BOBOT ISI (BI) TANAH
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Transcript of BOBOT ISI (BI) TANAH
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BOBOT ISI (BI)TANAH
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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.
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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.
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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.
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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.
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Bobot Isi vs. Bobot JenisBulk Density vs. Particle Density
http://soil.gsfc.nasa.gov/pvg/pd3.htm
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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