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Sumber: ppt‎

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KOLOID TANAH dan KTK Sumber: ppt‎

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Koloid Tanah Partikel yng ukurannya kurang 1 -2 m bersifat sebagai koloid tanah Total luas permukaannya m2·g-1 Internal and external surfaces have electronegative or electropositive charges (electronegative charge dominant) Each micelle adsorbs thousands of hydrated Al3+, Ca2+, H+, K+, Mg2+ and Na+ ions (enclosed within several H2O molecules) Cation exchange occurs when ions break away into the soil solution and are replaced by other ions Ionic double layer: negatively charged micelle surrounded by a swarm of cations. Sumber: ppt‎

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5 Liat Silikat Kristalin (Berbentuk Kristal)
Dominant colloid in most soils (not andisols, oxisols or organic soils) Crystals layered as in a book 2-4 sheets of tightly-bonded O, Si and Al atoms in each layer Misalnya: Kaolinit, Montmorillonit. Sumber: ppt‎

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Liat Silikat Non-kristalin Tidak terorganisir sebagai lembaran kristalin Both + and – charges; can adsorb anions such as phosphate Kapasitas menyimpan (menahan) air sangat besar Malleable when wet, but not sticky Often form in volcanic soils (especially in Andisols) Mis. Allophane dan Imogolite. Sumber: ppt‎

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Oksida-oksida Iron dan Aluminium Ditemukan dalam tanah-tanah yang sangat lapuk di daerah iklim hujid dan hangat (mis.. Oxisols) Terdiri atas atom-atom Fe dan Al yang dihubungkan dnegan atom-atom oksigen atau gugusan hidroksil Some form crystalline sheets (eg. gibbsite and geothite), but often amorphous Low plasticity and stickiness Sumber: ppt‎

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Humus Ada dalam kebanyakan tanah, terutama Horison A Bukan mineral atau Bukan Kristalin Consist of chains of C atoms, bonded to H, O & N Very high water adsorption capacity Not plastic or sticky Bermuatan listrik negatif. Sumber: ppt‎

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(Singer and Munns, 2002) Sumber: ppt‎

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Phyllosilicates Tetrahedra: Two planes of O, with Si in between Basic building block is silicon atom, connected to 4 O atoms Oktahedra: with Al or Mg in between is Al (or Mg), connected to six hydroxyl groups or O atoms. There are many layers in each micelle Sumber: ppt‎

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Trioctahedral Sheet Dioctahedral Sheet Isomorphous substitution 1 Al3+ atom, 1 Mg2+ atom Charge = -1 3 Mg2+ atoms Charge = 0 2 Al3+ atoms Charge = 0 Sumber: ppt‎

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Substitusi Isomorfik Each Mg2+ ion that substitutes for Al3+ causes a negative charge in a dioctahedral sheet Each Al3+ ion that substitutes for Si4+ causes a negative charge in a tetrahedral sheet Sumber: ppt‎

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1:1 Silicate Clay Each layer contains one tetrahedral and one octahedral sheet Eg. Kaolinite, halloysite, nacrite and dickite Sheets are held together because the apical oxygen in each tetrahedron also forms the bottom corner of one or more octahedra in the adjoining sheet Sumber: ppt‎

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Hydroxyl plane is exposed: removal or addition of hydrogen ions can produce positive or negative charges (hydroxylated surface also binds with anions) Hydroxyls of octahedral sheet are alongside Oxygens of the tetrahedral sheet: hydrogen bonding results, with no swelling in kaolinites! Kaolinite useful for roadbeds, building foundations and ceramics (hardens irreversibly) Sumber: ppt‎

19 2:1 Silicate Clay Each layer contains one octahedral sheet sandwiched
between two tetrahedral sheets. O on both ends No attraction without cations Sumber: ppt‎

20 Liat Silikat Tipe 2:1 Mengembang
Kelompok Smectite : Ekspansi (sifat mengembang) antar lapisan dapat terjadi kalau H2O mengisi rongga di antara lapisan dalam liat yang kering Montmorillonit : Liat smectite yang sangat banyak ditemukan Smectites mempunyai banyak muatan negatif karena substitusi isomorfik Mg2+ often replaces Al3+ in the octahedral sheet Al3+ sometimes replaces Si4+ in the tetrahedral sheet 5. Weak O:cation linkages between layers leads to plasticity, stickiness, swelling and a very high specific surface area Sumber: ppt‎

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(Singer and Munns, 2002) Sumber: ppt‎

22 Very high negative charge, due to frequent
Kelompok Vermikulit (Liat Silikat Tipe 2:1 mengembang) Very high negative charge, due to frequent substitution of of Si4+ ions with Al3+ in the tetrahedral Sheets Cation exchange capacity is higher in vermiculites than in any other clay Swelling occurs, but less than in smectites due to strongly adsorbed H2O molecules, Al-hydroxy ions and cations, which act more as bridges than wedges. Sumber: ppt‎

23 Mineral Silikat Tipe 2:1 Tidak-mengembang
Kelompok Mica (Illit dan Glauconit): Al3+ substituded for 20% of Si4+ in tetrahedral sheets K+ fits tightly into hexagonal holes between tetrahedral oxygen groups: virtually eliminates swelling Sumber: ppt‎

24 Khlorite bersifat Non-expansive (Tidak mengembang):
Mg-dominated trioctahedral hydroxide sheet fits between 2:1 layers (2:1:1). H-bonded to O atoms between sheets Fe or Mg occupy most octahedral sites Sumber: ppt‎

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26 Oksida Besi dan Oksida Aluminium
Modified octahedral sheets with either Fe2+ or Al3+ in the cation positions No tetrahedral sheets and no silicon Lack of isomorphous substitution (little negative charge) Small charge (+ or -) due to removal or addition of hydrogen ions from surface hydroxyl groups Non-expansive and relatively little stickiness, plasticity and cation absorption Sumber: ppt‎

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28 Muatan yang Variable (pH-dependent)
Hydrous oxides whether crystalline or amorphous get their charge from surface protonation and deprotonation >AlO- + H+  >AlOH + H+  AlOH2+ Negative Neutral Positive pH decreasing  Layer aluminosilicates have a small amount of variable charge because of OH at the edges Semua muatan negatif pada humus bersifat variable Oksida-oksida Hydrous bermuatan positive pada tanah-tanah yang sangat masam dan membantu mengikat anion. Sumber: ppt‎

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Muatan Negative menjadi Muatan Positive : As pH increases, more H+ ions bond to O atoms at the clay surface Protonation at very low pH (H+ ions attach to surface OH groups) Muatan Negatif: Dissociation of H+ ions, lack of Al & Si at edge to associate with O atom Sumber: ppt‎

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31 Pertukaran kation kurang efektif Pertukaran kation lebih efektif
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32 Kapasitas Tukar Kation
Nilainya sangat tinggi dalam tanah-tanah yang : Kaya humus Kapasitas mengembang snagat tinggi pH nya tinggi Sumber: ppt‎

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Humus Senyawa organik, Non-crystalline Molekul organik, ukurannya besar 50% C, 40% O, 5% H, 3% N and sometimes S Strukturnya sangat variabel. Very large negative charge due to three types of -OH groups (H+ ions gained or lost) (i) carboxyl group COOH (ii) phenolic hydroxyl group (due to partial decomposition of lignin by microorganisms) (iii) alcoholic hydroxyl group Sumber: ppt‎

34 Keadaan Bahan organik setelah satu tahun dibenamkan ke dalam tanah
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Substansi Humik Mikroba mer9ombak komponen yang kompleks Senyawa yang lebih sederhana dihasilkan; CO2 dilepaskan Sintesis biomolecules baru, dengan menggunakan C, N, S dan O. Lignin not completely broken down: complex residual molecules often retain lignin characteristics Microbes polymerize new, simpler molecules with one another and with residual molecules This creates long, complex chains, resistant to further decomposition Chains interact with amino compounds Polymerization process is stimulated by colloidal clays. Sumber: ppt‎

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Setelah satu tahun: 1/5 hingga 1/3 jumlah Karbon tetap dalam tanah (i) live biomass (5%) (ii) humic fraction (20%) (iii) nonhumic fraction (5%) Substansi Humik meliputi: (i) Fulvic acids: lowest molecular weight and lightest colour (most susceptible to microbes) (ii) Humic acid (intermediate) (iii) Humin: highest molecular weight, darkest, least soluble and most resistant to microbes Sumber: ppt‎

39 Humus: Amorphous and colloidal mixture of complex organic
substances no longer identifiable as tissues Note: non-humic substances are biomolecules produced by microbes Sumber: ppt‎

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