Soil texture and structure

SUMBER: jpkc.njau.edu.cn/land/ppt/4.Soil%20texture%20and%20structure.ppt

Soil density and bulk densityBobot Jenis (BJ) dan Bobot Isi (BI)

Soil density ( or Particle density)

Soil density is the density of the solid soil particles only; the measurement does not include water weight or pore (air) space. The dominant soil minerals- quartz, feldspars, micas, and clay minerals-

average approximately 2.65 g/cm3, the “standard” value used in calculations if particle density is not measured.

Individual minerals have densities from 2.0 g/cm3 for bauxite (aluminum ore) to 5.3 for hematite (iron ore) or 7.6 for galena (lead

Bobot Isi Tanah (Soil bulk density) 1. Bulk density, the density for a volume of soil as it exists naturally,

includes any air space and organic materials in the soil volume.

ρb = (mass of dry soil)/(total volume of soil) = Ms/Vt

= Ms/(Vs + Vw +Va)

A recently cultivated topsoil is likely to have a bulk density in the range from 0.9 to 1.2 g/cm3, while a compact subsoil may have a

bulk density of 1.6 g/cm3 or even more.

Penggunaan BI tanah ： ① untuk menghitung Porositas Tanah (p0):

② To calculate soil weight ③ To calculate storage of soil compositions ④ To calculate total water storage capacity

and irrigation (or drainage) quota.

2. Bulk density in water = (soil mass over-dry)/(precipitation volume)3. Affect the factors of soil bulk density: Texture, structure, content of organic matter, and various nature factors and anthropogenic factors.

P0 = 1- (Bulk density/soil density)

1 、 Index three phases constitution

Solid phase (%) = （ solid volume /soil body volume) ×100

Liquid phase (%) = （ liquid volume /soil body volume) ×100

Gas phase (%) = （ air volume /soil body volume) ×100

2 、 Porositas Tanah:

Soil porosity is the percentage of the volume of pores to the total volume of soil. Soil porosity ＝ 1 － Solid phase (%) = Liquid phase (%) + Gas phase (%)

The void ratio is the ratio of the volume of pores to the volume of solids.

Void ratio = (volume of pores)/(volume of solids)

Calculation of three phases constitution and porosity

1. Solid ratioSolid ratio = （ bulk density /density ） = ρb/ ρp

2. Liquid ratio (volumetric water content)θm = (mass of water /mass of dry soil) = MW/MS

θv = (volume of water/ total volume of soil) = Vw/Vt = Vw/(Vs+Vw+Va) = θm × ρb

3 、 Rasio Ruang - Void ratio

3. Rasio Fase GasPorosity(P0) =1- solid phase ratio =1- bulk density /density ） = ρb/ ρp

Gas phase ratio = porosity- volumetric water content = P0- θv

4. Actual volume ratioSolid phase ratio ＝ actual volume ratio － volumetric water content Gas phase ratio = 1 － actual volume ratioSoil three phases ratio ＝ solid phase ratio : volumetric water content : gas phase ratioRasio tiga fase tanah yang ideal ：Solid phase ratio is about 50% ，volumetric water content is 25% to 30% ， Gas phase ratio is 15% to 25%.

(1) Tipe Partikel Tanah ：• Mineral soil particle and organic soil particle• Single particle and compound particle• Primary particle and second particle

(2). Fraksi partikel tanah (separat tanah) Natural soils are comprised of soil particles of varying sizes. The soil particle-size groups, called soil particle fraction (soil separates), are sands (the coarsest), silts, and clays (the smallest).

Partikel Tanah & Fraksi Partikel (Separat Tanah)

Ukuran Diameter Partikel• Soil particle diameters range over 4

orders of magnitude– Boulders– Sand– Silt – Clay

Physical sandy particle: 1 mm to 0.01 mm.

Physical clay particle: < 0.01 mm

Kachinsky classification system of soil separates

Soil particle

Classification system of soil separates ： (mm)

Diameter International USDA Kachinsky Chinese

Boulders >2 >2 > 1 >1

Sand 2-0.02 2-0.05 1-0.05 1-0.05

Silt 0.02-0.002 0.05-0.002 0.05-0.001 0.05-0.002

Clay 〈 0.002 〈 0.002 〈 0.001 〈 0.002

(1). Komposisi Meknaik Tanah（ 2). Tekstur Tanah

1.Concept: Soil texture-The relative proportions of the various soil separates in a soil.2. Classification of soil texture.

Komposisi mekanik tanah dan Tekstur tanah

(1) International classification ：The textural triangle is used to determine the soil textural name

after the percentages of sand (2-0.02mm), silt (0.02-0.002 mm), and clay (<0.002 mm) are determined from a laboratory analysis.

The main criterion of classification ： Clay <15% is sand and loamy groups;

15 ％－ 25 ％ is clay loam group;

>25% is clay group.

When soil contains silt >45% ， soil will be called “silty” ； When soil contains sand in 55%-85% ， called “sandy” ， When soil contains sand >85% ， called “ loamy sand”or “sand”.

1. Sand• < 2 mm to > 0.02 mm

• Visible without microscope

• Rounded or angular in shape

• Sand grains usually quartz if sand looks white or many minerals if sand looks brown,

• Some sands in soil will be brown, yellow, or red because of Fe and/or Al oxide coatings.

The fertility characteristics, utilize and improves of different soil textures

The fertility characteristics of different soil textures

PASIR - Sand

• Feels gritty • Considered

non-cohesive – does not stick together in a mass unless it is very wet.

PASIR - Sand

1. Low specific surface area

2. Sand has less nutrients for plants than smaller particles

3. Voids between sand particles promote free drainage and entry of air

4. Holds little water and prone to drought

LIAT • < 0.002 mm • Flat palettes or tiny

flakes • Small clay particles

are colloids– If suspended in water

will not settle• Large surface area

– spoonful = football field

LIAT - Clay1. Wet clay is very

sticky and is plastic or it can be molded readily into a shape or rod.

2. Easily formed into long ribbons

3. Shrink and swell

LIAT - Clay• Pores spaces are very

small– Movement of water and air

very slow• Water holding capacity

– Tremendous capacity to adsorb water- not all available for plants.

• Soil strength- shrink/swell affects buildings, roads and walls.

• Chemical adsorption is large

LEMPUNG - Loam

• < 0.02 mm to > 0.002 mm

• Not visible without microscope

• Quartz often dominant mineral in loam since other minerals have weathered away.

LEMPUNG - Loam

• Does not feel gritty• Floury feel • Wet loam does not

exhibit stickiness / plasticity / malleability

LEMPUNG - Loam1. Smaller size allows rapid weathering of

non quartz minerals2. Smaller particles – retains more water for

plants and have slower drainage than sand.

3. Easily washed away by flowing water – highly erosive.

4. Holds more plant nutrients than sand.

• Silt is responsible for silting over gravel beds in rivers that are needed by fish for spawning.

Loess Cliff in China

Silt if often left as a vertical face since in this condition the

landscape is less prone to water erosion than if the area was graded

to a slope.

Menggunakan dan memperbaiki tekstur tanah

① Foreign soil methods Soil texture can be changed only by mixing with another soil with a different textural class in small quantities

② Deep ploughing, deep turn over etc.

Adding peat or compost to a mineral soil is not considered changing the texture – since it only adds organic matter not sand, silt or clay!!

一、 Soil structureness（一） Concept of soil structure Soil structure- The combination or arrangement of primary soil particles into secondary units or peds. The secondary units are characterized on the basis of size, shape, and grade (degree of distinctness).

Soil Structure

( 二 ) Classes and types of soil structureTypes of structure describe the ped shape with the terms granular, crumb, platy, blocky, subangular blocky, prismatic, and columnar.

Structure classes are the ped sizes such as very fine, fine, medium, coarse (or thick), and very coarse (or very thick).

Soil structureness

Struktur yang Jelek: platy, blocky, subangular blocky, prismatic, and columnar

Struktur yang baik: Granular

Genesis Struktur GranularProses pembentukan struktur granular

1. Cohesion aggregation

① Condense

②Cohesion of inorganic matter

③ Cementation and compound of organic matter

④ Complex of organic-mineral

⑤ Earthworms and other small animals

① Root Wetting and drying cycle ② ③ Alternate freezing and thawing Tillage④

2. Proses Pengirisan dan Pemodelan

The arrangement of soil particleSUMBER: jpkc.njau.edu.cn/land/ppt/4.Soil%20texture%20and%20structure.ppt

PARTIKEL TANAH

Agregat

AGREGAT MIKRO

Proses pembentukan agregat tanah

Proses Agregasi

PASIRDEBU

Humus (BOT) & Liat sebagai perekat

PARTIKEL TANAH

SENYAWA ORGANIK SEBAGAI PEREKAT

PARTIKEL TANAH

Ca++ dan senyawa organik sebagai perekat

PARTIKEL TANAH

SENYAWA ORGANIK SEBAGAI PEREKAT

Fe dan Al, dan senyawa organik sebagai perekat

1. Teori Liat

Mekanisme Mikrokosmik pembentukan agregat tanah

2. Keseimbangan air dan Udara dalam tanah

3.Coordinated to keep and apply fertilizer

4. Pengolahan tanah yang sesuai

5. Lapisan olah-tanah yang bagus

Pengelolaan struktur tanah1. Aplikasi pupuk organik

2. Rotasi (pergiliran ) tanaman yang sesuai

3. Reasonable tillage, water management and soil reclamation

4. Aplikasi bahan perbaikan struktur tanah

5. The electric current reclamation of saline-alkali soil

1. Soil porosity = pore volume/soil volume= (soil volume – soil particle volume)/soil volume = 1- （ soil particle volume/ soil volume ）= 1-[ （ soil particle volume×soil weight ） / （ soil volume×

soil weight ） ]= 1-[ （ soil weight/ soil volume ） × （ soil particle volume/

soil weight ） ]=1-[ （ soil weight/ soil volume ） / （ soil weight / soil particle

volume ） ]= （ 1 – BI / BJ)

Pori Tanah dan Tubuh Tanah

Porositas Tanah:Perhitungan porositas tanah

2. Scope of soil porositySandy soil 30 － 45 ％Loam soil 40-50%Clay soil 45-60%Peaty soil 〉 80 ％

3. Loose and tight arrangement of soil particles

2. Klasifikasi Porositas

3. Porositas Aerasi

The porosity model of granular structure (Studied by yourself)

Equivalent pore diameter (effective aperture)Aeration pores- Greater than 0.1 mm average diameter. Size of medium sands.

Capillary pores- 0.1-0.03 mm average diameter. Size of silt particles.

Storage pores-Less than 0.03 mm average diameter. Size of clay particles.

Profil Porositas Tanah

The suitable porosity for plant growth:Plowed layer soil : total porosity in 50% to 56%, aeration pores in 8% to 10%.

Soil texture and structure

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