POKOK BAHASAN DASAR-DASAR ILMU TANAH

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1 POKOK BAHASAN DASAR-DASAR ILMU TANAH
I. PENDAHULUAN: Pengertian tanah, Konsep tanah, dan Linkup Kajian tanah II. KOMPONEN TANAH Bahan Anorganik Bahan Organik Tanah Udara tanah Air Tanah III. PEMBENTUKAN TANAH Faktor Pembentuk Tanah (Iklim, Batuan, Organisme, Relief, Waktu), Pelapukan Profil Tanah IV. SIFAT FISIKA TANAH Warna Tanah Tekstur Tanah Struktur Tanah Konsistensi tanah Bji, BJp. Porositas Tanah UJIAN TENGAH SEMESTER

2 II. KOMPONEN TANAH Soil is dynamic resouce (sumber daya) that support plant life. Tanah adalah sistem dispersi. It is made up of different sized mineral particles (sand, silt, and clay) organic matter, and numerous species of living organism. Bahan utama penyusun tanah: Bahan mineral (anorganik) (45-50 %) Bahan organik ( %) Air (20 – 30 %) Udara (20 – 30 %) Komposisi ini berbeda untuk tiap jenis tanah ataupun tiap lapisan tanah

3 Soil = is a complex mixture of. weathered rock frag-. ments, minerals,
Soil = is a complex mixture of weathered rock frag- ments, minerals, water and the remains of dead plants and animals air Rock and mineral fragments produced by weathering (regolith) that supports the growth of plants Humus (decayed animal and plant remains) is a small, but essential, component

4 Titik layu tetap Kapasitas lapangan Kering Bhn. Mineral 38-50 % (v/v)
Bhn. organik 0-12% (v/v) Bhn. organik 0-12% (v/v) Bhn. organik 0-12% (v/v) Bhn. Mineral Bhn. Mineral Udara tanah 15 % Larutan tanah 15 % Larutan tanah 35 % Udara tanah 35 % Udara tanah 50 %

5 A. Anorganik Bahan mineral berasal dari pelapukan batuan
Apa itu batu (rock) atau batuan (sione)? Batuan dikelompokkan: 1. batuan beku (ignius, batu api) 2. batuan sedimen (endapan, mendapan) 3. batuan metamorfik (alihan, malihan)

6 Note: the minerals of igneous rocks are arranged randomly throughout the rock. There are no parallel alignments or fundamental segregations.

7 Aliran lava

8 Granite Rhyolite Figure 4.7 A

9 Andesite Diorite Figure 4.7 B

10 Basalt Gabbro Figure 4.7 C

11 Breccia - fragmental Clastic Sedimentary Rocks
A BRECCIA is made of varying sizes of angular fragments cemented together. The name is from the Italian word for “broken stones” or “rubble”. Many form as the result of fault movement; others form as the result of rapid and short transportation, such as landslides. The fragments in the upper photo are very well cemented by silica and the rock actually breaks through some of them. The cement in the lower photo is caliche (calcite) and the rock is much less durable.

12 Conglomerate - fragmental
Clastic Sedimentary Rocks Conglomerate - fragmental CONGLOMERATES are very similar to breccias, but the fragments are rounded. The name is from the Latin conglomeratus for “heaped, rolled or pressed together”. These rocks form in alluvial fans, stream beds and pebble beaches. Conglomerate is often used as a source of construction aggregate.

13 Sandstone - fragmental
Clastic Sedimentary Rocks Sandstone - fragmental SANDSTONE is made up of fine-grained particles (1/16 –2 mm). The sand grains (often quartz) are commonly cemented by silica, carbonates, clay or iron oxides. Sandstone is identified by its sandy texture – which often translates into a gritty feel. Environments in which sandstones form include beaches, sand bars, deltas and dunes. Coconino Sandstone, the result of a Permian age coastal dune field Sandstone is a source of sand for construction aggregate and as a silica source for glass. When quarried and separated into plates or sheets along bedding planes, it is used as flagstone (Arizona is the flagstone capital of the United States). Cut into blocks, it is used as a building stone.

14 Shale - fragmental Clastic Sedimentary Rocks
SHALE is a very common rock made of silt and clay sized particles. It is generally very thin-bedded and splits along the bedding planes. In fact, the name is probably from the Old English scealu, “shell or husk”. Normally gray to black, shale may be brown to dark red, depending on the amount of included iron oxide. Shales form in quiet environ- ments, such as lakes, swamps, deltas and offshore marine. Black shale, deposited in a offshore basin in a Middle Cambrian sea. Wheeler Shale with trilobite fossil (Elrathia kingii) Fossils, such as plants, soft bodied invertebrates, and vertebrates are often found in shale. Fish scales Utah

15 2. Biochemical Sedimentary Rocks
COAL - Biochemical COAL is considered a rock, although it is not composed of minerals, but rather the decomposed remains of large volumes of vegetation that accumulated in a wet, low oxygen environment, such as a swamp or marsh. Peat, Lignite and Sub- Bituminous & Bituminous are sedimentary varieties of coal and are used as fuels.

16 DIATOMITE - Biochemical
Biochemical Sedimentary Rocks DIATOMITE - Biochemical DIATOMITE, also known as diatomaceous earth, is composed of the siliceous shells of microscopic alga called diatoms. It is light weight and is generally white. Diatomite is used as an abrasive, insecticide, filtering medium, and paint “flattener”. Diatomite can be distinguished from chalk, by its non-reaction to HCl. San Manuel, AZ

17 Limestone - chemical 3. Chemical Sedimentary Rocks Uses:
LIMESTONE is composed primarily of calcite. Generally it is dense, fine-grained, and usually white to dark gray. Its most distinguishing feature is its solubility in weak hydrochloric or acetic acid accompanied by brisk effervescence. The environment of deposition if generally warm, shallow seas. Therefore, marine invertebrate fossils are common. Uses: Manufacture of lime and Portland cement & to neutralize smokestack gases. Finely ground, used as a functional filler in products such as paint, countertops & plastics. The dust on chewing gum is ground limestone. Mild abrasive additive to toothpaste. Soil conditioner Flux in processing iron and copper ores. Building and ornamental stone.

18 Limestone - chemical Chemical Sedimentary Rocks Coquina Crystalline
Pleistocene, Rocky Point, Mexico Redwall Limestone Travertine Mayer, AZ Fossiliferous

19 CHERT - chemical Chemical Sedimentary Rocks
CHERT is crypto-crystalline quartz. It is often the result of the dissolution of volcanic ash and is sometimes found in extensive beds, such as the novaculite of Arkansas. It has waxy luster, is translucent and fractures conchoidally. Chert can be any color, but extensive beds are generally white to gray. The uniform, fine texture of Arkansas novaculite has made it a popular (and expensive) whetstone.

20 GYPSUM - chemical Chemical Sedimentary Rocks
Satin Spar Alabaster GYPSUM (calcium sulfate) is found in geographically wide- spread deposits resulting from the evaporation of a body of water, such as ocean basin or playa lake. It is soft (H=2) & usually white to gray. Three varieties are: Alabaster, Satin Spar and Selenite. Gypsum is mined for use in wallboard and plasters, as an agricultural amendment and to control the set/cure time of Portland cement. Selenite Gypsum & Anhydrite (water-less calcium sulfate), Carlsbad, NM

21 ROCK SALT - chemical Chemical Sedimentary Rocks
ROCK SALT (halite – sodium chloride) is also a deposit resulting from evaporation of a marine basin or playa lake. It has cubic cleavage and tastes salty. Rock salt is used as a source of chlorine and sodium, as a food supplement, in water softeners and as a road de-icer. Halite Trona, CA

22 Note the relatively dull luster of slate.
SLATE - foliated SLATE is derived from shale. It is a dense, microcrystalline rock, but one in which parallel planes are very evident in its slaty foliation – a feature resulting from the alignment of clay and mica minerals,which allows it to split readily into sheets. It may be gray, black, green or red. Uses include roofing, flagstone, pool table tops and “blackboards”. Note the relatively dull luster of slate.

23 Note the phyllitic sheen.
PHYLLITE - foliated PHYLLITE is somewhat more metamorphosed than slate. The platy crystals of mica have grown and the rock displays a subtle, satiny shine referred to as “phyllitic sheen”. The name comes from its leaf-like (many fine layers) appearance. Note the phyllitic sheen.

24 SCHIST - foliated SCHIST is medium to coarse- grained, crystalline, with prominent parallel mineral orientation. Typically, it is predominately muscovite mica, which lends a silvery white to gray sparkly appearance. It is not unusual for accessory minerals (such as garnets, staurolite, tourmaline) to grow in the rock. Schist is added to clay mixtures as a strengthening material in vitreous pipe (red sewer) and clay roof tiles. Crumpling of schist due to pressure and collapse of mica crystals porphyroblasts tourmaline porphyroblast – note alignment garnet porphyroblast

25 GNEISS - foliated Gneissic granite – separation of dark & light minerals is just beginning Well banded gneiss GNEISS formed under conditions of high temperatures and pressures at great depth during regional metamorphism. It is characterized by foliation expressed as black and white banding. Because the rock becomes plastic, the banding is often contorted (squiggly). Augen = quartz pebble resistant to compression Augen Gneiss kink in gneiss

26 metamorphism of shale SHALE is the most common sedimentary rock.
Through the agents of metamorphism it changes to rocks that are stable at higher temperatures and pressures. These changes take place in the solid state. Shale Phyllite Schist Gneiss GRANITE Slate MELTING Produces GRANITE Increasing Temperature and Pressure

27 MARBLE – non-foliated MARBLE is metamorphosed limestone or dolomite. The colors can vary from pure white to gray, green, yellow, brown, black, red or any combination thereof, depending on the ‘impurities’ in the parent limestone. Bands or streaks result from plastic flow during extreme deformation, due to high pressure and temperature. It is calcite or dolomite and will fizz in weak acids. Marble is used for building facades, floors, countertops, statuary, landscaping, paving/roofing, poultry grit, and as filler/extender for paint, plastics, paper and adhesives. Hewitt Canyon, AZ Actually, the color banding can be construed to be a form, albeit not fully organized, or foliation.

28 QUARTZITE – non-foliated
QUARTZITE is metamor-phosed quartz sand-stone. It is a very dense,durable, massive, microcrystalline rock (but still may retain a slightly sandy look). It can be any color, but tends to be white, tan or pink.

29 SERPENTINITE – non-foliated
SERPENTINITE is composed of one or more minerals in the serpentine family. It is common where wet basalts or mantle rocks are metamorphosed, such as at convergent boundaries. Its green colors, waxy luster, often associated asbestos and common slickensided surfaces are clues to its identity. Chrysotile asbestos is used in heat resistant materials, such as brake linings, laboratory gloves/mats, pipe coatings. It has lost favor, due to lung complications from the inhalation of some varieties, but no fully satisfactory substitute exists. Chrysotile asbestos Salt River Canyon, AZ

30 METACONGLOMERATE – non-foliated
METACONGLOMERATE is metamorphosed conglomerate. It retains its pebbly appearance, but while a sedimentary conglomerate will break around the pebbles, a metaconglomerate will break through the pebbles. If temperatures are high enough in the presence of pressure, the pebbles may become squished or flattened and will be elongated parallel to each other (becomes foliated).

31 Primitive Rocks The other rock
“primitive rocks” formed directly from the protosolar nebula. Examples of primitive rocks include chondritic meteoritic material. Elemental ratios are in the same ratio as those in the Sun. We will talk more about these when we survey asteroids.

32 Iklim, TANAH B. Beku relief B. Endapan organisme B. Malihan waktu

33 PADATAN TANAH … Terdapat dalam berbagai ukuran: 50 µm – µm  pasir 2 – 50 µm  debu (lanau) < 2 µ  klei (liat = lempung) Bahan mineral > 2 mm terdiri atas kerikil, kerakal, dan bongkah

34 Padatan tanah Ukuran dan Susunan Ukuran diameter
> 2,0 mm  batu/batuan 2,0-20 mm kerikil < 2,0 mm  bahan tanah halus (fine earth) Bahan tanah halus -pasir 2,00-0,02 mm pasir kasar 2,0-0,2 mm pasir halus 0,2-0,02 mm Sistem International - lanau 0,02-0,002 mm - klei < 0,002 mm (lempung UGM+ITB, liat IPB):

35 Bahan tanah halus Pasir : 0,05 – 2,00 mm
Pasir sangat kasar 2,00 – 1,00 mm Pasir kasar ,00- 0,50 mm Pasir sedang ,50 – 0,25 mm Pasir halus , ,00 mm Pasir sangat halus 0, ,05 mm Lanau 0,05 -0,002 mm USDA system lanau kasar 0,05 – 0,02 mm lanau sedang 0,02-0,005 mm lanau halus 0,005-0,002 mm Klei < 0,002 mm Klei kasar 0,002-0,0002 mm Klei sedang 0,0002-0,00008 mm Klei halus < 0,0008 mm

36 Klei dapat berarti = ukuran < 0,002 mm (org. /anorg
Klei dapat berarti = ukuran < 0,002 mm (org./anorg.) = mineral (anorganik) = tekstur Bentuk padatan batang lempeng tidak teratur gumpal menyudut/membulat bola

37 A. MINERAL PRIMER & SEKUNDER
Mineral primer: mineral yang berasal langsung dari pembekuan magma (terdapat pada fraksi pasir dan debu) Mineral sekunder: mineral hasil bentukan pelapukan dan pembentukan tanah (terdapat pada fraksi klei)

38 Mineral Primer dalam tanah
Formula Keterangan Kuarsa SiO2 Tektosislikat Muskovit KAl2(AlSi3O10)(OH)2 Filosilikat Biotit K(Al,Fe)(AlSi3O10)(OH)2 Felspar ortoklas mikrolin Albit K[AlSi3O8 ] K[AlSi3O8] Na[AlSi3O8] Amfibol (Termolin) Ca2Mg5Si8O22(OH)2 Inosilkat ganda Piroksen enstatit diopsit rhodonit MgSiO3 Ca,Mg (Si2O6) MnSiO3 Inosilkat tunggal olivin (Mg, Fe)SiO4 Nesosilkat / Sorosilikat Epidot Ca2(Al, Fe)3Si3O12 (OH) Inosilikat tunggal

39 MINERAL PRIMER TANAH DAN UNSUR HARA
Mineral Unsur hara Kuarsa (SiO2) -- Kalsit Ca Dolomit Ca, Mg Feldspar: - Ortoklas K - Plagioklas Na, Ca Mika: - Muskovit K - Biotit K, Fe Amfibol (hornblende) Ca, Mg, Fe, Na

40 MINERAL PRIMER TANAH DAN UNSUR HARA
Mineral Unsur hara Piroksin Ca, Mg, Fe Olivin Mg, Fe Leusit K Apatit P

41 MINERAL SEKUNDER Beberapa jenis mineral sekunder (mineral liat) yang sering ditemukan di dalam tanah: 1. Kaolinit 2. Haloisit 3. Montmorilonit 4. Gibsit 5. Al-Fe oksida

42 Mineral Primer dan sekunder dalam tanah
Nama mineral Formula Mineral klei Kaolinit Si4Al4O10(OH)8 Monmorillonit Mx (Al, Fe, Mg) Si8O20(OH)4 Vermikulit Chlorit (Al,Mg,Fe)(Si,Al)8O20(OH)4 [M,Al,(OH)6](Al, Mg)4(Si,Al)8O20(OH)4 Alofan Si3Al4O12. nH2O Imogolit Si2Al4O10.5H2O Hematit α-Fe2O3 Maghemit γ-Fe2O3 Goetit FeOOH Ferihidrit Fe10O15.9H2O Boehmit γ-AlOOH

43 B. BAHAN ORGANIK Bahan organik kasar (particulate)
Bahan organik halus (humus) Humus terdiri dari bahan organik halus, berasal dari hancuran bahan organik kasar, serta senyawa baru yang dibentuk dari hancuran bahan organik tersebut melalui kegiatan mikroba dalam tanah

44 Komponen organik Sisa (residu) organik dan rombakan jaringan jasad Biomasa tanah (flora dan fauna tanah) Humus = bahan organik tanah Akar tumbuh an hidup 10 % b kering Humus 85 % berat kering Flora dan fauna tanah (edafon) 5 % berat kering, terdiri atas fungi, algae, bakteri, aktinomicetes, cacingtanah, makrofauna,

45 Manfaat Bahan Organik Pengaruh bahan organik terhadap sifat tanah dan pertumbuhan tanaman: memperbaiki struktur tanah sumber hara N, P, S dan unsur mikro Menambah kemampuan tanah menahan air Menambah kemampuan tanah untuk menahan unsur hara Sumber energi bagi mikroba

46 Humus = BOT Merupakan senyawa yang resisten (tidak mudah hancur), berwarna hitam atau coklat, mempunyai daya menahan air dan unsur hara yang tinggi Humus mempunyai kapasitas tukar kation yang tinggi yang disebabkan oleh gugus funsional (karboksil, karbonil, alkohol, dll.)

47 Struktur asam humat Ukuran koloid (1 nm-10um) Taklarut air

48 Tanah Organik (Gambut)
Dijumpai di daerah rawa-rawa Bila kandungan BO > 20 % (untuk tanah pasir) atau > 30 % (untuk tanah liat) dengan ketebalan > 40 cm  disebut tanah organik (tanah gambut)

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50 Top Soil Tanah yang banyak mengandung humus atau bahan organik adalah tanah lapisan atas atau top soil. Makin ke bawah, kandungan bahan organik makin berkurang, sehingga tanah makin kurus (tidak subur)

51 I. UDARA TANAH Susunan udara tanah berbeda dengan udara di atmosfir;
Kandungan uap air > tinggi Kandungan CO2 lebih besar Kandungan O2 lebih kecil Udara dan air mengisi pori-pori tanah. Air mengisi pori-pori mikro, sedangkan udara mengisi pori-pori makro

52 Udara Tanah dan Atmosfer
Komposisi Udara tanah (%) Udara atmosfer N2 O2 CO2 <78 20,6 >0,2 78 21 0,3 Ar He CH4 NO2 Sisa sisa

53 II. AIR TANAH Air terdapat dalam tanah karena:
Diserap (ditahan) oleh masa tanah Tertahan oleh lap. kedap air Keadaan drainase kurang baik. Fungsi air bagi tanaman: Sebagai unsur hara  H H O Sebagai pelarut unsur hara Sebagai bagian dari sel-sel tanaman (protoplasma)

54 Macam-macam Air Tanah Air tanah (H2O) Air bebas = air gravitasi
Air Kapiler = dipegang oleh pori/kapilar tanah Air higroskopis (air yang menyelimuti partikel tanah) Air tersediakan (KL-TLT) Air tak tersediakan (<TLT) Air tak berguna (air bebas) Kapasitas maksimum (keadaan jenuh) Kapasitas lapangan (jumlah airtanah setelah air gravitasi tersingkirkan) Tara lengas (kadar air disentrifusikan 1000 g, 40 menit) Titik layu tetap Kering angin (kadar air setimbang dengan kadar air udara) Kering oven 2. Larutan Tanah (H2O + solute (linarut) Kation = Na+, K+, Ca+2, Mg+2, Fe+2, NH4+ H+, Al+3 Anion = SiO4-4, H2PO4-, HPO4-2,SO4-2, NO3-1, BO3-3

55 MACAM AIR TANAH … Air higroskopik
Air yang diserap tanah sangat kuat sehingga tidak dapat digunakan tanaman Air kapiler Air yang dapat bergerak ke samping atau ke atas karena gaya kapiler. Sebagian besar air kapiler merupakan air yang tersedia bagi tanaman Air gravitasi Air yang tidak dapat diserap tanah karena adanya pengaruh gaya gravitasi

56 Air kapiler (tersedia bagi tanaman)
(1) Kapasitas lapangan Menunjukkan jumlah air terbanyak yang dapat ditahan oleh tanah Titik layu permanen Pada kondisi ini, akar tanaman mulai tidak mampu lagi menyerap air dari tanah, sehingga tanaman menjadi layu (3) Air tersedia Merupakan selisih antara kadar air pada kapasitas lapang dan kadar air pada titik layu permanen

57 TEGANGAN AIR TANAH Kandungan air pada kapasitas lapangan ditunjukkan oleh kandungan air pada tegangan 1/3 bar, sedangkan kandungan air pada titik layu permanen adalah pada tegangan 15 bar. Air yang tersedia bagi tanaman terletak pada tegangan 1/3 – 15 bar

58 Tegangan air Kelembaban tanah Tegangan air Bar (atm) pF Jenuh air 0 0 Kapasitas lapang 1/3 2,53 Titik layu permanen 15 4,18 Koefisien higroskopik 31 4,50 Kering oven ,

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60 Soil profiles O A E O A Bt E B R C

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62 TUGAS Jelaskan pengertian tanah ditinjau dari segi pertanian
Jelaskan perbedaan antara pedologi dan edafologi Sebutkan ilmu-ilmu yang berhubungan dengan ilmu tanah Sebutkan komponen utama tanah