullah Physical, chemical, and North Maluku Soil profiles meet the (2010) mineralogical requirement of andic characteristics of soil properties volcanic soils based on elevation 4 Van Ranst et al. Physico-chemical Java Island Soil properties (2002) properties of volcanic Soil classification ash soils

5 Alkasuma and Mineralogical North Lampung, Soil properties Badayos (2003) characteristics of Sumatra volcanic soils 6 Fiantis et al. Mineralogical and Mt.Talang Soil properties (2011) chemical characteristics of volcanic ash soils 7 Yatno and Zauyah Physical, chemical, and Lembang, West Java Soil properties Slope surface (2008) mineralogical Soil classification processes towards soil characteristics of Management profile development

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volcanic soils based on implication of volcanic differences in types of soils Slope deposit as the weathered parent rocks other soil parent material type 8 Hikmatullah and Physical, chemical, and Flores Island The soil profiles meet Nugroho mineralogical the requirement of (2010) characteristics of andic soil properties volcanic soils based on climatic characteristics and types of weathered parent rocks 9 Mastur et al., Soil characteristic and Java and Bali Island Conservation The anthropogenic (2000) farming system in strategies and human- influence on surface volcanic areas induced soils soils and its consequences for soil redistribution

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1.4 Objectives and Research questions Based on this specific complex situation in the study area, the basic research questions of this study is: How are soils formed and how do soils develop in the central part of Bogowonto catchment? As only few researches have addressed this topic, some questions remain open: Table 1.3: Objectives and Research questions

Objectives Research questions

To identify the spatial 1. How is the spatial pattern of soils in the study area? pattern and the 2. How are the characteristics of soils in the study characteristics of soils in area? the study area

To evaluate the soil 3. What are the specific factors that influence the soil formation and the soil formation and soils development in the study area? development in the study 4. What are the variations of soils in the study area? area 5. How do the variations of soils influence the soil formation and soils development in the study area?

Those questions are answered by addressing two objectives with a focus on evaluating the soil formation and soil development in the central part of Bogowonto Catchment. In order to improve the understanding of soil formation and soil development in the study area, the investigation of spatial patterns of soils based on soil profile description (sub Chapter 5.2) is required for a basic assessment. Then, the detail investigation is conducted through soil characteristics analyses (sub Chapter 5.3). After knowing the characteristics of representative soils in the study area, finding the specific local factors influencing on soil formation and finding the soil parent material variations in the study area will be proposed (sub Chapter 5.4). Furthermore, the influence of soil parent material variations towards soil formation and soil development cycles in the study area will be the last subject (sub Chapter 5.5). Within the combination of these results, the detail explanation will be evaluated (Chapter 6).

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1.5 State of the dissertation Various literatures have pointed out to the influence of soil-forming factors in soil formation as well as the effect of soil-forming processes in soil development degree. However, most of the researches only capture the ideal condition of the area through ignoring the additional effect of morphodynamic processes and human influence to the soil formation and soil development in that particular area. Similarly, those researches are more likely to focus on the influence of single soil- forming factors towards soil formation. In my view, the soil formation and soil development do not occur in a simple way. There are several factors and processes that simultaneously work during the soil formation and soil development. It may consequently result in the variations of soil formation cycle, and it assumes that the soil formation and soil development vary among one to other areas. Therefore, the understanding of complex processes is important before the evaluation of soil formation and soil development in particular area is conducted.

1.6 Dissertation outline The dissertation is organized in seven chapters. Following the introduction in Chapter 1, Chapter 2 gives the brief fundamental state of the art on relevant soil aspects, especially related to soil studies in the tropics, lithological discontinuous soils, soil geomorphology, human-soil interaction, and soil systems in general. Chapter 3 provides the approaches and the methods used in this study. Also, this chapter reviews the terminologies used in soil formation and soil development of this study, in order to avoid terminological misconceptions. Chapter 4 describes the study area and its environmental and social characteristics.

On the basis of soil profile description, relief mapping, landform mapping, laboratory analysis, and GIS analysis, the main results are explained in Chapter 5 and are discussed in Chapter 6. The chapter 5 discusses the analyses and the assessments in term of soil variation in the study area. This chapter consists of spatial analysis of soils, properties analysis of soils, assessment of soil parent materials variations, and assessment of soil formation variations. In addition to the analysis results, the discussion is revealed on Chapter 6. This chapter is focused on understanding and explaining of the soil variation conducted through evaluating the soil formation and soil development in the study area. Chapter 7 gives conclusions beyond the results and the achievements in this study, and finally is completed by suggestions on further research.

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CHAPTER 2 STUDIES ON RELEVANT LITERATURE

2.1 Introduction

The traditional soil concepts was based upon the ancient concept of the Earth from Aristoteles (384-322 B.C) which explained that the universe consists of four elementary things derived from the same amorphous matter. One of them is earth. The term of soil, then, was created by Aristoteles‟ student named Theophrastos (371-286 B.C.) who distinguished a soil from other matter of cosmic body. Hereinafter, his invention was more focused on the soil properties in relation to plants, called (Arnold, 1983).

The history of soil concepts was significantly influenced by the downfall of Rome. Before this downfall, the traditional knowledge of soils was so extensive. However, after the downfall of Rome, the agricultural soil science stagnated until the end of the nineteenth century. During that time, other Earth sciences such as geography, , and geomorphology claimed soils as a part of their science and developed their own definition of soils (Buol et al., 1997).

The concept of soil could also derive from a non-pedologic influence such as a cultural stigma and a crop husbandry perception. According to the cultural stigma, the concept of soil had been influenced by the primitive agriculturalist who experienced with working in the field and muddy for most of their time. Nevertheless, according to the crop husbandry perception, the concept of soil had been gained based on their trial and error practices towards the needs of knowledge of soil suitability for crop production (Arnold, 1983)

Today, the concept of soil has been widely developed and is used by many disciplines such as agriculture, geography, geology, geomorphology, and biology. Those disciplines have their own theory about defining what the soil is, based on their observable phenomena on the Earth surface. In agriculture theory, a soil is defined as a natural body consists of solid (mineral and organic matter), liquid, and gases that occurs on the land, occupies the space, and can be categorized as a horizon or a layer that are distinguishable from the parent material as a result of soil-forming processes, and considered as the combination of the natural bodies on the Earth surface which consists of the living matter that can support plants (Soil Survey Staff, 2014).

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Another definition was based on the geographical theory that soil is anisotropic natural body where its properties vary with direction in space. Soil is also defined as a natural individual without internal pedogeographic boundaries which has horizontal and vertical variability in a landscape level (Sommer & Schlichting, 1997). In biology-related theory, a soil is a biotic or abiotic of natural system which is homogeneous (Hillel, 1980; Schlichting, 1982; Hole and Campbell, 1985; cited in Targulian and Sokolova (1996). In geology-related theory, a soil is one geologic material besides rocks and sediments that are applicable however difficult to establish due to a significant transition zone among them where a rock is changing into a soil but the formation of a soil has acquired a rock-like property (Chesworth, 1973)

2.2 What is soil?

2.2.1 Soil definition

Soils, at the beginning, was considered as a natural body which was different from bedrock, and was a function of several interrelated factors such as climate, parent material, relief, and organism over the time (Dokuchaev, 1879). Later, Glinka (1927), Marbut (1927), Joffe (1936) cited in (Bockheim, et al., 2005) assumed that those factors were the causes of soil formation, and soil properties are the impacts of those factors in interaction. In other side, the previous statement was argued by Jenny (1941) who stated that the soil formation was not the causes of soil factors interaction meanwhile climate, organism, parent material, relief, and time are the independent variables which have no interdependency one to another.

The definition of soil continuously develops. In the early of 20th century, Hilgard (1906) and Simonson (1968) presented that a soil is a natural body having a function as a medium for plant growth. A soil was also previously defined as the mantle of loose and weathered rock (Ramann, 1928), and as the cover of the Earth‟s crust (Nikiforoff, 1959). In other perception, Targulian and Sokolova (1996) developed the definition of soil that a soil is a regulator of biosphere interactions. Following the ideas of Targulian and Sokolova (1996), Nikitin (2001) emphasized a soil as an abiotic system with a number of biospheric functions and considered a soil as a habitat and a source for organisms. In his definition, he also considered that a soil can act as a link of biological and geological cycle of a matter.

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2.2.2 Soil systems

A soil is a complex natural system that is presented by the interaction of many pedologic processes that work simultaneously, and describe an impact of the dependent and independent factors (Mcfadden & Knuepfer, 1990). A soil is a continuum entity in which the properties may change gradually with the distance(Soil Survey Staff, 2014). A soil is also considered as a dynamic system which is continuously affected by internal or external disturbances depending on the boundaries of the system (Smeck et al., 1983). The boundaries of the soil system can be landscape, catena, polypedon, pedon, profile, horizon, ped, and sample (Arnold, 1983). The detail hierarchy of the soil system is explained in Table 2.1.

Fig.2.1: Soil pedon, polypedon, and other units related to a soil-scape (after F.D. Hole, 1953)

A soil is characterized by an intrinsic variability through time and space with differentiated units, from a landscape or catchment scale up to a small volume of soils called pedon (F.D. Hole, 1953, see Fig.2.1). A pedon is a three-dimensional body of soil with lateral dimension that permit the study of horizon shapes and horizon relations. The range area of a pedon is about 1 to 10 square meters, depending on the nature of the variability of the horizons (Simonson and Gardiner, 1960, p.127-130). A soil profile is not allowed to be considered solely as a weathering zone or a pedogenic zone however it is considered as a four-dimensional body which is formed by a complex of surface/near-surface processes (Birkeland, 1984; Schaetzl and Anderson, 2005).

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A soil-scape body is a soil-landscape unit which is bordered by a lateral rate of change of soil characteristics (Schelling, 1970). Previously, Perfanova (1963) cited in had introduced the soil-scape as a mutual relationship of various soils that were found together in a landscape. The variability in the soil-scape is caused by the response of the soil system to the interaction of rock, water, air and living organisms under changing climatic/environmental conditions within a landscape.

Table 2.1: Hierarchy of soil systems for modelling soil development (modified after Dijkerman (1974); Smeck (1983)) Level System Definition 1 Pedological province Part of a region, isolated and defined by climate and topography and characterized by a particular group of soils 2 Compound landscape unit An area whose spatial distribution corresponds to a natural watershed or sub-watershed containing several order streams, various topography, and/or various lithology 3 Simple landscape unit A regular repetition of a sequence of soils in association with a certain topography (Milne, 1935) 4 Pedon / Polypedon A pedon is the smallest, 3-dimensional unit at the Earth surface that can be considered as a soil. A polypedon is a contiguous group of similar pedons (Soil Survey Staff, 1975) 5 A layer of mineral or organic soil material approximately parallel to the land surface that has characteristics formed by pedogenetic processes (Canada Soil Survey Comm., 1978) 6 Peds (macrostructural Natural soil aggregates consisting of a cluster of units) primary particles and separated from adjoining peds by surfaces of weakness which are recognizable as natural voids or by the occurrence of cutans 7 Microstructural units Includes micromorphological features, aggregate and microaggregate features (< 5mm), sand and silt particles and domains 8 Physical phase Mineral, gaseous or aqueous phase

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Schelling (1970) stated that the soil system can be divided into two: closed system and open system. The closed system is the simplest system because there is no material or energy added or lost. The most common example of the closed system in the soil genesis study is a soil profile. However, some approaches generate a perspective that the closed system seems not totally correct since this system is too limited. In addition, according to Schelling (1970), Ehwald (1960) had examined that a soil can be described with the theory of open system from Bertalanffy (1950). This idea was also supported by Russian literature of Parfenova (1963) which provided an insight that the approach of a soil-scape in the soil systems is not a totally closed system because this approach relates to the variation of soils within a landscape. Thus, to understand the soil systems, it requires a deeper comprehension of the complexity of soils and the related genetic processes in the context of soil development (Wilkinson et al., 2009).

The open system in soils (soil dynamic system) can be referred to a non-equilibrium thermodynamic state (Smeck et al., 1983). The non-equilibrium thermodynamic state actually uses the concept of entropy with a measure of disorder of a system. Any movement in the entropy will make a change in the system disorder. As a comparison, the input of energy and matter into the system can influence the dynamic system in the soil. An example is the changing of soil parent material into pedon, and horizonisation as the result of fluxes of energy and matter in surrounding, and thus decreases the entropy. The Law of Thermodynamics II is applied in this case. Thus, to be applied as an open system, the Thermodynamic concept should be considered not only for the system itself but also for the system‟s surrounding (Smeck et al., 1983).

Nikiforoff (1959, p.186) also stated that pedogenesis is a soil dynamic system. It is because the pedogenesis is consisting of a transaction in matter and energy between a soil and its surrounding. Furthermore, Nikiforoff explained that the soil dynamic describes an accumulation of continuously movements through the system. The movements can occur in a very slow speed or in a flash speed. However, the soil system tends to reach the equilibrium with its surrounding, and it may be achieved when the surrounding remains constant for a long time. Therefore, the dynamic system is more adequate for a soil than the static system because a soil involves the processes and the driving forces (Smeck et al., 1983).

Huggett (1975) explained that there were two approaches in the soil system modelling found by Patten (1971):

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(i) Isomorphic model: using an empirical physical science method, which involves all components in the soil system into the model (ii) Homomorphic model: using a system synthesis method which groups several components of the soil system into a single element in the model. This model seems to be appropriate with the concept of soil genesis because pedogenetic process is assumed as the result of several elements in a landscape.

Sylvester-Bradley (1969) cited in (Huggett, 1975) stated that the time study of the soil system can be categorized into three phases:

- Stationary, in , this type requires an extensive field study of soil to create the criteria for classification and to understand the genesis - Historical, this type is intended to describe genesis of the system based on the progression through the time. In pedology, it is consisted of the origin, the development, and the presence features of the soil to be genetically explained - Functional, this type is a control of historical progress from the experience obtained at the present and how it works, so that it is able to predict the future and the past state

In other perspective, Yaalon (1976) concluded that there were two approaches in soil system i.e. functional-factorial approach and deterministic approach. Both of them were complement and as alternative between one to another because no one of them is extraordinary to another. Furthermore, Yaalon (1976) stated that although the deterministic approach seems like more sophisticated due to material and energy in the flux model of the soil dynamic, the significance of many processes are still insufficient. The functional approach is more adequate because it can do quantification even if the process seems to be too complicated for a deterministic approach. Moreover, the factorials of multivariate function can be a predictive tool and may help in creating the parameters for deterministic model.

In comparison to Yaalon (1976), Huggett (1976) explained that in deterministic approach, the soil system is assumed as a stable process of transfer and transformation at and near the Earth surface. Here, the relation of and soil process is obvious. However, in functional – factorial approach, the five-state factors are relatively external of the soil system and worked individually. Thus, univariant function is established in this approach.

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Fig.2.2: Soil system behavior in time (source: Targulian and Krasilnikov, 2007)

Targulian & Krasilnikov (2007) emphasized that the system in soil formation is an irreversible phenomenon. The soil formation system actually never returns to its initial stage during its self-development (no reverse evolution). However, this principle process can be denied under special cases. The irreversible concept can be changed or can be destroyed or can be affected due to specific processes such as pedoturbation and/or denudation (e.g. erosion and landslides).

2.3 Soil genesis

The soil genesis is a principal aspect of the soil concept studying the formation of soil in a landscape (Buol et al., 1997). There are 5 concepts among 11 concepts of soil genesis in the Buol‟s theory that are really relevant to this study:

1) Soil, what we see today, is the result of pedogenic processes over the time and it is various in every location 2) Soil-forming processes occur simultaneously in a soil, and thus result in a profile which describe about what was happened in the past and what happens in the present

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3) Similar to geologic principle of “the present is the key to the past”, so that the present soil is the accumulation of pedogenic process that intensively happen in the past 4) Different pedogenic processes will produce different soils which is shown by their morphological features 5) Old soils rarely exist since most of them have been buried or modified by geomorphologic events

There are two main considerations in the soil genesis, such as: (i) the accumulation of parent material; (ii) the differentiation of horizons in a profile (Simonson, 1959). The soil genesis is assumed as the integration of several pedogenic processes (Targulian & Krasilnikov, 2007). In the concept of state factors, Schelling (1970) proposed a modelling of soil genesis as a direct relation between the state factors and the soil. The preferable model is shown as follows:

(Input) (Black box) (Soil)

State factors Soil forming processes Output

In this model, the emphasis is put on the fact that the state factors generate certain processes, and thus these processes have a close link to the genesis of the soils. As a system, the consideration should be put on the parts of elements as well as on the mutual relationships between the state factors and the soil.

The understanding and the knowledge of soil genesis are required for other soil fields. Several soil fields which are linked to the genesis study are soil properties and soil classification (e.g. (Bockheim & Gennadiyev, 2000); (Shaw et al., 2004); (Hartemink & Bockheim, 2013)). Soil genesis study also has a relation to soil conservation practices and land management (e.g. Junge and Skowronek, 2007), soil system study (e.g. Targulian & Krasilnikov, 2007), and soil mineralogy (e.g. (Van Wesemael et al., 1995); (Dultz, 2002)).

Among other soil fields, the soil mineralogy and the soil classification are closely related to the soil genesis. The soil mineralogy becomes one of the focus subjects in the soil genesis study (Buol et al., 1997) because it may reflect the degree of pedogenesis (Buehmann, 1994). Knowing the properties and the structure of minerals are important to understand the mineral transformation and transport processes in a soil profile, as those processes are crucial in soil

22 genesis study (Schaetzl & Anderson, 2013). The soil genesis is also important to the classification (Bockheim & Genadiyev, 2000) because it produces the observable or measurable differences that can be used as a differentiation (Smith, 1983, p.43).

The soil formation is the transformation in the soil system from the solid-lithomatrix phase into the pedomatrix phase (Targulian & Krasilnikov, 2007, p.373), and then it will develop until it reaches the steady-state or balanced condition with the other existing factors (Yaalon, 1971). The soil formation can be categorized into short period which is less than 1,000 years, and long period which covers several thousand years or even longer times (Duchaufour, 1982; cited in (Emadodin et al., 2011). The soil formation has been one of the key points in the soil research since the 19th century (Hartemink & Bockheim, 2013). The soil formation is closely linked to the soil-forming factors and soil-forming processes (Birkeland, 1999).

2.3.1 Soil-forming factors

The most influential theory by Hans Jenny, about five-state factors of soil formation, is still widely used as the basic concept in soil genesis studies up to now. In this theory, Hans Jenny used factorial approach, and thus assumed that a soil is a result of several independent factors. This traditional concept of soil formation is summarized in Jenny's (1941) equation:

S = f (C, O, P, R, T, …) …………………………………………………………………….. (1) where „S‟ is soil, „C‟ is climate, „O‟ is organisms, „P‟ is parent material, „R‟ is relief, and „T‟ is time. This concept was a further development of Dokuchaev's equation in the late 19th Century which said that a soil is a function of the interplay of those factors (Dokuchaev, 1879 cited in Bockheim et al., 2005).

Jenny‟s previous concept received several objections from other theories. Cited by Hugget (1975), several comments came out such as Crown (1953) who noted that Jenny‟s expression is difficult to be implemented; Kline (1973) stated that Jenny‟s equation is not flexible; Yaloon (1976) commented that the factorial approach of Jenny had obstacles in collecting the data in order to solve the equation of soil-forming function. Furthermore, Hugget (1976, p. 261) also stated that the factorial approach of Jenny‟s equation was assumed as the external elements to the soil system, and this approach formed a univariant function. In 1961, Jenny revised his equation and reduced the equation into three state factors of the soil-forming

23 function i.e. the initial state of the system, the external flux potential, and the time. Then, Runge (1973) tried to modify Jenny‟s equation, and stated that the development of soil is the function of organic matter, the amount of water available for , and the time. However, Runge‟s theory is difficult to be accepted as it seems to present only a part of the system without considering the geomorphic process (Hugget, 1976).

According to Dokuchaev (1889), all the soil-forming factors have the same significance towards the soil formation. In fact, there are numerous of researchers giving their opinions that one certain factor can become the leading in soil formation compared to other factors. As an example, Hilgard (1892), Sibirtsev (1951), Coffey (1912), cited in (Gennadiyev et al., 2010) stated that climate is the leading factor in soil formation, because many soil properties have a good response to the climatic input (Yaalon, 1983). Wilkinson et al., (2009) and Pietsch (2013) provide the opinion about the significance of organisms and biological activities such as bioturbation towards the soil formation. Parent material also was recognized as the key soil- forming factor in the beginning of pedology history (Dokuchaev, 1883; Hilgard, 1906; Coffey, 1912, cited in Bockheim et al., 2005). Another opinion also said that relief/topography takes a crucial effect in the vertical zonation of a soil (Dokuchaev, 1899), and has a connection to the soil catena concept (Milne, 1935; Bushnell, 1942; Fridland, 1972; Sommer and Schlichting, 1997, cited in Bockheim et al., 2005). Besides, time was considered as a maturing factor for soil development (Dokuchaev, 1883; Kossovich, 1911; Shaw, 1932; Marbut, 1935, cited in Bockheim et al., 2005), so that considerable length of time is required (Yaloon, 1976) as the soil attributes will keep changing towards the time (Yaalon, 1983).

The argument about the leading factor among other factors in soil formation is intended to differentiate a soil based on the major influence. Hence, the importance of one factor towards other factors in the soil formation can prove that there are different ratios and ranges among the soil-forming factors in affecting the soil-forming processes (Gennadiyev et al., 2010).

2.3.2 Soil-forming processes

As a generalization of soil genesis theory, Simonson (1959) stated that the development of soil consists of forming processes such as addition, reduction, translocation, and transformation within the soil system. The Simonson‟s terms actually were too general and only provide a little soil-specific characteristic on pedogenesis (Bockheim and Genadiyev, 2000).

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Hereinafter, the discussion of the soil processes lead to horizon differentiation within a soil profile, and thus they could be detailed as podzolisation, calcification, solodization, laterization and other processes as classified by WRB and Soil Taxonomy.

Table 2.2: Selected types of soil-forming processes mostly occurred in the study area based on Buol et al. (1997) and WRB (2007)

Term Categorization Description of process Littering Addition The deposits of organic litter on the mineral soil surface and associated humus within a depth of less than 30 cm Melanization Addition & The darkening of light-coloured mineral of unconsolidated translocation material by mixing with organic matter Anthosolization Addition The combination of geomorphic and pedogenic processes resulting from human activities Erosion Reduction Removal material from the soil surface Ferrallitization Transformation The increasing degree of weathering of primary minerals and an increased dominance of secondary clays from incongruent dissolution Resilication Transformation The formation of montmorillonite from kaolinite indicated

by abundance of Si(OH)4 at high pH values Iluviation Translocation The movement of material within a soil profile (i.e. argillic) Lessivage Translocation The mechanical movement of small mineral particles i.e. and/or clay from the A-horizon to the B-horizon, and forming the B-horizon Podzolisation Translocation The complex process of weathering, elluviation, transformation, transport, and mobilization of Fe, Al, Mn compound, and humus particle Biological Translocation The process of Na+, K+, Ca2+, Mg2+ transport either due to enrichment of biological process or elluviation process within the soil base cations & profile. base cation leaching

The soil-forming processes have a significant implication on soil taxa. When the soil- forming factors change, it will be followed by the change of soil-forming processes, and thus may cause the change in soil taxa (Smith, 1983). Many soil-forming processes occur

25 simultaneously in the soil profile reflecting the balance of both past and present processes (Simonson, 1959; Buol, et al., 1997). However, the soil-forming processes were considered to be poorly understood until the beginning of twentieth century (Simonson, 1959, cited in Bockheim and Genadiyev, 2000).

The contribution of the soil-forming factors into the soil-forming processes can be described related to the energy and substantive contributions of the factors which will influence the dynamic processes within a soil profile, as a micro-process (Genadiyev et al., 2010). Furthermore, the accumulation of micro-processes cause a specific soil macro-process (Rode, 1984) that leads to change in a soil. The understanding of the processes within a soil is a significant contribution to predict human influence through land management practices on a soil (Smeck et al., 1983). Bockheim and Genadiyev (2000, p.56) synthesized the level of soil- forming processes:

1. The highest level, generalized processes that delineate a soil from other sub-systems of the biosphere 2. The second level, depending on inputs, outputs, transfer (or translocation), and transformation of energy and matter (Simonson, 1959), and referring to a specific soil-forming process (macro-process) 3. The third level, emphasizing on a soil micro- or specific processes such as N- fixation, oxidation, and reduction of Fe and Mn, ionic substitutions, and other chemical, physical, and biological processes and reactions

2.3.3 Autochtonous versus Allochtonous The soil parent material deposition is an initial stage in the soil formation. According to the genesis of soil parent material/regolith, Lorz et al. (2011)divided the regolith into two types: (i) derived from in-situ parent rock (autochtonous regolith); (ii) derived from transported material (allochtonous regolith). The autochtonous regolith is defined as the type of regolith which is controlled by in-situ parent rock weathering, so that the regolith is originally developed from the underlying material. Otherwise, the allochtonous regolith is defined as the type of regolith that has not originally developed from the underlying material. It means that weathering process of the regolith has been occurred in other place before its material is transported to the depositional place.

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The study of regolith is not only focused on the regolith genesis but also focused on the regolith structure especially due to crucial effects of the environmental problem at landscape scale (Lorz, 2008). According to Schaetzl & Anderson (2005) and Lorz (2008), the regolith structure can be categorized into an upper-younger zone and a lower-older zone. The upper regolith is mostly indicated as the mixing material of translocation material (allochtonous regolith), underlying material (in-situ saprolith/regolith), and/or airfall material. The upper regolith has a latter deposition, and thus provides a younger age. The lower regolith is usually in situ that is not transported and originally derived from the underlying parent rock. The lower regolith has an older age, and may consist of regolith and saprolith.

The genesis of soil parent material/regolith is important because it influences the soil properties such as texture, clay mineralogy, and chemical composition (Arocena et al., 1999). The spatial variation of soil parent material/regolith may generate the heterogeneity in the soil formation. The temporal variation of soil parent material/regolith may result in stratification. However, the stratification is rather difficult to be assessed when the material has a heavily weathered so that the soil horizon border is often in line with the stratification border (Buurman, et al., 2004)

The presence of the stratification leads to a discontinuity in soil parent material/regolith (Ande & Senjobi, 2010). The discontinuity in soil parent material/regolith can result in a lithological discontinuous soil (LDS) which is a common phenomenon (Lorz, 2008). LDS is developed in layered-soil parent material. It is usually as a result of active morphodynamic processes that cause transportation and deposition as well as accumulation and homogenization of slope material. Lithologic discontinuities can be expressed by a presence of stone lines, an abrupt change in or subfractions, and a higher accumulation of cations in surface than in sub-surface horizons (Ande & Senjobi, 2010). In an area of such lithologic discontinuities, the upper-regolith formation becomes the main object for soil genesis studies. The uppermost- regolith is frequently influenced by surface processes. The surface/near-surface processes may cause the stratification, and result in allochtonouos regolith for another site (Lorz & Phillips, 2006).

The presence of stratifications is also known as cover-beds, another term that was promoted by Kleber (1997). Cover-beds mean a sequence for two or more different layers of soil

27 parent material/regolith. The layers in soil parent material/regolith are also as a result of geomorphic processes on the slopes. Any soils which develop on cover-beds sequence is also categorized into the LDS, because the interface between two cover-beds form the discontinuity (Lorz et al., 2011).

Pedologists and geomorphologists actually have concerned to the LDS for a long time. However, most of the soil scientists have ignored the genesis of stratified soil profiles (Lorz & Phillips, 2006). In several reviews are stated that a distribution of vertical soil properties with lithological discontinuities should be different from what occurs along depth function of top- down soil formation process (Lorz et al., 2011). Some researchers also argued that there is no single causality for soil profile stratification (Phillips, 2004), and thus the method to distinct pedological and geological processes cannot be separated (Lorz & Phillips, 2006).

2.4 Soil in the tropics

The tropics, geographically ranging from latitude 23.5oN to 23.5oS (Fig.2.3), have characteristics that are relevant to specific soil-forming processes compared to other regions. As defined by climatologists, tropics separate the tropical climate from the temperate climate, and thus influence the weather fluctuations. This geographic position also results in the day lengths which remain nearly unchanged during the whole year. Mainly, high temperature and high precipitation provide a significant impact on soil formation and soil development.

One-third of the soils in the world are tropical soils (Eswaren et al., 1992). The main aspect in the tropical soil formation that can distinguish them from the soils in the temperate regions is the soil climate consisting of soil temperature and (Van Wambeke, 1992). In the tropics, soil temperature has a strong relation to the sun radiation. Due to a greater sun radiation, the air temperature in the tropics is always high, and thus gives an affect to soil temperature (Nikita-Martzopoulou, 1981). However, soil moisture is often linked to the climatic variability due to seasonal variations of rainfall (van Wambeke, 1992). The rainfall variation is usually followed by moisture fluctuation (Hood, 2006).

In the term of soil climate, the most distinguished aspect between the tropical soils and the temperate soils is the absence of low-temperature seasons that cause soil freezing. The soil

28 freezing may have a great impact on soils in the temperate region (Hartemink, 2004). Freezing of wet soils often enhance the structure of the ploughing layer in the temperate regions (Van Wambeke, 1992). In addition, Van Wambeke (1992) stated that the other distinction of the tropical soils and the temperate soils is associated with the soil colors. Kampft & Schwertmann (1983) described that the wet-dry tropics has a strong reddish or yellowish color due to the active production of iron oxide minerals which acts as the pigment in the soil colors. Goethite mineral mostly results in yellowish-brown color, whereas, hematite mostly results in the red color.

Fig.2.3: Tropical and non-tropical climate range of the world (source: Prentice Hall, 2003)

The effects of soil climate on soil formation is mostly presented by the acceleration of chemical decompositions (e.g.(Ohta & Arai, 2007); (Bétard, 2012)). Van Wambeke (1992) stated that the temperature manages the kinetics of the chemical processes, and thus cause the transformation of mineral during the soil formation which is named as weathering, as well as the transformation of organic matter which is named as mineralization (Modenesi & Paulo, 1983). Further effect of mineral transformation is the formation of clay minerals in the soils. Velde & Meunier (2008) categorized four clay mineral types which have main interaction of plant-soil zone i.e. illite, kaolinite, oxides-hydroxides, and mixed layer minerals. On the other hand, the summer rains characteristic in the main parts of the tropical climate may moisten the soil when the temperature is high. Therefore, this characteristic significantly increase the weathering rates due to a faster chemical decomposition, and thus cause a greater decomposition rate of organic matter in the tropics than that in the temperate regions (Jiang et al., 2010).

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2.5 Volcanic soils

The soils developed on volcanic soil parent material have unique physical, chemical, and mineralogical properties which cannot be found on soils developed on other soil parent material (Georgoulias and Moustakas, 2010), due to the presence of noncrystalline minerals and the high content of organic matter (Tan, 1965; Shoji et al., 1993). Soils developed on volcanic parent material in wet and humid climates are classified as (Leamy et al., 1975), however, Moustakas & Georgoulias (2005) stated that not all soils developed on volcanic parent material are classified as Andisols. They are only classified as those if they meet the requirements of Andisols, i.e. andic and vitric properties. According to Soil Survey Staff (2006), the chemical and physical properties of Alo+1/2Feo and P-retention are two main indicators to fulfill the requirements of soil characterized by andic and vitric properties. To be classified as Andisols, soils must meet the standard of Alo+1/2Feo which is equal or greater than 2%, and P-retention which is equal or greater than 85% for andic properties, while, the standard of Alo+1/2Feo with a minimum value of 0.4% and P-retention which is greater than 25% for vitric properties.

Main characteristic of volcanic soils is the predominance of active forms of Al and Fe in the noncrystalline clay mineral like allophane, imogolite, ferrihydrite as well as Al/Fe humus complexes (Drouza et al., 2007). There are several types of noncrystalline minerals which are most of them are strongly dependent on climate, parent material, and stage of weathering (Wada, 1987b). Parfitt et al. (1983) stated that the minimum precipitation requirement to form an andic soil characteristic is about 1200mm/year. Georgoulias and Moustakas (2010) stated that climate is a significant factor controlling the evolution of volcanic soils. This shows that moisture regime which is determined by rainfall activities controls the formation of clay minerals.

The soils derived from volcanic soil parent material occupy 0.84% of the Earth‟s surface (Leamy et al., 1975). They are less resistance to weathering because the volcanic glass as the basic component in the volcanic soils enables a rapid weathering (Georgoulias and Moustakas, 2010). This is also in-line with the study of Drouza et al., (2007) which stated that the existence of noncrystalline minerals is a proof for rapid weathering of volcanic glass. Chadwick et al., 1994 stated that the low content of clay is an indicator for the early stages of weathering of the volcanic ash. Furthermore, they point to the fact that rainfall becomes one of factors that can influence the weathering of the volcanic ash.

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There are many methods used to analyze the volcanic soils. One of the methods is the determination of Si and Al dissolved which is treated by OX, and has been widely used for estimation of “amorphous” clay fraction. The OX treatment is purposed to result in dissolution of

Si, Al, and Fe from the clays. Wada et al. (1987) examined that the amounts of Si (Sio), Al (Alo), and Fe (Feo) found in the clays which is dominated by allophane and imogolite have greater value than those found in the clays which is predominanted by haloysite and embryonic of halloysite. In addition, Georgoulias and Moustakas (2010) stated that the soil solution concentration of Al and Si resulting from weathering of volcanic rock is the most predominant factor determining the clay mineral types that will be formed. Si is the most important component in pyroclastic material like tephra (Shoji et al., 1975). The amorphous Si will be formed in volcanic soils when the soil solution is highly saturated with Si, and also the available Al produced by weathering is taken by the formation of organic complexes rather than amorphous clay silicate such as allophane and imogolite (Dahlgren et al., 1997). However, the amorphous Si will remain in the soils and getting decreased as long as the rate of chemical weathering (Shoji et al., 1975).

Related to volcanic soils in Indonesia, most of studies examined the soils that have been developed from andesitic volcanic rocks (e.g. Hikmatullah et al., 2003; Van Ranst et al., 2002), and they are dominantly grouped into Andisols, , and (Hikmatullah et al.,

1997). The andesitic volcanic rocks were usually composed of SiO2 within the range of 53.5 to 62% (Shoji et al., 1975). Subardja and Buurman (1980) emphasized that the properties of soils derived from the andesitic volcanic rocks is influenced by topography whereby a decreasing of elevation results in a change from Andisols to Inceptisols and further on will change to // in lower elevations. These results show that with decreasing the elevation, the soils become more weathered and developed (Van Schyulenborg, 1957).

2.6 Hydrothermal alteration

Hydrothermal alteration is a process in rocks that have precipitated by hot water or have been altered by hot water passing through (Carlson et al., 2009). In more detail, the hydrothermal alteration system can be defined as a distribution of hot fluid circulating, both laterally and vertically, at various temperatures and pressures, below the Earth‟s surface (Pirajno, 2009). In

31 the context of hydrothermal alteration, there are terms of hydrolysis and hydration (Pirajno, 2009). The hydrolisis- or hydrolytic alteration is an essential phenomenon involving the ionic + - + - decomposition of H2O into H and OH . In the course of the hydrothermal alteration, H (or OH ) is consumed during the reaction with the silicate minerals. Therefore, the ratio H+/OH- is changed. The source of H+ ions can be subsolidus reactions during alkali metasomatism, water, or acids in the hydrothermal solution. The conversion of anhydrous silicates to hydrous, such as mica or clay is a reaction which consumes H+, and then releases the metal ions into the solution, as stated below (source: Pirajno, 2009, p.92).

Fig.2.4: Evolution of magmatic-hydrothermal system during a cooling process of a porphyry intrusion (Source: Burnham (1979), cited in Pirajno (2009) p.81) + + 1.17NaAlSi3O8 + H  0.5Na33Al2.33Si3.67O10(OH)2 + 1.67SiO2 + Na Albite Na-montmorillonite

On the other side, hydration is the transfer of molecular water from the fluid to a mineral which often accompanies the hydrolysis. In other cases, the reactions where a cation is replaced by another cation in a mineral are called as base exchange as stated below.

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+ + 3Na.33Al.33Si3.67O10 (OH)2 + H + 3.5H2O  3.5Al2Si2O5(OH)4 + 4SiO2 + Na Kaolinite Na-montmorillonite

+ + KAlSiO3O8 + Na  NaAlSi3O8 + K Microcline Albite

Overall, hydrolysis and hydration may control the stability of silicate minerals, the pH of solutions, and the transfer of cations. Thus, both of them are responsible for hydrothermal mineral deposits i.e. propylitic, argillic, phyllic, and potassic mineral assemblage.

The interaction of hydrothermal solutions with the wall rocks results in several types of alterations (Pirajno, 2009). These alterations are linked with the variations in the K+/H+ ratio. The ratio decreases when the system changes towards lower temperatures and pressures. This means that the increasing of H+ metasomatism alteration processes move from alkali to argillic. As a consequence, the types of alteration cause the sequentially decreasing K+/H+ ratio.

Fig.2.5: Types of alteration as a function of temperature, K+ and H+ activities (Source: Guilbert and Park (1985), cited in Pirajno (2009) p.96) The types of alteration will be in order of (i) alkali metasomatism and potassium silicate alteration; (ii) propylitic; (iii) phyllic; (iv) intermediate argillic; (v) advanced argillic, as illustrated in Fig. 2.5. Among those types of alteration, the most significant type of alteration in the study area is argillic alteration. Argillic alteration is strongly characterized by the formation of clay minerals due to intense H+metasomatism and acid leaching. Argillic alteration usually

33 occurs at temperatures of 100 – 300oC. Consequently, argillic alteration provides a strong effect to changes of minerals. In argillic alteration, clay minerals replace the plagioclases and the mafic silicates i.e. biotite and hornblende. In addition, base leaching of alumino-silicates results in silica enrichment, and thus becomes the zones of silica-rich material.

The argillic alteration is classified into: intermediate argillic alteration and advanced argillic alteration (see Fig.2.5). On one side, the intermediate argillic alteration is identified by the presence of montmorillonite, illite, chlorite, and kaolinite group clays, whereas, K-feldspar remains unaltered and Ca2+, Mg2+, Na+, K+ ions are not entirely leached out. On the other side, the advanced argillic alteration is formed due to intense acid attack, and more/less due tocomplete leaching of the alkali cations with the complete destroy of feldspar and mafic silicate phases, as described in Fig.2.6. Kaolinite, pyrophyllite, and alunite are typical mineral phases of this alteration type.

Fig.2.6: Diagram of hydrothermal alteration in rocks containing: (A) dominant alkali-feldspar; (B) dominant plagioclase (Source: Hemley and Jones (1964), cited in Pirajno (2009) p.93)

Hydrothermal processes may produce the metamorphic rocks due to metamorphism. There are two types of metamorphism (Carlson et al., 2009): (i) Contact metamorphism / Thermal metamorphism  Due to the high temperature influence usually not so far from the Earth's surface (<10 km)

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 It is occurred adjacent to a pluton when a body of magma intrudes relatively cool parent rock, as it is called baking (ii) Regional metamorphism / Dynamothermal metamorphism  Due to differential stress. It usually takes place greater than 5 km of distance

Table 2.3: Types of hydrothermal processes (Source: Carlson et al., 2009)

No Role of water Name of process/product 1 Water transports the ions between grains in a Metamorphism rock. Some water is incorporated into crystal structure

2 Water brings ions from outside the rock, and Metasomatism they are added to the rock during metamorphism. Other ions may be dissolved and removed

3 Water passes through cracks or pores in rock and Hydrothermal rocks precipitates minerals on the wall of cracks and within the pores

According to Carlson et al., (2009), in hydrothermal processes, beside metamorphism, hot water also plays an important role to create new rocks and minerals. It is due to precipitation of ions deriving from hydrothermal solutions. There are two important components in a hydrothermal system: a heat source that provides a significant energy, i.e. magnetic, geothermal gradient, radiogenic decay, metamorphism; and a fluid phase that includes solution derived from juvenile fluids, metamorphic fluid, meteoric, connate water, seawater. As a consequence, the hydrothermal mineral deposit is usually created by the circulation of warm to hot fluids (about 50 - > 500oC) that transport, leach, and subsequently precipitate their minerals in response to changing the physical-chemical conditions. Hydrothermal minerals can be formed in between the grains of parent rock. This hydrothermal mineral deposit is also occurred at the discharge site, such as a single conduit or a series of channel ways or fine network of fractures. Hydrothermal rocks may crystallize within a preexisting fracture in a rock to form hydrothermal vein.

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To distinguish it from other weathering products, alteration can be solely characterized in terms of their chemistry and mineral systems. There are various types and styles of hydrothermal alteration based on the nature, chemistry, temperature, and pressure of fluids as well as the nature and the composition of the rocks. When discussed about the hydrothermal alteration, the focus should be put on the aspect of intrusion-related, porphyry and epithermal systems, and, skarns and alteration processes (Pirajno, 2009).

2.7 Human-induced soils

Soils can describe a history of formation of a profile in term of pedogenesis (Buol et al., 1997). However, when human influences the soil formation, human may distract the past development of profile. Human may destroy some features of former properties of soil (Saiano & Scalenghe, 2009), and may change soil directly/indirectly indicated by changing in soil-forming processes (Sandor et al., 2001). Human also affect the pedogenetic capacity of a rock fragment transforming into a soil, and thus so-called anthropic pedogenetic process (see Wei et al., 2006)

Since a long time ago, human have been considered as a part of soil-forming factors (Yaalon and Yaron, 1996). Pedologists have been debating about the anthropogenic soil classification for decades (Capra et al., 2015). Wei et al., (2006) examined that the anthropic activities like tillage, crop planting, fertilization, and land reclamation, can accelerate the pedogenetical processes because those activities facilitate the rock fragment disintegration and mineral nutrient transformation. As an example, tillage is the clear representation of the anthro- pedoturbation activities (Capra et al., 2011). The human factor is a crucial component that should be recognized in a different function with biotic variable in order to assess human impacts on soil formation (Dudal, 2005; Sartohadi et al., 2013).

Nowadays, human may impact the soils not only on urban and agriculture areas but also on less populated areas (Volungevičius & Skorupskas, 2011). Almost all areas have been anthropogenically modified by various human activities that may cause a redistribution of surficial material (Crutzen, 2002). In fact, the soil material redistribution by antropogenic processes has a greater extent than the soil material redistribution by natural processes. The soil modification induced by human can be described from its pedogenetic effect resulting from disturbance from cultural activities. This human-soil modification can occur in a short term or a

36 long term, and it may cause the re-start of pedogenesis after the last disturbance (Saiano and Scalenghe, 2009).

The intervention of human can leave imprints on soils but often it is rapidly erased by pedogenesis (Saiano and Scalenghe, 2009). Certini and Scalenghe (2006) made the categorization of human intervention based on the type of influence: (1) bulk soil disturbance; (2) disposition of new parent material; (3) . However, they stated that in most cases it is rather difficult to separate bulk density disturbance and disposition of new parent material after a short time change. Human intervention can be resulting from various activities such as mining, agriculture, forest clearing, and urbanization. Among those activities, agricultural activities are the main human intervention towards soil development in the study area. Agricultural activities provide a clear evidence of human intervention due to intensive ploughing practices on the land, and thus resulting in . Moreover, the intentional fertilizing from human-made fertilizer or from domestic animal dung and urine also has been known as the active human intervention towards soils since the origin of agriculture (Wood, 2003). The fertilizer may enrich soils, and the translocation of it is depending on the different chemical reaction rate by distinct oxidation state, pH, solubility, and complex of organic matter (Saiano and Scalenghe, 2009).

Human impacts on soils have being a common view, and have expanded to the global scale. Many areas have been occupied by a lot of inhabitants, and thus cause various impacts. The presence of human is able to manipulate the soils, and thus causes an increasing of soil entisolization process leading to a shifting in soil taxonomy (Capra, 2012). In common, the variety of human impacts on soil formation can be seen in the form of relief changing, land management changing, plant management changing, even soil parent material changing (Dudal, 2005). The influence of cultural impacts of human on the soils i.e. urbanization and sewage sludge was also examined by Grieve (2001). Other studies mainly discuss about human impacts on chemical and physical soil properties changing due to agricultural practices (e.g. Dengiz et al., 2009; Jim & Chan, 2004; Kuklik & Hoang, 2014).

2.8 Soil geomorphology

The soil geomorphologic approach is applicable as a connector because the soil geomorphology has been concerned to be suited to investigate local soil processes at certain

37 landscape system s (Daniel & Hammer, 1992). The soil geomorphology is defined as the study of soils and their use in evaluating landform evolution, stability and age, past climate, and surface processes (Birkeland, 1999). Moreover, the term of soil geomorphology is described as the scientific study of the origin, distribution, and evolution of soils, landscape and surficial deposits, and the processes that create and alter them (Schaetzl and Anderson, 2013).

Soils and landform are a two-way study (Schaetzl and Anderson, 2013). This definition means that a soil and a landform develop together. A soil is affected by a landform, so that the development of soil is also able to affect the geomorphic processes. Hall (1983) stated that at the beginning soil survey was conducted by transect and grid approach in the field. However, after the soil mapper understood about the relationship of soil properties and the changing in a landscape, the soil geomorphology approach was started to be applied. Geomorphology is the study of landforms and of processes that creates them (Zuidam, 1983). Ruhe (1969), cited in Hall (1983) stated that there are more than one geomorphologic process that change a landscape in a certain area. However, those complex processes will reach a steady state, and at that time a soil will develop. Therefore, from this cycle, it can be understood that the relationship of soils and geomorphology is established.

Strzemski (1975), cited in Arnold (1983) explained that a geomorphologist who begin to study soils must be started with the study of soil in relation to landscape position and the process. In addition, Birkeland (1999) stated that it is difficult to work on soil analysis without using the available of geomorphic information, or vice versa. The geomorphic input, for soil scientists, can give a fundamental answer related to soil age and to geomorphic processes that influences a soil profile. The other way round, soil information input is required by a geomorphologist to explain soil distributions on a slope in order to get to know the surface processes.

Soils create a crucial part in landscape elements and geomorphic surfaces, whereas, the landscape evolution can reveal a history of a soil development. Hugget (1975) stated that in a new perspective of pedogenesis, the non-linear behavior of soil-landscape results in a soil evolution that requires a time-aspect for investigating the processes. The different deposition time of each material in an area reveals the different forming process of the material. Thus, soil- landform relationship studies have increased, and can help to understand those complex interactions (Mcfadden & Knuepfer, 1990).

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2.9 Soil redistribution

The soil redistribution across the landscape can be revealed by understanding the relationship of environmental factors (e.g. climate, topography, and parent material), and a range of soil properties (Gray et al., 2009). The soil redistribution may transform the soil spatial variation which is clearly detected in an agricultural landscape and in cultivated hillslopes (De Alba et al., 2004). The redistribution of soils is presented by the substitution of soil material in the surface horizon with the material deriving from upslope areas. As a consequence, the soil redistribution results in loss of soil mass in the convexities and in the upper areas of cultivated hillslopes as well as in addition of burial mass in the concavities and in the lower areas of hillslopes which is able to bury the original soil profiles (De Alba et al., 2004).

The soil geomorphologic approach is applicable for the soil redistribution study as the soil geomorphology has been concerned as a study which is suited to investigate local soil processes at certain landscape system (Daniel & Hammer, 1992). The soil geomorphologic approach is significant to describe land surface characteristics as the results of soil redistribution (Hirmas et al., 2011).

The tillage is the most significant practice that redistributes soils in an agricultural landscape (De Alba et al., 2004). Quine et al. (1999) stated that the tillage practice leads to two processes, i.e. soil detachment and soil redistribution. The tillage erosion is known as a crucial erosion process on a sloping agricultural land in relation to soil redistribution (Govers et al., 1999). Van Muysen at al. (2002) found that the variation in tillage speed and tillage depth can affect the soil redistribution and are assumed to set up erosion as the causing of soil redistribution. The effect of tillage depth on soil redistribution is dependent on the tillage direction, whereas, the effect of tillage speed among different tillage directions remains the same for tillage erosivity.

The agricultural terraces also may redistribute a soil due to providing a larger surface area for cultivation (Arnáez et al., 2015). The agricultural terraces are a common landscape in the hilly and mountain regions (Cerda, 1998; Tarolli et al., 2014). The presence of agricultural terraces as the causing of soil redistribution provides both a description of geomorphic setting and an anthropogenic use (Schönbrodt-Stitt et al., 2013).

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2.10 Conceptual framework

This subsection explains the framework of the study, as shown in Fig.2.7. This study attempts to reveal the dynamics of soil formation in the study area as it is located in the transitional landscape zone. The dynamic of soil formation in this study area is assumed to be initiated by the natural soil formation where the soils are formed by state factors, i.e. climate (C), organism (O), parent materials (P), and relief (R) which occurs during certain period (T-1). This process is categorized into soil formation – 1, and thus results in residual soils. Hereinafter, these residual soils are being developed, and there is also the presence of human impact towards the soils within certain period (T-2). This process results in human-redistributed soils. On the other way round, the human influence may also generate relief modification, and increase the morphodynamic processes. Therefore, it results is another type of redistributed soil, called as landslide-redistributed soils. Both of human and landslides has developed the natural soil formation into the soil formation - 2, with the product of redistributed soils. Later on, in some cases, these redistributed soils are also cultivated by human as an agricultural land, and these soils act as the new soil parent material for the soil formation - 3.

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Residual soils Redistributed soils

Climate (C)

Organism (O)

(P) is changing Soil parent material (P)

Relief (R)

Human impact

Morphodynamic processes

Lithomatrix Pedomatrix-1 Pedomatrix-2 Time-1 Time-2 Time-3

Soil Formation-1 Soil Formation-2

Fig.2.7: Conceptual framework of the study 41

CHAPTER 3 RESEARCH SYSTEMS, METHODS, AND TERMINOLOGY

3.1 System of the study

The system of this study was based on catchment boundaries. This catchment system is of importance to border/limit this study based on the characteristics presented in the catchment (Table 3.1). The central part of Bogowonto catchment was chosen because it presents the complexity of physiographic systems in the transition zone of Tertiary Volcanic Systems, Tertiary Structural Systems, and Quaternary Volcanic Systems. This transition zone describes the influence of Menoreh volcanic systems in the southeastern part of the study area, Halang structural systems in the central- and west parts of the study area, and Sumbing volcanic systems in the northern part of the study area. Therefore, the catchment system in this study controls the soil formation and the spatial arrangement of soil redistribution on the land surface.

Table 3.1: Characteristics of the catchment system in the study area

Categories Elements Characteristics Internal functioning of Climate 1. Humid tropical climate: the catchment system 2. –tropical monsoon type of

rainfall (unimodial peak of rainy season) 3. –average annual rainfall ranging from 2500 to 4000mm 4. –average temparature ranging from 18 to 29oC Vegetation 5. 1. Ground plants: bush/shrub 6. 2. Horticulture plants: fruit and vegetables 7. 3. Wood plants: 8. sengon (Albizia chinensis), 9. teak (Tectona grandis) Geological processes 10. 1. Volcanic-structural 11. 2. Structural Parent rock/lithology 12. 1. Old andesitic breccia 13. 2. Andesite 3. Tuff 42

4. Marl 5. Geomorphic units 1. Plain areas 2. Wavy 3. Hilly 4. Volcanic areas Geologic time Tertiary Oligocene – Quaternary Holocene External functioning Morphodynamic 1. Landslide of the catchment processes 2. Erosion system 1. 3. Deposition Human activities 1. 1. Cultivated 2. 2. Uncultivated

In specific, the soil system approach in this study was conducted through landform segmentation based on the soil-scape concept by Hugget (1975). The landform segment is an expression of similar landscape characteristics according to geological processes, cover material, and geomorphic unit which are divided into upper-, middle-, and lower parts based on river orders and topographic positions. The scale of the soil system in this study was emphasized on a regional dimension which was represented by a landform segment rather than only a pedon. It means that the soil sample taken in a particular landform segment will be considered as the representative of that landform’s characteristics, not only represent the pedon’s characteristics in a local dimension. Therefore, the soil system in this study was built by the relationship of soil characteristics that were found together in a landform segment. Table 3.2 presented the characteristics which are considered in the soil system based on the soil-scape concept.

Table 3.2: Characteristics of the soil system in the study area

Categories Elements Characteristics Functioning of Parent rocks 14. 1. Old andesitic breccia the soil body 15. 2. Andesite 3. Tuff 4. Marl 5. Sandstone Soil parent material 16. 1. Weathered material 17. 2. Altered material 3. Deposit material 43

Soil depth 18. 1. Shallow (0-2m) 19. 2. Thick (> 2m) Genesis of soils 20. 1. Residual soils 21. 2. Redistributed soil material Functioning of Geological processes 22. 1. Volcanic-structural the landscape 23. 2. Structural Cover material 1. Volcanic ash deposits 2. Landslide deposits Geomorphic unit 1. Plain areas 2. Wavy 3. Hilly 4. Volcanic areas Relief within the 1. Plain segment 2. Undulating 3. Moderately steep 4. Steep Human activities 3. 1. Land utility 4. 2. Terraces 5. 3. Tillages 6. 4. Fertilizing/manuring

3.2 Data acquisition The research method in this study was a sampling method. Several soil samples were taken to represent the soil properties within the landform segment. The soil samples were collected as disturbed samples. 3.2.1 Soil sampling in the field The soil sampling method applied in the field investigation was purposive sampling. It was conducted according to the landform segments. There were 43 profiles selected based on relief and soil parent material variation within the landform segments, as shown in Fig.5.2. Each profile was sampled from the upper-most horizon until the saprolite. Of the total 43 profiles, there were 16 profiles taken for residual soil analysis (Table 3.3); and 27 profiles taken for redistributed soils analysis (contained by 11 profiles of landslide deposits (Table 3.4) and 16 profiles of human-redistributed soil material (Table 3.5)). The profiles were described using the Guideline for Soil Description (FAO, 2006).

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Table 3.3: Soil profiles for residual soil analyzing

No Sites Coordinates Elevation Formation Soil parent material (masl) (Soil basement rocks) 1 Wuwuharjo (396980, 9163849) 451 Tmoa Quaternary deposit (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (volcanic ash) and andesitic lava intrusion) 2 Karangsari (394710, 9158303) 259 Tmph Tertiary rock (tuff, alternation of weathering marl-sandstone, and (marl) calcareous tufa) 3 Bener (395537,9156981) 259 Tmph Tertiary rock (tuff, alternation of weathering marl-sandstone, and (tuff) calcareous tufa) 4 Sedayu (402665, 9152062) 348 a Quaternary deposit (andesite) weathering (volcanic ash) 5 Guntur (393240, 9158336) 241 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) and andesitic lava intrusion) 6 Mayungsari (401785, 9152433) 227 Tmoa Quaternary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (volcanic ash) and andesitic lava intrusion) 7 Karangsari (394710, 9158303) 259 Tmph Tertiary rock (tuff, alternation of weathering marl-sandstone, and (sandstone) calcareous tufa) 8 Guyangan (400607, 9153013) 612 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccias) andandesitic lava intrusion) 9 Margoyoso (396880, 9162849) 409 Tmoa Quaternary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (volcanic ash) andandesitic lava intrusion) 10 Wonogiri (397820, 9163849) 453 Tmoa Quaternary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (volcanic ash) andandesitic lava intrusion) 11 Margoyoso (397260, 9163449) 413 Tmoa Tertiary rock alteration 45

(andesitic breccias, tuff, (altered andesitic lapili-tuff, agglomerate, breccias) andandesitic lava intrusion) 12 Jati (404791, 9152433) 307 a Tertiary rock alteration (andesite) (altered andesitic breccias) 13 Banyuasin (400327, 9153813) 524 Tmoa Tertiary rock separe (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion) 14 Pucungroto (401678, 9155429) 315 a Tertiary rock alteration (andesite) (altered andesitic breccias) 15 Semowono (402327, 9155130) 203 a Tertiary rock alteration (andesite) (altered andesitic breccias) 16 Ngargosari (400517, 9153431) 532 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andesitic lava intrusion)

Table 3.4: Soil profiles for landslide deposits analyzing No Site Coordinate Elevation Formation Soil parent (masl) (Soil basement rocks) material 1 Panungkalan 391671, 9156379 355 Tmoa altered andesitic (NL) (andesitic breccias, tuff, breccias lapili-tuff, agglomerate, andandesitic lava intrusion) 2 Guntur 393252, 9158389 341 Tmoa altered andesitic (NL) (andesitic breccias, tuff, breccias lapili-tuff, agglomerate, andandesitic lava intrusion) 3 Burat 390172, 9162650 506 Tmoa altered andesitic (L) (andesitic breccias, tuff, breccias lapili-tuff, agglomerate, andandesitic lava intrusion) 4 Burat 390190, 9162651 510 Tmoa altered andesitic (L) (andesitic breccias, tuff, breccias lapili-tuff, agglomerate, andandesitic lava intrusion) 5 Margoyoso 397995, 9163767 437 Tmoa altered andesitic (L) (andesitic breccias, tuff, breccias lapili-tuff, agglomerate, 46

andandesitic lava intrusion) 6 Margoyoso 396980, 9163849 449 Tmoa altered andesitic (L) (andesitic breccias, tuff, breccias lapili-tuff, agglomerate, andandesitic lava intrusion) 7 Guyangan 397330, 9153407 294 a weathered (NL) (andesitic intrusion) andesitic breccias 8 Rimun 3988495, 9151873 287 a weathered (L) (andesitic intrusion) andesitic breccias 9 Ketosari 395489, 9162211 431 Tmph weathered (NL) (tuff, alternation of sandstone with marl-sandstone, and claystone calcareous tufa) 10 Sukowuwuh 394781, 9158389 359 Tmph weathered (L) (tuff, alternation of sandstone with marl-sandstone, and claystone calcareous tufa) 11 Ketosari 395494, 9162171 425 Tmph weathered (L) (tuff, alternation of sandstone with marl-sandstone, and claystone calcareous tufa) *L = landslide sites; NL = non-landslide sites

Table 3.5: Soil profiles for human-induced soils analyzing No Site Coordinate Elevation Formation Soil parent material (masl) (Soil basement rocks) 1 Mayungsari (396790, 9162832) 359 Tmoa Quaternary deposit (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (volcanic ash) and andesitic lava intrusion) 2 Wonogiri (397460, 9163591) 461 Tmoa Quaternary deposit (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, ( volcanic ash) andandesitic lava intrusion) 3 Banyuasin (396967, 9163876) 459 Tmoa Tertiary rock kembaran (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion) 4 Legetan (394380, 9161503) 369 Tmph Tertiary rock (tuff, alternation of weathering marl-sandstone, and (tuff) calcareous tufa) 5 Karangsari (394781, 9158407) 339 Tmph Tertiary rock (tuff, alternation of weathering 47

marl-sandstone, and (sandstone) calcareous tufa) 6 Kemejing (397185, 9154303) 527 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion) 7 Tlogorejo (401785, 9152433) 227 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion) 8 Bleber (399601, 9162313) 312 a Quaternary deposit (andesite) weathering ( volcanic ash) 9 Limbangan (398680, 9162849) 579 Tmoa Quaternary deposit (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, ( volcanic ash) and andesitic lava intrusion) 10 Sukowuwuh (397820, 9162493) 451 Tmoa Tertiary rock alteration (andesitic breccias, tuff, (altered andesitic lapili-tuff, agglomerate, breccia) andandesitic lava intrusion) 11 Jati (397260, 9163491) 502 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion) 12 Medono (399191, 9162423) 357 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) and andesitic lava intrusion) 13 Burat (400027, 9163814) 541 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion) 14 Kuwaderan (402678, 9155429) 415 Tmoa Tertiary rock (andesitic breccias, tuff, weathering lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion) 15 Ketosari (399327, 9162830) 403 Tmph Tertiary rock (tuff, alternation of weathering marl-sandstone, and (tuff) calcareous tufa) 16 Cacaban (400517, 9163482) 528 Tmoa Tertiary rock Kidul (andesitic breccias, tuff, weathering 48

lapili-tuff, agglomerate, (andesitic breccia) andandesitic lava intrusion)

3.2.2 Environmental data

The environmental data were collected to support field soil sampling. The data required in this study are climate, lithologic, geomorphic, and land cover data. These data were obtained from map and satellite imagery interpretations, and statistical data from governmental offices. The data are presented in section 4.2.

3.3 Soil sample analysis

The soil sample analysis was conducted to obtain the properties of soils, i.e. morphological, physical, chemical, and mineralogical. The morphological properties were assessed qualitatively during the field investigation. The physical-, chemical-, and mineralogical properties were analyzed quantitatively in the laboratory.

3.3.1 Soil sample preparation for laboratory analysis All the soil samples were air dried for several days. Stones (>2mm) and roots were removed from the soil samples. The clear soil samples were crushed for further physical, chemical, and mineralogical analysis in the laboratory. All analysis followed the standards of Soil Survey Laboratory Methods Manual (Burt, 2004).

3.3.2 Soil morphological properties The morphological properties were assessed directly in the field. These morphological properties consist of depth, texture, structure, consistence (wet and moist), and color. The soil depth was measured from the upper-most horizon to the saprolite using the tape-measure. The qualitative texture was estimated using hand-texture chart by S. Nortcliff and J.R. Lang from Rowell (1994). The was assessed at the soil profiles based on the type and the grade of structure. The soil consistency was also assessed at the soil profiles through estimating the adhesion-cohesion of soil particles. The soil color was defined based on the soil Munsell color chart. The soil pH was measured using a pH stick scale and a soil pH meter.

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3.3.3 Soil physical properties The particle size analysis, as an important physical property, was crucial for differentiating the types of soil parent material. The particle size analysis was treated on Ф< 2mm of air-dried soil by separating the soil particles through destruction or dispersion of soil aggregates. The particle size criteria are based on the combination of USDA- and CSSC textural classification system. The USDA system was used to classify the general textural groups of sand (Ф2mm – 0.05mm), silt (Ф0.05mm - 0.002mm), and clay (Ф< 0.002mm). In addition, the CSSC system was used to obtain the detail analysis of silt fraction separation into fine silt (Ф 0.002- 0.005mm), medium silt (Ф 0.005-0.01mm), and coarse silt (Ф 0.01-0.05mm). The detail analysis of the silt fraction was conducted to check the influence of volcanic ash deposits as a main cover material in the study area.

To obtain the detail particle-size distribution, two techniques were conducted in this study. The Robinson’s pipette method (Gee and Or, 2002) was applied on coarse particle size analysis, whereas, the laser diffraction technique was applied on fine particle size analysis. Previously, the soil samples were pretreated using HCl 1M to remove the carbonate. Afterwards, they were oxidized using H2O2 (30%) to remove the organic matter. The separation of silt and clay fractions from sand fraction in the suspension has been done on 0.05mm sieve through wet sieving. Later, the separation between coarse and fine sand were fractionated by dry sieving on 0.5mm sieve.

The silt and clay fractions were analyzed in the remained suspension of the wet sieving by means of laser diffraction method which were performed with the Mastersizer 2000 instrument (product of Malvern). The wet dispersion was applied on this tool. Three-times measurement was conducted to obtain the intensity of light scattered as a laser beam passes through a dispersed sample. The average of those measurements was calculated to define the sizes of the sample particles, and to produce the final graphic of the silt and clay distribution.

3.3.4 Soil chemical properties The analysis of chemical properties was mainly conducted in order to measure the content of soil nutrients and the impacts of human activities on the soils. Soil Organic Matter

(SOM), Organic Carbon (C), N-total, C/N ratio, COLE Index, P2O5, pH, Base saturation, Cation Exchange Capacity, Na+, K+, Ca2+, and Mg2+ were the chemical properties analyzed in this study. 50

The Soil Organic Matter (SOM) was analyzed to assess the effect of vegetation cover, and thus land use on the soils in the study area. The SOM was measured by applying a wet method from Walkley and Black. Through this method, several amount of volume of acidic dichromate solution is mixed with the soil sample in order to oxidize the organic matter. The oxidation step is followed by a titration of an excess dichromate solution with a ferrous sulfate. With the amount of this titration (in ml), SOM can be calculated. Following this analysis, the organic carbon (C) was obtained by dividing the SOM by a conversion number (1.724).

The N-total was analyzed to assess the influence of fertilizer and the decomposition rate of organic matter in the upper-most horizon. The N-total was analyzed through some steps, i.e. (i) digestion and (ii) determination. For digestion stage, we apply the Kjeldahl method which is + proposed to convert an organic N into NH4 -N. The sample, then, is digested using H2SO4. Afterwards, determination stage is applied by a distillation for about 30 minutes, and is continued by a titration using NaOH 0.1N.

C/N ratio was analyzed in order to know the comparison of the decomposition rate and the carbon content on the soil surface. As located in the tropical area, the C/N ratio seems to be crucial to analyze the soil development in the study area. The C/N ratio was assessed through C and N content by using CN elemental analyzer in the microbiology laboratory.

The cation exchange capacity (CEC) is an analysis used to assess the cation exchanging capability among the soil aggregate of all soil particles. It is strongly related to the clay and the organic matter content as soil colloids. The CEC analysis was extracted with NH4OAc at pH 7.0 method, continued with a distillation of soil-filtered sample. Furthermore, the liquid resulted in the CEC extraction (aliquot) was used for the analysis of major bases (Na+, K+, Ca2+, and Mg2+). In order to obtain the amount of each base, the base is reacted with different specific indicator. Other chemical analysis, the percentage of base saturation is obtained from the calculation of the major bases based on the CEC values. The base saturation has a linear effect to the soil pH where the increasing of base saturation will be followed by high values of soil pH. The soil pH in this study is analyzed by a digital pH meter when the soil liquid for pH analysis is previously tested using KCl solution.

The P2O5 analysis was conducted by using the Olsen method (e.g. Horta and Torrent,

2007). This phosphate analysis was conducted by extracting with NaHCO3. The Olsen method 51 was chosen for this study because most of the soil pH samples are > 5.5 (weak acidic pH).

However, Bray-I method is more appropriate for acid soil with pH < 5.5. The P2O5 analysis was purposed to assess the effect of fertilizer and manure on the soil surfaces.

The COLE Index was conducted to assess the swelling-shrinkage capacity of the clayey soils. This analysis used an injection tube which was applied to the soil paste. After leaving the soil paste for 2 nights, the soil paste was assessed by detecting the fracture on the soil paste body as an indicator for soil shrinkage characteristics. In addition, the soil paste was also measured for its length differences between wet and dry condition.

3.3.5 Soil mineralogical properties The mineralogical analysis was conducted for determining the clay-type. The pretreatment procedures for mineralogical analysis were similar to those used for particle-size distribution analysis. However, in this mineralogical analysis, during pretreatment the soil sample was coupled with 400W ultrasonic dispersion under 30-50 Hz for about 4 minutes to disperse the soil particles, and it was possible to yield maximum clay concentrations (Burt, 2004). The clay fraction was then assessed from the remained suspension of the wet sieving from the sand separation process.

The gravity was conducted during overnight in order to separate the clay from the silt fraction. The remained suspension from the sand separation process was diluted into 1l Atterberg sedimentation cylinder without any peptisator, and then mechanically shaken. The sedimentation has been done in certain interval following the principle of Stoke’s Law (Kalra and Maynard, 1991). Then, 25ml aliquot was taken by a pipette and was oven-dried at 60oC.

The XRPD (X-Ray Powder Diffraction) was carried out for clay-type analysis. The Bruker D-8 Advance was used as an XRPD scanner tool in this analysis. Several grams of clay sample were prepared into a preparat glass. The diffractogram was made of well oriented clay samples. The Mg-saturated samples were solvated by adding glycerol directly onto the moist clay, the K-saturated samples were solvated by ethylene glycol, and then heated to 550°C respectively (Bullock & Loveland, 1982).

The XRF (X-Ray Fluorescence) was used to measure the quantitative mineral content in the soil parent material. The FeO and the total Fe contents were measured titrimetrically. And then, the Fe2O3 content was calculated from those results. The Si and Al contents were 52

determined using XRF after fusion in Na2B4O7. The contents of the other elements in iron ore such as Ti, P, Pb, Mg, Mn, Zn, and Cu were determined using ICP-OES.

3.4 Results analysis

The results were analyzed quantitatively and qualitatively. The quantitative analyses were conducted through profile development analysis and descriptive-statistic analysis. The qualitative analysis was conducted through spatial analysis on topographical and geological maps. Table 3.6 explains the detail of how the objectives were achieved with respect to the data and methods, and thus produce the final results of this study

3.4.1 Profile development analysis Profile development analysis is a quantitative assessment of soil profile development degree. In this study, the profile development was assessed by two ways: (i) Ratio of soil organic matter (SOM); (ii) Ratio of clay percentage. The ratio of the SOM was conducted by assessing the SOM in A-horizon towards the SOM in the horizon underlying the A-horizon. This ratio was intended to describe the effect of organic matter translocation from the surface horizon to the sub-surface horizon due to of vertical water movement and bioturbation. The ratio of the clay percentage was intended to describe the development of soil parent material into the soils by assessing the percentage of clay in the C-horizon towards the percentage of clay in the A/A+B horizons.

3.4.2 Descriptive-statistic analysis Descriptive-statistic analysis was used to describe the data of soil properties. The descriptive statistic was proposed to simplify a large number of analysis data and to see the patterns of the data descriptively. In this study, the simple summaries of the data measured were mostly shown in tables and graphics.

3.4.3 Spatial analysis Spatial analysis was intended to simplify the spatial patterns of phenomena. The area and line spatial analysis were used to figure out environmental characteristics of the study area. The area spatial analysis was applied in evaluating the climate, land use, and slope characteristics. The line spatial analysis of contour and river pattern was applied in evaluating the lithology of particular areas. The patterns of the area and line represent the characteristics of specific sites. 53

Table 3.6: Relation of research questions, objectives, data, methods, and results

Research questions Objectives Data Methods Results

1. How are the spatial patterns of -Geologic map -Map interpretation Spatial patterns of soils in the study area? -Geomorphologic map -DEM interpretation soils in the study area -Topographic map -Field investigation (sub section 5.2) To identify the - Soil profile data spatial patterns and 2. How are the characteristics of Soil sampling -Field sampling Soil characteristics the characteristics soils in the study area? -Laboratory analyses: (sub section 5.3) of soils in the study (physical, chemical, area and mineralogical properties) -Statistical analysis -Index analysis 3. What are the specific factors -Geologic map -DEM interpretation Specific factors that that influence the soil -Geomorphologic map -Field investigation control the variation formation and soil -Topographic map of soils in the study development in the study area? -Land use map area (sub section 5.3) -Landslides data -Institutional data To evaluate the soil -Soil properties data formation and the 4. What are the variations of soil soil development in -Soil properties data -Map interpretation Soil parent material parent material in the study -Geomorphologic map -DEM interpretation variations (sub the study area area? -Topographic map -Soil analysis result section 5.4)

-Land use map -Landslides data 5. How do the variations of soil -Geologic map -Map interpretation The way of specific parent material influence the -Geomorphologic map -DEM interpretation factors influencing soil development and restart the the variation of soils soil formation in the study area? in the study area (sub section 5.5) 54

3.5 Terminology definition This terminology definition is intended to explain the meaning of specific terms applied in this study based on my own approach. The own approach has been adjusted with the characteristics or phenomena found in the study area.

Soils: Three-dimensional natural body containing of fertile material that covers the Earth’s surface, and is built from a sequence of horizons as a result of soil development process, and has particle sizes that less than 2 mm. Soil material: The mixed soil component material consist of sand, silt, and clay. Soil parent material: The source material of the soils that derives from either weathering of the underlying parent rock or weathering of the parent rock of the surrounding area or alteration of the underlying parent rock or other material that are removed / transported geomorphologically from their origin place. Soil-scape: A part of the Earth’s surface that is genetically related and is composed by continuum of soil units within a landscape. Landform: A unity of land surface morphology, component material, and formation as well as modification of processes during the time, of which consists of 4 aspects such as morphology, morphogenesa, morphochronology, and morphoarrangement. Component material of landform including the underlying soil parent material and the surface cover material. Landform segment: A grouping of similar geological settings which are divided based on the topographic position (e.g. upper, middle, lower parts) into spatial units as a sequence of landscape based on topographic position and river order. Relief: A description of land surface roughness such as smooth, wavy, hill, or mountain. Slope: A line that connects two points from different elevations. It forms flat, undulating, steep, or very steep of slope degrees.

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CHAPTER 4 UNDERSTANDING THE CHARACTERISTICS OF STUDY AREA

4.1 Geographical sites

Bogowonto River divides two mountainous landscape units, i.e. South Serayu in the west and Kulonprogo in the east. Bogowonto River flows from young Sumbing Volcano (elevation 3.300 m.s.l) in the north to the Indian Ocean in the south across a Tertiary structural-volcanic landscape in the center. This study focuses only on the central part of Bogowonto catchment because this area includes a transitional zone of Quaternary and Tertiary volcanic landscape. Therefore, this area is not only formed by Tertiary structural-volcanic material, but also in some part has been influenced by redistributed volcanic ash deposit from Sumbing in the north. The variation of material in this area may determine the soil formation and soil development.

The study area is administratively under Wonosobo, Purworejo, and Magelang Regencies in Central Java Province as well as a small part of Kulonprogo Regency in Yogyakarta Province (Fig.4.1). It comprises 64 municipalities covering ca. 234.51 km2 (see Table.4.1) between 7017’00”S - 8047’00”S and 109034’30”E - 110009’00”E. The study area, as the central part of the catchment, is densely populated, and seems causing multiple social-economic activities with massive affects on the formation and development of soils.

Table 4.1: Administration boundary of the study area

No Regency District Municipality 1 Wonosobo Kepil Burat Rejosari Kagungan Gadingrejo Randusari

2 Purworejo Loano Kedungpoh Ngargosari Maron Banyuasin Separe Jetis Banyuasin Loano Kembaran Kalinongko Sedayu Trirejo Karangrejo Kebongunung Kalikalong Mudalrejo Rimun Kalisemo Tepansari Kemejing Kaliglagah Guyangan Tridadi

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Bener Ngasinan Kamijoro Sidomukti Medono Nglaris Bleber Sukowuwuh Pekacangan Limbangan Kedungloteng Legetan Wadas Ketosari Cacaban Kidul Karangsari Cacaban Lor Bener Kalitapas Kalijambe Kaliwader Mayungsari Kedungpucang Jati Kaliurip

Kaligesing Gunungwangi Sudimoro Hardimulyo Donorati Tlogorejo Wonotulus

3 a. Magelang Kajoran Wuwuharjo Kwaderan Wonogiri Madukoro

Salaman Margoyoso

4. Kulon Progo Samigaluh Pucungroto Semowono

Source: Data Analysis of Podes of Central Java 2010 (BPS, 2015)

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Fig.4.1: Location of the study area: (a) Indonesia; (b) Bogowonto Catchment; (c) Study area

4.2 Physical-Environmental Setting 4.2.1 Climate and soil hydrologic condition

With regards to soil formation, rainfall and temperature are the main climatic aspects to be considered. They determine the weathering process of parent rock in soil formation, and influence on pedogenic processes in soil development. Furthermore, those climatic aspects support the soil hydrological conditions, i.e. runoff, and seepage which are crucial for soil development.

Rainfall and temperature

The rainfall characteristics of the study area were described from rainfall intensity data recorded from 2001 to 2010. The data were adopted from four adjacent rainfall stations, namely Guntur, Kaligesing, Kedungputri, and Ngasinan stations. These data illustrate that the annual rainfall patterns among four stations are similar, showing the uni-modial type. The data show an

58 abrupt distinction between the rainy and the dry season. The rainy season occurs from November to March with its peak in January, whereas the dry season occurs from April to October (see Fig.4.2). The maximum annual rainfall is ranging from 3400 to 4800 mm.

a mean min max b mean min max

700 1000 600 800 500 400 600 300 400 200 200

100

Monthly rainfall (mm) rainfall Monthly (mm) rainfall Monthly

0 0

Jul Jul

Jan Jan

Jun Jun

Oct Oct

Apr Apr

Feb Feb

Dec Dec

Nov Nov

Mar Mar

Agst Agst

May May

Sept Sept

c mean min max d mean min max 1200 1000

1000 800 800 600 600 400 400

200 200 Monthly rainfall (mm) rainfall Monthly

0 (mm) rainfall Monthly 0

Jul Jul

Jan Jan

Jun Jun

Oct Oct

Apr Apr

Feb Feb

Dec Dec

Nov Nov

Mar Mar

Agst Agst

May May

Sept Sept

Fig.4.2: Rainfall pattern in the study area: (a) Banyuasin station; (b) Guntur station; (c) Kaligesing station; (d) Ngasinan station

The patterns of maximum and minimum monthly rainfall differ among the four stations (see Fig.4.2). In one hand, the maximum monthly rainfall tends to vary from January to December with its lowest valley in July/August and its highest peak in December/January. This maximum monthly rainfall is ranging from 200 to 1000 mm. In another hand, the minimum monthly rainfall shows a nearly constant intensity from January to December. This minimum monthly rainfall is ranging from 0 to 180 mm.

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The distinct patterns of maximum and minimum monthly rainfall result from the influence of west monsoon, which moves the wind forward from the Asian continent (high pressure) to the southeast (low pressure) during summer time in Australia. Consequently, this west monsoon causes the rainy season from November to March. In addition, the study area has a fluctuate temperature. The maximum average temperature is 29.4oC and the minimum average temperature is 18.6oC.

The variation of maximum and minimum monthly rainfall is important for evaluating the Monsoon type Equatorial type storage. Based on Fig.4.2, the highest difference between maximum and minimum Local type monthly rainfalls occurs in January ranging from 500-800 mm. However, the lowest difference between maximum and minimum monthly rainfalls occurs in August ranging from 200-400 mm. Overall, the data show that there are still rainfall events in the study area even if in the dry months (month having rainfall < 60mm/month, based on Schmidt Fergusson classification). It means that the rainfall input infiltrates into the soil along the year. Thus, it supports the soil water storage that is necessary for soil profile development.

Both, high rainfall and high temperature cause intensive parent rock weathering in the study area which follow Hilgard (1882), Marbun (1935), Boneau (1982) who determined climate to be the most significant factor in the soil formation (Bockheim et al., 2005). Often, the weathering process is linked to geochemical and mineral variations in the soils (Bétard, 2012). However, similar climatic conditions in the entire study area result in low variation of rainfall and temperature, and thus results in a less significant effect on parent rock weathering stage.

The high rainfall intensity and high temperature fluctuation also lead to intensifying geomorphic processes i.e. gully erosion and landslides. Furthermore, the high rainfall intensity and long duration of rainfall have a significant influence on and soil structure dispersion (see Aleotti, 2004; Valigi & Melelli, 2007). Therefore, these high rainfall and high temperature contribute to intensive soil redistribution in the study area.

Runoff, infiltration, and seepage

The soil hydrological conditions closely relate to rainfall characteristics of the study area. Under normal conditions, the rainfall input may encourage the soil profile development through vertical water movement during infiltration. This infiltration water causes clay and bases mobile

60 along the profile. But in case of long duration of rainfall, it may cause soil-water saturation, and thus obstruct the percolation water in the soil profile. As a consequence, this condition forms lateral water movement in the profile, and thus causes bases leaching. Also, the heavy rainfall may result in high velocity of runoff (Fig.4.3) leading to intensive soil erosion, and detain the soil profile development. This situation commonly occurs in a rough topography as dominating in the study area.

Photo credit by: Nur Ainun Pulungan, 2013 Fig.4.3: Heavy rainfall in the study area affecting high velocity of runoff

The soil hydrological condition in the study area is also shown by the presence of seepage. This presence of seepage is mainly caused by differences of permeability and porosity between upper material and underlying material. The seepage is mostly found in the area where it has unconsolidated volcanic deposit as the upper material, but it has weathered rock as the underlying material. The differences of permeability and porosity in both materials have caused

Photo credit by: NurAinunPulungan, 2014 Fig.4.4: The presence of seepage in the study area found 30 cm below the surface

61 lateral water movements in the contact side (see Fig.4.4). This lateral water movement may result in bases leaching and dissolve certain rock minerals. Consequently, it influences on pedogenic processes of the upper material. Besides, this lateral water movement also intensifies clay formation in the bottom part of the upper material. And thus, this clay formation often becomes a slip plane, and generates landslides in such area.

4.2.2 Parent rocks and soil parent material

Parent rock is the principle origin of soil parent material forming. The environmental conditions during the period of parent rock formation are reflected in the weathered parent material. The weathered parent material determines the inherited chemical and physical characteristics of soils. Under specific condition, the weathered parent material does not derive from underlying parent rocks. The weathered parent material can be resulting from other material that may be transported to adjacent locations, and covering the in-situ parent rock. In that case, the overlaying recent material retards the underlying parent rock (Kirkpatrick et al., 2014) in soil formation.

KULON PROG O Study Area

Fig.4.5: Physiographic units of Java Island and the study area located (source: Pannekoek, 1949)

The formation of parent rock is closely linked to the physiographic system. According to Pannekoek (1949), the study area was formed by volcanic and tectonic processes in the south of Java (see Fig.4.5). Therefore, it covers parts of three systems: (1) Menoreh System; (2) South

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Serayu Mountain System; (3) Sumbing System. The Menoreh System is the result of Tertiary volcanic processes associated with the uplifting of Kulon Progo Dome. The South Serayu Mountain System is the result of a depression zone in the southern part of Java which is strongly controlled by Tertiary structural process of a north-south fault resulting in Bogowonto River. The Sumbing System is the result of Quaternary volcanic processes of Sumbing volcano in the central line of Java. This system creates volcanic slope and produces abundant pyroclastic material mostly covering the Tertiary lithologies in the northern part of the study area.

Fig.4.6: Distribution of lithology in the study area

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The formation of parent rock determines the lithologies in the study area (see Fig.4.6). The Tertiary volcanic rock formation (Tmoa) consists of andesitic breccias, lava andesite, tuff, lapili-tuff and agglomerate, and is considered as the oldest rocks formation in Bogowonto. It was produced in miocene Era. The andesitic breccias are found as the predominant parent rock in the study area. However, these Tertiary volcanic rocks formation in some locations was also followed by andesitic intrusion (a). The major minerals contained in andesitic intrusion are hiperstein andesitic mineral and augit-hornblende andesitic mineral. Another Tertiary rock formation had derived from shallow-sea water sedimentation (Tmph) containing tuff, alternation of marl-sandstone, calcareous tufa. It was produced in miocene-pleocene Era. The Quaternary volcanic rock formation (Qsm) consists of pyroclastic and laharic sediment from Sumbing Volcano as well as fluvial sediment (Qa). Most of this pyroclastic sediment, e.g. volcanic ash was deposited unevenly on the land surface, and buried the former Tertiary lithologies. Thus, the upper-most soil parent material will determine the developed soil characteristics (Badia et al., 2013; Dultz, 2002; Osher & Buol, 1998).

4.2.3 Land surface morphology

Land surface morphological setting in this study is represented by relief. The other land surface morphological aspects are less considered in this study. The study area is widely constructed by Menoreh system from the East creating a rough relief with multiple ridges and valleys (see Fig.4.7). Multifarious of tectonic and volcanic processes determine this rough relief construction with slopes ranging from moderate steep (15-25o) up to very steep (>45 o). This rough relief mainly causes geomorphic processes, i.e. erosion and landslides that largely affect the soil redistribution in the study area. Furthermore, in relation to soil development, the rough relief strongly influences on pedogenic processes (Neil et al., 1990) because this relief also controls water infiltration rate that determines vertical water movement along the soil profile.

Land surface morphological setting in the study area can be distinguished into three major geomorphic units: (i) volcanic toe-slope, (ii) volcanic-structural hills, and (iii) fluvio- colluvial plain, as shown in Fig.4.7. These geomorphic units classification are based on the physiographic systems of the study area as explained in section 4.2.2 (see Fig.4.5).

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Fig.4.7: Geomorphic units of the study area

4.2.4 Vegetation cover

In the study area, there are five types of land uses, i.e. shrub/bush, mixed garden (garden with mix of vegetation), irrigation paddy field, rainfed paddy field, and dryland agriculture. Each types of land use showing a variety of vegetation cover. Mixed garden has a typical structure of strata plantation which combines ground plants, seasonal plants, and perennial plants within an area. The typical plants in mixed garden are cassava, tomato, ginger, turmeric, cinnamon, coffee,

65 teak, and sengon. Shrub/bush is a typical of ground plant which often covers the surface densely. Irrigation and rainfed paddy fields both are planted with paddy however they are different in their land management. Dryland agriculture is a kind of agriculture that is planted by vegetables or fruit plants, and seasonally changes. The typical plants in dryland agriculture are maize, cassava, groundnut, and long bean. The distribution of land use types in the study area is shown in Fig.4.9. Based on the figure, mixed garden is the predominant land use type in the study area.

1 3

2

Photo credit by: NurAinunPulungan, 2013 Fig.4.8: Types of land uses: (1) dryland agriculture; (2) irrigated paddy field; (3) mixed garden

Each land use type has specific responds towards rainfall and sun radiation, which is essential for micro-climate. The irrigated/rainfed paddy field is a type of monoculture agriculture (Fig.4.8(2)), and thus it allows rainfall or sun radiation penetrate to the ground widely. The dryland agriculture are usually characterized by multi vegetation types within an area (Fig.4.8(1)), whereas, the mixed garden is amplified by the strata structure of vegetation which provides dense vegetation cover (Fig.4.8(3)). Consequently, in comparison to paddy field, the dryland agriculture and mixed garden result in a limited sun radiation and rainfall reaching into the ground. This condition controls the temperature above the soil surface, and to some extent controls the decomposition rate of litter and organic matter on the soil surface.

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Fig.4.9: Land use map of the study area

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Vegetation cover can act as the organism (O) function in soil formation. The vegetation cover can be naturally grown or planted. Hence, the vegetation cover closely relates to land management which influences on soil development in a particular area. The vegetation cover and its varieties affect soil formation by controlling the overland flow and runoff (Solé-Benet et al., 1997), and managing the micro-climate conditions (Fu et al., 2003).

4.3 Socio-Cultural-Economic Setting 4.3.1 Demographic condition The demographic condition describes the development of human population. The demographic data of Central Java Province show the continuous increasing population year by year, as shown in Fig.4.10. This increasing population may reflect the development of human activities in such areas. Dudal (2005) stated that nowadays human are considered as one of soil- forming factors. Therefore, the increasing population in the study area is assumed as the increasing of intensity of human impact on the soils.

34 32 30 28 26 24 22 in million in 20 1971 1980 1990 1995 2000 2010 2011 2012 2013

Fig.4.10: Development of the population in Central Java Province (source: BPS, 2014)

The demographic calculation of the study area needs to be adjusted since the border of study area does not fit with the border of the administrative areas. A mathematical demographical approach by Keyfitz (1977) is applied to calculate the population in the study area. This calculation uses the spatial-weighted equation which assumes that the human population in the areas is homogeneously distributed (see Table 4.2a).

The growing population has caused a linear increase of the population density. In the period of 2010-2013, the specific population density for each region in the study area is 501 persons per km2 (Purworejo); 156 persons per km2 (Wonosobo); and 2 persons per km2

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(Magelang), as shown in the Table 4.2b. According to Agrarian Acts (UU No.56/PRP/1960), Purworejo is categorized as densely populated (having > 401 people/km2); Wonosobo is categorized as slightly dense populated (51-250 people/km2); Magelang is categorized as rarely populated (1-50 people/km2). Consequently, this population density will relate to the agricultural activities developed in such areas.

Table 4.2: Population statistic data of Central Java Province

Population Density of Jawa Tengah by Regency/City 2013 Kepadatan Luas Jumlah Penduduk Daerah Kabupaten/Kota Penduduk per km2 (km2) Regency/City Number of Population Area Population Density by (km2) km2 01. Kab. Cilacap 2,138.51 1,676,089 784 02. Kab. Banyumas 1,327.59 1,605,579 1,209 03. Kab. Purbalingga 777.65 879,880 1,131 04. Kab. Banjarnegara 1,069.74 889,921 832 05. Kab. Kebumen 1,282.74 1,176,722 917 06. Kab. Purworejo 1,034.82 705,483 682 07. Kab. Wonosobo 984.68 769,318 781 08. Kab. Magelang 1,085.73 1,221,681 1,125 09. Kab. Boyolali 1,015.07 951,817 938 10. Kab. Klaten 655.56 1,148,994 1,753 11. Kab. Sukoharjo 466.66 849,506 1,820 a) Population number in the study area 12. Kab. Wonogiri 1,822.37 942,377 517 13. Kab. Karanganyar 772.20 840,171 1,088 Regency Area Population 14. Kab. Sragen 946.49 871,989 921 (%) (people) 15. Kab. Grobogan 1,975.85 1,336,304 676 Purworejo 73.48 518,389 16. Kab. Blora 1,794.40 844,444 471 Wonosobo 19.98 244,092 17. Kab. Rembang 1,014.10 608,903 600 Magelang 6.54 50,313 18. Kab. Pati 1,491.20 1,218,016 817 Total 100 812,794 19. Kab. Kudus 425.17 810,810 1,907 Source: Data analysis, 2015 20. Kab. Jepara 1,004.16 1,153,213 1,148 21. Kab. Demak 897.43 1,094,472 1,220 22. Kab. Semarang 946.86 974,092 1,029 23. Kab. Temanggung 870.23 731,911 841 24. Kab. Kendal 1,002.27 926,812 925 25. Kab. Batang 788.95 729,616 925 b) Population density in the study area 26. Kab. Pekalongan 836.13 861,082 1,030 Regency Area Population 27. Kab. Pemalang 1,011.90 1,279,596 1,265 (%) (people) 28. Kab. Tegal 879.70 1,415,009 1,609 Purworejo 73.48 501,134 29. Kab. Brebes 1,657.73 1,764,648 1,064 Wonosobo 19.98 156,044 30. Kota Magelang 18.12 119,935 6,619 31. Kota Surakarta 44.03 507,825 11,534 Magelang 6.54 1,721 Total 100 812,794 32. Kota Salatiga 52.96 178,594 3,372 33. Kota Semarang 373.67 1,644,800 4,402 Source: Data analysis, 2015 34. Kota Pekalongan 44.96 290,870 6,470 35. Kota Tegal 34.49 243,860 7,070 Jumlah/Total 2013 2) 32,544.12 33,264,339 1,022 2012 2) 32,544.12 33,270,207 1,022 2011 2) 32,544.12 32,643,612 1,003 2010 32,544.12 32,382,657 995 2009 1) 32,544.12 32,864,563 1,010 Source : Population Census 2010, BPS-Statistics of Central Java Province Note : 1) Projection of Inter-Census Population Survey 2005 2) Projection of preliminary number SP2010

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However, in relation to human impact on soils, the population density across the area cannot be considered as equal. In the study area, the population density strongly depends on characteristics of a particular area. Some years ago, high population density occupies the area where it can provide the agricultural land. Mostly, it can be found in the lowland area. However, nowadays, the high population density has also been expanded to the upland area following the land availability. This expansion of population density widely occurs in Purworejo where having a dense population.

4.3.2 Cultural development

Farming is the culture for local people of Java to support their lives (Raffles, 2010). Farming has been further developed during the last seven decades under three different leadership regimes, i.e. Orde lama, Orde baru, and Reformation with various focuses depending on the policy made by the leader.

Agricultural sector became the most emphasize sectors under Orde baru. A successful program developed for the agricultural sector in Orde baru was Repelita (5-Year Development Plan) which had the major purpose to increase the productivity of agriculture. Growing agricultural productivity was the main purposed of this regime under Soeharto’s command (2nd President of Indonesia). Every regulation was tended to consider the agricultural productivity.

According to the document of Repelita by Bappenas (National Planning and Development Agency), the Repelita worked from 1969-1997, however, the agricultural purpose was specifically focused on Repelita I-IV. The Repelita I (1969-1974), as the initial period in Orde baru, put the aims to fulfill the basic needs of society. The Repelita I carried out the renewal processes of agricultural sector in order to gain the economic improvement. This program was essential because the majority of the society’s income still relied heavily on agricultural products. Under Repelita II & III, the purpose was to increase agricultural productivity, e.g. by increasing human labor, enhancing industrial sector in order to produce more agriculture machines, and also applying extensification of agriculture land by providing land clearings. All these efforts were intended into one target heading to Swasembada Pangan (food self-sufficiency). The Repelita IV (1984-1989) still focused on the target of stabilizing Swasembada Pangan. Due to this program, in 1984 Indonesia succeeded to produce enough rice

70 for the amount of 25.8 million tons. Thus, rice self-sufficiency was reached at that time, and gained an achievement from FAO in 1985.

After heading to rice self-sufficiency in Repelita I-IV, the 3rd regime named as Reformation tended to develop a diversification system rather than an extensification system for agriculture. The food diversification is a development program to support food self-sufficiency, however, people are expected not to depend on one main food such as rice. The alternative for food diversification can be proposed by the new variety of non-rice plants, e.g. potato, maize, wheat, and sago. This program can be applied on intensification of the crop system. Moreover, it is also supported by a new legislation for farmers and agriculture land, procurement better seeds, better fertilizer and better technology, and regular socialization to improve farmers’ knowledge.

The farming culture, especially paddy farming, has become a custom for local people since their ancestors. The paddy farming is considered to assure their survival. The paddy farming is usually cultivated in a gentle slope area and is located near the river. The main reason is the need of water supply for irrigation. The irrigated paddy farming is usually applied in this area with the requirement of daily watering.

This farming culture forces the local people to cultivate paddy intentionally even on rough relief. Rainfed paddy farming is applied in this case. This rainfed paddy farming does not need an intensive irrigation, and strongly depends on wet season. However, besides the rainfed paddy farming, the irrigated paddy farming has also occupied rough and steep areas nowadays. As a consequence, the irrigation system has been built and developed in these areas. Deficiency of land availability in the lowland has forced human to occupy and to utilize the marginal and hill areas.

The intensive paddy farming in rough relief, consequently, increases the frequency and the intensity of geomorphic processes, i.e. landslides. The presence of landslides may provoke the soil redistribution in a large volume. Irrigation and crop rotation can be assumed as the triggering factor of landslides. Irrigation is a crucial part of paddy farming requiring daily watering. It strongly leads to soil saturation and weakens the soil stability on the slopes. On other side, crop rotation can aggravate the surface soil stability because it requires vegetation cover changing at once a year or twice a year during a fallow-time.

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Table 4.3: Agricultural land in the study area Regency Area Wetland area (ha) Dryland area (ha) (%) Purworejo 73.48 22.08 53.95 Wonosobo 19.98 3.43 16.18 Magelang 6.54 2.43 4.67 Source: Modified BPS-Statistics of Jawa Tengah Province (2010)

The diversification system of agriculture is also commonly applied in the study area. The development of food diversification can be shown by the domination of non-wetland agriculture in the study area (Table 4.3). Nearly 85% of the agricultural activities in the study area is applied to non-wetland agriculture. Non-wetland agriculture consists of forestry, plantation, dryland agriculture, and mixed garden. The percentage of agriculture types are shown in Fig. 4.11.

forestry 20%

wet plantatio land n+mix 30% garden dryland 48% agricultu non- re wet 32% land 70%

(Source: Statistic Center Bureau of Central Java, 2013) Fig.4.11: Land uses percentage in Central Java Province

4.3.3 Economy and livelihood The economy may influence human behavior on soils utilization. The economy in the study area is categorized into low to moderate level. This economic condition often determines people to utilize or to cultivate the land to fulfill their basic needs.

Types of livelihood set the economic growth of the study area. The types of livelihoods in the study area can be classified into agricultural and non-agricultural sectors. The agricultural sectors are the dominant driving wheel of economics in the study area. They consist of paddy

72 field, plantation, dryland agriculture, mixed garden, fishery and animal husbandry. Almost all people conduct the agricultural activities either as a primary or as a secondary job. According to BPS (Statistic Center Bureau) of Central Java Province (2013), more than 38% of people in Purworejo choose agricultural activities as their main livelihood; followed by trading and public services (25% and 16%). These conditions are consistent with the livelihoods in Wonosobo and Magelang.

The types of livelihood in the study area are also determined by gender. Regarding gender, BPS (Statistic Center Bureau) of Wonosobo Regency (2010) shows that job opportunities between male and female are quite balanced which is about 94%. However, the labor participation rate in 2010-2012 was dominated by male rather than female. Compared to Purworejo and Magelang, female mainly has a job in trading and industrial sector, whereas, male, mainly has a job in agriculture sector.

To address the existing conditions, urbanization seems to be a wise choice to gain a better life for local people in the study area. The paradigm of urbanization has influenced most of local people in Bogowonto, especially young people. This urbanization paradigm, lately, causes a secondary impact on the agricultural sector growth in Bogowonto. The urbanization has caused a declining of young people who may continue the farming culture. The fact is that there are only older people who remain to continue to cultivate their land. And thus it becomes a serious problem in the study area nowadays.

Photo credit by: NurAinun Pulungan, 2013 Fig.4.12: Sengon and Cinnamon as the wood commodity in the study area

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As the solution, most of paddy fields nowadays are shifted into non-wetland agriculture in order to solve the limited manpower. Woody production (Fig.4.12) is a wisely alternative to solve the limited number of farmers. Woody plantation has less land management than paddy field. Sengon (Albizia chinensis), teak (Tectona grandis), and cinnamon (Cinnamomum verum) are the main plantations of wood commodity in the study area. These plants are widely cultivated because they grow up faster in any soil and it doesn’t need an intensive management.

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CHAPTER 5 RESULTS: Soil Variations in the Central Part of Bogowonto Catchment

5.1 Overview

The chapter explains about the characteristics and the categories of soil variation in the transitional zone of Menoreh Tertiary Volcanic Systems, Halang Tertiary Structural Systems, and Sumbing Quaternary Volcanic Systems. This chapter is intended both to answer the research questions and to achieve the objectives as mentioned in section 1.3. Overall, the explanation in this chapter is focused on the spatial variation of soils, properties of soils, genesis of soil parent material, and types of soil formation. Those focuses are going to be explained in detail in the section 5.2 to 5.5.

The soil variation in a transition zone, such as the study area needs a concept which describes the configuration of a landscape. The soil variation discussion in a transition zone not only requires the understanding of soil-slope relation, but also needs the understanding of soils related to soil parent material and to morphodynamic processes on the landscapes. Therefore, the soil variation discussion in a transition zone, such as the study area is better approached by a soil-scape concept.

In the soil-scape concept, the landscape changes become a crucial aspect for soil formation and soil development. The landscape systems in the study area are mainly based on the geological processes that form the areas. The landscape changes affect the soil parent material deposition and redistribution. The landscape changes can be naturally occurred due to geomorphologic process and can be artificially induced by human activities on the slope surface. In the study area, the landscape changes frequently occur due to landslide and erosion processes. The landscape changes also can be caused by agricultural land management practices. Furthermore, the landscape changes will closely link to soil development.

Soils in the study area are various spatially and genetically because they are located in three different landscape systems, i.e. Quaternary volcanic-structural, Tertiary volcanic- structural and Tertiary structural. The spatial variation of soils was determined by the main landscape systems as mentioned in section 4.2.4, and will be explained in section 5.2. This spatial variation of soils results in a large variety of soil profile development and soil 75

properties (section 5.3). According to the soil properties analysis, it is found that there is a high variability of soil parent material leading to genesis variation of soils. The genesis variation of soils is categorized into the weathered bedrocks material, volcanic ash material, altered bedrocks material, and redistributed soil material (section 5.4). As a result, soils in the study area mostly have been experienced with several series of soil formation (section 5.5). The variation of soil formation in the study area is often formed as residual soils overlaid by burial volcanic ash deposit or burial slope surface deposit. In addition, the variation of soil formation also can be caused by intensive agriculture land management practices.

Due to the described soil properties, the soils in the study area can be categorized into: (i) soils derived from soil parent material transformation, (ii) soils redistributed by landslides and/or human. The morphological and physical properties among different soil units are clearly recognized by color differentiation and vertical textural contrast. The comparison of chemical properties among different soil units indicates that there is no noticeable variation in respect to slope position. The soil chemical properties variation is mostly controlled by relief variation which affects the vertical water movement within the soil profile. Moreover, in relation to mineralogical properties, kaolinite seems to be the most dominant clay mineral in the soil samples. There is an appearance of halloysite in some volcanic ash soils, however, its presence is often biased and mostly overlap with kaolinite. Therefore, it assumes that the volcanic ash soil in the study area is on the transferring stage from noncrystalline structure (e.g. halloysite) into a crystalline structure (e.g. kaolinite) due to intensive weathering processes.

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5.2 Spatial variation of soils

This subchapter focuses on applying soil-scape concept in the study area. The soil- scape concept (see the earlier section of 2.2.2) is intended to describe the spatial variation of soils in the study area because this concept may reveal the spatial pattern of soil characteristics within the landscapes. With regards to the soil-scape concept, landscape features in this study are approached by landform segmentation (see section 3.1). The assessment of landform segments in the study area is described in Table 5.1.

There are seven landforms segmented in the study area. Those landform segments vary in slope position, parent rocks, and geological processes. Slope positions are divided into upper, middle, and lower parts of the slope through considering the elevation and river order. Parent rocks strongly depend on geological processes in the study area which consist of three main processes that form the landscape systems in the study area, i.e. Quaternary volcanic-structural, Tertiary volcanic-structural and Tertiary structural, as addressed on section 4.5.3. Those geological processes provide a variety of parent rocks and cover materials deriving from the Quaternary Sumbing volcano system, Tertiary Menoreh volcano system, and Tertiary Halang structural system (see section 4.5.2 and Fig.5.1). Variation of parent rocks and cover materials create various geomorphic units with varying relief and slope steepness (see Fig.5.2 and Table 5.2), and thus cause geomorphological processes on the slope surfaces. All variations in landform segments are intended to distinguish the landscapes in the study area, in order to clearly describe the relationship between soils and landscape in more detail.

There are 43 sites of soil profile representing the landform segments. These representative sites of soil profile were chosen to describe the soil-landscape relation in the study area. Table 5.2 presents the landscape characteristics of soil profiles within each landform segment. The landscape characteristics of soil profiles were assessed based on qualitative assessment in the field.

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Fig.5.1: Map of landscape systems of the study area 78

Table 5.1: Characteristics of landform segments of the study area

Landscape Slope Parent Dominant cover Geomorphic unit Elevation Landform Landform system position rocks material types (msl) description segment Quaternary Upper slope Andesitic Volcanic ash Steep volcano slope and 450-625 Upper slope of U-Q-VS Volcanic- breccias deposit and plain areas Quaternary volcanic- structural landslide- structural hills (Q-VS) redistributed soil materials Quaternary Middle Andesitic Volcanic ash Moderately steep volcano 350-500 Middle slope of M-Q-VS Volcanic- slope breccias deposit slope Quaternary volcanic- structural structural hills (Q-VS) Tertiary Upper slope Andesitic Weathered Steep hillslope 450-1012.5 Upper slope of U-T-VS Volcanic- breccias andesitic breccias Tertiary volcanic- structural and altered structural hills (T-VS) andesitic breccias Tertiary Middle Andesitic Weathered Wavy hillslope 300-500 Middle slope of M-T-VS Volcanic- slope breccias and andesitic breccias Tertiary volcanic- structural andesite and landslide- structural hills redistributed soil (T-VS) materials Tertiary Lower slope Andesitic Weathered Moderately steep hillslope 250-450 Lower slope of L-T-VS Volcanic- breccias andesitic breccias Tertiary volcanic- structural structural hills (T-VS) Tertiary Lower slope Tuff, marl, Weathered tuff, Moderately steep hillslope 200-400 Lower slope of L-T-S Structural sandstone weathered marl, Tertiary structural (T-S) weathered hills sandstone Fluvial Lower slope Andesitic Colluvium and Plain areas 67.5-150 Fluvio-colluvial CP (F) breccias weathered tuff plain

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Fig.5.2: Map of landform segments of the study area and soil profile sites 80

Landform segmentation was firstly assessed based on the three systems which are resulting from geological processes in the study area. Those three systems (Fig.5.1) i.e. Quaternary Sumbing volcano systems, Tertiary Menoreh volcano systems, and Tertiary Halang structural systems are the major systems that may reflect the landscapes in the study area. Those three systems are segmented by slope differentiation.

Landform segmentation of Quaternary Sumbing volcanic systems is divided into two segments. Those segments are upper slope of hills (U-Q-VS) and middle slope of hills (M-Q- VS), as shown in Fig.5.2. The segments of upper slope of hills generally show the predominant of thick soil depths (at most about 200cm towards C horizon), as shown in Table 5.2. It is because this segment is mainly dominated by smooth relief, such as plain up to undulating relief. Thick soil depth in this segment is a contradictory to the common soil depth setting in upper slope of the hills. The smooth relief in this segment strongly influences the soil depths although it is located on the upper slope position. This smooth relief leads to maintain the surface soil removal on the upper slope position, and thus causes less intensive of slope surface processes. As a consequence, this relief setting keeps the surface horizon thick.

The segment of middle slope of hills shows shallower soil depths than those in the segment of upper slope of hills. It is also a contradictory to the common soil depths in the middle slope of hills where usually have thicker soil depths than those in the upper slope of the hills. As a consequence, the rough relief causes this segment has various depths of soils ranging from 45 – 186 cm towards C horizon, as shown in Table 5.2. The shallow soil depths in the middle slope of hills are mainly due to the domination of rough relief (see Fig.5.2). The rough relief in this segment is indicated by a strong notch on the most hill slopes. This rough relief leads to intensive slope surface processes causing surface soil removal. Therefore, it shows that the rough relief setting mainly controls the soil development in this segment.

Landform segmentation of Tertiary Menoreh volcano systems is divided into three segments. The segments are upper slope of hills (U-T-VS), middle slope of hills (M-T-VS), and lower slope of hills (L-T-VS), as illustrated in Fig.5.2. Unlike the segments in Quaternary Sumbing volcano systems, the segments of upper slope of hills in Tertiary Menoreh volcano-

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Table 5.2: Landscape characteristics of soil profiles within the landform segments

Soil Slope Parent Soil Parent Slope Profile Land Utility Profile position Relief Rock Material steepness Depth (Types) number

(cm) Landform Q-VS segment Andesitic Volcanic ash Uncultivated land 6% 191 9 breccias materials (bushes/shrubs) Andesitic Cultivated land Volcanic ash breccias 8% 173 (dryland 29 materials agriculture) Undulating Andesitic Volcanic ash Cultivated land slope 10% 157 35 breccias materials (paddy field)

Andesitic Cultivated land Volcanic ash breccias 20% 94 (dryland 28 materials agriculture) Andesitic Altered andesitic Uncultivated land 11% 274 11 breccias breccias (bushes/shrubs) Andesitic landslide- Cultivated land breccias redistributed soil 6% 176 19 (mixed garden) materials Andesitic landslide- Cultivated land breccias redistributed soil 7% 176 22 (mixed garden) materials Andesitic Volcanic ash Moderately Uncultivated land 18% 134 1 breccias materials steep slope (bushes/shrubs)

Andesitic Weathered Uncultivated land breccias andesitic 20% 212 5 (bushes/shrubs) breccias Andesitic Volcanic ash Uncultivated land Steep slope 33% 220 10 breccias materials (bushes/shrubs) Andesitic Weathered UPPER PART UPPER Cultivated land breccias andesitic 14% 74 33 (mixed garden) breccias Andesitic landslide- Cultivated land breccias redistributed soil 27% 53 18 (mixed garden) materials Andesitic landslide- Uncultivated land breccias redistributed soil 31% 63 24 (bushes/shrubs) materials T-VS

Andesitic Undulating Altered andesitic Uncultivated land breccias slope 13% 91 12 breccias (bushes/shrubs) Andesitic Altered andesitic Moderately Cultivated land 15% 102 37 breccias breccias steep slope (mixed garden) Andesitic Weathered Cultivated land breccias andesitic Steep slope 29% 87 39 (mixed garden) breccias Andesitic Volcanic ash Uncultivated land breccias materials 41% 188 4 (bushes/shrubs)

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Q-VS

Andesitic Undulating Volcanic ash Uncultivated land breccias slope 8% 276 6 materials (bushes/shrubs)

Andesitic Cultivated land Volcanic ash breccias 11% 121 (dryland 36 materials agriculture) Andesitic Weathered Moderately Uncultivated land breccias andesitic 16% 186 16 steep slope (bushes/shrubs) breccias Andesitic Weathered Cultivated land breccias andesitic 20% 96 34 (mixed garden) breccias Andesitic Landslide- Cultivated land breccias redistributed soil 20% 98 (dryland 20 materials agriculture)

Andesitic Landslide- Cultivated land

breccias redistributed soil 25% 45 (dryland 17 materials agriculture) T-VS

Andesitic Altered andesitic Undulating Cultivated land 11% 148 15

breccias breccias slope (mixed garden) MIDDLE PART MIDDLE Andesitic Weathered Cultivated land Moderately breccias andesitic 18% 109 (dryland 41 steep slope breccias agriculture) Andesitic Weathered Cultivated land breccias andesitic 35% 84 43 (mixed garden) breccias Andesitic Weathered Cultivated land breccias andesitic 47% 67 (dryland 38 breccias agriculture) Andesite Landslide- Cultivated land redistributed soil Steep slope 20% 73 26 (mixed garden) materials Andesitic Weathered Uncultivated land breccias andesitic 22% 138 13 (bushes/shrubs) breccias Andesitic Landslide- Cultivated land breccias redistributed soil 86 (dryland 23 materials agriculture) T-VS

Andesitic Cultivated land Altered andesitic Moderately breccias 15% 164 (dryland 14 breccia steep slope agriculture) Andesite landslide- Cultivated land redistributed soil Steep slope 51% 74 21 (mixed garden) materials Andesitic Weathered

LOWER PART LOWER Uncultivated land breccias andesitic 53% 87 8 (bushes/shrubs) breccias

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Soil Parent Soil Parent Slope Profile Land Utility Profile Relief Rock Materials steepness Depth (Types) number (cm) T-S

Tuff Weathered tuff Undulating Cultivated land 14% 91 31 slope (paddy field) Sandstone Weathered Cultivated land sandstone 13% 84 (dryland 32 agriculture) Sandstone landslide- Cultivated land redistributed soil 21% 73 (dryland 27

materials agriculture)

Tuff landslide- Cultivated land Moderately redistributed soil 9% 231 (dryland 25 steep slope materials agriculture) Sandstone Weathered Cultivated land sandstone 17% 106 (dryland 7

LOWER PART LOWER agriculture) Tuff Cultivated land Weathered tuff 18% 78 (dryland 42

agriculture Marl Cultivated land Weathered marl 22% 96 (dryland 2

agriculture) F

Andesitic Weathered Moderately Cultivated land breccias andesitic 14% 88 30 steep slope (paddy field) breccias Tuff Cultivated land Weathered tuff Steep slope 29% 41 (dryland 3

agriculture)

systems have shallower soil depth. However, the segments of upper slope of hills have thicker soil depth than that in the segments of middle and lower slopes of hills. It is due to the fact that the segments of upper slope of hills do not have the relief as rough as that in the segments of middle and lower slopes of hills (see Fig.5.2). The rough relief in the segments of middle slope of hills is shown by the wavy hills, whereas, that in the segments of lower slope of hills is shown by the predominance of steep hill slopes. The impact of this rough relief is indicated by a strong notch on the most hill slopes. This rough relief leads to intensive slope surface processes causing surface soil removal. As a consequence, this rough relief results in shallower soil depth than that of the segments of upper slope of hills. 84

The landform segmentations in the lower slope of hills are differentiated into the lower slope of Tertiary volcanic-structural hills (L-T-VS) and lower slope of Tertiary structural hills (L-T-S), as shown in Fig.5.2.Those segmentations are derived from the same deposition period of soil parent materials while they consist of different types of soil parent materials. Different types of soil parent materials at those segmentations do not give a significant difference on soil depth. These landform segmentations consist of various soil parent materials, i.e. weathered andesitic breccias, weathered tuff, weathered marl, and weathered sandstone.

There are various soil depths in the lower slope of hills segment. Soil depths in this segment range from 80 - 230 cm towards C horizon, as shown in Table 5.2. However, it is also a contradiction to the common soil depths in the lower slope of hills which usually have a thick soil as it is a depositional area. The wide range of soil depths in the lower slopes of the hills seems to be caused by a great variety of relief in this segmentation (see Fig.5.2). The lower slope of the hills has a combination of smooth and rough reliefs. Therefore, the lower slope of hills is influenced by various intensities of slope surface processes, and thus controls the surface soil removal.

Each segment consists of different types of soil parent materials such as volcanic ash materials, weathered andesitic breccias, altered andesitic breccias, and landslide-redistributed soil materials. Differentiation of soil parent materials in each segment results in various depths within soil profile. Based on the soil parent materials, the landform segment of having volcanic ash materials shows thicker soil depth than that of having weathered andesitic breccias. It is because the landform segment of having volcanic ash materials has more rapid weathering process than that of having weathered andesitic breccias (Fiantis et al., 2001). As noted in Table 5.2, the landform segment of having volcanic ash materials mainly has soil depth >200cm towards C horizon, whereas, the landform segment of having weathered andesitic breccias has the average soil depth about 100cm.

Differences in soil parent materials within the segments may result in the variation of soil morphological characteristics, as shown in section 5.3. The segmentation of volcanic ash materials presents the dominant silt texture. However, some profiles in this segmentation show more advance weathering level indicated by the dominance of clay texture. This segmentation has the dominance of weak and single-grain structures, slightly sticky and a 85 slightly plastic in wet consistency and firm in moist consistency. In contrast to the segmentation of volcanic ash materials, the segmentation of weathered andesitic breccias presents the variation of soil textures, i.e. loam, silt loam, silt, clay loam, and clay. This segment is supported by weak grade in soil structure under varying wet consistency from no sticky and no plastic to very sticky and very plastic; and also varying moist consistency from very friable to very firm. In other side, the segmentation of tuff- and marl-weathered sandstone produces silty clay and silt loam textures. This segmentation shows the dominance of moderate grade in soil structure with slightly sticky and slightly plastic in wet consistency; and firm in moist consistency.

Colluvial plain segment (CP) describes a medium soil depth compared to other segments. Colluvial plain segment has 80 cm depth of soils towards a series of C horizon. The depth of soil in this segment reflects that the depositional and the removal processes are balance. However, its position in the toe slope causes this segment is very prone to river erosion and deposition. The influence of both processes causes the soil structure in this segment is dominated by single grain, in addition, the wet consistency in this segment is slightly sticky and slightly plastic, while dry consistency in this segment is friable (Table 5.2). 86

5.3 Soil development The soil development in this study was characterized by soil profile investigation and soil property analysis. The soil properties were analyzed morphologically, physically, chemically, and mineralogically, as explained in section 5.3.1. The soil profile development was assessed quantitatively through profile development index (PDI), as discussed in section 5.3.2. Overall, the soil development was described based on 43 profile sites. With regard to the results, the soil development in the study area leads to the categorization of: (1) residual soils and (2) redistributed soil material. In the following, the soil development in the study area will be presented according to these categories. 5.3.1 Analysis of soil properties 5.3.1.1 Residual soils

In this study, 16 sites were investigated for residual soils (Table 5.3). The residual soils are the soils which have no disturbance from slope surface deposits or human influences during the profile development. Thus, the residual soils are characterized by the continuity of soil profile development from their in-situ soil parent material. The analysis of the residual soil properties will be described in section (i) – (iii), and the recapitulation of the residual soil properties will be done in section (iv). The profiles of the residual soils were chosen based on the variation of soil parent material such as weathered parent rock material, weathered volcanic ash material, and altered parent rocks material. The explanation of the soil parent material characteristics will be given later in subchapter 5.4.

(i) Morphological and physical properties

The morphological properties are the soil properties which were observed directly in the field. The morphological properties assessed in this study are soil color, consistency, structure, and texture. The morphological properties are closely related to the physical properties. To complete the qualitative analysis of texture, the particle size distribution analysis was also conducted in the laboratory. Another physical property analyzed in the laboratory was COLE Index.

The soil color, in this study, was used to characterize the morphological property. It is because the soil color is an indicator for soil parent material differentiation in the field. The differences of soil color indicate the soil parent material variations (Fig.5.3). Moreover, the soil color is also an indicator for soil horizon differentiation. The differences of soil color in a horizon are determined by the content of organic matter and 87

of free-iron oxide (Foth, 1994). According to Table 5.3, A-horizons usually present a darker color than their soil parent materials due to higher organic contents. This darker color is shown by its lower soil value than that of sub-surface horizon. However, B- horizons usually show a lighter color than A-horizons as a result of illuviation, as shown in profile 4, 7, 9, 11 and 15. Therefore, the soil color variation within a profile also describes the stage of soil development, as shown in Table 5.3.

The brownish soil color is usually presented by volcanic materials i.e. andesitic breccias and volcanic ash deposit (see Fig.5.3). Yellow-brown to red-brown soil color is resulting from the activity of iron compound (Schaetzl and Anderson, 2005). The yellow- brown (yellowish) soil color is usually formed in the soils where Fe is reduced indicated by Hue 10 YR, as shown in profile 1, 4, 5, 8, 9, 10, 13, and 16 (Table 5.3). The red-brown (reddish) soil color is usually formed in the soils where Fe is oxidized indicated by Hue 7,5YR, as shown in the profile 2, 3, 6, and 7 (Table 5.3).

Profile 1 Profile 11 Profile 5 Profile 3 10 YR 5/6 5 YR 5/6 10 YR 3/6 7.5 YR 6/4 Volcanic ash Altered andesitic Weathered Weathered tuff material breccias material andesitic breccias material material Photo credit by: NurAinun Pulungan, 2013 Fig.5.3: Soil profile examples showing the soil color variation due to different soil parent materials The grayish soil color in the study area is usually shown by weathered marine sedimentary material. The grayish soil color is shown in the soils developed on marl, tuff, and sandstone (see Table 5.3). The grayish soil color is described by low soil chrome, as shown by the profile 2 and 3 (Table 5.3). The grayish soil color can be an indicator of loss of Fe due to water inundation in marine sedimentary material, and consequently produces the grayish or pale color (Schaetzl and Anderson, 2005). 88

Another specific soil color is shown by the soils developed on altered andesitic breccias material. The reddish to orange soil color is often found in the altered material indicated by Hue 2,5YR and 5YR, as shown in profile 6, 11, 12, 14 and 15 (Table 5.3). As the study area was affected by a hydrothermal alteration (see explanation in section 5.5), the water in the hydrothermal alteration takes a part in dissolving and removing the rock minerals, of which called as metasomatism process (Carlson et al., 2009). This process is described in the reactions below (Pirajno, 2009, p.91), where K-feldspar as the main mineral in most of parent rocks in the study area will release some elements during the hydrothermal alteration and remain the Quartz. Furthermore, during K+ for Na+ exchange, there is Fe released from the lattice and oxidized to form hematite producing the reddish coloration (Kinnaird, 1985 in Pirajno, 2009, p.105), as shown in Fig.5.3 (profile 11) and Fig.5.4. The reddish color is caused by less of oxygen content during oxidation process of altered material. However, in some areas, the white color also can be formed in the altered material, as shown in Fig.5.5. The white color is mainly caused by the bases leaching during alteration process, and thus results in Silica enrichment (Pirajno, 2009, p.103).

+ - 1.5KAlSi3O8 + H2O  0.5KAl3Si3O10 (OH)2 + K + 3SiO2 + OH …………….. (1) (K-feldspar) (K-mica) (Quartz) + - H + OH  H2O ……………………………………………………………………. (2) + + 1.5KAlSi3O8 + H  0.5KAl3Si3O10 (OH)2 + K + 3SiO2 …………………………(3) Thus, when (1) + (2)  in the sum reactions (3), K+ is released while H+ is consumed

Photo credit by: NurAinun Pulungan, 2015

Fig.5.4: Reddish coloration in altered material due to Fe oxidation and hematite development during hydrothermal alteration 89

solum

Altered parent material

Photo credit by: NurAinun Pulungan, 2015 Fig.5.5: White coloration of altered material due to Silica enrichment during hydrothermal alteration

The soil consistency and soil structure were also used to characterize the morphological properties in this study. According to Table 5.3, the consistency of the soils mainly shows the same characteristics as the consistency of their soil parent material. Only some profiles show the increased level of consistency and structure of the soil parent material compared to those of the soils. Profile 4, 7, 9, and 15 illustrate the gradual increasing of consistency and structure grade of the soil parent material and of the soils (see Table 5.3). This situation indicates that the soils are presenting an initial stage of soil development. 90

Table 5.3: Morphological and physical properties of residual soils based on field assessment

Structure Consistency Soil parent Horizon Color No Soil type* Texture material (depth in cm) (Munsell) Type Grade Wet Moist

Leptic A (0-27) 10 YR 4/4 Silt Crumb Weak slightly sticky – no plastic very friable 1 Volcanic ash AC (27-68) 10YR 4/6 Silt Crumb Moderate slightly sticky – no plastic friable material Eutric C (68-134+) 10YR 5/6 Silt loam Structureless Single grain slightly sticky – no plastic friable Leptic A (0-21) 7,5YR 4/2 Silty clay Crumb Moderate sticky - plastic Firm 2 Weathered Regosols marl Eutric C (21-96+) 7,5YR 5/2 Silty clay Structureless Massive very sticky - plastic very firm Leptic A (0-19) 7,5YR 6/4 Silt loam Crumb Weak slightly sticky – no plastic Friable Weathered 3 Regosols tuff Eutric C (19-41+) 7,5YR 7/2 Silt loam Structureless Massive sticky – no plastic Firm A (0-28) 10YR 3/4 Silt Crumb Weak slightly sticky - slightly plastic very friable Volcanic ash material - Lixic Bw (28-49) 10YR 4/4 Clay Blocky Moderate sticky - slightly plastic friable 4 Weathered C (49-92) 10YR 4/6 Silt loam Structureless Single grain slightly sticky - slightly plastic friable

andesitic Eutric 2Bt (92-160) 10YR 3/6 Clay Blocky Moderate sticky – slightly plastic firm breccias 2C (160-188+) 10YR 3/6 Loam Structureless Massive slightly sticky – no plastic firm Weathered Leptic A (0-30) 10YR 3/4 Silt loam Crumb Weak slightly sticky – no plastic friable 5 andesitic Regosols

breccias Eutric C (30-212+) 10YR 3/6 Silt loam Structureless Massive slightly sticky – no plastic firm A (0-31) 5 YR 4/6 Silty clay Crumb Moderate sticky-plastic firm C (31-74) 5 YR 5/8 Silty clay loam Structureless Moderate very sticky – very plastic very firm 6 Volcanic ash Haplic material - 2B1 (74-97) 7,5 YR 5/8 Clay Blocky Moderate very sticky – very plastic very firm Altered Nitisols

andesitic Rhodic 2B2 (97-170) 7,5 YR 5/6 Clay Blocky Moderate very sticky – very plastic very firm

breccias 2BC (170-199) 7,5 YR 7/6 Clay Blocky Moderate very sticky – very plastic very firm 2C (199-276+) 5 YR 7/1 Clay Structureless Hard very sticky – very plastic very firm 91

7 Weathered Lixic A (0-28) 7,5YR 4/6 Loam Crumb Moderate slightly sticky – no plastic friable sandstone Nitisols Bw (28-47) 7,5YR 6/6 Silt loam Blocky Moderate sticky – no plastic Firm Eutric C (47-106+) 7,5YR 5/8 Loam Structureless Massive sticky – no plastic very firm Weathered Leptic A (0-24) 10YR 3/6 Silt loam Crumb Weak slightly sticky – no plastic friable 8 andesitic Regosols breccias Eutric C (24-87+) 10YR 4/4 Sandy loam Structureless Massive slightly sticky – no plastic firm A (0-22) 10YR 4/3 Silt loam Crumb Weak slightly sticky - slightly plastic very friable Lixic Bw (22-40) 10YR 5/4 Silty clay loam Blocky Moderate sticky - slightly plastic friable Volcanic ash Nitisols C (40-87) 10YR 4/4 Silt loam Structureless Single grain slightly sticky - slightly plastic friable 9 material Eutric 2C (87-149) 10YR 5/4 Silt loam Structureless Single grain slightly sticky - slightly plastic friable 3C (149-191+) 10YR 4/4 Silt loam Structureless Single grain slightly sticky - slightly plastic friable A (0-29) 10YR 4/3 Silt loam Crumb Weak slightly sticky - slightly plastic very friable

Leptic C (29-78) 10YR 5/6 Silt loam Structureless Single grain slightly sticky - slightly plastic friable Volcanic ash Regosols 2Bw (78-96) 10YR 4/6 Silty clay loam Blocky Moderate sticky - slightly plastic friable 10 material Eutric 2C (96-168) 10YR 5/6 Silt loam Structureless Single grain slightly sticky - slightly plastic friable 3C (168-220+) 10YR 5/4 Silt loam Structureless Single grain slightly sticky - slightly plastic friable A (0-27) 2,5YR 3/4 Clay Crumb Moderate very sticky – very plastic firm B1 (27-59) 2,5YR 4/6 Clay Blocky Moderate very sticky – very plastic very firm Altered Haplic B2 (59-90) 5YR 5/8 Clay Blocky Moderate very sticky – very plastic very firm 11 andesitic Nitisols breccias Rhodic B3 (90-157) 2,5YR 4/8 Clay Blocky Moderate very sticky – very plastic very firm BC (157-216) 5YR 4/6 Clay Blocky Moderate very sticky – very plastic very firm C (216-274 +) 5YR 5/6 Clay Structureless Hard very sticky – very plastic very firm Altered Haplic A (0-26) 5YR 4/6 Clay Crumb Moderate very sticky – very plastic very firm 12 andesitic Nitisols breccias Rhodic C (26-91+) 5YR 5/6 Clay Structureless Massive very sticky – very plastic very firm Weathered Leptic A (0-23) 10YR 3/4 Silt loam Crumb Weak slightly sticky – no plastic friable 13 andesitic Regosols C (23-138+) 10YR 3/6 Silt loam Structureless Massive slightly sticky – no plastic firm 92

breccias Eutric

A (0-28) 5YR 4/4 Clay Crumb Weak sticky - plastic friable Altered Haplic 14 andesitic Nitisols AC (28-58) 5YR 4/6 Clay Blocky Moderate sticky - plastic firm breccias Rhodic C (58-164) 5YR 5/8 Clay Structureless Massive very sticky – very plastic very firm

Altered Haplic A (0-27) 5YR 4/6 Clay Crumb Moderate very sticky – very plastic firm 15 andesitic Nitisols Bt (27-69) 5YR 5/4 Clay Blocky Moderate very sticky – very plastic very firm breccias Rhodic C (69-148+) 5YR 6/6 Clay Structureless Massive very sticky – very plastic very firm Weathered Leptic A (0-27) 10YR 4/6 Silt loam Crumb Weak slightly sticky – no plastic friable 16 andesitic Regosols breccias Eutric C (27-186) 10YR 4/4 Silt loam Structureless Massive slightly sticky – no plastic firm *Soil types are based on World Reference Base criteria (WRB, 2007) 93

To complement the soil consistency and soil structure assessments, the texture analysis was also conducted to describe the soil development stage. The changes of texture within a profile may present a particular stage of soil development. Based on Table 5.4, most of the soil profiles show the same texture of C horizon and A horizon. This situation indicates that the soils are presenting an initial stage of soil development. Only some soils developed on weathered parent rock material show a gradual level of the texture between C horizon and surface/sub-surface horizon, for instance profile 1, 4, and 8. These profiles show that texture of the surface/sub-surface horizon is finer than texture of the C horizon. On the other side, in the soils developed on altered parent material, both textures of the surface horizon and the C horizon are dominated by clay texture because the altered parent material is mainly contained by clay-particle (see Table 5.4). There are only limited profiles (e.g. profile 4, 7, 9, 11, and 15) showing the accumulation of silicate-clay indicated by cambic- and argillic horizons (Table 5.4). This is caused by the active slope surface processes that lead to less developed soil profiles both in the depletion- and in the accumulation zones, and hence result in the initial stages of soil development.

Table 5.4: Physical properties of residual soils based on laboratory analysis

Particle size distribution Soil parent Horizon No COLE material (depth in cm) Texture % clay % silt % sand Index < 2µm 2-50 µm >50-2000 µm

A (0-27) Silt 10.4 80.4 9.2 0.2 1 Volcanic AC (27-68) Silt 5.8 81.6 12.7 0.2 ash material C (68-134+) Silt loam 8.2 67.1 24.7 0.2 2 Weathered A (0-21) Silty clay 42.2 55.1 3.8 0.2 marl C (21-96+) Silty clay 41.5 50.6 7.9 0.2 Weathered A (0-19) Silt loam 10.8 70.8 18.4 0.2 3 tuff C (19-41+) Silt loam 8.6 76.9 14.5 0.2

Volcanic A (0-28) Silt 20.7 70.1 9.2 0.2 ash material Bw (28-49) Clay 41.8 37.6 20.7 0.2 4 - C (49-92) Silt loam 13.6 61.3 25.1 0.2 Weathered andesitic 2Bt (92-160) Clay 46.6 32.6 20.8 0.3 breccias 2C (160-188+) Loam 25.3 46.4 28.4 0.2 Weathered A (0-30) Silt loam 5 18.2 70.6 11.2 0.2 andesitic

breccias C (30-212+) Silt loam 11.3 73.2 15.4 0.2 6 Volcanic A (0-31) Silty clay 48.6 36.5 14.9 0.3 94

ash material C (31-74) Silty clay loam 29.3 50.2 20.5 0.2 - Altered andesitic 2B1 (74-97) Clay 79.4 16.7 3.9 0.3 breccias 2B2 (97-170) Clay 81.5 16.3 2.2 0.3 2BC (170-199) Clay 83.5 13.8 2.7 0.3 2C (199-276+) Clay 80.5 15.7 3.8 0.3 A (0-28) Loam 17.1 59.0 24.0 0.2 7 Weathered sandstone Bw (28-47) Silt loam 17.5 63.2 19.2 0.2 C (47-106+) Loam 16.9 61.1 22.0 0.2 Weathered A (0-24) Silt loam 12.8 51.3 35.9 0.2 8 andesitic C (24-87+) breccias Sandy loam 4.0 36.7 59.3 0.2 A (0-22) Silt loam 27.2 55.6 17.2 0.2 Bw (22-40) Silty clay loam 38.3 52.6 9.1 0.2 Volcanic 9 C (40-87) Silt loam 23.4 54.2 22.4 0.2 ash material 2C (87-149) Silt loam 18.8 50.3 30.9 0.2 3C (149-191+) Silt loam 17.2 69.6 13.2 0.2 A (0-29) Silt loam 17.2 69.6 13.2 0.2 C (29-78) Silt loam 14.1 70.8 15.1 0.2 Volcanic 10 2Bw (78-96) Silty clay loam 30.8 54.6 14.6 0.3 ash material 2C (96-168) Silt loam 19.8 50.3 29.9 0.2 3C (168-220+) Silt loam 16.9 52.3 31.8 0.2 A (0-27) Clay 63.6 20.5 15.9 0.3 B1 (27-59) Clay 76.4 18.0 5.6 0.3 Altered B2 (59-90) Clay 87.3 11.6 1.1 0.3 11 andesitic breccias B3 (90-157) Clay 83.2 15.9 0.9 0.3 BC (157-216) Clay 62.4 31.2 6.4 0.3 C (216-274 +) Clay 63.0 23.5 13.5 0.3 Altered A (0-26) Clay 66.6 27.0 6.4 0.2 12 andesitic Clay breccias C (26-91+) 60.1 30.4 9.5 0.2 Weathered A (0-23) Silt loam 11.6 61.5 26.9 0.2 13 andesitic Silt loam breccias C (23-138+) 10.9 55.0 34.0 0.2 A (0-28) Clay 66.2 25.0 8.8 0.3 Altered 14 andesitic AC (28-58) Clay 71.5 21.7 6.8 0.3 breccias C (58-164) Clay 57.6 32.7 9.7 0.2 Clay Altered A (0-27) 77.5 18.5 4.1 0.3 15 andesitic Bt (27-69) Clay 85.7 12.1 2.2 0.3 breccias C (69-148+) Clay 58.2 34.5 7.3 0.3 Weathered A (0-27) Silt loam 14.0 80.3 5.5 0.2 16 andesitic Silt loam breccias C (27-186) 10.8 70.5 18.5 0.2 95

The texture analysis was also conducted to differentiate the soil parent material types. In the study area, the textures in C horizons vary among different soil parent material types. According to Table 5.4, the weathered andesitic breccias- and the weathered sandstone material have predominantly coarse particle sizes shown by the majority texture of loam to sandy clay loam. This situation is performed by profile 5, 7, 8, 13, and 16. On the other side, the weathered marl material, the volcanic ash material, and the altered andesitic breccias material are dominated by fine particle sizes. However, each of them shows a distinct majority of fine particles resulting in different textures (see Table 5.4). The weathered marl material is characterized by the dominance of clay texture, as illustrated in profile 2; the volcanic ash material is characterized by the majority of silt loam texture, as presented in profile 1, 4, 9, and 10; while the altered andesitic breccias material also have a clay-rich texture, as shown in profile 6, 11, 12, 14 and 15 (Table 5.4).

The result of particle size analysis shows the dominance of clay- and silt loam textures. According to the results in Table 5.4, the high content of clay is mostly formed in soils developed on the altered parent rock material which is mostly indicated by > 60% of clay. This high content of clay could not be found in soils developed on any other soil parent materials. Such a high content of clay can only be explained due to alteration process. This alteration process releases the heat that induces an intensive transformation of primary minerals into secondary minerals (Bove et al., 1651, p.179). It shows that the alteration process of parent rock becomes the main decisive factor resulting in a high content of clay in certain soil profiles in the study area, as shown in profile 6, 11, 12, 14 and 15 (Table 5.4). The characteristics of altered parent rock are discussed in section 5.5.

The clay content within the soil profiles is not only the result of soil development processes but also the result of parent rocks weathering. Often, the clay content in the soils is formed due to intensive clay translocation within the soil profile. The clay content in the soils is usually described by the presence of B-horizon as shown in Profile 6, 7, 14 and 15. However, the clay content in the saprolite usually performs as the result of parent rocks alteration. The high content of clay in saprolite due to alteration is indicated by more than 60% of clay (see Table 5.4). Profile 2, 9, 10, 11, 12, 14 and 15 are examples of soil parent material deposition effect. The clay content is also related to the COLE index which can describe the mechanical properties of soils. COLE index in the study area are categorized into high level ranging from 0.15 – 0.32 (Table 5.4). 96

The high content of silt fraction leads to the majority of silt loam texture at most profiles. Profile 1, 3, 5, 9, 10, 13, and 16 are characterized by the dominance of silt fraction within the profiles (Table 5.4). The dominance of the silt fraction in volcanic ash deposit is mainly followed the domination of the silt-particle in the volcanic ash soils. However, the dominance of the silt fraction in weathered parent rock material depends on the dominant matrix composing the parent rocks, especially in the case of volcanic breccias rocks (Pettijohn et al., 1987, p.149). This condition then influences the dominating of minerals during soil development.

Profile 2 (marl) Horizon A Horizon C

Profile 7 (sandstone) Horizon A Horizon Bw

Horizon C

97

Profile 8 (andesitic breccias) Horizon A Horizon C

Profile 16 (andesitic breccia) Horizon C Horizon A

Fig.5.6: Horizon-based distribution of grain size of fine earth (<2mm) of selected soil profiles

The detailed silt analysis was also applied to complete the particle size distribution analysis. It was conducted automatically by laser diffraction technique and then the silt was classified based on the CSSC textural classification system (see section 3.3.3). This analysis was conducted because the silt is one of the predominant particle sizes in all profiles. This detail silt analysis shows that the tendency of silt sizes in the soils is strongly depended on the type of soil parent material. According to Figure 5.6, the distribution of silt sizes in the C horizons presents an asymmetric graphic showing the tendency of silt- sizes within a profile. The soil parent material of volcanic ash describes the similar pattern to that of weathered marl which is dominated by fine silt-size. This fine to medium silt- size is shown by the asymmetric graphic tending to the left. In comparison to volcanic ash; the soil parent material of weathered andesite, of weathered andesitic breccias, and of weathered sandstone is dominated by coarse silt-size. The domination of coarse silt-size is shown by the asymmetric graphic tending to the right. 98

(ii) Chemical properties

Soil chemical properties are various in the entire profiles. Soil chemical properties depend on the organic matter as well as the chemical properties of minerals in the soil parent material (Junge, 2001). Soil chemical properties of this study were characterized by soil organic matter (SOM), cation exchange capacity (CEC), pH, base saturation (BS), + + 2+ 2+ P2O5, C, N-total, and exchangeable base cations (Na , K , Ca , Mg ). The results of chemical properties analysis of the entire profiles are compiled in Table 5.5.

The amount of exchangeable base cations (Na+, K+, Ca2+, Mg2+) is strongly depending on the types of soil parent material. Figure 5.7 shows that the order of amount of exchangeable base cations among the soil parent material types is weathered tuff > weathered marl > weathered sandstone > weathered andesitic breccia > volcanic ash > altered andesitic breccias. These exchangeable base cations have the order value of Ca2+ > Mg2+ > K+ > Na+ (see Fig.5.8). This graphic shows that the content of Ca2+ is mostly above 6 me/100gr, Mg2+ ranges from 0.2 to 26.7 me/100gr, K+ ranges from 0.05 to 0.7 me/100gr, and Na+ is often lower than 0.1 me/100gr. The higher content of Ca2+and Mg2+ is affected by the ease mineral released of the plagioclase and calcite compounds. Consequently, the influence of soil parent material mainly results in the dominance of Ca2+and Mg2+, and thus produce a high value of those cations in the C-horizon (see Table 5.5).

Altered andesitic breccias

Weathered andesitic breccias

Weathered sandstone

Weathered tuff

Weathered marl

Volcanic ash materials

0 20 40 60 80 CEC (me/100gr) Mg2+ Ca2+ K+ Na+ Fig.5.7: CEC and exchangeable base cations of various soil parent materials

The amount of exchangeable base cations also has a close relation to the cation exchange capacity (CEC). The graphic illustrates that a greater amount of exchangeable base cations results in a higher CEC (see Fig.5.7 and Table 5.5). The cation exchange 99

Na+ K+ 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

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C C C C C C C

C C C C C C C C C

A A A A A A A A A

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Fig.5.8: Exchangeable base cations per horizon of residual soils 100

Table 5.5: Chemical properties of residual soils based on laboratory analysis

CEC Exchangeable base cations pH BS P2O5 SOM C N-total No Soil parent Horizon C/N + + 2+ 2+ material (depth in cm) Na K Ca Mg H2O KCl Ratio (me/ (%) (ppm) (%) (%) (%) 100gr) (me/100gr)

A (0-27) 38.4 0.02 0.06 11.8 3.4 6.0 4.5 39.8 4.8 4.3 2.5 0.9 2.7 1 Volcanic ash AC (27-68) 23.6 0.02 0.05 5.1 3.6 6.0 4.9 37.1 5.2 3.1 1.8 0.8 2.3 material C (68-134+) 20.7 0.02 0.05 6.1 4.2 6.3 4.2 50.0 5.6 2.9 1.7 0.9 1.9 2 Weathered A (0-21) 54.9 0.40 0.08 29.7 19.0 6.2 5.0 89.6 3.1 1.8 1.0 1.2 0.9 marl C (21-96+) 52.1 0.40 0.08 32.9 19.2 6.2 5.1 * 3.6 1.6 0.9 1.0 0.9 A (0-19) 64.1 0.17 0.50 49.7 24.3 7.0 5.6 * 1.5 2.0 1.1 0.9 1.3 3 Weathered tuff C (19-41+) 47.9 0.19 0.50 50.9 26.7 6.9 5.7 * 3.8 1.5 0.9 0.7 1.3 A (0-28) 30.2 0.02 0.06 7.6 4.9 5.9 4.6 41.7 2.3 3.4 2.0 1.0 1.9 Volcanic ash Bw (28-49) 25.6 0.03 0.06 7.8 4.2 5.9 5.1 47.2 2.9 2.6 1.5 0.8 1.9 material - 4 Weathered C (49-92) 23.1 0.03 0.07 8.3 3.9 6.0 5.3 53.2 3.8 2.1 1.2 0.6 2.0

andesitic 2Bt (92-160) 29.2 0.21 0.65 14.3 5.8 6.2 5.3 71.7 2.4 2.5 1.5 0.8 1.8 breccias 2C (160-188+) 26.4 0.23 0.68 15.5 6.8 6.2 5.4 87.9 2.9 2.4 1.4 0.6 2.3 Weathered 5 A (0-30) 18.3 0.18 0.51 12.1 6.2 6.5 5.7 * 1.9 3.3 1.9 0.9 2.1 andesitic

breccias C (30-212+) 27.9 0.20 0.58 16.2 7.4 6.6 5.0 * 2.4 3.2 1.8 0.8 2.3 A (0-31) 7.0 0.03 0.06 2.2 0.6 6.0 5.0 41.2 3.4 1.6 0.9 2.6 0.4 Volcanic ash 6 material - C (31-74) 6.9 0.03 0.04 2.1 0.2 6.2 5.2 34.3 3.5 0.9 0.5 2.5 0.2 Altered 2B1 (74-97) 7.3 0.02 0.05 2.3 0.6 6.3 5.2 40.6 2.7 1.4 0.8 2.2 0.4 andesitic 2B2 (97-170) 7.8 0.03 0.05 2.3 0.7 6.3 5.3 39.4 1.9 1.8 1.0 1.1 0.9 breccias 2BC (170-199) 7.8 0.03 0.06 2.5 0.8 6.4 5.4 43.4 2.7 1.9 1.1 0.9 1.2 101

2C (199-276+) 8.1 0.03 0.06 2.6 0.8 6.4 5.4 43.0 2.8 1.7 1.0 0.9 1.1

7 Weathered A (0-28) 48.0 0.17 0.5 26.8 4.9 6.3 6.0 67.3 3.6 3.1 1.8 1.3 1.4 sandstone Bw (28-47) 30.6 0.15 0.44 29.5 4.3 6.3 5.8 * 3.7 2.9 1.7 0.9 1.8

C (47-106+) 33.3 0.18 0.53 30.1 3.8 7.3 5.5 * 4.0 2.9 1.7 1.0 1.6 Weathered A (0-24) 38.7 0.02 0.07 23.8 6.2 6.1 5.3 77.7 2.8 2.4 1.4 0.9 1.5 8 andesitic breccias C (24-87+) 35.7 0.03 0.07 24.1 6.5 6.5 6.4 86.2 3.3 2.1 1.2 0.8 1.6 A (0-22) 29.1 0.03 0.05 8.1 2.7 5.7 4.0 37.3 2.1 3.7 2.1 1.0 2.1 Bw (22-40) 27.1 0.03 0.05 9.2 3.3 5.8 4.2 46.4 2.6 3.3 1.9 0.8 2.4 Volcanic ash 9 C (40-87) 23.8 0.02 0.06 10.8 3.4 6.0 4.4 60.0 3.9 3.2 1.9 0.8 2.4 material 2C (87-149) 19.8 0.03 0.07 8.8 4.4 6.0 4.5 67.1 5.1 3.3 1.9 0.9 2.1 3C (149-191+) 22.4 0.02 0.07 11.8 4.9 5.9 4.3 74.9 5.4 3.2 1.9 1.0 1.9 A (0-29) 24.9 0.02 0.04 6.1 4.7 5.8 4.3 43.6 4.4 2.6 1.5 1.2 1.2 C (29-78) 19.3 0.03 0.05 7.2 5.3 5.9 4.6 65.1 4.7 2.4 1.4 0.9 1.5 Volcanic ash 10 2Bw (78-96) 29.3 0.02 0.05 5.8 3.7 6.0 4.2 32.6 5.3 2.5 1.5 1.0 1.5 material 2C (96-168) 26.8 0.02 0.07 8.2 4.3 6.1 4.4 46.9 5.6 2.3 1.3 0.9 1.4 3C (168-220+) 23.2 0.03 0.07 6.2 4.8 6.2 4.3 47.8 5.5 2.2 1.3 0.7 1.8 A (0-27) 7.1 0.02 0.03 1.8 0.4 6.0 4.0 31.7 1.2 1.3 0.8 1.1 0.7 B1 (27-59) 7.7 0.03 0.04 1.9 0.5 6.1 4.4 32.0 1.4 2.0 1.2 1.0 1.2 Altered B2 (59-90) 8.3 0.02 0.04 2.1 0.6 6.1 4.6 33.2 1.2 2.0 1.2 1.0 1.2 11 andesitic breccias B3 (90-157) 8.6 0.02 0.05 2.1 0.6 6.2 4.5 32.2 1.5 2.0 1.2 0.8 1.5 BC (157-216) 8.4 0.03 0.06 2.4 0.6 6.2 4.6 36.7 2.0 2.0 1.2 0.9 1.3 C (216-274 +) 8.7 0.03 0.06 2.4 0.6 6.3 4.6 35.5 2.0 1.8 1.1 0.9 1.2 Altered A (0-26) 38.7 0.03 0.08 21.8 4.3 6.4 5.9 67.6 2.3 1.6 0.9 1.1 0.8 12 andesitic breccias C (26-91+) 37.2 0.02 0.07 23.1 5.6 6.4 5.3 77.3 2.6 1.5 0.9 0.8 1.1 Weathered A (0-23) 31.0 0.23 0.65 14.3 5.8 6.7 4.6 67.8 2.8 3.3 1.9 0.9 2.2 13 andesitic breccias C (23-138+) 25.8 0.24 0.68 15.5 6.8 6.5 4.0 90.3 3.1 3.2 1.9 0.8 2.3 102

Altered A (0-28) 50.1 0.21 0.61 24.4 8.8 6.9 5.1 67.9 2.3 3.8 2.2 1.2 1.9 14 andesitic AC (28-58) 55.4 0.23 0.66 32.6 27.7 6.8 4.9 * 2.4 3.8 2.2 1.5 1.5 breccias C (58-164) 56.4 0.23 0.68 35.1 28.4 6.5 4.8 * 2.7 3.2 1.9 1.3 1.4

Altered A (0-27) 28.8 0.03 0.08 8.3 4.5 6.7 5.4 44.9 3.1 2.6 1.5 0.9 1.6 15 andesitic Bt (27-69) 19.4 0.03 0.08 6.8 6.1 6.1 5.2 67.3 2.8 2.4 1.4 1.2 1.1 breccias C (69-148+) 24.6 0.03 0.08 9.3 6.4 6.3 4.6 64.7 3.0 2.6 1.5 1.3 1.1 Weathered A (0-27) 19.9 0.26 0.74 8.9 5.0 6.7 4.6 74.4 2.5 3.2 1.9 0.9 2.1 16 andesitic breccias C (27-186) 17.1 0.21 0.61 8.2 4.0 6.9 5.7 75.6 2.9 3.0 1.8 0.7 2.4 *Overestimate value ( > 100%)

103

capacity (CEC) shows a dominant of decreasing values from A-horizon to C-horizon, as shown in Table 5.5. In some cases, there are also the increasing values of CEC from A- horizon to C-horizon. The increasing values of CEC from A-horizon to C-horizon are mainly happened on redistributed material both due to human and landslides activities (see Table 5.5).

The CEC also has a strong relation to SOM and clay contents in the soils. The decreasing of CEC is linear with the decreasing of the clay fraction in the C-horizon (see Table 5.5). In other case, the higher CEC in A-horizons is also in line with the higher SOM in the A-horizons (see Table 5.5). The SOM content in A-horizons ranges from 1.3 to 4.3%. Based on Jackson (1958) and Nelson & Sommer (1982), the SOM in A-horizon is mainly classified into a high level.

The soil pH of the study area generally indicates weakly acid to neutral condition.

The data show that the pH (H2O) at all soil parent materials range from about 6 to 7, and mainly has an increasing value at the depth (see Table 5.5). This weakly acid to neutral soil pH is followed by high base saturation value that exceeds 60% and increase with the depth, as shown in Table 5.5. Only profile 1 and 11 are less saturated with bases (<40%).

The variety of chemical properties in residual soils also can be illustrated by the C/N ratio. The content of organic carbon (C) in the study area is mainly > 1.3% which is categorized into moderate to high level, except the profile 2, 3, 6, 11, and 12 (see Table 5.5). The contents of N total are various from 0.6 to 2.6%. Consequently, nearly all soil profiles results in the C/N ratios > 1.4, of which is categorized into high level.

(iii) Mineralogical properties

The qualitative analysis of mineralogical properties by X-ray diffractometry (XRD) shows that kaolinite is the dominant clay type in all samples. Illite and montmorillonite also present in the XRD result but their presence are only in the some profiles, such as in the soils derived from weathered marl and weathered sandstone materials, as illustrated in the Fig.5.10 (A) and (C). However, the montmorillonite in this result is always interstratified with illite. The peak of illite/montmorillonite and montmorillonite often overlap each other so that they cannot be clearly distinguished. Other mineral properties are various depended on the soil parent material (see Fig.5.10). Indonesia_Nur__2micron-fraction_sample3

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2003 10 20 30 40 50 60 100 2-Theta - Scale 0 Indonesia_Nur__2micron-fraction_sample33 10 20 - File:30 Indonesia_Nur__2micron-fraction_sample3.raw40 50 60 2-Theta - Scale Operations:Indonesia_Nur__2micron-fraction_sample3 Import - File: Indonesia_Nur__2micron-fraction_sample3.raw Operations: Import 00-012-0447 (D) - Kaolinite 1T - Al2Si2O5(OH)4 00-012-044700-013-0375 (D) - Halloysite (D) - Al2Si2O5(OH)4 - Kaolinite 1T - Al2Si2O5(OH)4 00-013-0375 (D) - Halloysite - Al2Si2O5(OH)4 Fig.5.9:XRD diagram showing the presence of halloysite and kaolinite in volcanic ash soil from profile-1 horizon C

The result of XRD also illustrates that there is a presence of noncrystalline mineral (e.g. halloysite which interstratifies with kaolinite) in volcanic ash soils (Fig.5.9). The presence of halloysite indicates that the soil material is originally derived from weathered volcanic ash parent material. The halloysite has a similar mineral structure to kaolinite

which is Al2SiO5 (OH)4 (Sposito, 2008). The presence of both minerals is often bias and mostly overlap in the whole weathered volcanic ash parent material samples. However, according to Fig.5.9, the curve shows that the kaolinite-line fits better than the halloysite- line. Also, the presence of kaolinite seems to be more dominant compared to the presence of halloysite. This assumes that the volcanic ash parent material in the study area is on the transferring stage from noncrystalline structure (e.g. halloysite) into crystalline structure (e.g. kaolinite) due to the intensive weathering process.

The result of XRD also presents that the mineral properties of soils developed on marine sediments e.g. marl, sandstone, and tuff are dominated by montmorillonite, kaolinite, cristobalite, quartz, gypsum, bassanite and boehmite (Fig.5.10 (A), (B), and (C)). Montmorillonite and kaolinite show that the clay transformation has been occurring in these soils. The presence of cristobalite describes that these marine materials are originally derived from the volcanic materials which were sunk into the ocean, and were uplifted to the surface. In other side, boehmite, as oxides and hydroxides mineral groups (Sposito, 2008) are typically found in the soils developed on intensive leaching process. Gypsum and bassanite are parts of sulfates group so that their presence indicates Sulfur in the soil. As marine sediments, these soil parent materials must have experienced with the 105

leaching process under marine environment. Therefore, this condition is in-line with the presence boehmite in these soils. Besides, the presence of quartz indicates that the soils derive from sandstone material, as shown in Fig.5.10 (C).

(Note: The graphic only shows the presence of minerals. It isn’t related to the amounts of minerals)

Profile 2 (Weathered marl material) A

Profile 3 (Weathered tuff material) B

Fig.5.10: XRD result of each soil parent material in the study area

106

Profile 7 (Weathered sandstone material) C

Profile 10 (Volcanic ash material) D

Fig.5.10: XRD result of each soil parent material in the study area

2

107

Profile11 (Altered andesitic breccia material) E

Profile 13 (Weathered andesitic breccia) F

Fig.5.10: XRD result of each soil parent material in the study area

The mineral properties of soils developed on volcanic ash deposit are dominated by cristobalite, quartz, kaolinite, and halloysite (Fig.5.10 (D)). Cristobalite is a typical of mineral existed in a volcanic area. The presence of these minerals is clearly shown both in the soil and in the regolith. Cristobalite is usually found in a high temperature environment, and also together with Quartz belongs to silicates group (SiO2) (Sposito, 2008). Kaolinite is a proof of the ultimate stage of soil parent material weathering. In 108

addition, the presence of non-crystalline mineral of halloysite becomes a difference of volcanic ash deposit with other volcanic materials.

The mineral properties of soils developed on volcanic rocks (e.g. altered andesitic breccias material and weathered andesitic breccias material) consist mainly of kaolinite, cristobalite, boehmite, basanite, quartz, montmorillonite and hematite (Fig.5.10 (E) & (F)). As the oldest soil parent material of other soil parent materials in the study area, the volcanic rocks must have experienced with very active weathering process. The active weathering processes in the volcanic rocks are indicated by the presence of kaolinite. However, in several samples, there are also the presence of montmorillonite indicated that the weathering process in those samples is still in the initiate stage. Quartz, as the last weathered mineral, also indicates that the volcanic rocks are intensively weathered, and is usually presented in the volcanic rocks. Besides, cristobalite and basanite are also the typical of minerals existed in a volcanic area. Bassanite specifically indicates Sulfur in the soil which is identically contained in the volcanic materials. However, the most difference of altered andesitic breccias and weathered andesitic breccias materials is shown by the presence of hematite. Hematite is Fe released from the lattice and oxidized during alteration that produces a reddish coloration because of the less of oxygen content during oxidation of altered material (Kinnaird, 1985 in Pirajno, 2009, p.105).

The quantitative mineralogical analysis of soil parent materials using X-Ray Fluorescence (XRF) was also conducted in this study, to complete the qualitative mineralogical analysis. The results of XRF show that SiO2 is the dominant mineral for all

XRF samples. The presence of SiO2 indicates that the parent rock has been weathered and altered intensively, so that those processes leach the major as well as minor minerals and alkali elements of the parent rocks (Klika et al., 2005). As the consequence, it remains the dominant of Silicate (Si) and Aluminum (Al), of which the resistant minerals (Schaetzl and Anderson, 2005) in the soil parent material, as shown in Table 5.6.

Table 5.6: XRF analysis of altered- and weathered soil parent materials

Altered material Weathered material Concentration Concentration

Formula Z Formula Z (%) (%)

SiO2 14 45.10 SiO2 14 29.53

Minerals Al2O3 13 31.62 Fe2O3 26 28.02

Fe2O3 26 19.08 Al2O3 13 22.81 109

Altered material Weathered material Concentration Concentration Formula Z Formula Z (%) (%)

TiO2 22 1.25 Na2O 11 9.98

P2O5 15 0.75 MgO 12 2.54

SO3 16 0.47 TiO2 22 1.91 Cl 17 0.41 CaO 20 1.11

CaO 20 0.36 P2O5 15 0.82

K2O 19 0.32 K2O 19 0.75

MnO 25 0.17 SO3 16 0.70

Nd2O3 60 0.17 Cl 17 0.52

Pr6O11 59 0.06 MnO 25 0.25

ZrO2 40 0.06 La2O3 57 0.17

CuO 29 0.03 CeO2 58 0.15

Cr2O3 24 0.02 Nd2O3 60 0.13

SnO2 50 0.02 ZrO2 40 0.12

V2O5 23 0.02 Pr6O11 59 0.07

ZnO 30 0.02 V2O5 23 0.07

Ga2O3 31 0.01 CuO 29 0.05 CoO 27 0.01

O 8 46.13 O 8 40.83 Si 14 21.08 Fe 26 19.60 Al 13 16.73 Si 14 13.81 Fe 26 13.35 Al 13 12.07 Ti 22 0.75 Na 11 7.41 Cl 17 0.41 Mg 12 1.53 P 15 0.33 Ti 22 1.14

K 19 0.27 Ca 20 0.79 Ca 20 0.26 K 19 0.62 S 16 0.19 Cl 17 0.52 Nd 60 0.15 P 15 0.36

Alkali elements Alkali Mn 25 0.14 S 16 0.28 Pr 59 0.05 Mn 25 0.19 Zr 40 0.04 La 57 0.15 Cu 29 0.02 Ce 58 0.12 Sn 50 0.02 Nd 60 0.11 Cr 24 0.02 Zr 40 0.09 Zn 30 0.01 Pr 59 0.06 Ga 31 0.01 Cu 29 0.04

110

The different percentage of minerals and alkali elements describes different soil parent material types. There is a different order of minerals and alkali elements in those soil parent materials based on their percentage in the soil samples (see Table 5.6). In the study area, the major minerals contained in all soil parent material are SiO2, Al2O3, Fe2O3,

TiO2, P2O5. The major alkali elements contained in the soil parent material are O, Fe, Si,

Al, Ti (Table 5.6). However, the percentage of SiO2, Fe2O3, and Al2O3 can be used to distinguish the crucial processes occurred in the parent rocks. The weathered parent rock material are mostly contained by SiO2 > Fe2O3 > Al2O3 where the percentage of SiO2 ranges 37.89% - 41.32%; Fe2O3 ranges 27.87% - 28.32%; Al2O3 ranges 23.08% - 27.69%

(Table 5.6). In contrast, the altered parent materials have much higher content of SiO2 due to the intensive alkali elements leaching during alteration. Therefore, the altered parent rock materials are consisted of SiO2 > Al2O3 > Fe2O3 where the percentage of SiO2 is

45.10%; Al2O3 is 31.62%, Fe2O3 is 19.08% (Table 5.6). The dominance of SiO2 and Al2O3 in altered parent materials rather than in weathered parent rock material shows the intensity of mineral transforming process in altered parent material.

(iv) Recapitulation of residual soil property results

To recapitulate the soil properties results, the residual soils can be classified into two: (i)soils developed on weathered parent materials; (ii)soils developed on altered parent materials due to hydrothermal alteration. Both residual soil classifications show their significant differences of morphological, physical, chemical, and mineralogical properties. The parameters used to compare the analysis result of those classifications are color, texture, CEC, clay type, bases cation, base saturation, SOM, and P2O5 (see Table 5.7).

The soil color becomes the first parameter that can be used to compare between the soils developed on weathered parent materials and the soils developed on altered parent materials. As shown in Fig.5.2, the difference of soil color of both classifications is contrast. The soils developed on weathered parent materials show the brownish to grayish color, whereas the soils developed on altered parent materials show the reddish to orange color (Table 5.7).

The results of texture analysis among the residual soil classifications also present a considerable difference. According to Table 5.4, the soil textures in the study area are dominated by silt loam and clay. In detail, the texture of soils developed on weathered parent materials shows less than 30% of clay content, whereas the texture of soils 111

developed on altered parent materials shows much higher clay content, at most > 60% (Table 5.7).

Table 5.7: Recapitulation of residual soil property results

Comparative Weathered parent rock Altered parent rock material parameters material

Soil color Hue: 7.5YR – 10YR Hue: 2.5YR – 5YR

Texture Clay ≤ 30% Clay > 60%

CEC Medium – High Very low

(20-70 me/100gr) (< 10 me/100gr)

indicated clay type: illite – indicated clay type: kaolinite montmorillonite

Bases cation Medium – High Very low

(Ca, Mg, Na, K) (depended on soil parent (kaolinite has difficulties in material types) cations absorption)

Base saturated Medium – High Very low

(depended on the exchanging (the exchanging capacity of and holding capacity of cations is very low) cations)

SOM 1.8 – 4.3% 1.4 – 2.0%

P2O5 2 – 5 ppm 1 -3 ppm

The significant difference of clay content between the soils developed on weathered parent materials and the soils developed on altered parent materials also relates to the CEC, cation bases, base saturated, and clay types in the profiles. According to the previous Table 5.5, the weathered tuff and weathered marl materials have the highest CEC that is > 50 me/100gr. This high CEC is followed by a greater amount of exchangeable cations in the weathered tuff and weathered marl materials. This high CEC indicates that 112

the clay type of those materials is montmorillonite. The weathered tuff and weathered marl materials, of which derive from the are dominated by carbonate minerals i.e. CaCO3 and MgCO3 as the main cations for montmorillonite formation (Muniers, 2005). It is because the montmorillonite has a weak oxygen bonding that is easily substituted. During formation of montmorillonite, the alumino (Al3+) is mostly substituted by Mg2+, as described in section 2.10. Consequently, it results in the excess negative charge, and thus causes high CEC. This high capability of exchanging and binding cations leads to increase the base saturation in weathered tuff and weathered marl materials (see Table 5.7).

On the other side, the weathered sandstone, weathered andesitic breccias, and weathered volcanic ash materials have a medium CEC that is 10-40 me/100gr. Such CEC indicates that the clay type of those materials is illite which is usually found in the soils contained by plagioclase feldspar (Munier, 2005), as the main mineral contained in the most soils in the study area (see Table 5.17). This CEC value is also found in the developing or young soils (Hardjowigeno, 2003) as the main soil development stage in the study area. Moreover, the medium CEC of those materials causes a lower amount of exchangeable cations than that of the weathered tuff and weathered marls (see Table 5.5). This lower amount of exchangeable cations is because the illite is dominated by partial substitution of aluminium and silicate due to weak K-bonding among the alumino-silicate layers (Hardjowigeno, 2003), as discussed in section 2.10. Therefore, it results in fewer negative charges than montmorillonite, and leads to medium CEC and medium base saturation (see Table 5.5).

In contrast to those weathered parent materials, the altered parent material have the lowest CEC that is < 10 me/100gr. This low CEC indicates that the clay type of those materials is kaolinite which is mainly formed due to intensive weathering or hydrothermal alteration of alumino-silicates (Lal & Sanchez, 1992). Therefore, the alteration towards andesitic breccia, of which is contained by plagioclase feldspar, mainly forms kaolinite. Furthermore, this low CEC is followed by a fewer amount of exchangeable cations in altered parent rocks material. It is because the kaolinite is dominated by hydrolysis (Hardjowigeno, 2003), as explained in section 2.10. The hydrolysis causes the replacement of cation bases by the ion H+. As the consequence, the cation bases are released (Fitzpatrick, 1980) and leads to the low base saturation in altered parent rocks material 113

(see Table 5.5). Furthermore, the kaolinite has a strong hydrogen bonding so that the possibility for isomorphic substitution is low. Therefore, the negative charge is low, and thus results in low CEC.

The differences between the soils developed on weathered parent materials and the soils developed on altered parent material are also described by SOM and P2O5 although they are not as significant as previous properties. Based on Table 5.5, the soils developed on altered parent material have a lower content of SOM and P2O5 than those of the soils developed on weathered parent materials.

5.3.1.2 Redistributed soil material

In this study, 27 sites were investigated for redistributed soil material (Table 5.8). The redistributed soil material was chosen according to the influence of (i) landslides and (ii) human activities. There were 11 sites selected to characterize landslides-redistributed soil material (Table 5.9, Table 5.11) and 16 sites selected to characterize human- redistributed soil material (Table 5.10, Table 5.12, Table 5.13).

The landslide-redistributed soil material was analyzed by comparing the soil properties at landslide sites and nearby non-landslide sites. The soil properties were analyzed according to three different soil parent materials: altered andesitic breccias, weathered andesitic breccias, and weathered sandstone-marl. There were 6 non-landslide soils taken from nearby non-landslide sites provided as references for comparison to landslide-redistributed soils properties.

The human-redistributed soil material was assessed according to the types of human influence on soils in the study area, i.e. fertilizing, manuring, crop rotation, terraces and tillage practices. The influences of human on redistributing the soils are assumed to accelerate or to retard the soil profile development in that particular area.

(i) Morphological properties  Landslide-redistributed soil material The presence of landslide-redistributed soils is usually described by the changes of soil color between surface and sub-surface layers. The surface layer reflects the landslide deposit, whereas, the sub-surface layer reflects the former soils. The soil color of the surface layer is created by the mixture material, whereas, the soil color of the sub-surface 114

Table 5.8: Morphological and physical properties of soils based on field assessment

Soil parent Horizon (depth Structure Consistency No Soil type* Color Texture material in cm) Type Grade Wet Moist 17 C (0-45) 7,5YR 5/4 Silt loam Structureless Massive sticky - slightly plastic friable 18 C (0-53) 5YR 7/4 Silt loam Structureless Massive sticky - slightly plastic firm 19 C (0-176) 5YR 7/8 Loam Structureless Massive no sticky – no plastic firm 20 C (0-98) 5YR 7/8 Loam Structureless Massive no sticky – no plastic friable

21 Landslide- Leptic C (0-74) 7,5YR 4/4 Silt loam Structureless Massive slightly sticky – plastic friable 22 redistributed Regosols C (0-176) 7,5YR 7/8 Silt loam Structureless Massive sticky - slightly plastic firm soil material Eutric 23 C (0-86) 10YR 5/6 Silt loam Structureless Massive sticky - slightly plastic firm 24 C (0-63) 10YR 4/4 Silt loam Structureless Massive slightly sticky – no plastic friable 25 C (0-231) 5YR 7/4 Silt loam Structureless Massive slightly sticky – no plastic friable 26 C (0-73) 10YR 7/8 Silt loam Structureless Massive sticky - slightly plastic firm 27 C (0-84) 10YR 7/8 Loam Structureless Massive no sticky – no plastic friable Ap (0-20) 10YR 5/4 Clay loam Crumb Weak slightly sticky – slightly plastic friable Lixic 28 Volcanic ash Nitisols Bw (20-44) 10YR 5/6 Clay Blocky Moderate very sticky – very plastic firm material Eutric C (44-94+) 10YR 7/6 Loam Structureless Massive slightly sticky – no plastic firm Ap (0-19) 7,5YR 5/6 Clay Crumb Weak very sticky – very plastic friable Leptic Volcanic ash 29 Regosols Bw (19-42) 7,5YR 6/6 Clay Crumb Moderate very sticky – very plastic firm material Eutric C (42-173+) 7,5YR 7/6 Clay Structureless Single grain very sticky – very plastic firm Weathered Leptic A (0-18) 10YR 5/8 Clay loam Crumb Weak sticky - plastic friable 30 andesitic Regosols breccias Eutric C (18-88+) 10YR 6/8 Clay loam Structureless Single grain sticky - plastic firm Leptic Weathered Ap (0-36) 7,5YR 6/1 Silty clay Crumb Weak slightly sticky – slightly plastic friable 31 Regosols tuff Eutric C (36-91+) 10YR 6/2 Silt loam Structureless Massive no sticky – no plastic firm 32 Weathered Lixic Ap (0-18) 10YR 5/4 Sandy clay Crumb Weak sticky - slightly plastic firm 115

sandstone Nitisols loam Eutric A (18-33) 10YR 6/4 Clay loam Crumb Moderate sticky - plastic firm Bw (33-42) 10YR 7/6 Clay loam Blocky Moderate very sticky – plastic Very firm Sandy clay C (42-84+) 10YR 7/8 Structureless Massive sticky - slightly plastic firm loam Weathered Leptic A (0-27) 7,5YR 4/4 Sandy Clay Crumb Weak sticky - slightly plastic friable 33 andesitic Regosols breccias Eutric C (27-74+) 7,5YR 5/2 Sandy Loam Structureless Massive slightly sticky – no plastic firm Sandy clay Weathered Leptic A (0-23) 10YR 3/4 Crumb Weak slightly sticky – slightly plastic friable 34 andesitic Regosols loam breccias Eutric C (23-96+) 10YR 5/8 Sandy loam Structureless Massive slightly sticky – no plastic firm Ap (0-18) 7,5YR 5/6 Clay Crumb Weak very sticky – plastic friable Leptic Volcanic ash 35 Regosols Bw (18-96) 7,5YR 5/8 Clay Crumb Moderate very sticky – very plastic firm material Eutric C (96-157+) 7,5YR 6/8 Clay Structureless Single grain very sticky – very plastic firm Ap (0-26) 7,5YR 5/4 Clay Crumb Weak very sticky – plastic friable Leptic Volcanic ash 36 Regosols Bw (26-108) 7,5YR 5/6 Clay Crumb Weak very sticky – very plastic firm material Eutric C (108-121+) 7,5YR 6/6 Clay Structureless Massive very sticky – very plastic firm Altered Haplic A (0-26) 5YR 5/6 Clay Crumb Weak very sticky – very plastic friable 37 andesitic Nitisols breccias Rhodic C (26-102) 5YR 6/8 Clay Structureless Single grain very sticky – very plastic firm Sandy clay Weathered Leptic Ap (0-20) 7,5YR 4/6 Crumb Weak very sticky – very plastic firm loam 38 andesitic Regosols Sandy clay breccias Eutric C (20-67+) 7,5YR 5/6 Structureless Massive very sticky – very plastic very firm loam Sandy clay Weathered Leptic A (0-28) 10YR 5/4 Crumb Weak sticky – plastic friable 39 andesitic Regosols loam breccias Eutric C (28-87+) 10YR 5/8 Clay Loam Structureless Single grain sticky – plastic firm Weathered Leptic A (0-21) 7,5YR 4/6 Sandy Loam Crumb Weak very sticky – very plastic firm 40 andesitic Regosols Sandy clay C (21-73) 7,5YR 5/6 Structureless Massive very sticky – plastic very firm breccias Eutric loam 41 Weathered Leptic Ap (0-17) 10 YR 5/4 Silt loam Crumb Weak no sticky – no plastic very friable 116

andesitic Regosols A (36-109+) 10YR 5/6 Silt loam Crumb Moderate slightly sticky – no plastic friable breccias Eutric Ap (0-23) 10 YR 5/8 Silty clay loam Crumb Weak slightly sticky – no plastic friable Leptic Weathered 42 Regosols A (23-53) 10YR 6/8 Silt loam Crumb Moderate slightly sticky – no plastic firm tuff Eutric C (53-78+) 10YR 7/8 Silt loam Structureless Massive no sticky – no plastic firm Weathered Leptic A (0-26) 7,5YR 4/3 Silt loam Crumb Weak slightly sticky – no plastic friable 43 andesitic Regosols breccias Eutric C (26-84+) 7,5YR 5/3 Silt loam Structureless Massive slightly sticky – no plastic firm *Soil types are based on World Reference Base criteria (WRB, 2007)

117

layer is created by the original former soils. The soil color of the landslide deposit is depended on the color of the source soils nearby non-landslide sites.

The vertical textural contrast is also commonly found in the landslide-redistributed soil materials. The landslide-redistributed soil materials often consist of the mixture of soil, regolith, and/or saprolite. The textural changes in landslide-redistributed soil materials are indicated by the absence of soil textural sequence as usually shown by the soils developed on residual soil parent material. In addition, the textural changes in landslide-redistributed soil materials are also depended on the depth of soil in the nearby non-landslide sites. The landslide-redistributed soil materials are contained by mix of soils and underlying saprolite when it is derived from the shallow soil depth. The landslide- redistributed soil materials can be also contained by full of soil materials when it is derived from thick soil depth such as volcanic ash deposit.

 Human-redistributed soil material The soil color does not particularly change on human-redistributed soils. However, the soil structure distribution shows its significance towards the influence of human on redistributing the soils. In the study area, the soil structure types are easily disturbed by human activities especially due to agricultural practices. Different soil structure grades characterize the human-redistributed soils. This condition is usually shown by friable structure in the surface layer and firm structure in the sub-surface layer.

The soil structure type in human-redistributed soils is mostly influenced by tillage types. The results show that tillage types play an important role in breaking down a larger into a smaller soil structure (see Table 5.8). Among three types of tillage practices existed in the study area, the conventional tillage causes a significant change in the soil structure. The main effect of conventional tillage is the turbation of soils and the refinement of soil structure. Profile 32 is the example for soil turbation activities showing high amount of larger soil structures in the surface layer than that in the sub-surface layer. In comparison, profile 30, 31, 34, 35, 36, 38, and 42 present the examples for the soil structure refinement showing high amount of finer soil structures in the surface layer than that in the sub- surface layer. However, under the reduce tillage and minimum tillage, the soil structure refinement presents more uniform soil structure type distribution from the surface to the sub-surface layers. Profile 28, 29, 33, 34, 37, 39, 40, 41, 43 shows the uniform soil structure type distribution from the surface to the sub-surface layers. 118

(ii) Physical properties  Landslide-redistributed soil material The particle size distribution can reflect the impact of landslides on soil redistribution. In the study area, the particle size distribution of landslide-redistributed soil material is generally dominated by fine particles, and there is a decreasing of sand fraction compared to that of their reference soils (see Table 5.9). It is shown in the soils derived from weathered breccias andesitic and weathered sandstone-marl. The domination of fine particles in landslide-redistributed soil materials is described by a widening range of clay and silt fractions towards their reference soils’ range (see Table 5.10). This wider range of clay and silt fractions indicates that landslides has broken coarse fraction into finer fractions due to mass movement.

Table 5.9: Particle size distribution and COLE Index of landslide-redistributed soil material (L) and non-landslide soils (NL)

Particle size distribution Soil parent L / COLE No material NL % Clay % Silt % Sand Index (0.2-2 µm) (>2-50 µm) (>50-2000 µm) 17 10.1 57.8 32.1 0.08 18 17.7 57.3 25.0 0.12

19 Altered andesitic 12.9 39.7 47.4 0.10 L 20 breccias material 11.7 53.7 34.6 0.06 21 28.2 47.1 24.8 0.06 22 30.9 52.5 16.6 0.08

* Altered andesitic 76.4 18.0 5.60 0.28 NL * breccias material 57.6 32.7 9.70 0.26 23 Weathered 10.6 61.5 27.9 0.11 andesitic breccias L 24 material 19.9 49.6 30.3 0.14 * Weathered 12.8 51.3 35.9 0.18 andesitic breccias NL * material 10.9 55.0 34.1 0.17 25 13.23 55.78 30.95 0.09 Weathered 26 sandstone–marl L 13.6 78.6 7.8 0.09 intercalation 27 10.9 70.8 18.3 0.07 * Weathered 17.1 58.9 24.0 0.19 sandstone–marl NL * intercalation 16.9 61.1 22.0 0.14 *non-landslide soils data taken from Table 5.4 for comparison as references 119

The particle size distribution of landslide-redistributed soil material can also vary depending on the types of landslides (e.g. shallow landslides or deep-seated landslides). This is due to the shallow landslide-redistributed soil material mostly comprises soils, and thus results in the amount of fine particles. However, the deep-seated landslide- redistributed soil material comprises mix of soils and regolith materials, and thus results in the majority of coarse particles. The shallow landslides usually occur on weathered andesitic breccias and weathered sandstone-marl areas, and they are indicated by the increasing of fine fractions compared to that of their reference soils (see Table 5.9). On the other side, the deep-seated landslides usually occur on altered andesitic breccias areas, and they are indicated by the increasing of sand fraction compared to that of their reference soils (see Table 5.9).

Table 5.10: Range and average of particle size distribution of landslide- redistributed soil material (L) and non-landslide soils (NL)

Particle size distribution Soil parent COLE Index L/NL % Clay % Silt % Sand material (0.2-2 µm) (>2-50 µm) (>50-2000 µm) Range Average Range Average Range Average Range Average Altered L 10.1-30.9 18.6 39.7-57.8 51.4 16.6-47.4 30.1 0.06-0.12 0.08 andesitic breccias NL 57.6-76.4 67.0 18.0-32.7 25.4 5.6-9.7 7.65 0.26-0.28 0.27 material Weathered L 10.6-19.9 15.25 49.6-61.5 55.5 27.9-30.3 29.1 0.11-0.14 0.13 andesitic breccias NL 10.9-12.8 11.9 51.3-55.0 53.2 34.1-35.9 35.0 0.17-0.18 0.18 material

Weathered L 10.9-19.5 14.7 70.8-78.6 75.9 2.3-18.3 9.5 0.07-0.09 0.08 sandstone– marl NL 16.9-17.1 17.0 58.9-61.1 60.0 22.0-24.0 23.0 0.14-0.19 0.17 intercalation

The pattern of particle size distribution of landslide-redistributed soil material is consistent with that of nearby non-landslide soils. For example: the landslide-redistributed soil material which has weathered andesitic breccias and weathered sandstone-marl as their soil parent material shows higher percentage of silt and/or sand than the percentage of clay. These results are consistent with their references which are nearby non-landslide soils (see Table 5.9). However, the landslide-redistributed soil material which has altered andesitic breccias as the soil parent material does not show the same predominant particle size distribution as its reference (see Table 5.9). 120

The COLE Index also shows the crucial effect of landslide in soil redistribution. The results show that the COLE index of landslide-redistributed soil material is much lower than that of nearby non-landslide soils (see Table 5.9). The most significant decreasing of COLE Index occurs in landslide redistributed soil material derived from weathered sandstone-marl and altered andesitic breccias. In altered andesitic breccias, the COLE Index of nearby non-landslide soils is ranging from 0.26-0.28; however the landslides have dropped the COLE Index of redistributed soil material into a range of 0.06-0.12 (Table 5.10). Similar situation also happens to weathered sandstone-marl where the COLE Index of nearby non-landslide soils is ranging from 0.14-0.19, but the COLE Index of landslide-redistributed soil material is ranging from 0.07-0.09 (Table 5.10). According to the results, the decreasing index of COLE mainly occurs in the soils which have high content of clay, i.e. soils derived from altered andesitic breccias and from weathered sandstone-marl. In this case, landslides cause a good impact on clayey soils especially regarding with agriculture. The decreasing of COLE Index may reduce shrinking-swelling capacity of this clayey soil, and thus ease the soils to be cultivated. The COLE Index of landslide-redistributed soil material and of non-redistributed soil are both categorized into high level (>0.06) according to FAO (1973) classification. The COLE Index also relates to the dominant particle size and clay type of its soil parent material. The COLE Index determined the shrinking-swelling behavior of soils which is crucial for agricultural activities. Overall, there is only some profiles showing the lowest limit (0.06 - 0.09) of high shrink-swell behavior, whereas, others show very high shrink- swell behavior (>0.09) as shown in Table 5.9. This high shrinking-swelling behavior indicates that the dominant clay type in this landslide-redistributed soil material is montmorillonite.  Human-redistributed soil material

The tillage practices may accelerate the translocation of clay from the surface to the sub-surface layers. According to the results, profile 28, 29, 30, 32, 35, 36, and 37 shows the translocation of clay, and are accumulated in the sub-surface horizon (Table 5.11). In contrast, profile 31, 33, 34, 38, 39, 40, 41, 42, 43 does not show any accumulation of clay in the sub-surface horizon, and thus indicates the absence of clay translocation due to tillage practices (see Table 5.11). Therefore, the amount of clay content as an effect of tillage practices along the profile does not always gradually increase at the depth (see Table 5.11). 121

Table 5.11: Particle size distribution of human-redistributed soils

Soil parent Horizon Particle size distribution Type of tillage No material (depth in cm) (treatment) % Clay %Silt % Sand < 2µm 2-50 µm >50-2000 µm Ap (0-20) 28.5 43.5 27.9 Volcanic ash 28 Bw (20-44) RT (strip tillage) 79.4 14.5 6.0 material C (44-94+) 18.3 39.6 42.1 Ap (0-19) 66.7 21.3 8.4 Volcanic ash CT (mechanic 29 Bw (19-42) 70.3 23.8 9.5 material ploughing) C (42-173+) 67.3 25.8 6.9 Weathered A (0-18) CT (traditional 28.2 31.9 39.8 30 andesitic ploughing) 29.0 33.3 37.7 breccias C (18-88+) Weathered Ap (0-36) CT (traditional 35.1 55.3 9.5 31 tuff C (36-91+) ploughing) 39.7 52.7 7.6 Ap (0-18) 22.1 19.7 58.3 Weathered A (18-33) CT (mechanic 28.7 35.9 35.3 32 sandstone Bw (33-42) ploughing) 38.5 38.3 23.3 C (42-84+) 20.7 15.1 64.2 Weathered A (0-27) 48.6 7.4 44.0 33 andesitic ZT (-) C (27-74+) 17.3 32.5 50.2 breccias Weathered A (0-23) RT (raised bed) 23.8 15.3 61.0 34 andesitic

breccias C (23-96+) 14.4 7.8 77.8 Ap (0-18) 72.5 15.4 12.1 Volcanic ash CT (mechanic 35 Bw (18-96) 77.8 16.1 6.1 material ploughing) C (96-157+) 77.7 17.0 5.3 Ap (0-26) 61.4 26.6 11.9 Volcanic ash CT (traditional 36 Bw (26-108) 73.8 23.3 2.9 material ploughing) C (108-121+) 68.3 27.6 4.0 Altered A (0-26) 60.1 30.4 9.5 37 andesitic ZT (-) 66.6 27.0 6.4 breccias (26-102) Weathered Ap (0-20) CT (traditional 20.2 24.1 55.7 38 andesitic ploughing) 20.0 30.1 49.8 breccias C (20-67+) Weathered A (0-28) 40.2 32.6 27.3 39 andesitic ZT (-) 21.7 30.1 48.2 breccias C (28-87+) Weathered A (0-21) 25.2 17.3 57.6 40 andesitic ZT (-) 9.8 28.5 61.7 breccias C (21-73) Weathered Ap (0-17) 19.4 72.2 8.4 41 andesitic MT (mulch) 11.1 61.1 27.8 breccias A (36-109+) Ap (0-23) 30.9 45.8 23.3 Weathered CT (mechanic 42 A (23-53) 15.8 65.8 18.4 tuff ploughing) C (53-78+) 25.9 52.2 21.9 122

Weathered A (0-26) 25.0 66.5 8.5 43 andesitic RT (raised bed) 24.4 58.9 16.7 breccias C (26-84+)

Soil treatment = ZT (zero-tillage); RT (reduced tillage); MT (minimum tillage); CT (conventional tillage)

Different types of tillage practices leads to various effect on particle size fragmentation and distribution within the soil profile. There are three types of tillage practices in the study area: (i) reduced tillage (RT), (ii) minimum tillage (MT), and (iii) conventional tillage (CT). According to the field assessment, the conventional tillage causes a significant particle size fragmentation rather than the minimum- and the reduced tillages. In addition, the fragmented particle size under conventional tillage shows a high percentage of sand fractions in the upper-most horizon as the result of soil turbation due to tillage practice, as shown in profile 29, 30, 31, 32, 35, 36, and 42 (Table 5.11).

Different types of tillage practices also influence the organic matter within the soil profile. According to the field assessment, the conventional tillage (CT) strongly affects the translocation of organic matter from the surface into the deeper soils compared to the reduce tillage (RT) and minimum tillage (MT). The effect of conventional tillage towards organic matter translocation is shown in the profile 29, 32, 35, and 42, which are influenced by mechanic ploughing (Table 5.15). This organic matter translocation is mainly caused by deep soil turbation due to mechanic ploughing. However, the reduced- and the minimum tillages have lower intensity of soil turbation than the conventional tillage. Consequently, the organic matter translocation under these tillages strongly depends on the type of treatment (see Table 5.15). The profile 28 under the strip tillage can cause a significant organic matter translocation. However, the profile 34, 41 and 43 which are only affected by raised bed and mulch do not show a significant impact on organic matter translocation within the profile (see Table 5.15).

The clay accumulation in the sub-surface layer also influences the CEC within the soil profile. Profile 28, 29, 32, 35, 36, 41, and 42 shows the increasing of CEC value in the sub-surface layer (see Table 5.16). The increasing of CEC in the profile 28, 29, 32, 35, and 36 is in line with the presence of clay accumulation in the sub-surface layer within those profiles. However, the increasing of CEC in the profile 41 and 42 is not linier with the clay translocation because there is no clay accumulation in the sub-surface layer within those profiles (see Table 5.11 and 5.16). The increasing of CEC within those profiles might be mainly affected by the clay type. The tuff as the soil parent material causes the clay type 123

formed in those profiles is montmorillonite. Consequently, CEC of those profiles is higher in the sub-surface layer even though it is not followed by increasing of clay content.

(iii) Chemical properties  Landslide-redistributed soil material The landslides significantly influence the content of organic matter, carbon and nitrogen in the soils. The landslides cause soil turbation while sliding down the soils on the slope, and hence disturb the content of organic matter, carbon and nitrogen of the surface and subsurface soils. The result analysis shows that the average of those properties in landslide-redistributed soil material is mostly lower than that of non-landslide soils (see Table 5.14). Overall, according to Puslittanak (1993), both ranges of organic matter and carbon in landslide-redistributed soil material and non-landslides soils are categorized into low which is less than 3.5% and less than 2% respectively (Table 5.14). On the other side, the ranges of nitrogen in landslide-redistributed soil material and non-landslides soils are categorized into high which is more than 0.5% (Table 5.14).

P2O5 of both landslides-redistributed soil material and non-landslide soils are categorized into low due to having value less than 10, according to Puslittanak (1993) (see

Table 5.12). The average of P2O5 in landslide-redistributed soil material is ranging from

3.1 to 5.7; however the average of P2O5 in non-landslide soils is ranging from 2.1 to 3.65 (Table 5.14). In addition, the soil pH does not show a significant change between the landslide-redistributed soil material and non-landslide soils as shown in its ranging values (see Table 5.13). Therefore, the results show that landslides do not affect to the soil pH values.

The CEC of landslide-redistributed soil material and of non-landslide soils varies depending of the type of soil parent materials. The CEC of altered andesitic breccias and of weathered sandstone-marl shows a significant changes between landslide-redistributed soil material and non-landslide soils, whereas, the CEC of weathered andesitic breccias does not show a significant changes between landslide-redistributed soil material and non- landslide soils (see Table 5.12).

124

Table 5.12: Chemical properties of landslide-redistributed soil material (L) and non-landslide soils (NL)

Cation bases pH P2O5 SOM C N-total Soil parent Layer CEC No L/NL Na+ K+ Ca2+ Mg2+ material depth H O KCl (ppm) (%) (%) (%) -1 2 (cmolc+ kg ) 17 45 cm L 14.4 0.20 0.10 11.3 6.7 5.9 4.1 6.6 0.4 0.3 0.10 18 53 cm L 38.7 0.20 0.10 13.6 5.8 6.1 5.9 7.4 0.4 0.3 0.04

19 Altered andesitic 76 cm L 28.3 0.30 0.10 11.8 4.1 6.2 5.7 5.8 0.3 0.2 0.03 20 breccia material 98 cm L 18.5 0.30 0.10 15.6 7.5 6.2 5.9 5.9 2.2 1.3 0.10 21 63 cm L 19.5 0.30 0.10 18.2 8.7 5.9 4.9 5.6 2.1 0.8 0.23 22 231 cm L 18.1 0.20 0.60 25.6 23.3 6.9 6.1 3.1 1.1 0.7 0.09 * NL 7.7 0.03 0.04 1.9 5.0 6.1 4.4 1.4 2.0 1.2 1.00 Altered andesitic * breccia material NL 56.4 0.23 0.68 35.1 28.4 6.5 4.8 2.7 3.2 1.9 1.30

23 Weathered 74 cm L 30.9 0.23 0.65 14.3 5.8 6.8 4.6 2.9 3.2 1.8 0.86 andesitic breccias 24 material 73 cm L 38.4 0.10 0.10 8.8 4.4 5.7 5.1 3.3 2.3 1.3 0.14

Weathered NL 38.7 0.02 0.07 23.8 6.2 6.1 5.3 2.8 2.4 1.4 0.90 * andesitic breccias * material NL 25.8 0.24 0.68 15.5 6.8 6.5 4.0 3.1 3.3 1.9 0.80

25 Weathered 128 cm L 37.8 0.30 0.80 15.6 7.9 6.9 5.1 1.8 3.8 2.2 0.79 sandstone 26 86 cm L 18.1 0.20 0.30 19.3 8.3 6.6 5.7 3.9 0.6 0.3 0.88 intercalation with 27 marl 84 cm L 64.1 0.20 0.50 49.7 24.3 6.8 5.6 3.8 1.9 1.1 0.88 * Weathered NL 47.9 0.17 0.50 26.8 4.9 6.3 6.0 3.6 3.1 1.8 1.30 sandstone intercalation with * NL 33.3 0.18 0.53 30.1 3.8 6.3 5.8 3.7 2.9 1.7 0.90 marl *non-landslide soils data taken from Table 5.4 for comparison as references 125

Table 5.13: Range and average of chemical properties (CEC, Cation bases, and pH) of landslide-redistributed soil material (L) and non- landslide soils (NL)

Cation bases pH CEC Na+ K+ Ca++ Mg++ Soil parent L/NL H2O KCl material -1 (cmolc+ kg )

Range Average Range Average Range Average Range Average Range Average Range Average Range Average

Altered andesitic L 14.4-38.7 22.9 0.20-0.30 0.25 0.10-0.60 0.18 11.3-25.6 16.1 4.1-23.3 9.4 5.9-6.9 6.2 4.1-6.1 5.4 breccia material NL 7.7-56.4 32.1 0.03-0.23 0.13 0.04-0.68 0.36 1.9-35.1 18.5 5-28.4 16.7 6.1-6.5 6.3 4.4-4.8 4.6

Weathered andesitic L 30.9-38.4 34.7 0.10-0.23 0.17 0.10-0.65 0.38 8.8-14.3 11.6 4.4-5.8 5.1 5.7-6.8 6.3 4.6-5.1 4.9 breccias material NL 28.5-38.7 32.3 0.02-0.24 0.13 0.07-0.68 0.38 15.5-23.8 19.7 6.2-6.8 6.5 6.1-6.5 6.3 4-5.3 4.7

Weathered L 18.1-64.1 40.0 0.20-0.30 0.23 0.30-0.80 0.53 15.6-49.7 28.2 7.9-24.3 13.5 6.6-6.9 6.8 5.1-5.7 5.5 sandstone intercalation with marl NL 33.3-47.9 40.6 0.17-0.18 0.18 0.50-0.53 0.52 26.8-30.1 28.5 3.8-4.9 4.4 6.3-6.3 6.3 5.8-6 5.9

126

Table 5.14: Range and average of chemical properties (P2O5, SOM, C, N-total) of landslide-redistributed soil material (L) and non-landslide soils (NL)

P2O5 SOM C N-Total

Soil parent L/NL (ppm) % % % material Range Average Range Average Range Average Range Average

Altered andesitic L 3.1-7.4 5.7 0.3-2.1 1.1 0.3 – 1.8 0.8 0.03-0.23 0.10 breccia material NL 1.4-2.7 2.1 2.0-3.2 2.6 1.2-1.9 1.6 1.00-1.30 1.15

Weathered andesitic L 2.9-3.3 3.1 2.3-3.2 2.8 1.3-1.8 1.6 0.14-0.86 0.50 breccias material NL 2.8-3.1 2.95 2.4-3.3 2.8 1.4-1.9 1.7 0.80-0.90 0.85

Weathered L 1.8-3.9 3.2 0.6-3.8 2.1 0.3-2.2 1.2 0.79-0.88 0.85 sandstone intercalation with marl NL 3.6-3.7 3.65 2.9-3.1 3.0 1.7-1.8 1.8 0.90-1.30 1.10 127

a) CEC Clay b) CEC SOM 70 35 70 4 60 30 60 3.5 50 25 50 3 2.5 40 20 40 30 15 2 (%)

(%) 30 20 10 1.5

(me/100gr) 20 10 5 1 (me/100gr) 10 0 0 0.5 0 0 17 18 19 20 21 22 23 24 25 26 27 17 18 19 20 21 22 23 24 25 26 27 Profile Profile

Fig.5.11: Comparison of CEC with: (a) clay content; (b) SOM

The CEC of landslide-redistributed soil material is not always in line with the content of clay and/or soil organic matter (SOM). In the redistributed-altered materials, (e.g. profile 17-21), the CEC mainly shows a good relation to the clay content but shows a poor relation to the SOM (see Fig.5.11 (a) and (b)). However, the CEC shows a poor relation to clay content but it shows a good relation to SOM in the redistributed-weathered materials (e.g. profile 22, 23, 25, 27), as shown in Fig.5.11 (a) and (b). The inconsistency of CEC to clay content and SOM can be caused by the type of soil parent material and the type of clay formed in the source soils of landslide-redistributed soil material.

The inconsistency of CEC also is followed by the insignificant changes of cation bases (Na+, K+, Ca2+, Mg2+). In detail, the average of cations with valency +1 shows a higher value in landslide-redistributed soil material than that in non-landslide soils (see Table 5.13). On the other hand, the average of cations with valency +2 shows a lower value in landslide-redistributed soil material than that in non-landslide soils (see Table 5.13). It is because the cations with valency +1 is easier to be soluted and to be removed from its material. Therefore, the higher value of Na+, K+ in landslide-redistributed soil material may not be derived only from the source soils but also from the regolith mixed together in the landslides redistributed soil material.

 Human-redistributed soil material Crop rotation, manuring, and fertilizing are the significant human activities influencing the soil chemical properties in the study area. Different land utilities require different types of crops. The types of land utilities found in the study area are paddy field, 128

dryland agriculture, and mixed garden (see Table 5.15). Each type of land utilities may have various types of crops such as paddy field (paddy), dryland agriculture (cassava, chili, corn, ground nut, curcuma, ginger), and mixed garden (cacao, coffee, cloves, teak wood, Albazia marina, rambutan, jack fruit, banana, durian). Different land utilities also require various intensity and types of land management i.e. fertilizing and manuring. The common fertilizer type used in the study area is artificial fertilizer which is necessary to improve N, P, K, and S content in the soils. On the other side, the common manuring types applied in the study area are derived from goat and poultry dung.

Table 5.15: N-total, P2O5, SOM, pH of human-redistributed soils

Soil N- Horizon P O SOM pH parent Fertilizer total 2 5 No (depth in cm) Land utility material (type) (%) (ppm) (%) H O KCl 2 Ap (0-20) Dryland 0.8 4.8 2.1 5.3 5.2 Volcanic Yes (ZA agriculture 28 ash Bw (20-44) & cow 0.9 5.1 2.4 5.6 5.4 (onion leaf, chili, material dung) C (44-94+) tomato) 0.6 5.8 1.9 5.9 5.5 Ap (0-19) 0.9 2.2 2.2 6.9 4.8 Volcanic Dryland 29 ash Bw (19-42) agriculture No 1.0 2.2 2.6 6.7 4.6 material (maize, cassava) C (42-173+) 0.9 2.7 2.1 6.9 5.5 Yes Weathered A (0-18) 0.9 8.0 1.0 5.9 4.5 Rainfed paddy (NPK & 30 andesitic field cow breccias C (18-88+) 0.7 8.3 0.9 6.0 4.9 dung) Yes Ap (0-36) 0.8 1.4 1.4 7.4 7.3 Weathered Rainfed paddy (Urea & 31 tuff field cow C (36-91+) 0.7 1.6 0.9 7.9 7.8 dung) Ap (0-18) 1.1 3.4 1.2 6.2 5.0 Dryland Yes Weathered A (18-33) agriculture (NPK & 1.1 3.5 1.7 6.6 5.4 32 sandstone Bw (33-42) (long bean, cow 1.0 3.6 1.4 6.7 6.0 maize) dung) C (42-84+) 0.8 1.8 1.0 6.6 5.6 Mixed garden Weathered A (0-27) 1.0 2.5 3.3 6.7 4.6 (strata vegetation 33 andesitic No of albasia, ginger, breccias C (27-74+) 0.7 3.7 1.4 6.9 5.5 jackfruit, bush) A (0-23) Dryland 0.9 4.0 2.1 6.1 5.3 Weathered agriculture Yes 34 andesitic (maize, ground (NPK) breccias C (23-96+) nut, cassava) 0.8 5.0 1.4 6.3 4.6

Ap (0-18) 0.9 1.6 1.0 6.2 5.3 Volcanic Yes (ZA Rainfed paddy 35 ash Bw (18-96) & cow 0.8 1.8 1.0 6.4 5.6 field material dung) C (96-157+) 0.8 3.9 1.4 6.0 5.2 36 Volcanic Ap (0-26) Dryland Yes 0.9 3.7 1.4 5.7 4.8 129

ash Bw (26-108) agriculture (NPK) 0.9 3.6 1.0 5.8 4.9 material (long bean, C (108-121+) maize, cassava) 0.7 4.0 1.0 6.0 4.9 Mixed garden Altered A (0-26) 0.9 5.0 2.8 5.4 4.8 (strata vegetation 37 andesitic No of albasia, breccias C (26-102) 0.8 5.4 2.4 5.6 4.1 chocolate) Weathered Ap (0-20) Rainfed paddy Yes 1.0 2.4 0.9 6.5 5.1 38 andesitic field (NPK) breccias C (20-67+) 0.9 3.0 0.5 6.5 4.7 Mixed garden Weathered A (0-28) 0.4 3.9 2.6 6.5 5.4 (strata vegetation 39 andesitic No of albasia, coffee breccias C (28-87+) 0.8 4.0 2.4 6.6 5.9 curcuma) Mixed garden Weathered A (0-21) 0.8 1.5 3.1 6.3 5.4 (strata vegetation 40 andesitic No of albasia, breccias C (21-73) 0.3 1.6 2.8 7.2 5.9 rambutan banana) Dryland Yes Weathered Ap (0-17) agriculture 0.6 2.8 3.3 6.8 4.5 (NPK & 41 andesitic (tomato, maize cow breccias chili) C (36-109+) dung) 0.8 3.3 2.9 6.9 4.9

Ap (0-23) Dryland 1.2 3.8 1.4 6.6 5.0 Weathered agriculture Yes 42 A (23-53) 1.0 3.6 2.1 6.8 5.4 tuff (long bean, (NPK) C (53-78+) maize, cassava) 0.9 3.2 1.7 7.9 4.0 Mixed garden Weathered A (0-26) 1.0 2.5 3.3 6.7 4.6 (strata vegetation 43 andesitic No of albasia, breccias C (26-84+) 0.8 3.7 1.2 6.9 5.5 cassava, bush)

In the study area, the crop rotation is conducted to deal with the climatic seasons. The crop rotation may control the N fixation of plant because the types of crops applied on every rotation influence on the N content in the soils. Table 5.15 shows that generally the content of N in the mixed garden is lower compared to the content of N in the paddy field and in the dryland agriculture. The N content in the mixed garden ranges from 0.3 to 1%.; the N content in the paddy field ranges from 0.7 to 1.1%; the N content in the dryland agriculture is about 0.6 – 1.2% (Table 5.15). The lower N in the mixed garden is mainly influenced by land management intensity. The mixed garden has less crop rotation, and thus it produces less N content in the soils. However, the paddy field and dryland agriculture are often rotated seasonally. Consequently, the crop rotation leads to gain more N content in soils.

The manuring is mainly purposed to enhance the organic matter. In the study area, the manuring is also intended to increase the aggregate stability in unconsolidated material because the additional organic matter can build colloids in the soils. The manuring is 130

conducted by applying animal dung as an organic fertilizer, as applied on the profile 28, 32, 35, 36, and 41 (Table 5.15). Consequently, the additional organic fertilizer through manuring also increases the presence of earthworm and other animals in the soils. The manuring is usually applied on dryland agricultures to increase crops productivity.

The increasing of organic matter (SOM) in the soils significantly influences the N content (see Table 5.15). An intensive releasing of SOM decomposition mainly causes the higher N content in the surface soils. Almost all profiles show that SOM content is linear with N content. The higher content of SOM in the surface soils is mainly followed by the higher N content in the surface horizon. In some cases, there are also the increasing of SOM and N content in the lower horizon as shown in the profile 28 and 32 (Table 5.15). The higher content of SOM and N in the lower horizon can be shown as the result of soil turbation due to tillage practices.

Table 5.16: Exchangeable base cations, Base saturation, CEC of human-redistributed soils

Exchangeable base cations Soil parent Horizon Type of tillage CEC BS No material (depth in cm) (treatment) Na+ K+ Ca2+ Mg2+

(me/100gr) (%) Ap (0-20) 30.9 0.08 0.03 17.1 5.3 73.0 Volcanic ash 28 Bw (20-44) RT (strip tillage) 31.1 0.07 0.02 16.3 4.3 66.3 material C (44-94+) 28.7 0.07 0.03 18.4 5.9 85.1 Ap (0-19) 27.5 0.07 0.02 5.6 8.4 51.1 Volcanic ash CT (mechanic 29 Bw (19-42) 27.7 0.07 0.02 5.6 5.5 40.5 material ploughing) C (42-173+) 27.0 0.09 0.03 6.9 6.7 50.9 Weathered A (0-18) CT (traditional 27.7 0.08 0.03 15.1 6.2 77.5 30 andesitic C (18-88+) ploughing) breccias 25.2 0.06 0.04 17.3 7.9 * Weathered Ap (0-36) CT (traditional 53.7 0.09 0.03 49.6 8.9 88.1 31 tuff C (36-91+) ploughing) 54.9 0.09 0.04 50.2 10.2 * Ap (0-18) 28.6 0.09 0.04 11.1 6.7 62.7 Weathered A (18-33) CT (mechanic 28.9 0.11 0.04 11.6 13.5 87.4 32 sandstone Bw (33-42) ploughing) 28.8 0.09 0.03 13.6 8.3 76.4 C (42-84+) 37.7 0.08 0.03 15.6 7.9 62.6 Weathered A (0-27) 25.7 0.1 0.03 2.5 1.3 15.1 33 andesitic ZT (-) C (27-74+) 13.2 0.1 0.04 2.6 1.3 breccias 30.0 Weathered A (0-23) RT (raised bed) 28.8 0.08 0.03 8.3 4.5 44.8 34 andesitic C (23-96+) 24.5 0.08 0.03 9.4 6.4 breccias 64.7 Volcanic ash Ap (0-18) CT (mechanic 22.8 0.06 0.04 8.7 4.6 58.7 35 material Bw (18-96) ploughing) 20.1 0.05 0.04 6.9 2.9 49.2 131

C (96-157+) 23.6 0.06 0.03 10.4 5.1 65.7 Ap (0-26) 19.3 0.05 0.02 8.3 3.8 62.8 Volcanic ash CT (traditional 36 Bw (26-108) 20.3 0.07 0.03 11.6 4.3 78.9 material ploughing) C (108-121+) 24.9 0.07 0.03 12.8 4.6 70.2 Altered A (0-26) 23.3 0.09 0.03 9.3 3.4 55.2 37 andesitic ZT (-) C (26-102) 19.8 0.07 0.02 7.8 2.2 breccias 50.5 Weathered Ap (0-20) CT (traditional 33.9 0.1 0.04 20.5 11.1 93.6 38 andesitic C (20-67+) ploughing) 26.7 0.14 0.05 23.8 2.7 breccias * Weathered A (0-28) 22.9 0.07 0.02 9.6 4.7 62.8 39 andesitic ZT (-) C (28-87+) 14.1 0.08 0.03 8.8 5.9 breccias * Weathered A (0-21) 29.9 0.07 0.02 14.3 7.9 74.4 40 andesitic ZT (-) C (21-73) 23.9 0.09 0.02 16.2 8.3 breccias * Weathered Ap (0-17) 20.4 0.11 0.04 4.7 4.7 88.3 41 andesitic MT (mulch) A (36-109+) 29.5 0.08 0.03 7.2 3.5 breccias 46.8 Ap (0-23) 23.5 0.09 0.04 9.1 4.2 56.5 Weathered CT (mechanic 42 A (23-53) 24.1 0.09 0.04 9.5 4.6 59.0 tuff ploughing) C (53-78+) 31.2 0.1 0.04 11.6 6.4 58.2 Weathered A (0-26) 25.7 0.1 0.03 2.5 1.3 15.1 43 andesitic RT (raised bed) C (26-84+) 13.2 0.1 0.04 2.5 1.3 breccias 30.0 * = over estimate Soil treatment = ZT (zero-tillage); RT (reduced tillage); MT (minimum tillage); CT (conventional tillage)

The soil organic matter (SOM) associates with organic fertilizer and crop residue as an input matter on the surface soils. The additional input matter in each land utilities results in various SOM on the surface soils. Table 5.15 shows that the SOM in the paddy field ranges from 0.3 to 1%; SOM in the dryland agriculture ranges from 0.6 to 1.4%; SOM in the mixed garden is about 0.8 – 1.8%. Compared to all land utilities, SOM under the mixed garden is greater than that of the dryland agriculture and paddy field (see Table 5.15). The higher SOM in the mixed garden is caused by the abundant of crop residue under the vegetation.

The fertilizing is usually applied on paddy field to increase the soil nutrients. The fertilizing provides a significant impact on increasing N and P content, soil pH, and exchangeable base cations i.e. Na+, K+, Ca2+, Mg2+. The fertilizers are often used in the study area because they are cheaper and more efficient than the manure. In some case, the fertilizers are also applied to support manuring activity. The influence of fertilizing in increasing soil bases can be described from a higher content of Ca2+ and Mg2+ in the upper horizon as shown in the profile 28, 35, 38 (see Table 5.16). 132

The tillage practices also cause base cations enrichment in the sub-surface layer. Profile 29, 32, 36, and 42 shows the base cation enrichment in the sub-surface layer due to tillage practices. However, profile 28, 31, and 35 does not show any base cation enrichment in the sub-surface horizon indicated by less base cations translocation along the profiles (see Table 5.16).

The Phosporous (P) is one of major soil nutrients mostly associated with soil parent material. The greater P content in the lower horizon still indicates that the soil parent material has a strong influence in supporting P nutrient (see Table 5.15). The P fertilizer addition is usually applied on the dryland agriculture and the paddy field. However, the P fertilizer addition does not provide a strong effect to the available P in the soils (see Table 5.15). Less effect of P fertilizer addition in the soils is shown by the low P content in the upper horizon. In other side, relatively low P content in the upper horizon might be caused by the high amount of nutrient uptaking by plant. Overall, the P contents in the whole profiles are categorized into low (< 15 ppm) based on Puslittanak (1993).

The soil pH relates to exchangeable base cations. The results show that the soil pH increases following the depth (see Table 5.15). The increasing soil pH in the lower horizon is influenced by the higher content of Ca2+ and Mg2+ in the soils (see Table 5.16). The soil pH also has a relation to base saturation where high value of base saturation results in high pH value (see Table 5.16). As the example, the influence of Ca2+ and Mg2+ content is clearly shown by the profile 4 which is developed from marl parent material. This profile shows the greatest soil pH (7.94 for pH H2O and 7.76 for pH KCl) among other profiles.

5.3.1.3 Recapitulation of soil properties based on soil-scape concept

To recapitulate the soil properties based on soil-scape concept, the entire soil property results are grouped based on landform segments as determined in section 5.2. These soil properties are assessed according to seven landform segments (see Table 5.1) which are specified more detail based on their relief setting and types of soil parent materials, as shown in Table 5.17. The parameters used to compare the soil properties result of those segments are percentage of clay, percentage of sand, N-total, SOM, K,

P2O5, and pH (see Table 5.17).

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Table 5.17: Recapitulation of soil properties based on soil-scape concept

Part of the Soil Profile Average value of selective properties within the profile Soil Parent Land Utility Profile study area Relief Depth Materials (Types) number N- (cm) % clay % sand K P pH SOM total Landform Q-VS segment Volcanic ash Uncultivated land 191 9 29.6 16.2 0.1 0.9 2.9 5.8 3.4 materials (bushes/shrubs) Cultivated land Volcanic ash 173 (dryland 29 68.1 8.3 0.1 0.9 2.4 6.8 2.3 materials agriculture) Volcanic ash Undulating slope Cultivated land 157 35 76.0 7.8 0.1 0.8 2.4 6.2 1.1 materials (paddy field) Cultivated land Volcanic ash 94 (dryland 28 42.1 25.3 0.1 0.8 5.2 5.6 2.1 materials agriculture) Altered andesitic Uncultivated land

274 11 72.7 7.5 0.1 1.0 1.3 6.1 1.8 breccias (bushes/shrubs) landslide- Cultivated land redistributed soil 176 19 17.66 57.26 25.1 0.1 0.1 7.4 6 (mixed garden) materials landslide- Cultivated land UPPER PART UPPER redistributed soil 176 22 28.21 47.02 24.8 0.1 0.2 5.6 5.9 (mixed garden) materials Volcanic ash Moderately steep Uncultivated land 134 1 8.1 15.5 0.1 0.9 5.2 6.1 3.4 materials slope (bushes/shrubs) Weathered Uncultivated land andesitic 212 5 14.8 13.8 0.4 1.4 2.6 6.4 2.7 (bushes/shrubs) breccias Volcanic ash Uncultivated land Steep slope 220 10 15.7 14.3 0.1 1.0 4.8 5.9 2.5 materials (bushes/shrubs) Weathered Cultivated land andesitic 74 33 33.0 47.1 0.1 0.9 3.1 6.8 2.3 (mixed garden) breccias 134

Soil Profile Selective properties value Soil Parent Land Utility Profile Relief Depth N- Materials (Types) number % clay % sand K P pH SOM (cm) total landslide- Cultivated land redistributed soil 53 18 9.18 50.59 40.2 0.1 0.1 6.1 5.7 (mixed garden) materials landslide-

Uncultivated land redistributed soil 63 24 19.94 49.57 30.3 0.1 0.1 6.3 5.7 (bushes/shrubs) materials T-VS

Altered andesitic Undulating slope Uncultivated land 91 12 63.4 14.3 0.3 0.9 2.6 6.5 2.1 UPPER PART UPPER breccias (bushes/shrubs) Altered andesitic Moderately steep Cultivated land 102 37 63.4 8.0 0.1 0.9 5.2 5.5 2.6 breccias slope (mixed garden) Weathered Cultivated land andesitic Steep slope 87 39 31.0 37.8 0.1 0.6 4.0 6.6 2.5 (mixed garden) breccias Volcanic ash Uncultivated land 188 4 25.4 18.3 0.1 0.8 3.0 5.9 2.7 materials (bushes/shrubs) Q-VS

Volcanic ash Undulating slope Uncultivated land 276 6 39.0 13.1 0.1 2.4 3.2 6.2 1.3 materials (bushes/shrubs) Cultivated land Volcanic ash 121 (dryland 36 67.8 6.3 0.1 0.8 3.8 5.8 1.1 materials agriculture) Weathered Moderately steep Uncultivated land andesitic 186 16 12.4 12.0 0.7 0.8 2.7 6.8 3.1 slope (bushes/shrubs) breccias Weathered Cultivated land MIDDLE PART MIDDLE andesitic 96 34 19.1 69.4 0.1 0.9 4.5 6.2 1.7 (mixed garden) breccias Landslide- Cultivated land redistributed soil 98 (dryland 20 12.95 39.66 47.4 0.1 0.1 5.8 6.2 materials agriculture)

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Soil Profile Selective properties value Soil Parent Land Utility Profile Relief Depth N- Materials (Types) number % clay % sand K P pH SOM (cm) total T-VS

Altered andesitic Cultivated land Undulating slope 148 15 73.8 4.5 0.1 1.1 3.0 6.4 2.5 breccias (mixed garden) Weathered Cultivated land Moderately steep andesitic 109 (dryland 41 15.3 18.1 0.1 0.7 3.1 6.9 3.1

slope breccias agriculture) Weathered Cultivated land andesitic 84 43 24.7 12.6 0.1 0.9 3.1 6.8 2.2 (mixed garden) breccias Weathered Cultivated land andesitic 67 (dryland 38 25.1 47.8 0.1 1.0 2.7 6.5 0.7

MIDDLE PART MIDDLE breccias agriculture) Landslide- Cultivated land redistributed soil Steep slope 73 26 13.6 78.58 7.8 0.3 0.1 5.9 6.6 (mixed garden) materials Weathered Uncultivated land andesitic 138 13 11.3 23.2 0.6 1.0 2.7 6.7 3.4 (bushes/shrubs) breccias Landslide- Cultivated land redistributed soil 86 (dryland 23 5.84 60.22 33.9 0.1 0.1 5.4 6 materials agriculture) L-T-VS

Cultivated land Altered andesitic Moderately steep 164 (dryland 14 65.1 8.4 0.7 1.3 2.5 6.7 3.6 breccia slope agriculture) landslide- Cultivated land redistributed soil Steep slope 74 21 11.71 53.68 34.6 0.1 0.1 5.9 6.2 (mixed garden) materials

LOWER PART PART LOWER Weathered Uncultivated land andesitic 87 8 8.4 37.5 0.1 0.9 2.7 6.1 2.7 (bushes/shrubs) breccias

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Soil Profile Selective properties value Soil Parent Land Utility Profile Relief Depth N- Materials (Types) number % clay % sand K P pH SOM (cm) total L-T-S

Weathered Cultivated land sandstone Undulating slope 84 (dryland 32 27.5 45.3 0.1 1.0 3.1 6.5 1.3 agriculture) Weathered tuff Cultivated land 91 31 39.9 6.1 0.1 0.8 1.5 7.7 1.1 (paddy field) landslide- Cultivated land redistributed soil 73 (dryland 27 30.87 52.43 16.6 0.6 0.1 6.1 6.9 materials agriculture)

landslide- Cultivated land Moderately steep redistributed soil 231 (dryland 25 19.53 78.18 2.3 0.3 0.1 6.6 6.3 slope materials agriculture) Weathered Cultivated land sandstone 106 (dryland 7 17.2 21.7 0.5 1.1 3.8 6.6 3.0 agriculture) LOWER PART LOWER Cultivated land Weathered tuff 78 (dryland 42 24.2 17.9 0.1 1.0 3.5 7.1 1.7

agriculture Cultivated land Weathered marl 96 (dryland 2 41.9 10.0 0.2 1.0 2.7 6.5 1.8

agriculture) F

Weathered Moderately steep Cultivated land andesitic 88 30 28.6 36.8 0.1 0.8 8.2 6.0 0.9 slope (paddy field) breccias Cultivated land Weathered tuff Steep slope 41 (dryland 3 9.7 14.0 0.4 0.9 2.5 6.6 2.3

agriculture) 137

The percentage of clay and of sand shows a significant description about the differences of soil properties based on the soil-scape. According to Table 5.17, it shows that the percentage of clay and of sand are various within its upper, middle, and lower parts of the study area. The sequences of upper to lower part of the study area do not determine the sequences of clay translocation and of sand fragmentation among those parts. However, the sequences of clay translocation and of sand fragmentation are closely depended on the regional relief setting within the particular parts of the study area. It is clearly shown that the regional relief setting varies within the particular parts of the study area (see Fig.5.2). As the example, within the upper part of the study area the soil profiles having undulating relief have much higher percentage of clay than those having moderately-steep and steep reliefs. The soil profiles having undulating relief have >40% of clay percentage but the soil profiles having moderately steep up to steep relief have about 9-30% of clay percentage (Table 5.17). Therefore, the slope position does not determine the grouping of clay percentage within the upper part of the study area.

The elevation and slope position also do not affect K content. K content becomes one of parameters that can be affected by relief setting. The soil-water movement which is induced by the relief setting may influence the content of K+, as the most soluble exchangeable base cation (Foth, 1994). As the examples, in residual soils, the undulating relief causes lower K content even though it is located in the upper-, middle-, or lower zone (see Table 5.17). K content in the undulating relief is mostly 0.1 me/100gr. K content in the moderately steep up to steep slopes ranges from 0.2 to 0.7 me/100gr. However, the types of soil parent materials affect the K content in the particular relief setting. K content in the landslide-redistributed soil materials is often much higher than that in the residual soils. K content in the landslide-redistributed soil material is about 25-47 me/100gr, but K content in the residual soils only ranges from 0.1-0.7 me/100gr (Table 5.17).

The relief setting affects other chemical soil properties i.e. SOM and N-content in relation to the intensity of slope surface processes. The relief setting is mainly responsible for slope surface processes which result in landslide-redistributed soil materials. Consequently, the landslide-redistributed soils usually have lower SOM and N-content compared to the residual soils (see Table 5.17). However, the presence of human-induced in the residual soils also affects the SOM and N-content. Mostly, the cultivated land 138

results in higher SOM and N-content that uncultivated land as the effect of soil-turbation by human (see Table 5.17).

5.3.2 Assessment of soil profile development

As located in the tropics, the development of soil profiles is mainly controlled by climate and vegetation. As the main effect of climate, the development of soil profile can be identified through clay translocation along profiles. Moreover, the climate together with vegetation may affect the development of soil profiles through organic matter mineralization or humification in the top soils.

In specific, the development of soil profiles in the study area is various due to soil parent material types, reliefs, slope surface processes, or human influences. Those parameters cause the variation of particle size distribution, clay transformation, clay translocation, and organic matter mineralization and humification which are important processes of soil profile development.

The development of soil profiles in the study area was assessed through the ratio of soil properties within the profiles. The soil properties that are strongly related to the development of soil profiles are clay and SOM. Therefore, the development of soil profiles in the study area is assessed by: (i) the ratio of SOM in A-horizon towards SOM in B- or C-horizon; (ii) the ratio of clay formation in C-horizon towards clay formation in A or A+B horizon. In this study, the development of soil profile was solely conducted to the residual soils (section 5.3.2.1) and human-redistributed soil material (section 5.3.2.2). Table 5.18 presents the soil profile development of residual soils in the variation of soil parent material in the study area. Table 5.19 presents the soil profile development of human-redistributed soil material in the variation of human activities in the study area.

On the other hand, the development of soil profile in landslide sites shows a different view. Landslides, as the main slope surface process in the study area, may disrupt the soil development results in a landslide-redistributed soil material and an interrupted soil profile. Therefore, the development of soils in landslide sites can be assessed from the landslide zonation as presented in section 5.3.2.3.

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5.3.2.1 Residual soils (i) Ratio of SOM in A-horizon toward SOM in B- or C-horizon Soil Organic Matter (SOM) is related to the decomposition and mineralization of organic matter. The more develop a soil shows a higher organic matter in the profile (Foth, 1994). Furthermore, the organic matter is mostly associated with the vegetation cover and climate, of which strongly influence the upper-most layer of profile. Therefore, the ratio of SOM in A-horizon towards SOM in B- or C-horizon is intended to describe the development of soil profile in the particular areas.

The variety of SOM in A-horizons becomes the indicator for a different stage of soil profile development. The important differences were noted between SOM in A- horizon and SOM in B- or C-horizon where the organic matter is mostly reduced (see Table 5.5 in section 5.3.1.1). According to previous Table 5.5, SOM content in A-horizons ranges from 0.9% to 4.3%. The average SOM in A-horizons is 2.51%. Also, the SOM usually decreases with the depth.

Table 5.18: Soil profile development assessments of residual soils

Ratio of Ratio of No Soil parent Clay in C-horizon and SOM in A-horizon and profile material Clay in A or A+B SOM in B- or C-horizon horizon 1 Volcanic ash 1.39 0.79 material 2 Weathered marl 1.13 0.98

3 Weathered tuff 1.33 0.80 4 Volcanic ash 1.31 0.66 material 5 Weathered 1.03 0.62 andesitic breccias 6 Volcanic ash 1.78 0.60 material

7 Weathered 1.07 0.99 sandstone

Weathered 8 1.14 0.31 andesitic breccias

Volcanic ash 9 1.12 0.86 material

Volcanic ash 10 1.08 0.82 material 140

Altered andesitic 11 0.65 0.99 breccias

Altered andesitic 12 1.07 0.90 breccias

Weathered 13 1.03 0.94 andesitic breccias

Altered andesitic 14 1.00 0.87 breccias

Altered andesitic 15 1.08 0.75 breccias

Weathered 16 1.07 0.77 andesitic breccias

The ratio of SOM in A-horizons towards SOM in B- or C-horizon mainly produces the value of more than 1.0 (see Table 5.18). This ratio value means that the A-horizons as the surface horizon have a higher value of SOM than the underlying horizons, and thus it indicates that the soil profile has already developed. There is only one profile (profile 11) which has the ratio of SOM less than 1.0. Therefore, the ratio of SOM in A-horizons towards SOM in B- or C-horizon is ranged from 0.65 to 1.78 (Table 5.18). There is no significant pattern of SOM towards the soil parent material types. The SOM value is partly due to the influence of vegetation cover on the soil surface.

(ii) Ratio of percentage of clay in C-horizon towards percentage of clay in A or A+B horizon

The formation of clay also indicates the development of soil profile. The formation of clay is related to the weathering stage of soil parent material. Therefore, the clay percentage is mainly depended on the types of soil parent material. The increasing of clay percentage from an underlying soil parent material to a soil describes the development of soil profile.

The important differences were noted between the percentage of clay in C-horizon towards the percentage of clay in A or A+B horizon where the percentage of clay mostly increases (see Table 5.4 in section 5.3.1.1). According to previous Table 5.4, the percentage of clay in C-horizons ranges from 4% to 63%. The percentage of clay in soils ranges from 5.8% to 85.7%. Often, the percentage of clay increases from the soil parent material to the surface/subsurface soils. 141

There are various ratio of percentage of clay in C-horizons towards percentage of clay in A or A+B horizon. The ratio of percentage of clay in C-horizons towards percentage of clay in A or A+B horizon ranges from 0.31 to 0.99 (Table 5.18). The range of ratio shows that all the profiles have the ratio of less than 1.0. This range of ratio shows that all the profiles have the increasing of percentage of clay in C-horizons towards percentage of clay in A or A+B horizon, and thus indicates the development of soil profiles in the study area. However, in detail, the farer ratio of percentage of clay from 1.0 means that the more develop of soil profile. On the other side, the nearer ratio of percentage of clay to 1.0 means that the soil profile does not develop yet because there is no significant different of percentage of clay in C-horizon towards percentage of clay in A or A+B horizon.

There is noticeable pattern of percentage of clay in C-horizons towards percentage of clay in A or A+B horizon. According to Table 5.18, it shows that the range of ratio of percentage of clay in the altered material is about 0.9; in the volcanic ash material is from 0.6 to 0.8; in the weathered of marine sediment (marl, tuff, sandstone) is from 0.8 to 0.99; in the weathered andesitic breccias is from 0.3 to 0.9. Among others, the weathered andesitic breccias have a wide range of percentage of clay ratio. It means that the soil profile development of weathered andesitic breccias is various depended on its location, slope position, and vegetation cover, in responding to the climate effect during weathering process.

5.3.2.2 Human redistributed-soil material (i) Ratio of SOM in A-horizon towards SOM in B- or C-horizon Differences in SOM in A-horizon become an indicator for a different stage of soil profile development. The important differences were noted between SOM in A-horizon and SOM in B- or C-horizon where the organic matter is mostly reduced (see Table 5.15 in section 5.3.1.2). According to Table 5.12, SOM in the A-horizon ranges from 0.9% to 3.3%. The average of SOM in A-horizons is 2.1%.

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Table 5.19: Soil profile development assessments of human-redistributed soils

Ratio of Ratio of No Clay in C-horizon Soil parent material SOM in A-horizon and profile and Clay in A or SOM in B- or C-horizon A+B horizon Volcanic ash 28 0.86 0.64 material Volcanic ash 29 0.87 1.01 material Weathered andesitic 30 1.20 1.03 breccias 31 Weathered tuff 1.60 0.99 32 Weathered sandstone 0.70 0.94 Weathered andesitic 33 2.38 0.36 breccias Weathered andesitic 34 1.50 0.61 breccias Volcanic ash 35 1.00 1.07 material Volcanic ash 36 1.33 1.11 material Altered andesitic 37 1.14 1.11 breccias Weathered andesitic 38 1.67 0.66 breccias Weathered andesitic 39 1.07 0.54 breccias Weathered andesitic 40 1.13 0.39 breccias Weathered andesitic 41 1.12 0.57 breccias 42 Weathered tuff 0.67 0.84 Weathered andesitic 43 2.71 0.98 breccias

Similar to residual soils development, the SOM ratio mainly produces the value that is more than 1.0 (see Table 5.19). This ratio value means that the A-horizons as the surface horizon have already developed compared to the underlying horizons. Therefore, the ratio of SOM in A-horizons towards SOM in B- or C-horizon has a range from 0.67 to 2.83 (Table 5.19). There is no significant pattern of SOM among the soil parent material which is described by the differences of SOM under various soil parent material types are 143

fairly minimum. This condition shows that the influence of vegetation cover on the soil surface is more influenced rather than the soil parent material types.

(ii) Ratio of percentage of clay in C-horizon towards percentage of clay in A or A+B horizon Similar to residual soils development, the formation of clay may also indicate the development of soil profiles. The increasing of clay percentage from the underlying soil parent material to the soils describes the development of soil profile. However, in this human-redistributed soil, the clay percentage is mainly depended on the human activities applied on its soil surface. Often, human activities cause the soil turbation and lead to influence the clay percentage within the soil profile.

The significant differences of clay percentage also were noted between percentage of clay in C-horizon towards percentage of clay in A or A+B horizon. However, there is no linier pattern of the percentage of clay between one to other profiles even though most of the percentage of clay shows an increasing to the depth (see Table 5.11 in section 5.3.1.2). Based on Table 5.11, the percentage of clay in C-horizon is ranged between 14.4% - 77.7%. However, the percentage of clay in the soils is ranged between 9.8% - 72.5%.

There are various ratio of percentage of clay in C-horizons towards percentage of clay in A or A+B horizon. The ratio of percentage of clay in C-horizons towards percentage of clay in A or A+B horizons is ranged from 0.36 to 1.11 (Table 5.19). This range of ratio shows that there is various range of percentage of clay ratio. The range of ratio which is less than 1.0 strongly shows that there is an increasing of percentage of clay in C-horizons towards A or A+B horizon, and thus indicates the development of soil profiles. However, the range of ratio which is more than 1.0 shows that there is a decreasing of percentage of clay in C-horizons towards A or A+B horizon. This higher percentage of clay (> 1.0) is occurred due to agricultural practices applied on the soil surface. This agricultural practices lead to the inversion of clay from upper layer to lower layer within the soil profiles. Overall, there is no noticeable pattern of percentage of clay in C-horizons towards percentage of clay in A or A+B horizon in these human- redistributed soils. It is because human influences on the soil surface strongly affect development of soil profiles.

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5.3.2.3 Landslides redistributed-soil material Landslides, as the dominant slope surface process in the study area, cause a significant impact on soil formation and soil development. Landslides from the soil study’s perspective may act as the agent that is able to remove the soils, regolith, and/or parent rock in a large volume. The influence of landslides in the soil study can be focused on two zones i.e. the depletion zone taking place at the head of landsides, and the accumulation zone taking place at the toe slope of landslides (Fig.5.12).

(i) Depletion zone of landslides The depletion zone of landslides is able to redistribute the disturbed material downslope. Consequently, in the depletion zone the soil development is disrupted. Based on the variation of depletion zones, landslides in the study area are classified into three categories: (A) landslides that remove the surface soil and/or sub-surface soil; (B) landslides that remove the soils up to regolith; (C) landslides that remove the soils up to underlying parent rock. Those three categories of landslides not only influence the soil profile development and the soil formation in that particular area, but also control the form of agricultural activities in adapting to landslides deposit as discussed in section 6.3.1.

Landslide transports the surface soil and/or the subsurface Depletion soil zone

Accumulation zone Landslide- transported soil materials bury the former soil profile

Photo credit by: NurAinun Pulungan, 2013 Fig.5.12: Soil material redistribution by landslides 145

The landslides that remove the surface and/or sub-surface soils still can continue the former soil profile development. It is because this landslide type does not overly distract the soil profile development in the cut area. This landslide type just removes the surficial cover material as shown in Fig.5.13. Therefore, the remaining soil in this landslide zone can continue the development of soil profile. In addition, this remaining soil also can act as a medium for plant growth and can be directly used by human as a cultivation land. This landslide type is commonly found in the northern part of the study area in which it is mostly covered by volcanic ash soils.

(b) (a)

(c)

Photo credit by: NurAinun Pulungan, 2015 Fig.5.13: Landslides that remove the surface soil and/or subsurface soil Locations: (a) Wonogiri district; (b) Loano district; (c) Mayungsari district

The landslides that remove the material up to regolith will remain the regolith as the upper-most layer of the profile (Fig.5.14, 5.15, 5.16). In this landslide type, the former soil profile development is terminated because the solum has been removed by the landslides. As a consequence, the regolith is revealed, and thus redeveloping of soil profile 146

is started. The further soil profile development in this landslide zone is strongly determined by the type of regolith in that area. The types of regolith that are possibly found in the study area are: (i) saprolite, (ii) colluvium, and (iii) airfall deposit.

Surface soils

Saprolite

Soil

material Saprolite

Surface soils

Soil Saprolite Saprolite material

Photo credit by: NurAinun Pulungan, 2015 Fig.5.14: Landslides that remove the soil material up to regolith (saprolite-type) 147

The saprolite-type of regolith, of which it is derived from the in-situ weathered rock, is mostly revealed by landslides in the central and the southern part of the study area. Fig.5.14 illustrates this type of landslide.

Altered soil material

Altered soil material

Photo credit by: Rini Meiarti, 2013; NurAinun Pulungan, 2015 Fig.5.15: Landslides that reveals the altered soil material to the surface

The landslides that remove the material up to regolith also become a crucial agent that reveals the altered parent material to the surface. The altered parent material is another type of saprolite which is commonly found in the intrusive areas. As mentioned previously in the section 5.5.3, the formation of old volcanic systems in the study area was also 148

followed by the intrusion which causes the hydrothermal alteration in some locations. However, most of these altered materials have been widely covered by volcanic ash deposit. The occurrences of landslide which remove the soil up to regolith make the extensive cover of volcanic ash soils and of volcanic ash deposit are removed, and thus reveal the altered parent material to become the upper-most regolith (see Fig.5.15). As the consequence, in such areas, these altered parent materials become the recent regolith, and develop into the recent soil profile which is mainly characterized by high clay content.

Colluvium

Colluvium

Photo credit by: NurAinun Pulungan, 2015 Fig.5.16: Landslides that remove the soil material up to regolith (colluvium-type) 149

The colluvium-type of regolith of which it is derived from the previous landslide deposit also is mostly revealed by landslides in the central and the southern part of the study area. Fig.5.16 illustrates this type of landslide.

Surface soils

Surface soils Airfall deposit

Airfall deposit

Surface soils

Airfall deposit

Photo credit by: NurAinun Pulungan, 2013, 2015

Fig.5.17: Landslides that remove the soil material up to regolith (airfall deposit-type)

The airfall deposit-type of regolith, of which it is derived from volcanic ash deposit, is mostly revealed by landslide in the northern part of the study area. Fig.5.17 illustrates this type of landslide.

150

The landslides that remove the material up to the underlying parent rock also cause the soil profile development to stop. In this landslide type, the solum and the regolith have been removed by the landslides, and thus the soil formation must be reformed. This landslide type mostly occurs in the areas having shallow soil depth which usually develops on weathered parent rocks. The occurrences of this landslide type are mainly caused by human disturbances on slope stability, such as cutting slope for road construction, as shown in Fig.5.18. In the study area, this landslide type is commonly found in the southern part of the study area.

Surface soils

Saprolite Rock

Surface soils

Saprolite

Rock

Photo credit by:Rini Meiarti, 2013

Fig.5.18: Landslides that remove the soils up to the underlying parent rocks 151

(ii) Accumulation zone of landslides The accumulation zone of landslide deposits may interrupt the soil formation in the affected area. This is due to the fact that the landslide deposit creates lithological discontinuity soils, and thus causes the setting timezero for a new soil formation. However, different classification of landslides results in distinct characteristics of landslide deposit in the accumulation zone.

According to the classification of landslides in the study area, the specific patterns of soil properties in landslide deposit have been found. These patterns are observed based on the type of parent material of landslide deposit i.e. weathered soil parent material, volcanic ash parent material, and altered soil parent material. The soil properties used to observe the patterns are particle size distribution, texture, CEC, Cole Index, SOM, and N. The particle size distribution, texture, SOM, and N are the parameters used for describing the effect of mixing process in soil material during landslides. The CEC and COLE Index are the parameters used for detecting types of clays and behavior of soils toward additional and removal of water, of which they are crucial for determining the soil stability on slopes.

In volcanic ash material, the landslide deposit is only derived from landslide categories A and B. The silt content in particle size distribution becomes a difference among those landslide categories. The silt content of landslide deposit in B category is greater than that of landslide deposit in A category (see Table 5.20). It is because the landslide deposit in B category have a mixed of soils and volcanic ash deposit, which contain a higher silt content. However, the silt content of landslide deposit in A category must be less than that of landslide deposit in B category since the landslide deposit in A category is dominated by volcanic ash soils where clay fraction has been more developed.

The pattern of soil properties in landslide deposit of volcanic ash material can also be observed from COLE Index, CEC, SOM, and N content. Based on Table 5.9, COLE Index of landslide deposit in A category is higher than that of landslide deposit in B category. The pattern of COLE Index is also in line with the pattern of CEC. Higher value of COLE Index and CEC of landslide deposit in A category is determined by a close relation of those properties to the clay content. Landslide deposit in A category, which contains a lot of soil material, have higher clay content than landslide deposit in B category. Consequently, this high clay content leads to the high COLE Index and CEC of 152

Table 5.20: Landslide-soil material properties concerning landslide classification in the study area

Particle size Parent material Landslide COLE CEC SOM N No Texture classification % Clay % Silt % Sand Index (me/100gr) (%) (%)

(0.2-2 µm) (>2-50 µm) (>50-2000 µm) Volcanic ash- weathered Silty clay 17 A 30.01 60.88 9.11 0.12 27.9 0.7 0.6 andesitic loam breccias material

Weathered 18 andesitic B 23.59 32.19 45.22 Loam 0.10 18.8 0.5 0.5 breccias material

Altered tuff 19 B 57.28 17.06 25.66 Clay 0.06 8.7 0.4 1.1 material

Altered 20 sandstone B 49.38 12.95 37.66 Clay 0.08 8.3 0.3 0.8 material

Weathered Sandy 21 andesitic C 11.69 33.80 54.51 0.09 14.5 2.2 0.5 loam breccias material

Volcanic ash- 23 altered andesitic B 19.53 78.18 2.29 Silt loam 0.09 14.4 0.4 0.1 breccias material

Volcanic ash 25 A 27.53 62.18 10.29 Silt loam 0.17 21.1 0.6 0.7 deposit

Volcanic ash- 26 B 13.60 78.58 7.79 Silt loam 0.10 14.6 0.3 0.1 altered tuff

153

landslide deposit in A category. The same pattern is also shown by SOM and N content. SOM is in line with N content where they also have a greater value in landslide deposit in A category than that in B category (see Table 5.20). The reason is these properties are mostly related to decomposition activities which intensively occur in the surface material rather than in the sub-surface material.

In the areas underlain by weathered andesitic breccias, the landslide deposit is mainly derived from landslide categories B and C. It is because the soils developed on weathered andesitic breccias are usually shallow. Hence, the landslides in this area are mostly in close connection with saprolite and/or parent rock. Based on soil properties analysis, the sand content in particle size distribution may differentiate those landslide categories. The sand content of landslide deposit in C category is greater than that of landslide deposit in B category (see Table 5.20). It is because the landslide deposit in C category has a mixed of more rock and gravel, whereas the landslide deposit in B category has a mixed of soils and regolith which are already dominated by clay fraction.

The pattern of soil properties in landslide deposit of weathered andesitic breccias can be observed from COLE Index and CEC. Similar to the pattern of soil properties in volcanic ash material, the COLE Index pattern is consistent with the CEC pattern where the value of those properties is higher in landslide deposit in B category than that in landslide deposit in C category. However, the different values between those landslide deposit categories are not too significant because both of them are less dominated by clay content. Furthermore, there is no significant difference in soil properties related to SOM and N when comparing landslide deposit in B category to landslide deposit in C category. The reason is because both landslide categorizes are not dominated by soil material of which high content of SOM and N is usually produced.

In the areas underlain by altered soil parent material, the landslide deposit is mostly derived from landslide category B. The uniform landslide category in this area produces a similar type of landslide deposit. Thick layer of altered soil parent material cause the landslide deposit to be mainly dominated by altered material and soils, rather than a mixture of rock fragment. Based on the soil properties analysis, the landslide deposit in this category has a very high content of clay (see Table 5.20). However, based on Table 5.15 & Table 5.16, there is no other noticeable pattern of soil properties in landslide deposit of altered material due to the similar categorization of landslides. 154

5.4 Genesis of soil parent material This subchapter studies the variation of soil parent material in the study area. The variation of soil parent material determines genetic variation of soils. Based on the data in Section 5.3, the soil parent material in the study area are derived not only from the underlying weathered parent rocks but also from the altered parent rocks, burial volcanic ash, or burial redistributed material. The soil parent material of profile sites is distributed as shown in Fig.5.19.

Fig.5.19: Distribution of soil parent material in the study area according to geological formations 155

5.4.1 Soil parent material from weathered parent rock

Weathered parent rock material or saprolite are mostly found in the central and in the southern parts of the study area (see Fig.5.19). This is because these parts of the study area are not buried by volcanic ash deposits from the Sumbing Volcano. Unlike those parts, saprolite in the northern part of the study area has been obviously buried by volcanic ash deposits which become the latter soil parent material, as shown in Fig.5.19. Overall, saprolite that was found in the study area is the weathering results of old volcanic rocks, marine sedimentary rocks, and andesite (Fig.5.20).

a b

c d

Photo credit by: NurAinun Pulungan, 2014 Fig.5.20: Weathered parent rocks in the study area: (a) weathered andesitic breccias, (b) weathered andesite, (c) weathered sandstone, (d) weathered tuff

The most dominant saprolite in the study area is weathered andesitic breccias as presented in Section 4.2.3. This is in-line with the geological map which shows that the andesitic breccias are the dominant parent rock in the study area, as categorized into Tmoa 156

Formation (see Fig.4.8). Most of the weathered andesitic breccias are buried by volcanic ash deposits or redistributed material. The weathered andesitic breccias are often dominated by coarse grains compared to any others weathered parent rock material, as presented in Table 5.4 in Section 5.3.

In some locations, the old volcanic rocks were also intruded by andesite. The weathered andesite is mainly found in the southern part of the study area (see Fig.5.24). The presence of weathered andesite often distracts the formation of weathered andesitic breccias, and thus causes lateral intersection of soil parent material deriving from andesite and andesitic breccias.

Another type of saprolite in the study area originates from weathered marine sedimentary rocks. They are also formed in the central part of the study area (see Fig.5.19). The weathered marine sedimentary rocks found in the study area are weathered tuff, weathered marl, and weathered sandstone, as mentioned in Section 4.2.4. The weathered tuff and the weathered marl are often dominated by clayey material, as earlier presented in Table 5.4 in Section 5.3. The dominant of clay in this weathered material is due to weathering of fine volcanic particles in the marine sedimentary rocks, as stated in the earlier Section 4.2.3. However, the weathered sandstone is mainly composed by stable mineral such as quartz (Mubiayi, 2013), and hence is resistant to weathering forming relatively thin soils (see Table 5.3).

Table 5.21: Mineralogical composition of parent rocks in the study area based on X-ray powder diffraction (XRPD) analysis results Parent rocks Contents

Andesite Plagioclase, Illite/Smectite and probably a bit Pyroxene/Hornblende

Sandstone Plagioclase, Illite/Smectite and Pyroxene/Quartz

Marl Plagioclase, Illite/Smectite, Quartz, Calcite and probably a bit Amphibole

Overall, the parent rocks in the study area are commonly composed of plagioclase mineral (see Table 5.21). According to the result of XRPD analysis, the parent rocks in the study area consist of plagioclase, illite/smectite, quartz, pyroxene, amphibole, calcite, and 157

hornblende (Table 5.21). However, the variety of minerals among different parent rocks are small. The andesite and the sandstone are only distinguished by the presence of hornblende and quartz in pyroxene intercalation, whereas, the presence of amphibole and calcite distinguishes the marl from the other parent rocks.

5.4.2 Soil parent material from volcanic ash deposit

Volcanic ash material is mainly found in the northern part of the study area (see Fig.5.19). It is genetically derived from Sumbing Volcano located in the north of the study area. The volcanic ash material has covered the underneath material of Menoreh volcanic systems in the northern part of the study area, which have andesitic breccias as the original material of this area. The volcanic ash material in this area acts as the burial deposit, and thus becomes the upper-most soil parent material in this area. Thereby, the covering of volcanic ash material becomes the dominant soil parent material in this area (see in the earlier Section 4.2.3).

Photo credit by: NurAinun Pulungan, 2013 Fig.5.21: Thick volcanic ash soil in the northern part of the study area (e.g. profile 10 & 9)

Based on field observation, the volcanic ash material is porous, fine-grained, and light-weight compared to any other soil parent material. Unlike the weathered parent rock material, the volcanic ash material has high weatherable minerals (Fiantis et al., 2011). The easy weathering volcanic ash material is characterized by thick volcanic ash soils as mostly found in the field (Fig.5.21). This thick volcanic ash soil can be distinguished clearly from its volcanic ash deposits by their morphological characteristics and their 158

textures (see Table 5.3 and Table 5.4 in Section 5.3). The volcanic ash material is also homogenously distributed at vertical-scale within the same deposition period.

5.4.3 Soil parent material from altered parent rock

In some locations, the formation of old volcanic systems is followed by the hydrothermal alteration. In the Sumbing volcanic system, the alteration mainly occurs in the eastern part of the system (Fig.5.23 (a)). However, in the Menoreh volcanic system, the hydrothermal alteration unevenly appears at old andesitic geological formation (Fig.5.23 (b)). This altered material is indicated by the pinkish-red soils color (5YR), as mentioned in subchapter 5.3.1. In the study area, the hydrothermal alteration is derived from the heated by andesite intrusion during the Pleistocene (van Bemmelen, 1949). Furthermore, the presence of gypsum as the mineral composition in altered material also indicates that this altered material is the products of low-temperature hydrothermal alteration (Sun, 2015), as shown in Fig.5.22.

Fig.5.22: Presence of smectite type of clay (montmorillonite) in altered material based on XRD analysis results (e.g. profile 12)

The hydrothermal alteration material produces extremely high clay contents in soil parent material, as presented in Table 5.4 in Section 5.3.1. The hydrothermal alteration material usually presents >60% of clay content while other soil parent material only presents <30% of clay content. Actually, the hydrothermal alteration material is the result 159

of in-situ parent rock which is then induced by the heated groundwater. The continuation of heated groundwater contacted with parent rocks causes the breaking of primary minerals to form secondary minerals assemblage (Bove et al., 1651, p.199). In the study area, the hydrothermal alteration material produces specific clay, i.e. montmorillonite as shown in Fig.5.22.

Fig.5.23: Presence of altered material due to hydrothermal alteration in some parts of the study area: (a) in the Sumbing volcanic system (location: Margoyoso village), (b) in the Menoreh volcanic system (location: Pucungroto village)

160

5.4.4 Redistributed soil material

Redistributed material is mostly found in non-plain and non-depression areas. Redistributed material is mainly caused by landslides and human activities on the slopes. In the study area, redistributed material is widely cultivated as new soil parent material, as it will be explained in the following Section.

5.4.4.1 Landslide-redistributed soil material

Landslides often redistribute the material in the study area in a large volume. Landslides may cause soil profile rejuvenation because landslides can redistribute the material from the upper/middle slopes downwards to the lower slopes in large quantities of volume. Landslides may peel the underneath weathered bedrock up to perform new soil parent material. While redistributing the material, landslides not only move the surface soils but also sometimes move the whole of soil profiles.

a b Landslide Landslide crown crown

saprolite

Soil material

Soil material

Photo credit by: Elok Surya Pratiwi, 2013 Fig.5.24: Types of landslides-redistributed material: (a) dominated by soil material; (b) mixed of soil material and saprolite

Landslide-redistributed material is widely found in the central part of the study area as it is mostly affected by landslide events. However, there are also found landslides- redistributed material in the northern and in the southern parts of the study area despite in smaller number of landslides. Fig.5.25 shows the distribution of landslides in the study area. This distribution presents all landslides found in the study area from 2007 until 2014 161

for all landslide sizes. There are two types of landslides-redistributed material in the study area (Fig.5.24): (a) contained by soil material; (b) contained by a mix of soil material and saprolite. Landslides-redistributed material contained by a domination of soil material is commonly found in the northern part of the study area where it is mostly covered by volcanic ash and related soils. However, landslides-redistributed material contained by a mix of soil material and saprolite is usually found in the central part of the study area where it is dominated by thin residual soils. Thus, the variation of landslides-redistributed material contributes to variation of soil parent material in the study area.

Fig.5.25: Distribution of landslides in the study area based on field survey 2007-2014 162

Fresh landslide-redistributed soil material which is directly cultivated with seasonal plants and wood plants

Photo credit by: NurAinun Pulungan, 2014 Fig.5.26: Landslide-redistributed material as new soil parent material in the study area: (a) dominated by soil material; (b) mixed landslide-redistributed soil material

Landslide-redistributed material often becomes a new soil parent material at landslide deposit areas. This is because most of the landslide-redistributed materials forms the upper-most layer and retards the underneath soil development. Landslide-redistributed material is usually loose material and unwell-sorted grain sizes. It also has been contained by certain amount of soil material. Therefore, landslide-redistributed material is easy to be directly cultivated. As an example, in the study area, landslide-redistributed material containing domination of soil material is mainly cultivated with seasonal plants i.e. 163

cassava, long bean, curcuma, and sweet potato. It is due to the fact that the landslide- redistributed material which is contained by certain amount of soils has provided the soil nutrients for plant growth. This soil nutrient in landslide-redistributed soil material is already available from the source soil material of landslides. However, landslide- redistributed material contained by mix soil material and saprolite are widely cultivated by woods i.e. teak wood and sengon. This is because the mix of soil material and saprolite in the landslide-redistributed soil material are contained by less of soils, and thus causes a low level of soil nutrients. Therefore, it is appropriate to be cultivated by woods which do not need soil nutrients as much as the seasonal plants. Those types of cultivation in landslide-redistributed soil material are illustrated in Fig.5.26.

5.4.4.2 Human-redistributed soil material Humans are able to redistribute soil and soil parent material artificially. In the study area, humans redistribute significantly the soil material spatially and temporally. The activities of humans like agricultural practices on the slope surface become the agent for material redistribution in the study area. However, humans more often redistribute the surfacial soil material rather than saprolite / weathered parent rocks. Fig.5.27 shows the intensive human activities on the slope surface causing material redistribution. In the study area, human redistribute the soil material spatially by terracing and tillage practices (see Fig.5.27 (a), (b), (c)). Thus, humans become an active agent by redistributing the soil material from upper slope to lower slope or vice versa through terracing. Humans are also able to turn-over surface and sub-surface horizons vertically during deep tillage practices. However, the role of human in the study area is not only essential for vertical soil material redistribution but also significant for lateral soil material redistribution. Human often redistribute lateral organic soil material during agriculture land preparation.

Humans often redistribute the surface material within a short temporal-scale. The role of human in temporally redistributing the material is commonly shown during crop rotation. In the crop rotation management, human intensively conducts the surface material redistribution in every certain period of land cover changes (see Fig.5.27 (d)). It is a common to have surface material redistribution during fallow-period in crop rotation. Therefore, this activity may control the surface material redistribution temporally. 164

a b

c

d

Photo credit by: NurAinun Pulungan, 2014 Fig.5.27: Human activities on slope surface: (a) Human-tillage practice to overturn the soils; (b) Mechanic tillage practice to overturn the soils; (c) terracing as one of soil redistributing management in slope areas; (d) crop rotation (paddy into ginger) 165

Photo credit by: NurAinun Pulungan, 2013 Fig.5.28: Mixed soil material of human-redistributed material

Human-redistributed material is not evenly distributed in the study area. Based on field observation, human-redistributed material is mostly found in the agricultural areas. Human-redistributed material usually contains a mix of soil material from surrounding cultivation parcels. Also, human-redistributed material is characterized by friable and unwell-sorted grain sizes, as shown in Fig.5.28. Therefore, the presence of human- redistributed material may cover the in-situ soil material, and thus becomes the new surface soil material. 166

5.5 Variations of soil formation

Soil formation variations in the study area can be categorized into monogenetic and polygenetic. The soil formation variations are determined by the number of soil formation cycle. The soils resulting from single soil formation cycle are monogenetic soils, whereas, the soils resulting from more than one soil formation cycle are polygenetic soils (Bruce, 1996). In the study area, the soil formation cycles are controlled by multi periods of soil parent material deposition and by slope surface processes.

5.5.1 Monogenetic soils

The monogenetic soils are rarely found in the study area because complex processes of landscape formation are more common than the simple processes. In the study area, the monogenetic soils can be found, but in very limited areas. These soils are usually found in the lower parts of the study area. It is because this area is not covered by the volcanic ash deposit and is rarely affected by slope surface processes as found in the upper and central parts of the study area. The monogenetic soils are formed in contact with the underlying parent rocks, as illustrated in Fig. 5.29.

A-horizon: is the upper-most mineral horizon, strongly weathered, and usually due to high humus contents resulting in a dark color

C-horizon: is the soil parent material horizon which is derived from the weathered parent rock

R: is the fresh underlying parent rock

Fig.5.29: Sketch of monogenetic soils illustrating the single soil formation cycle

Based on the field observation of this study, the monogenetic soils can derive from two different processes: (i) weathering of parent rock and (ii) alteration of parent rock. The monogenetic soils from parent rock weathering show that the climate becomes the influencing agent in soil formation, as shown in Fig. 5.30(a). The monogenetic soils from parent rock weathering are indicated by the gradual transformation of parent rock into the soils through the appearance of fractures on the rock (e.g. spheroidal weathering in Fig. 167

5.30(a)). The monogenetic soils from parent rock alteration show that the hydrothermal alteration becomes the influencing agent in soil formation, as shown in Fig. 5.30(b). The monogenetic soils from parent rock alteration are indicated by the chemical alteration of parent rocks resulting in white/pinkish altered soil parent materials due to the heat released in the parent rock during alteration.

a b

Soil gradation derived from weathered materials

Parent rock weathering Parent rock alteration

Spheroidal weathering

Photo credit by: NurAinun Pulungan, 2015 Fig.5.30: Monogenetic soils in the study area: (a) derived from weathering of parent rock; (b) derived from alteration of parent rock

In the study area, the monogenetic soils from parent rock weathering are found as the result of andesitic breccias weathering, andesite weathering, marl-sandstone weathering, and tuff weathering. These monogenetic soils usually develop under a single pedogenic process such as vertical translocation of fine particles and of base ions enriched into the sub-surface soil horizon. However, the monogenetic soils from parent rock weathering are mainly found as a thin soil solum (see Table 5.3) due to intensive slope surface processes. Those slope surface processes (e.g. shallow landslides and soil erosion) become a decisive factor for monogenetic soil profile development in the study area. Usually, the monogenetic soils from parent rock weathering only form A-horizons, as shown in Table 5.3. There are only limited numbers of monogenetic soils from parent rock weathering that form B-horizons (Bw). Based on the soil profile description, the monogenetic soils from parent rock weathering reflect a soil color gradation between the weathered parent rock and the soils during soil formation (see Fig. 5.30(a)). 168

The monogenetic soils from parent rock alteration are found in the volcanic areas which are induced by hydrothermal effect near the subsurface. This type of monogenetic soils develops under the influence of hydrothermal alteration which hits the underlying parent rock, and is characterized by clayey materials, as shown in Table 5.3. These monogenetic soils are mainly found with a thick solum due to intensive transformation by hydrothermal effects. Usually, they form a developed soil which consists of several layers of B-horizon. Based on the soil profile description, the monogenetic soils from parent rock alteration show thick reddish clayey profiles due to the impact of argillic alteration (see section 5.3.1) during soil formation.

5.5.2 Polygenetic soils

The polygenetic soils are commonly found in the study area. Based on the field observation of this study, the polygenetic soils are formed when the monogenetic soils have been buried by volcanic ash or landslide deposits. The polygenetic soils are dominantly formed in the upper part of the study area where it is dominated by the presence of burial volcanic ash deposits. In this area, the polygenetic soils are characterized by multi cycles of soil development within a profile, as it is shown in Fig. 5.31(a) and (c). Also, they can be characterized by multi layers of soil parent materials within a profile, as it is shown in Fig. 5.31(b).

1 1 2

2 2

1 1 2 2 2

3 2

(a) (b) (c) Fig.5.31: Sketches of polygenetic soil types in the study area: (1) soils, (2) soil parent materials, (3) parent rock 169

The multi layering of the soil profiles which lead to polygenetic soils can form lithological discontinuity soils. The polygenetic soils usually describe a lack of relationship with the underneath parent rocks (Lorz et al., 2011). The polygenetic soils are characterized by the latter soil development in the upper layer and the buried soil development in the lower layer, as shown in Fig.5.32. In these polygenetic soils, the soils are developed from the latter soil formation based on the upper-most soil parent material deposition. The stratification of different types of soil parent materials in polygenetic soils (see Fig. 5.31(a)) results in various soil properties within the profile because several properties (e.g. texture, clay mineralogy, and chemical composition) are strongly affected by soil parent material types (Buol, 1997; Arocena and Sanborn, 1999).

Volcanic ash soils-2 The latter soil development

Volcanic ash deposit-2

Volcanic ash soils-1

The buried soil development

Volcanic ash deposit-1

Fig.5.32: Polygenetic soils in the study area developed from layered volcanic ash deposit located in Randusari village

There are two types of polygenetic soils found in the study area (Fig.5.34): (i) Quaternary materials overlaying on Tertiary materials (Q-T), (ii) Quaternary materials overlaying other Quaternary materials (Q-Q).

(i) Q-T is mostly found in the study area. This type of polygenetic soils is mostly found as Quaternary volcanic ash deposit overlaying Tertiary volcanic residual soils or Tertiary marine sedimentary residual soils. Quaternary volcanic ash deposit creates the surfacial deposits, whereas Tertiary materials are the 170

basement for Quaternary deposits. Therefore, this type of polygenetic soils describes multi periods of soil development within a profile. In some parts of the study area, Q-T polygenetic soils also commonly form in landslide and erosion prone areas. Q-T polygenetic soils can occur in the unstable slope of Tertiary material due to topographical setting. The rough relief mainly controls the unstable slope to move the soil material from upslope to downslope. In addition, the intensive human activities also may trigger the slope surface processes. As a consequence, most of landslides and erosion produce the recent surfacial material in the study area, and thus it overlays the former Tertiary material.

b

a

Q (Redistributed Q (volcanic ash) materials)

T (altered material)

c T (Weathered Q4 (volcanic ash andesitic breccias) deposit)

Q3 (volcanic ash deposit)

Q2 (volcanic ash deposit)

Q1 (laharic sediment)

Photo credit by: NurAinun Pulungan and Aries Rahmadana, 2013 Fig.5.33: Types of polygenetic soils in the study area: (a) & (b) Q-T; (c) Q-Q

(ii) Q-Q is mainly found in the upper part of the study area. Q-Q polygenetic soils are created by the inter-bedded between several layers of Quaternary materials. 171

In the study area, stratification of Quaternary materials is often caused by different deposition period of volcanic ash. Therefore, the stratification creates multi layers of soil parent materials within a profile. However, Q-Q polygenetic soils also can be found as a result of redistributed Quaternary materials overlaying Quaternary volcanic ash deposit. In some areas, most of landslides and erosion occur on the Quaternary volcanic ash slope due to its instability. Thus, the stratification of Quaternary materials in this area enables multi periods of soil development within a profile.

The appearance of contrast of color, texture, and structure indicate that the soils have been experienced with more than one soil formation cycle, and hence form polygenetic soils (see Fig.5.33). These contrasts will not be found in monogenetic soils. With regards to soil development assessment, the whole soil profile is considered in monogenetic soils, whereas, only the upper-most soil profile will be considered in polygenetic soils as it is developed on the latter soil parent material deposition.

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CHAPTER 6 DISCUSSION

This chapter presents about the results of our study that will be discussed against the background from other studies and related literatures. Thereby, the research questions will be reconsidered and at least in part answered. The discussion in this chapter will cover the soil- scape relationship in the transitional landscape zone as detail explained in section 6.1, the soil formation and soil development as presented in section 6.2, and the soil-human interaction as explained in section 6.3.

6.1 Soil-scape relationships

The study area, located in the central part of Bogowonto watershed, is geologically the transitional zone of Menoreh Tertiary Volcanic Systems, Halang Tertiary Structural Systems, and Sumbing Quaternary Volcanic Systems. The study area mainly consists of short sequences of hill slopes with various soil parent materials along the slopes, and intensive slope surface processes. These geological and topographical conditions lead to typical soil profile characteristics and soil patterns in the study area.

As a transitional zone, the study area does not show a regional sequential pattern of soil characteristics along its upper, middle, and lower parts (see section 5.2 and 5.3). This condition is due to the fact that relief setting in the regional scale is not laid sequentially from the upper part to the lower part of the study area. The relief along the upper, middle, and lower parts of the study area is formed through various ways.

In this study, of which the regional scale approach is applied, the soil characteristics are strongly depending on the relief setting and types of soil parent material along the slopes. With regard to soil parent material, the soil characteristics show that not all the soil parent material is derived from weathered underlying bedrocks (e.g. weathered Tertiary volcanic rocks and weathered Tertiary marine sedimentary rocks). The soil characteristics indicate that there is also soil parent material derived from the burial of Quaternary volcanic ash and from the redistributed soil material induced by landslides or human. 173

The implementation of soil catena concept has been proven to be insufficient to explain the soil variation in the study area (see section 5.2). The soil catena concept is not applicable for the study area because this concept uses two-dimensional analysis of soils (Joffe, 1949), and hence focuses on the slope position along toposequences. The study area varies not only in the slopes but also in the relief, in the types of soil parent material, and in the slope surface processes. Therefore, a more sophisticated concept is required to explain the soil variation in the study area.

The soil-scape concept is found to be more suitable for explaining the soil variation in the study area. It is because the soil-scape concept emphasizes on the variation of soils under various landscape setting. The soil-scape concept considers the soil processes within a pedon as well as the slope surface processes in a landscape. This finding is in line with Hugget’s observation (1975) that soil development in a complex landscape setting can be clearly described by a landscape analysis as it considers a three-dimensional body of land.

The field observation of this study proves that the assessment of soil and landscape relationship in the study area requires a greater depth (>2m) of soil profile description. It is because the thickness of C-horizon in some areas exceeds the thickness of the overlaying A and B-horizons. Such situation is mainly found in the upper part of the study area, as mentioned in Table 5.3. In this particular area, the thick soil profiles are formed by a series of Quaternary volcanic ash which occupies the wavy relief of the hill slopes. Therefore, the thickness of the soil profile is mostly greater than 2m. The assessment conducted in this study is supported by the study of Wysocki, et al. (2005) who stated that soil profile description up to deeper subsurface material is necessary in order to link to stratigraphic information and soil parent material at greater depths. Also, the assessment of this study argues the Soil Taxonomy’s assessment which only considers up to 2m depth of soil profile description as the optimum range for plant growth.

The soil depth, as an indicator for soil development, is more influenced by the relief setting, rather than the slope position (see Table 5.2). This finding is in contrast with the findings of Kirkpatrick et al. (2014) which showed that soil depth is strongly influenced by the slope position. Most of previous studies showed that thick soils are usually formed in the lower slope position due to high soil-moisture content (Birkeland, 1994; Applegarth & Dahms 2001; Moura et al. 2012). However, in the study area the relief varies along the slopes (see Fig.5.1). Thus, this 174 relief variation affect the vertical water movement within the profile along the slopes (Durak & Surucu, 2005), and results in the various soil depths (Table 5.3 and Table 5.8).

The soil depth in the study area is also influenced by the types of soil parent material (see Table 5.3 and Table 5.8). Based on the field observation of this study, the thick soils are mainly found in the upper part of the study area consisted of a series of Quaternary volcanic ash acting as the layers of C-horizons. The volcanic ash contains fast weatherable minerals (Shoji et al., 1993; Dahlgren et al., 1993) which develop into the soils immediately after the volcanic ash is deposited (Fiantis et al., 2011). The thick soils are also found in the central part of the study area where it was induced by a hydrothermal alteration. In this particular area, the thick soils are developed on altered parent rocks. This thick soil is the result of layering of argillic horizons under different intensities. Consequently, the thick soils on these altered parent rocks form several B-horizons within the soil profile (Table 5.3). This finding is in line with that of Pirajno (2009) who stated that a hydrothermal alteration may generate an argillic alteration resulting in the formation of clay minerals. The argillic alteration is due to the increasing of H+ activities during a metasomatism, by which mineral exchanging occurs between the altered rocks and the ions carried by water (Carlson et al., 2009).

Most of the shallow soils are formed in the central- and in the lower part of the study area which are dominated by landslides and erosion processes on the slope surface. These shallow soils are formed because those intensive slope surface processes strongly cause soil redistributions, and thus interrupt soil development in that particular area. In addition, these shallow soils are related to human activities which are significant in redistributing the soil material along the slope surface. This situation is in contrast to such of Badia et al. (2013) which indicate that soils in the central- and in the lower slope hills usually form a thick depth because of less slope steepness. Another perspective was also given by Drouza (2007) who stated that the shallow soils are usually formed due to slow rate of parent rocks weathering. This perspective can be accepted since these parts of the study area are underlain by volcanic bedrocks and marine sedimentary bedrocks, which are more resistance to weathering than volcanic ash deposit in the upper part of the study area.

Another distinctive indicator for soil development in the study area is shown by vertical particle size distribution (see Table 5.4 and Table 5.9). Based on Table 5.4, the residual soil 175 development has a clear gradation of vertical particle size distribution. However, in areas having active landslide disturbance, the soil development shows an abrupt changing of vertical particle size distribution. The vertical particle size distribution in this area is disrupted by the presence of slope deposits which often contains mixed-particle size of soil material. Finding from this study is consistent to those of Casagli, et al. (2003) and Jeong et al. (2011) who presented that landslide deposits often has a mix of coarse and fine particle sizes. Phillips (2004) also stated that the presence of landslide deposits often results in vertical textural contrast within the profile, and indicates lithologic discontinuous soils (Ande & Senjobi, 2010; Lorz, 2008).

The particle sizes in the area within the uniform soil parent material can be strongly controlled by the relief setting, as shown in Fig.5.1 and Table 5.2. Based on the field observation of this study, the smooth relief is more characterized by fine-particle size as it has fewer disturbances of slope surface processes. On the other side, the rough relief usually varies in particle size because it significantly relates to the slope surface processes (Osher & Buol, 1998). Most of the rough relief sites in the study area are characterized by a short slope length and a large slope inclination (see Fig.5.1). Consequently, this rough relief generates more dynamic processes on the slope surface, and hence results in colluviums with various particle sizes. These results of this study are contradictive to those of who conveyed that smooth relief is usually formed by coarse-particle ranging from 6-16%, whereas rough relief has the predominant of fine particles that is up to 36%.

The relief setting also influences the C and N content (see section 5.3). Based on the field observation of this study, the rough relief which is largely formed in the central part and lower part of the study area has high potentials for slope surface processes. The soils on the rough relief are characterized by lower C and N content than the soils on the smooth relief (see Fig.5.11). This result is consistent with the result of several studies which found that in the rough mountainous terrain landslides reduced C content significantly (Mucci & Edenborn, 1992). Also, Badia et al. (2013) added that C content is often high in the wavy and smooth reliefs because the C content in the rough relief may be diminished by enhanced erosion and deposition. This C content situation is also similar to N content situation as landslides often destroy the land cover in the rough relief, and thus reduce the N content on the slopes (Shiels et al., 2006). 176

There is a weak correlation between the relief setting and soil pH in the study area. The results show that soil pH in the smooth and the rough reliefs are almost similar (approximately pH 6). In detail, the results show that the soil pH in the smooth relief is lower than that in the rough relief. This result is consistent to that of (Miller & Birkeland, 1992) which showed that most of soil pH values decrease downslope due to less water movement in the subsurface. Also, Rubinic et al. (2015) stated that soil pH in relation to elevation is found lower on lowland than on plateaus because shallow groundwater table on lowland results in high soil moisture that decreases the soil pH.

Variation in the soil pH is clearly shown when comparing the soils developed on different soil parent material as mentioned in Table 5.5, Table 5.11, and Table 5.12. These tables present that the measured soil pH in the study area classified the soils as weakly acid soils (in most cases > 6.2). Marine sedimentary residual soils have high soil pH ranging from 6.3-7.96. This high soil pH is caused by precipitated of marine minerals such as CaCl2, MgCl2, and NaCl (e.g. Georgoulias & Moustakas, 2010). In contrast, based on Table 5.5, andesitic breccias residual soils and volcanic ash soils mainly perform an acid soil pH which is less than 6. This result is in line with the result of Nanzyo (2002) which also presented that volcanic soils significantly show the acid soil pH. In specific case of landslide-redistributed and human-redistributed soil material, the soil pH often follows pH value of the source soils.

The weakly acid pH of soils in the study area is strongly related to the soil bases and/or Ca2+ content of soil parent material (see section 5.3). Based on Table 5.5, most of the soils are categorized into a high level of soil bases, and thus have predominant weakly acid pH values. This result is supportive to those of Van Ranst et al. (2002) who stated that volcanic soils pH in Central- and East Java have weakly acid pH values. This weakly acid pH value, which is indicated by pH range 6-7, is due to the drier climate of Central- and East Java than of West Java where higher precipitation promotes leaching intensity in the soils. High content of exchangeable Ca2+ (see Table.5.8) also raises the pH value of soils. The high Ca2+ content is mainly resulting from volcanic material which is rich in plagioclase mineral (Davis, 1967). Furthermore, Getaneh et al. (2007) found that the accumulation of soil bases can be influenced by land management such as fertilizing, manuring, and drainage. This finding is in line with the results of this study as the soils under intensive land management result in lower soil pH than those without land management (Table.5.8). 177

The dynamic of P adsorption is strongly influenced by soil pH. The results show that soil pH increases with the depth whereas the P adsorption decreases with the depth (Table 5.5, Table 5.11, and Table 5.12). These results are in line with the results of Gustafsson, et al. (2012) and Perassi & Borgnino (2014) who also presented the decreasing of P adsorption while the increasing of soil pH. Based on the Table 5.5, the decreasing of P adsorption at the depth is indicated by the higher available P following the depth. Stevenson (1982) stated that the higher available P following the depth is due to a strong relation of P content to the soil parent material. However, the available P in this study area remains low (< 15 ppm) based on the Puslittanak classification (1993). It is because the available P is often limited in volcanic soils (Egawa, 1977) due to absorbed by iron oxides (Poudel & West, 1999).

There is no noticeable relationship between the relief setting and the available P, major soil bases, and CEC (Table 5.5, Table 5.11, and Table 5.12). These results are supportive to those of Beckett (1968) which examined that chemical properties are not strongly influenced by the relief setting and surface water distribution ( e.g. Khomo et al., 2013). Most of chemical properties in the study area are found to be closely linked with the variation of soil parent material.

The mineralogical properties of the soils in the study area are mainly characterized by the presence or the absence of non-crystalline mineral i.e. halloysite (see Fig.5.9). This result is in line with that of Drouza et al. (2007) which pointed out that the main distinguishing of volcanic ash soils is the presence of non-crystalline mineral i.e. halloysite in the clay fraction. Fig.5.8 illustrates that there are halloysite in the volcanic ash soils of the study area however its presence is mostly followed by the presence of kaolinite. Wada (1987(b)) and Chadwick et al. (2003) stated that the effect of climate may determine the volcanic ash soils in producing the non- crystalline mineral of clay. This is also supported by another study of Wada et al. (1987) which demonstrated that halloysite may undergo transition into kaolinite under humid-tropical climate due to having an advance stage of weathering of volcanic ash parent material.

The absence of non-crystalline minerals in the clay fraction is shown in the soils developed on weathered parent rocks material and on altered parent rock material (Fig.5.9). This absence of non-crystalline minerals is because those soils are dominated by kaolinite clay type. The domination of kaolinite in those soils is acceptable because the study area is located on the 178 tropics in which soils usually have an advance weathering stage. This condition is consistent to that of Wada et al. (1987) who figured out that tropical climate may control the kaolinite formation in the clay fraction. In some parts of the study area, the weathered parent rocks material form 2:1 and 2:1:1 layered silicates i.e. montmorillonite and illite/montmorillonite which is the common mineral resulting from quartz-rich parent rocks (Devnita et al., 2010). Montmorillonite is also mainly found in altered parent rock material. It is because the hydrothermal alteration influences the stability of silicate minerals, and thus this process is responsible for the formation of montmorillonite in the parent rocks contained by the dominant Ca-plagioclase (Pirajno, 2009).

The soil mineralogical properties also reveal the relationship between the clay types and the CEC (see Table 5.7). Clay types become the main controlling factor to the CEC of soils (Foth, 1994). Kaolinite, montmorillonite, and halloysite result in various CEC (see Table 5.5 and Fig.5.9). Among those clay types, the presence of montmorillonite results in the highest CEC as it is described in the soils developed on altered parent rocks material and on weathered marine sedimentary material. This highest CEC of montmorillonite is due to its high capacity of cation absorption (Steven and Zelazny, 1980 cited in Birkeland, 1999) as an effect of high amount of negative charge in its lattice (Ma & Eggleton, 1999). In comparison, the presence of kaolinite and halloysite results in a lower CEC than that of montmorillonite (see Table 5.5). The lower CEC could mostly be found in the soils developed on weathered volcanic rocks material and volcanic ash material.

6.2 Soil formation and soil development

Commonly, soil formation always starts by parent rock weathering. Several studies have proven the link between parent rock weathering and soil formation rate (e.g. Scarciglia et al., 2005; Webb and Girty, 2016). Physical weathering, often seen as the initial step in weathering process, is indicated by the breaking of parent rocks into several small portions through the appearance of fracturing (Dultz, 2002). Subsequently, the parent rock changing is intensified by the transformation of primary minerals into secondary minerals, as a form of chemical weathering (e.g. Su et al., 2015). Many earlier studies have reviewed the importance of climate to weathering in soil formation (e.g. Chadwick et al., 1994;Ugolini & Dahlgren, 2002; Behrens 179 et al., 2015). Other authors suggest that vegetation is also a crucial factor for weathering because the biological activity can accelerate a local weathering (Wierzchos & Ascaso, 1998). Various weathering processes result in different mineral transformation, and control the stage of soil development (Dubroeucq et al., 1998).

A contrary occurrence of soil formation is found in this study. Soil formation in the study area is not always started by parent rock weathering (see section 5.5.1). In some location, the soil formation is also controlled by parent rocks alteration due to hydrothermal effects. In hydrothermal alteration, the soil formation is initiated with the alteration of parent rock by hot water passing through, which plays an important role for the precipitation of ions and for creating new minerals (Carlson, 2009). Furthermore, Wilson (2010) added that during alteration, the outer part of altered parent rock will be rapidly cooled and solidified but the inner part of altered parent rock will cool slowly, as illustrated in Fig.2.4. These distinct temperatures between the inner and the outer parts of altered parent rocks cause mineral changing and rock fracturing (Fig.6.1). However, the degree of alteration during all soil formation processes is influenced by lithologic characteristics (Bove et al., 1651).

a b

Photo credit by: Nur Ainun Pulungan, 2014 Fig. 6.1: Altered parent rocks: (a) fractures in the altered layer; (b) mineral changes indicated by cutan formation

Soil formation is linked to soil parent material deposition. The soil formation in this study does not only consider the weathering of parent rock but also the other processes supporting the soil parent material deposition such as hydrothermal alteration, burial process, and anthropogenic 180 process. Therefore, the soil parent material found in the study area are derived from weathered parent rock, altered parent rock, volcanic ash deposits, landslide deposits, and human- redistributed soil material (see section 5.4).

According to the variation of soil parent material (Section 5.4), soil development in the study area is categorized into three major types: (1) top-down, (2) anthropo-turbational, and (3) depositional. The top-down soil development is caused by vertical water movement which transforms the weathered parent rocks into soils. Based on the field observation of this study, the top-down soil development is rarely found in the study area because most of the areas have been disturbed by both antropogenic and geomorphic processes. In the study area, the top-down soil development which results in residual soils mostly forms A-C profiles (Table 5.3). Only in some areas which have smooth relief, this top-down soil development performs Bw horizons as a result of intensive vertical water movement. This finding is supportive to the result of Steven and Walker (1970) cited in Alexandrovskiy (2007) stated that the top-down soil development normally requires 1500 to 7000 years to be well-developed. Moreover, Alexandrovskiy (2007) illustrated that pedogenic processes in a top-down soil development exponentially decreases with time, and consequently these pedogenic processes takes longer time until it reaches steady state conditions. Hence, the top-down soil development in the study area still reflects its initial stage.

In intruded areas, the top-down soil development is actually initiated by a bottom-up process of soil parent material development. The bottom-up process occurs due to the presence of hydrothermal alteration of parent rocks (see Fig.2.4). The bottom-up process means that the alteration becomes the main agent for parent rock transformation into soil parent material, instead of weathering. As a result, the bottom-up process of alteration forms the altered parent rock material in the subsurface, as shown in Fig.5.24 This altered parent rock material can be exposed to the slope surface due to intensive mass-movement on the slopes (see Fig.5.34 (b)). Subsequently, this exposed altered-parent rock material is modified by weathering process and vertical water movement that transform this soil parent material into soils. And now the formation of top-down soil development occurs. Furthermore, the alteration of parent rocks has produced very high clay contents (see Table 5.4). Consequently, the top-down soil development of altered parent rock material results in several B-horizons within a profile indicated by different argillic intensity. 181

The soils developed on altered parent rock material show specific characteristics as they are resulted from two processes (bottom-up and top-down) during profile development (see Table 5.7). Unlike the soils developed on weathered parent rock material, the soils developed on altered parent rock material are mainly characterized by extreme clay contents, mostly >60% (see Table 5.4). The extreme clay contents in this altered parent rock material are possibly formed by feldspar kaolinitization (Sun et al., 2013), as the alteration process transforms the feldspar minerals of volcanic rock into kaolinite minerals (Bove et al., 1651). Zhang (2007) also explained that intensive magmatic activities result in clay-altered material due to mineralization of metallic sulfide deposits, which are mainly found in volcanic material (Taylor & Fryer., 1982). Hence, the mineral compositions of parent rock (Table 5.17) become the main aspect for the forming of extreme clay contents in the altered parent rock material in this study area.

In comparison to the top-down soil development, anthropo-turbational soil development is formed by human-redistributed soil material. This type of soil development will have a faster rejuvenation rate of soil nutrients due to soil turbational process (Alexandrovskiy, 2007). Based on the field observation of this study, the anthropo-turbational soil development is mainly found in agricultural areas where people have many tillage practices. Taboada-Castro et al., (2004) examined that soils under tillage practices have a better aggregate stability than those under no- tillage practice. However, the finding of Taboada-Castro et al. (2004) is in contrast to the findings from this study. The anthropo-turbational soil development in the study area usually leads only to the crushing soil aggregates having more friable surface soils than those found in the top-down soil development (see Fig.5.29).

The depositional soil development, widely found in the study area, is depended on the types of deposit material on the soil surface. Based on the field observation of this study, the depositional soil development in the upper part of the study area is mainly formed due to volcanic ash burial, whereas, the depositional soil development in the central and lower parts of the study area is formed due to landslides activities. According to Alexanderovskiy (2007), the development of depositional soils depends on the sedimentation rates on the soil surface. In the study area, soils derived from the volcanic ash deposit are more developed than those from the landslide deposit (see Table 5.8). It is because the volcanic ash deposit is rich of weatherable minerals (Mizota, 1981) that are easy to transform into soils. However, the landslide deposit contains mixed of old soil material that already has fewer weatherable minerals resulting in 182 slower soil development. Also, the former landslide deposit is often replaced by the following landslide deposit, and thus the soil development can be disturbed in many times.

The soil development in the study area is mostly found in the form of polygenetic soils (see section 5.5.2). These polygenetic soils are mainly the result of the overlaying between weathered/altered parent rock material and burial of volcanic ash/landslide deposits. Consequently, the presence of polygenetic soils is reflected in multi-soil formations within the profile in particular areas (see Fig.5.34). The finding of this study is consistent with the finding of Srivastava & Parkash (2002) which indicates that the polygenetic soils in Gangetic Plain were formed due to the presence of buried soils, and thus cause mineralogical and chemical changes within a profile. Besides that, Muggler & Buurman (2000) also indicated that the polygenetic development of soils in south-eastern Brazil is caused by soil-sediment sequences of stable landscape and graben filling sediment.

In contrast to the common polygenetic soils, the polygenetic soils in the study area are not caused by the effects of climatic differences. It is because there was no drastic climatic change in Indonesia (Bemmelen, 1949) during several soil formation sequences. The polygenetic soils in the study area are mainly formed by the different periods of soil parent material deposition (see section 5.5.2). These polygenetic soils which can be seen within a profile were developed under the influence of leaching process as the dominant process in the tropics. According to field observation of this study, the same dominant leaching process repeats in every period of soil parent material deposition, and hence forms polygenetic soils within the profile, as shown in Fig.5.33. However, many polygenetic soils were examined with regards to paleoclimatic implication on soil formation (e.g. Bruce, 1996;Pal et al., 2001; Moghiseh & Heidari, 2012). In those studies, the polygenetic soils were the indication for climate changes in the period of glaciations. This climate change effects were reflected by distinctive micromorphologic features in the soils. In such condition, the polygenetic soils are formed due to different processes occurred during soil profile development such as leaching process during wet seasons and strong evaporation with accumulation of bases at soil surface during dry seasons, that finally form the polygenetic soils.

The areas dominated by polygenetic soils mostly have lithologically discontinuous soils (LDS), as illustrated in Fig.5.32. The LDS are often described by a lack of relationship between 183 the overlaying soils and the underlying bedrock (Brewer, 1972, cited in Lorz 2008). In the study area, the LDS are mainly found in the upper and central parts of the study area where the depositional soil development is dominating. The unconsolidated volcanic ash deposits in the upper part of the study area and landslide deposits in the central part of the study area have been creating surficial deposits. Consequently, those surficial deposits have discontinued the influence of local bedrock to the overlaying soils (see Fig.5.34 (a)&(b)). In other cases, different periods of volcanic ash deposition also cause that the latter deposits overlays the former deposits of volcanic ash (see Fig.5.34 (c)). As a consequence, the presence of overlying material results in stratification within a profile (Ande and Senjobi, 2010), and thus causes lateral variation of the upper-most soil parent material (Lorz & Phillips, 2006).

The overlying of Tertiary material and Quaternary volcanic ash deposits represents a common LDS in the study area (see Fig.5.34). As stated by Widodo (2002), most of Java is covered by several overlapping volcanic ash material that are weathered quite fast forming volcanic ash soils. Large distribution of unconsolidated volcanic ash deposits is often overlaid on consolidated weathered/altered volcanic parent rocks. This condition becomes a significant landslide controlling factor in the study area.

The deposits of landslides mostly cause LDS in areas having active slope surface processes. The landslides are considered as the significant factor for redistributing the soils in the study area (Fig.5.25). Finding from this study is in contrast to the finding of Pradhan, et al. (2012) showed that the soil erosion is the most crucial agent for soil redistribution because it can sweep away the soil 10 to 40 times faster than its natural development. However, the soil erosion only removes the surface soil layer (Labriere et al., 2015) transporting less amount of deposits compared to landslides. Based on the field observation of this study, it was found that the landslides not only remove the surface soil layer but also fail the slopes that might contain the saprolith or bedrock (see Fig.5.25 (b)). The landslides can redistribute soils from the upper to the lower slopes in a large block of soils. Therefore, the landslides remove high amounts of slope material as a hillslope deposit (Daniels and Hammer, 1992;Kleber, 1997; Jien et al., 2009), and can redistribute soils suddenly and faster (Osman, 2012).

Landslides are the influencing factor for soil formation and soil development in the hill areas of the study sites. The effect of landsides in redistributing soils are focused on two zones 184 i.e. depletion zone and accumulation zone, as discussed earlier in section 5.3.2.3. The soil development in the depletion zone of landslide is cut off. On the other side, the presence of landslide deposits on the accumulation zone is able to interrupt the influence of underlying weathered parent rock in soil development (Kleber, 1997; Lorz et al., 2008). In this accumulation zone, the landslide deposits may bury the former soil profile in the deposition area and bring about the new soil formation.

6.3 Soil-Human interaction 6.3.1 Influences of soil properties to human activities

The variation of soil parent material determines the types of agricultural in the study area. It is because each soil parent material may result in different soil characteristics (see section 5.3) that need to be considered in agriculture. In the study area, the volcanic ash soils are often cultivated as dryland agriculture which is planted with cassava (Manihotutilissima), corn (Zea mays), chilli (Capsicum annuum L.), cacao (Theobroma cacao), and durian (Duriozibetinus). The volcanic ash soils promote the accumulation of humus (Devnita et al., 2010) and are rich in soil nutrients (Drouza et al., 2007) making these soils suitable for seasonal crops (Fig. 6.2(a)). The breccias andesitic residual soils are mainly cultivated by mixed-cropping (Fig. 6.2(b)). They usually are rich in clay (Wada, 1987), and therefore rather unsuitable for intensive agriculture. Similar to breccias andesitic residual soils, the marine sedimentary residual soils and the altered residual soils also have high amount of clay. As a consequence, those residual soils require other cultivation types than monoculture, and also type of plants which need less water such as coconut (Cocos nucifera), sengon (Albazia marina), rambutan (Nepheliumlappaceum), mango (Mangiferaindica) and banana (Musa acuminata). 185

a b

Photo credit by: Nur Ainun Pulungan, 2014 Fig.6.2: Variation of agricultural plants based on soil parent material: (a) seasonal crops in volcanic ash parent materials; (b) mixed crops in weathered andesitic breccias

The variation of soil parent material also influences the agriculture land management. Based on the field observation of this study, the volcanic ash soils are able to be managed by terraces (see Fig.6.2). Usually, these soils have interlock grain characteristics due to high proportion of amorph minerals (Mizota, 1981), so that they are not prone to landslides. However, residual soils developed on weathered parent rock material and on altered parent rock material are unsuitable to be managed by terraces. These residual soils contain a lot of clay which is prone to landslides, and consequently the terraces may aggravate the landslide susceptibility in the sloping areas.

Redistributed soil material is widely found in the rough relief area where landslides intensively occur (see section 5.5.4.1). In this area, the landslide-redistributed soil material becomes the major cover material, and act as the latter soil parent material (Fig.5.27). This landslide-redistributed soil material disturbs the development of underlying soils, and hence creates a new soil formation in that particular area. This finding is in line with those by Birkeland and Burke (1988), and Sokolov (1989) which showed that since a long time landslide- redistributed soil material have been commonly recognized as a soil parent material, because it contributes to create the new soils due to its specific pedogenesis (Kleber, 1997). 186

4 month later

The rill erosion may initiate the following landslide

Photo credit by: Zuhara, 2014 Fig.6.3: Cultivated landslide-redistributed soil material that may generate next landslides

The landslide-redistributed soil material has the potential to be cultivated immediately (Fig.5.27). It is because landslide deposit in the study area has provided mixed soil material, as a medium for plants. The landslide-redistributed soil material is the results of cover material removal from the upper/middle slopes downward to the lower slopes in large quantities of volume (Daniels and Hammer, 1992;Hilton et al., 2013). Hence, the landslide-redistributed soil material usually produce weak soil aggregates that can be easily cultivated (Fig.5.27).

Each type of the landslide-redistributed soil material provides various cultivation capabilities. Unconsolidated landslide-redistributed soil material, entirely consisting of soil material, is mainly cultivated with crops i.e. cassava, long bean, curcuma, ginger, and sweet potato (see Fig. 5.27(a)). The domination of soil materials in this type of landslide-redistributed soil material causes this soil is unable to adequately hold wood plants. On the other side, mixed landslide-redistributed soil material, involving soil material and saprolith, are cultivated by 187 wood plant i.e. teak wood (Tectonagrandis) and sengon (Albazia marina) (see Fig. 5.27(b)). This mixed material makes the soils more solid, and is possible to be cultivated by wood plants.

The cultivated landslide-redistributed soil material may generate the next slope surface processes following the main landslides (Fig.6.3). This finding is in line with the result of Alexander (1992) which showed that landslides are often provoked by intensive tillage; and the findings of Beach et al. (2009) and Mugagga et al. (2012) which stated that landslides are aggravated by organic matter addition. The landslide-redistributed soil material usually has a decline of soil aggregate stability and of soil moisture changing (Malgot & Baliak, 2002). Therefore, the landslide-redistributed soil material may have more intensive erosion which is the case in the initial stage of the following landslides, as shown in Fig.6.3.

Photo credit by: Nur Ainun Pulungan, 2014 Fig.6.4: Traces of seepage within landslide-redistributed soil material 30 cm below the surface

The landslide-redistributed soil material, in some parts of the study area, has also a potential for natural water storage (see Fig.6.4). These soils, which are dominated by clayey material, have a high capability to store the infiltration water as they have finer soil aggregates. The difference in permeability between the landslide-redistributed soil material and the underlying material may initiate the typical seepage pattern. As an impact, in the study area, much seepage is found around the toe of landslide deposits. Based on the field observation, the higher capability of water storage in landslide-redistributed soil material influences this soil material to have a better support for plant growth than that in the residual soils.

188

6.3.2 Impact of human activities on soils

Most of the soils in the study area have been influenced by different types of human activities. These activities change not only the land uses types, land management, vegetation cover, but also the slope features, and even the soil parent material. These changes must be taken into account in related to soil development because they affect the intensity of soil processes (Dudal, 2005; Emadodin et al., 2011), and change the soil properties (Jim & Chan, 2004).

Human activities may modify the soil characteristics chemically. Thereby, soil nutrient addition is the main effect. The soil nutrient addition is significantly required in the study area because the amount of nutrients may decline due to crop harvesting or through leaching and erosion (Ngetich et al., 2011), especially in the rough relief area. This finding is in line with those of Redel et al., 2007 and Changhui et al., 2013 which stated that the soil nutrient addition is crucial for generating the N fixation and influencing the microbial activity.

The soil nutrient addition, through fertilizing and manuring, is a common land management practice in the study area. Based on the field observation of this study, soil nutrient addition is usually applied on irrigated paddy field and dryland agriculture. Fertilizing is necessary to enhance the N content and other nutrient content in the upland soils (Table.5.12). Furthermore, the application of manure as an organic fertilizer is intended to fast the nutrient absorption by the soils.

The land management may also retard soil development. Ploughing, irrigation, and building of agricultural infrastructure are examples of land management activities that retard soil development in the study area. In areas of smooth relief, the ploughing is applied for soil aggregate refinement and soil overturning. This ploughing sometimes can cause the formation of densic material in the subsurface (Fig.6.5). However, in areas of rough relief, the ploughing determines lateral redistribution of soil material to the downslope (see Fig. 5.28(a)), and hence may bury the former soil material in the deposited area. Soil saturated condition that is reached by irrigation results in mineral precipitation in the subsurface layer as shown in Fig.6.5, and also modifies the soil structure (Murray and Grant, 2007). Therefore, its inundated environment retards the soil development in irrigated areas. Agricultural infrastructure such as irrigation canal and retaining wall construction are also considered to retard the soil development. It is because further horizon development is limited after such constructions (Grieve, 2001). 189

Mineral precipitation due to saturated inundation Densic material as an of irrigation effect of ploughing

Photo credit by: Febrian Maritimo, 2013 Fig.6.5: Some effects of land management on soil development

Land management also modifies the direction of soil development. Based on the field observation of this study, the land management is found to modify the direction of , the dominant soil type in the study area, into . Such change is due to intensive clay translocation resulting from land management practice. This change is usually as the impact of ploughing in the soil profile. This finding can be shown by the presence of fragipan in B horizon indicated by densic material in subsurface diagnostic horizon (see Fig.6.5). The presence of fragipan within the profile may restrict the entry of water and roots into the subsurface horizon (USDA, 1999).

Human activities can also physically modify the soil development. Tillage, often applied on paddy field and dryland agriculture, is the main example of human activities of intensive land management in the study area. Tillage is a representation of the anthro-pedoturbation activities (Capra et al., 2015). Furthermore, tillage depth and tillage speed also affect the pedoturbation (Muysen et al., 2002). Taboada-Castro et al. (2004) added that tillage depth can perform the favorable soil aggregate for plant growth. In the study area, the tillage activities are intended to loosen the soils and to speed the soil infiltration up because most of the soils in the study area are clay-rich soils (see Fig. 5.28(b)). The deep tillage is mostly applied in the study area as it is not only intended to turn over the surface and/or subsurface soils but also to break the saprolith. 190

Crop rotation is a common land management practice in the study area. It is a kind of rotational vegetation cover within a certain period. In the study area, the crop rotation is mainly applied in dryland agriculture, usually conducted in a 3 months rhythm. This rotation is intended to give a chance for soil mineral balancing. The rotation of crops may cause the inversion of soil and, thus, influence on soil nutrient (e.g. Misra & Padhi, 2014;Wang et al., 2014). The application of crop rotation is usually followed by the tillage activity influencing soil organic matter (Shrestha et al., 2015) and soil aggregation (Taboada-Castro et al., 2004). In the study area, crop rotation sometimes is applied on rainfed paddy fields, and it is usually conducted during an intercrop-period. The types of vegetation used during intercrop-period in the study area are maize, ginger, leguminous, and grasses (see Fig. 5.28(d)). Shrestha et al (2015) showed that there was a higher SOC under continuous crop rather than that under intercrop-period. However, in our study, there is no significant difference of SOC under no-tillage and minimum tillage (see Table 5.12).

Terracing is a common slope modification applied agriculturally in the study area. The purpose is to gain relatively flat areas for cultivation of crops. Usually, in the steep slopes, agricultural terracing is applied for paddy fields. It is designed to hold irrigation water for puddling as a paddy cultivation media. In contrast to the previous purpose, the agricultural terracing often becomes a triggering factor for landslides in the study area. It is because the agricultural terracing makes an artificial flat relief within the steep slopes (Richardson and Girdner, 1973), which increase soil-water pressure in the subsurface, and consequently generates slope instability. In some areas, the agricultural terracing is applied for dryland agriculture. In this agriculture practice, the terracing purposes to prevent erosion at the slope surfaces (Cerda et al., 2016), and consequently it increases the infiltration and suppress (e.g. Arnáez et al., 2015). For non-irrigated land, the terracing is often combined with contour parallel tillage. However, this tillage practices are often followed by surface soil material displacement. Therefore, both terracing and tillage result in human redistributed-soil material.

A slope modification also controls the water distribution and water movement in soils and soil parent materials. In the study area, most of the modified slopes change the impact of rainfall significantly by decreasing surface runoff, and thus increasing water infiltration (see Fig. 5.28(c)). The plain or even concave topography of terraces gives a chance for rainfall to be infiltrated to the soils, and thus, changes the soil moisture (e.g. Pellenq et al., 2003) and affects 191 the percolation water mobility which is crucial to translocate ions and even particles within soil profiles (e.g. Osher and Buol, 1998; Kirkpatrick et al., 2014). In contrast, the convex topography of terraces promote rainwater inducing surface runoff and thus generate soil erosion (e.g. Guzman & Al-Kaisi, 2011).

Land use change is also a fact in the study area. Based on the field observation of this study, land use change is often applied on abandoned land towards commercial forests and dryland agricultural land, and it is mainly conducted due to economic reasons. Different land uses result in different amounts of soil organic matter (SOM). Almost all SOM contents in the study area are categorized into high level (at most > 3%), as shown in Table 5.12. However, it is rare to have a high SOM in the tropical areas due to a higher decomposition rate (van Wambeke, 1993). Therefore, probably, the high values of SOM in the study area indicate as the effect of manuring activities by giving additional organic input i.e. dung from animals which is intensely applied on cultivation land. This result is supportive by the result of Douglas et al. (1986) which showed that soils under cultivation often have small SOM (less than 2%) if there is no manure input. Furthermore, the high value of SOM in the study area can be also influenced by land cover density. Mixed-cropping as the dominant land use in the study area has a high crop density. The multi-leveled strata of the crops within this land use type results in high value of SOM on the soil surface (e.g. Chang et al., 2012).

Types of land uses also influence the N content in the soils (Table 5.12). In the study area, most of the available N is high, at both cultivated and abandoned land. This high N availability in the study area may be caused by the dominance of orok-orok (Crotalaria juncea) which is mainly used as the plant cover in abandoned land. This plant belongs to the family of Leguminoseae which lives in symbiosis with Rhyzobium bacteria as a microorganism. This bacterium is able to bind the free Nitrogen of the atmosphere. Subsequently, the plant transforms this N into organic compound, and later on, with the litter this organic compound is given back to the soils, named as N fixation (Jarvis, 2002). However, the high available N content in the study area is also a result of intensive fertilizing activities on the cultivated land because the fertilizing significantly increase soil nutrients in the soils. It can also be the result of fast decomposed litter which is mainly occurred in the abandoned land. This assumption is in line with the result of Chang et al. (2012) which showed that a fast decomposed litter and other organic input on the soil surface may significantly increase the N-content in the soils. When 192 studying the available N, it is important to consider the effects of organic fertilizer (Diacono & Montemurro, 2010). The chemical fertilizer application may result in a fast N release within a short period. Nevertheless, over the medium-term the chemical fertilizer application induces poor soil structures (Alfaro et al., 2006).

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CHAPTER 7 CONCLUSIONS AND OUTLOOK

7.1 Conclusions Soil formation is closely related to soil parent material. Based on the observation in the study area, the soil formation is not always started from the parent rock weathering. The soil formation can be also started from other processes that also can form a typical soil parent material, such as alteration, burial, and anthropogenic processes. Therefore, to understand the soil parent material, the sequences of processes influencing the formation of soils are strongly required.

Soil development processes, within the soil profile, occur after the soil parent material is formed. The soil development can be proceed monogenetically or polygenetically. Monogenetic soil development is usually formed in the areas where the disturbance of geomorphic and anthropogenic processes is limited. On the other hand, polygenetic soil development can be observed in the areas where having active disturbance by geomorphic and anthropogenic processes. This condition shows that soil development processes varies and depends on the processes occurring in the soils and on the soil surface.

Geomorphic and anthropogenic are the external processes that may influence both soil formation and soil development. The geomorphic and anthropogenic processes are not only able to accelerate or to retard the process of soil development but also able to alter the direction of soil development. Those processes result in different impacts on soils. The geomorphic processes are closely linked to the landform formation which controls the soil parent material deposition. Intensive geomorphic processes within certain landform unit are, therefore, controlling the water movement both on soil surface and in soil profile to result in soil horizons. On the other side, the anthropogenic processes are closely linked to the human activities which modify and distribute the surface soils. The anthropogenic processes are reflected by land use units and land management practices by human. Both the geomorphic and anthropogenic processes are dynamic and closely embedded on soil formation and development. As a consequence, the sustainable 194 land cultivation and land utility shall consider the dynamic of soil formation and soil development.

This study finds three categories of soil parent material in the study area: (i) weathered parent rock material; (ii) altered parent rock material; and (iii) volcanic ash material. Each of them results in specific characteristics when they are induced by geomorphic process and/or anthropogenic process. The soil parent material which is induced by geomorphic processes results in landslide-redistributed soil material, while the soil parent material which is induced by human results in human-redistributed soil material. Landslide-redistributed soil material usually has an inconsistency of CEC and low content of C and N. Nevertheless, human-redistributed soil material often results in higher organic matter. For example: manuring and fertilizing increase the aggregate stability of the soils, the enrichment of cation bases, as well as clay in the sub- surface layer, and tillage practices may refine the soil structure

Weathering and alteration are also two different significant processes that influence the soil formation in the study area. Weathering strongly influences the soil formation through vertical water movement within the soil profile, while alteration influences the soil formation through H+ metasomatism and argillic alteration. Both soils developed on weathered parent rock material as well as soils developed on altered parent rock material show their distinction of morphological, physical, chemical, and mineralogical properties. The most distinguishing properties between weathered- and altered material are related to the clay content and the clay type of the soils. Therefore, those properties will then relates to the exchanging and holding capacity of cations.

Soil redistribution in a transitional landscape zone is not always determined by the sequence of slope position. It is because the transition zone is usually consists of numerous short sequences of hill slopes with varying slope parameters. However, soil redistribution in a transition zone is strongly influenced by the relief settings. The relief in a transition zone is closely related to the arrangement of landforms. In addition, the relief also affects the dynamic of geomorphic processes controlling the soil redistribution from upper slopes downwards to the lower slopes. As a consequence, in a transition zone, the redistributed soils have a strong possibility to become the soil parent material and to affect the following soil formation and soil development processes. 195

Soil-scape concept has been considered as the appropriate concept to be applied on the area constructed by complex reliefs and lithologies. Such a complex area is insufficient to be explained by the soil catena concept which only emphasizes on the slope position within a toposequence. In contrast, soil-scape concept describes three-dimensional body of soils within a landscape. Soil-scape concept is able to reveal the relationship of soil material and land surface/subsurface processes within a landscape. As an implication, soil-scape concept is able to explain both the soil processes within a pedon and the slope processes influencing soils within a landscape or in a region. Natural characteristics

Soil Parent Soils Land utility Material SOIL HUMAN SYSTEM SYSTEM Land management: Possibilities of -Modified soil characteristics morphodynamic -Soil material redistribution labour or technology processes

Human modification

Fig.7.1 Dynamic of the soil-human system

196

The interaction between soils and humans may be illustrated in a close cycle (Fig.7.1). The interaction can start with soils influencing the humans, then humans influencing the soils. It is a general view that the beginning of a cycle shall be determined by nature, in this case: the soils. Soil characteristics influence humans, as the user of the nature, performing a special form of land management. Along the time, humans may modify the soils through technology creating sophisticated land management tools. At this stage, humans cause the modification of the soils. Human impact on soils can affect not only the micro-relief (e.g. terracing on the slopes) but also the macro-relief (e.g. slope cutting and valley leveling). As the soils are disturbed by humans, new development processes in soils may occur and these processes may limit the human activities by managing the soils. Furthermore, the human-disturbed soils may induce the intensification of slope surface processes i.e. landslides and soil erosion. Finally, the slope surface material reforms the soil system and restarts the soil formation. Therefore, the interaction between soils and human may result in a cycle of soils – humans systems.

7.2 Outlook

This research studies the dynamic processes of soil formation and soil development in the transitional zone of Quaternary Sumbing Volcano and Tertiary Menoreh Volcano. It demonstrates a potential application of integrated soil studies which can be used for regional development that promotes sustainable land cultivation and land utilization. Due to the scope of study, several gaps remain and should be addressed in the future.

The study could be extended by analyzing soil parent material or saprolith for improving the understanding of landslides. Although the soil parent material is a crucial factor determining soil characteristics on the slope surfaces. Information about soil parent material is rarely to be considered in landslides studies up to now. In addition, the in-situ soil parent material or saprolith is the upper-most soil parent material in a profile which may maintain the slip plane for landslide occurrences. Therefore, it is crucial to understand the interaction between soil parent material (as the underlying layer) and soil layers (as the oncoming landslide material). The variation of soil parent material controls the susceptibility and the types of landslides.

The study of soil variation modeling in a volcanic landscape would be a great idea for the future research. The volcanic landscape is a dynamic landscape which produces a variety of 197 disturbances towards soil formation and soil development. The volcanic landscape is an essential area for supporting the sustainable and the productive cultivation land. Parent material in the volcanic landscape provides abundant volcanic minerals which are important for soil fertility. Using soil variation modeling, one may be better understand the pattern of soil variation in a given volcanic landscape, and thus may optimize the land cultivation.

The study of soil fertility in a contradictive condition of fertile volcanic soils and active morphodynamic areas would be a challenging research. Soil degradation due to landslides and erosion, and intensive land cover changes due to economical purposes are two further main problems affecting soils in the study area. Detail analysis of soil fertility will assist promoting appropriate land utility and related crops for each specific area.

The study of human interventions on soils is also warranted for future research. Nowadays, it is difficult to find areas that have not been modified by humans. Human have widely modified the soils especially in the form of cultivated land. Most of the human intervention has caused a redistribution of surficial material. Human interventions also can occur within a short- or long period of disturbances. Human interventions may stop or affect pedogenesis. Therefore, detail analysis of human interventions on soils using several comparison methods are needed to evaluate the soil development and the soil properties transformation in human influenced areas.

A further study could assess the rate of pedogenesis for soils developed on different material (e.g. between weathered- and altered material, or between weathered- and redistributed material). The significant presence of altered material in volcanic landscape cannot be ignored. The altered material provides specific soil formation and soil development compared to the weathered material. On the other side, soils are also the essential object for cultivation activities which promote the human-redistributed soil material. This human-redistributed soil material should provide different characteristics compared to weathered material with regards to the pedogenic rate.

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