Jurusan Tanah FP UB Februari 2012

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1 Jurusan Tanah FP UB Februari 2012
BAHAN KAJIAN MK. DASAR ILMU TANAH SIFAT FISIKA TANAH Dihimpun oleh Soemarno Jurusan Tanah FP UB Februari 2012

2 Efek Ukuran partikel tanah
TEKSTUR TANAH Efek Ukuran partikel tanah

3 Tipe-Tipe Struktur Tanah
Common to Ohio soils just below Ap (> 8”) Plow layer Sand Deeper in profile (>3-4’) Granular Platy Prismatic Columnar Blocky Single Grain Massive … Diunduh 15/2/2012

4 Relative proportion of the various size separates in a soil.
TEKSTUR TANAH Luas permukaan internal Pori tanah Relative proportion of the various size separates in a soil. Important because it affects and is related to several soil properties such as soil structure, aeration, water holding capacity, nutrient storage, water movement, and bearing strength.

5 Fraksi Tanah = Soil Separates
TEKSTUR TANAH Fraksi Tanah = Soil Separates Mineral soil is considered as a porous mixture of inorganic particles, decaying organic matter, water and air. Particle size and particle size distribution of these inorganic particles have an important bearing on the physical properties of soil.

6 It is difficult to alter the soil texture on the field level.
TEKSTUR TANAH Soil separates do not act as individuals, but as partners, or aggregates. Aggregates are the clumps of soil separates. When aggregates are bound together into large masses they are called peds It is difficult to alter the soil texture on the field level.

7 TEKSTUR TANAH Mineral fraction of soil is divided into are called soil separates. three major size groups. These groups Sand mm to 2 mm in diameter Silt mm to 0.05 mm in diameter Clay - <0.002 mm Gravel - 2 mm to 2 cm Stones - >2 cm Particles of <0.001 mm are designated as colloids - clay, a colloid is unique because of its large surface area.

8 TEKSTUR TANAH Klasifikasi tekstur tanah Penentuan tekstur tanah

9 TEKSTUR TANAH Karakteristik kelas tekstur Modifiksi tekstur tanah

10 Perbandingan ukuran partikel tanah
“Big”  smaller  really small Sand  silt  clay

11 TEKSTUR TANAH Surface area per unit volume 1 g sand ~ 0.1 m2
1 g silt ~ 1 m2 1 g clay ~ m2 Gee whiz fact: Fine clay has ~10,000 times as much surface area as the same wt. med. grain sand lowest highest Large surface area means more charge so greater ability to hold water and nutrients Coarse textured soils have larger pores, fine textured soils have greater total pore space h Surface area h weathering

12 Surface area, pore volume, nutrient supply capacity, plasticity and cohesion, swelling
Teton Dam failure story: used silt instead of clay as dam’s core, and it failed, killing 11 people and wiping out thousands of homes. Clay Silt Sand Particle Size

13 Pore size, infiltration rate, drainage rate, aeration
Clay Silt Sand Particle Size Pore size, infiltration rate, drainage rate, aeration

14 Siklus Hidrologi dan Tanah
Sifat tanah yang menjadi bagian dari siklus hidrologi. Moisture Color Temperature Structure Moisture and color relate to temperature. pH Texture Horizon Depths Bulk Density

15 PENGARUH TEKSTUR Pasir Debu Liat Water-holding capacity Aeration
Drainage Nutrient retention Low Medium High Good Poor Medium Slow Very slow Fast High Low Medium

16 DENSITAS DAN PERMEABILITAS TANAH
Kerapatan partikel = Particle density

17 DENSITAS DAN PERMEABILITAS TANAH
Bobot Isi Tanah Porositas Tanah Permeabilitas tanah ditetapkan dalam keadaan jenuh pada contoh tanah yang tidak terganggu yang dirumuskan : K = (QL) / t.h.A. Dimana : K = Permeabilitas ( cm/jam ) Q = Banyaknya air setiap pengukuran ( cm3 ) L = Tebal contoh tanah ( cm ); H = Tinggi permukaan air dari permukaan tanah ( cm2 ) A = Luas permukaan contoh tanah ( cm2 ) t = Waktu ( jam )

18 DENSITAS DAN PERMEABILITAS TANAH
Permeability

19 BOBOT ISI – BULK DENSITY
Calculate soil bulk density and % pore space Discuss factors influencing the above soil properties Identify the difference between texture and structure Bobot isi tanah merupakan kerapatan tanah per satuan volume yang dinyatakan dalam dua batasan berikut ini: Kerapatan partikel (bobot partikel = BP) adalah bobot massa partikel padat per satuan volume tanah, biasanya tanah mempunyai kerapatan partikel 2,6 gram cm-3, dan (2) Kerapatan massa (bobot isi = BI) adalah bobot massa tanah kondisi lapangan yang dikering-ovenkan per satuan volume. Diunduh 16/2/2012

20 BOBOT ISI – BULK DENSITY
Porosity particle density: mass per unit volume (not pore space) ~ 2.65 Mg/m3 (Dp of quartz mineral, dominant mineral in most soils) bulk density: mass per unit volume (including pore space) ranges 0.1 – 2.65 Mg/m3 the volume percentage (%) of the total bulk soil NOT occupied by solids

21 BOBOT ISI – BULK DENSITY
Mass of dry soil per unit bulk volume, INCLUDING pore space O.M. decreases bulk density Compaction increases bulk density Increased bulk density lowers water infiltration and restricts root growth Bulk density is relatively high in coarse-textured soils because total pore volume is low

22 BOBOT ISI – BULK DENSITY
Histosols ( Mg/m3) Cultivated clay and silt loams ( Mg/m3) Cultivated sandy loams and sands ( Mg/m3) Concrete (ca. 2.4 Mg/m3) Quartz mineral (2.65 Mg/m3) LOW HIGH

23 BOBOT ISI – BULK DENSITY
OM: ~0.5 Mg/m3 “normal” soils: Db ~ Mg/m3 Clayey soils lower than sandy soils Upper limit: ~2.65 Mg/m3 Kerapatan massa lapisan yang bertekstur halus biasanya antara 1,0-1,3 g/cm3. Jika struktur tanah kasar maka kerapatan massa 1,3-1,8 g/cm3. Semakin padat suatu tanah makin tinggi kerapatan massa atau bulk densitynya sehingga makin sulit meneruskan air atau ditembus oleh akar tanaman. Diunduh 15/2/2012

24 BOBOT ISI – BULK DENSITY
Effect varies with soil texture!

25 Soil bulk density on skid trails: does tillage help??

26 BOBOT ISI – BULK DENSITY
Texture Yrs cropped Increase in Db due to texture and cultivation Loam 58 Silt loam 40 Clay 70 Coarse Fine 0.18 0.26 0.30 In general, the finer the texture, the more it compacts if aggregates are destroyed

27 BOBOT ISI – BULK DENSITY

28 STRUKTUR TANAH Tanah tidak berstruktur

29 STRUKTUR TANAH Tipe-tipe struktur tanah Pembentuka struktur tanah
Agregasi tanah merupakan proses-proses dimana partikel tanah utama (pasir, debu, liat) terikat bersama-sama oleh gaya alami dan bahan-bahan yang dihasilkan oleh eksudat akar dan aktifitas mikrobia. Agregat Suatu unit struktur tanah yang terbentuk oleh proses alami yang berlawanan dengan proses buatan, dan biasanya berdiameter <10 mm. Agregat yang stabil air adalah suatu agregat yang stabil dengan gaya-gaya yang diakibatkan oleh air seperti titik hujan, atau agitasi dalam analisa saringan basah.

30 STRUKTUR TANAH Structure spatial arrangement of primary soil particles
Aggregate stability spatial arrangement of primary soil particles how easily or not do the peds fall apart? Low bulk density Lots of macropores Stable aggregates Goal of good soil mgmt.

31 STRUKTUR TANAH The arrangement of primary soil particles into groupings called aggregates or peds Binding agents provided by plant roots (exudates), organic matter (OM), and clays Most important contributor to good structure is OM

32 Perbedaan antara Tekstur dan struktur
STRUKTUR TANAH Perbedaan antara Tekstur dan struktur Texture = proportions of different particle sizes (% sand, silt, clay) Structure = spatial arrangement of those particles

33 STRUKTUR TANAH Particles bind because organic compounds and some minerals are “sticky” Biological sources: polysaccharides, proteins, bacterial “glues” Mineralogical sources : oxides, carbonates, silicates (clay particles) Agregasi tanah dihasilkan dari penyusunan partikel, flokulasi, dan sementasi yang diperantarai oleh bahan organik tanah, biota tanah, jembatan ionik, liat, dan karbonat. Struktur tanah yang baik memiliki kemantapan agregat yang diperlukan untuk meningkatkan ketersediaan hara bagi tanaman, produktivitas tanaman, porositas, dan menurunkan tingkat erosi. Konsep dasar dari agregasi adalah pembentukan partikel sekunder melalui penggabungan partikel mineral dengan bahan organik dan anorganik. Dinamika agregasi sangat kompleks dan dipengaruhi oleh interaksi beberapa faktor seperti lingkungan, pengelolaan tanah, tanaman, komposisi mineral, tekstur, konsentrasi karbon organik tanah, proses pedogenesis, aktivitas mikroorganisme tanah, ion-ion yang dapat dipertukarkan, cadangan nutrisi di dalam tanah, dan kelembaban don’t skip this!

34 KARAKTERISASI STRUKTUR
Type: Four (4) principal shapes Granular (A), platy (E), blocky (B), prismatic (B) Size fine, medium, coarse Grade: Strong, moderate, or weak In general, if lots of clay STRONG structure, bigger blocks If lots of OM granular structure Shape of the aggregates distinctness (how obvious)

35 TIPE STRUKTUR: Spheroidal

36 Structure type: Platey

37 Structure type: Blocky

38 Sodium induced – disperses clays
Structure type: Prism-like Sodium induced – disperses clays

39 Granular A E Platy B Blocky C Massive

40 TELADAN LABEL STRUKTUR TANAH
GRADE SIZE TYPE Moderate coarse subangular blocky Weak medium platy Strong very coarse prismatic Moderate very fine granular ASK STUDENTS which identifies grade, etc.

41 AGREGAT ADALAH UNIT STRUKTUR
The same things that lead to strong structure make stable aggregates! Amount of OM Type and amount of clay Amount of stabilizing/flocculating minerals (calcium carbonate, gypsum, etc.) (kaolinite more stable than montmorillonite)

42 AGREGAT Aggregates contain many small pores; area between aggregates large pores Total ruang pori dapat dihitung dengan menggunakan data bobot jenis partikel – partikel dan bobot isi tanah sebagai berikut: TRP = 1 - BD/PD . 100% Dimana: TRP = Total Ruang Pori ‘ BD = Bulk Density (g/cm3) ; PD = Partikel Density

43 MENGAPA AGREGAT TANAH SANGAT PENTING?
Increase porosity Increase water infiltration, drainage, decrease runoff Increase water holding capacity Ruang pori tanah ialah bagian yang diduduki udara dan air. Jumlah ruang pori sebagian ditentukan oleh susunan butir-butir padat, apabila letak keduannya cenderung erat, seperti pada pasir atau subsoil yang padat, total porositasnya rendah. Sedangkan agregat bergumpal seperti yang kerap kali terjadi pada tanah-tanah yang bertekstur sedang yang besar kandungan bahan organiknya, ruang pori persatuan volume akan tinggi.

44 KONDISI YANG MEMPERBAIKI STABILITAS AGREGAT
Low disturbance High root abundance High fungal biomass High OM High clay content Pembentukan agregat terjadi melalui beberapa cara dan dikelompokkan dalam tingkat ukuran yaitu makroagregat (> 250 μm) dan mikroagregat (< 250 μm). Teori agregasi yang dikemukakan Tisdall (1996) adalah mikroagregat (< 250 μm) dibentuk oleh molekul organik (MO) yang menempel pada liat (L) dan kation polivalen (P) membentuk partikel (L-P-MO), yang saling berikatan dengan partikel (L-P-MO) lainnya membentuk makroagregat [(L-P-MO)x]y.

45 EFEK BOT TERHADAP STABILITAS AGREGAT
Mekanisme agregasi melalui proses flokulasi dan fragmentasi. Flokulasi terjadi jika partikel tanah yang pada awalnya dalam keadaan terdispersi, kemudian bergabung membentuk agregat. Sedangkan fragmentasi terjadi jika tanah dalam keadaan masif, kemudian terpecah-pecah membentuk agregat yang lebih kecil. Semakin mantap suatu agregat tanah, semakin rendah kepekaannya terhadap erosi (erodibilitas tanah).

46 Efek akar dan pengolahan tanah terhadap stabilitas agregat
Kemantapan agregat tanah dipengaruhi oleh : jumlah dan jenis bahan organik di dalam tanah, khususnya lem dan musilage, (ii) keberadaan bakteri dan fungi serta akar tanaman berukuran mikro, (iii) pembasahan dan pengeringan, (iv) freezing dan thawing, (v) situs pertukaran kation alami, dan (vi) aktivitas biota tanah khususnya cacing tanah.

47 Cara memperbaiki struktur tanah
Reduce disturbance Work soil when dry Mulch soil surface Add organic materials (crop residues, compost, manure) Use cover crops diunduh 15/2/2012

48 KONSISTENSI TANAH Wet soil Moist soil Dry soil
Soil consistency states for a sand and a clay soil (friable soil is best for tillage).

49 SIFAT OLAH TANAH Compaction Aggregate destruction Puddling and clods
Surface crusts Improving tilth Soil channels Kemantapan agregat tanah dapat didefinisikan sebagai kemampuan tanah untuk bertahan terhadap gaya-gaya yang akan merusak. Gaya-gaya tersebut dapat berupa kikisan angin, pukulan hujan, daya urai air pengairan, dan beban pengolahan tanah.

50 PEMADATAN - LENGAS STANAH
maximum density 1.8 1.6 Bulk density (g/cm3) 1.4 dry wet Water content of soil

51 PEMADATAN TANAH DAN PERTUMBUHAN TANAMAN
Silt loam in Arkansas: decreasing Db by 16% increased cotton yields 13% during a normal year 59% during a dry year Medium textured soils in Washington Db > 1.2 Mg/m3; positively correlated with diseases in peas and beans (h pore space= h water storage capacity)

52 Increasing soil compactiong(increasing bulk density)
EFEK PEMADATAN TANAH Increasing soil compactiong(increasing bulk density)

53 KERAPATAN PARTIKEL = Particle Density
Mass of dry soil per unit volume of solids, this EXCLUDES pore space So if you compact a soil, does particle density change?? No!

54 Comparison of bulk and particle density
g/cm3 = Mg/m3 1.32g 1.32g

55 Soil Pans Lapisan tanah yang diperkeras Claypans Fragipans Plinthite
Caliche and duripans Any harden layer is called a pan Claypans occur with extreme illuviation Fragipans are a hard brittle claypan Plinthe is a tropical hardpan that can not be soften by wetting Caliche and duripans, layer of soil cemented by lime cement leaving white hardened layer

56 PORI TANAH - POROSITAS % PS = 100 * (1-[Db/Dp])
If you compact or till a soil, the pore space decreases. Large pores are filled with air Small pores are filled with water Clay soils have greater total pore space than sandy soils Porositas tanah erat hubungannya dengan bulk density serta permeabilitas. Apabila total ruang pori tinggi maka memiliki tekstur tanah yang halus yang dapat menyimpan air dan udara dalam tanah sehingga menyebabkan kerapatan massa (bulk density) yang rendah.

57 % Pore Space = 100 * (1-[Db/Dp])
PORI TANAH - POROSITAS Permeabilitas merupakan kemampuan tanah untuk meneruskan air atau udara. Permeabilitas umumnya diukur sehubungan laju aliran air melalui tanah dalam suatu massa waktu dan dinyatakan sebagai cm per jam. Hal ini mengakibatkan pergerakan udara yang berhubungan dengan volume tanah yang kosong, bukan ukuran pori dan kesinambungan ruang pori. % Pore Space = 100 * (1-[Db/Dp])

58 PORI TANAH - POROSITAS A pattern to note: As clay content increases, pore volume increases and bulk density decreases h Clay content

59 PORI MAKRO - MIKRO Macropores are usually air-filled, whereas micropores are typically water-filled The size of pores rather than their combined volume is the important factor in determining soil drainage, aeration, and other processes

60 HUBUNGAN TEKSTUR DENGAN PORI (data for 10 cm depth)
Texture O.M. (%) Total pore space (%) Micropores (%) Macropores (%) Sandy loam 2 42 Silt loam good structure poor structure 5 50 17 25 27 23 40 10

61 http://www.egyptastic.co.uk/_25.html …. Diunduh 15/2/2012
WARNA TANAH Color as a guide to soil use Dark brown to black White to light gray Light brown, yellow to red Bluish-gray Mottled colors Describing soil color …. Diunduh 15/2/2012

62 WARNA TANAH “quantified” using the Munsell system
Hue (e.g., 5R) tells you general shade; DOES NOT tell you how dark the soil is Value (e.g., 5R 5/ ) tells you how dark the soil is: (0 darkest) may indicate current moisture status (dark = wet) and/or amount of organic matter Chroma (e.g., 5R 5/8) tells you color intensity (0 = gray). Indicator of hydrologic regime (well drained = h O2 = high chroma)

63 WARNA TANAH Hue, Value & Chroma

64 WARNA TANAH Chroma is used in defining wetlands.

65 Tanah-tanah coklat tua hingga hitam
O.M. can reach high level in waterlogged soil Usually smells sour, oily O.M. can also reach high level in aerated soil. It smells earthy Dark parent materials can affect color of soil..smells chalky Soil color Soil attributes Environmental conditions Brown to black (surface horizon) accumulation of organic matter (OM), humus low temperature, high annual precipitation amounts, soils high in soil moisture, and/or litter from coniferous trees favor an accumulation of OM

66 Tanah-tanah Putih hingga Kelabu Muda
Light color may indicate the presence of chemicals such as gypsum or other salts Munsell soil color chart. diunduh 15/2/2012

67 Tanah-tanah Coklat muda, Kuning, Merah
Indicate iron oxides, indicates good drainage Blue-gray soils indicate a lack of oxygen in the soil Mottled wetland soils indicate waterlogged soil for at least part of the year Soil color Soil attributes Environmental conditions Bright-light Eluvial horizon (E horizon) In environments where precipitation > evapotranspiration there is leaching of sequioxides, carbonates, and silicate clays. The eluviated horizon consists mainly of silica Yellow to reddish Fe3+ (oxidized iron) Well-aerated soils

68 Deskripsi Warna Tanah The Munsell system is a widely used color I.D. system Hue is the color such as red or yellow Value is the lightness or darkness of hue noted by numbers zero to ten Chroma is the purity of the dominate color denoted by a number diunduh 15/2/2012

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71 SISTEM MUNSELL A 10YR3/6 soil has: The hue 10YR, a yellow red
The value of 3 (dark) Chroma of 6 This is described as a dark yellow brown soil This would be recognized internationally

72 WARNA TANAH - DRAINAGE ….. Diunduh 15/2/2012

73 DRAINAGE INTERNAL TANAH.
Important for proper plant growth Permeability can be determined by the color of the subsoil. Grey with some red or yellow streaks - poorly drained soils Yellowish-brown or reddish brown with some grey mottling - as internal drainage improves Uniform bright color with few or no grey streaks or mottling – good internal drainage and aeration Poorly drained Water is removed so slowly in relation to supply that the soil remains wet for a comparatively large part of the time the soil is not frozen. Excess water is evident in the soil for a large part of the time. Subsurface flow or groundwater flow, or both, in addition to precipitation are the main water sources; there may also be a perched water table, with precipitation exceeding evapotranspiration. Soils have a wide range in available water storage capacity, texture, and depth, and are gleyed subgroups, Gleysols, and Organic soils. … Diunduh 15/2/2012