BOBOT ISI (BI)TANAH

Bobot Isi Tanah = Bulk Density

• Soil bulk density is the mass per unit bulk volume of soil that has been dried to a constant weight at 105 °C.

Bobot Isi

• If we have a soil that weighs 50 grams after being oven-dried and has a volume of 30 cm3, what will be the bulk density?

• It would be 50 g/30 cm3 or 1.67 g/ cm3.

Bobobt Isi di lapangan

• Bulk density of organic soils can be very low, such as 0.5 g/cm3.

• Clayey soils have higher bulk densities.• Compacted clay soils have very high bulk

densities, between 1.6 and 1.8 g/cm3.

Bobot Jenis = Berat Jenis = Kerapatan Partikel dan Porositas Tanah

• Particle density is the mass per unit volume of soil particles.

• Particle density is a relatively constant parameter and is sometimes assumed to be 2.65 g/cm3.

Bobot Isi vs. Bobot JenisBulk Density vs. Particle Density

http://soil.gsfc.nasa.gov/pvg/pd3.htm

Porositas Tanah• Soil porosity is the percentage of a soil that is pore space

or voids. • The average soil has a porosity of about 50%, and the

pores are filled with air or water depending on the moisture content.

• Sands have larger pores, but less total pore space than clays.

• If both bulk density and particle density are known, the total porosity can be calculated using these values.

Permeabilitas Tanah• Soil permeability is the ease with which air, water,

or plant roots penetrate or pass through soil.• Soils with large pores that are connected are more

permeable. • Rainwater soaks in readily and moves down

through the soil profile. • Clayey soils can have greater total porosity than

sand and still be less permeable than sand since the pores are small.

Soil Strength = Kekuatan Tanah

• Soil strength is defined as the amount of force required to move or rearrange soil particles.

• Soil strength is an important physical property affecting plant growth and seedling emergence.

• It is affected by three main factors; moisture content, soil texture, and bulk density.

Kadar Air & Kekuatan Tanah

• Water content is the most important factor determining soil strength.

• The lower the soil water content, or the drier the soil, the greater the soil strength.

• Soils that are saturated, or waterlogged have weak soil strengths.

Kadar Air Tanah (Lengas Tanah)

• Which soil would have the greater soil strength?

http://www.wy.blm.gov/botany/pics/cob-

duckswamp-500wfo.jpg

http://www.research.noaa.gov/spotlite/archive/images/

drysoil.jpg

Tekstur & Kekuatan Tanah

• Soil texture also affects soil strength. • Soil strength of aggregated soils increases as clay content

increases. • Poorly aggregated or single grain soils (sands, loamy sands,

sandy loams) usually have the weakest soil strengths unless they are cemented or compacted.

• Individual particles of single grain (sandy) soils are easy to rearrange, but these soils are susceptible to compaction, sometimes resulting in the formation of hard pans.

Bobot Isi & Kekuatan Tanah

• Bulk density is the third factor affecting soil strength.

• As bulk density of a given soil increases soil strength also increases.

• Remember that soil is composed of solids and pores, and the greater the bulk density the greater the amount of solids, and the smaller the amount of pore space.

Problem Pengelolaan Tanah

• Two examples of management problems caused by increasing soil strength are soil crusts and tillage pans.

• A soil crust is a thin soil layer that forms at the soil surface following heavy rains.

• Tillage or hard pans are high bulk density (>1.7 g/cm3) layers that occur within the Ap and E horizons.

• Compaction caused by traffic of equipment, vehicles, or even foot traffic often increases soil strength to levels that restrict root penetration and plant growth.

Penetrometers

• The force required to push a rod into the soil is a measure of soil strength.

• Penetrometers are devices used to measure the resistance of a soil to penetration to estimate the effect of compaction on growth, and to detect layers of different soil strength.

http://agnews.tamu.edu/dailynews/stories/SOIL/photos/May0505a-lr.jpg