Soil Sci

• Soil density is defined in physics as mass per unit volume.
• Soil as a three-phase system consists of solid, liquid, and gas, each with different mass and volume parameters.
• These parameters dictate the use of soil and its productivity for agricultural crop production.
• The oven-dried weight of soil in g (Ws) is 30 g.
• The bulk density (BD) is calculated as Ws Vt, which is 1.25 g/cm3.
• The total volume of soil solids (Vs) is 18 cm3.
• The total volume of soil (Vt) is 24 cm3.
• Using SI units, the unit for mass is in grams (g) and cubic centimeters (cm3) for volume.
• There are five ways to define the mass-volume relationship of soil: particle density, dry bulk density, wet bulk density (total), and dry specific volume.
• The air composition of the soil is measured as porosity and void ratio.
• The density (D) of the given material is mass (M) per unit volume (V): Density (D) = 𝑀 (𝑀𝑎𝑠𝑠) 𝑉 (𝑉𝑜������𝑒) in g/cc or kg/l or t/m3.
• Mass total is equal to the mass of solids, the mass of water.
• Mass of water is equal to the mass total subtracted by mass of solids.
• The volume total is equal to the volume of solids, the volume of water, and the volume of gas.
• The volume of pores is equal to the volume of water and the volume of gas.
• Both expressions of density use only the mass of the solids in a soil; therefore, any water present is excluded from consideration.
• Particle density (PD) is calculated by dividing the weight of soil in g (Ws) by the volume of soil solids in cm3 (Vs).
• The more compacted the soil, the greater is the bulk density value and the less porous it is.
• The range of bulk density values for sand and sandy loam soils is 1.20 to 1.80 gm/cm3, while for clay, clay loam and silt loam it is 1.00 to 1.
• The solid particle density is calculated by dividing the weight of solids by the volume of solids.
• The volume of soil solid (Vs) is calculated by dividing the weight (Ws) by the particle density (PD).
• Bulk density values of coarse textured soils are generally higher than medium and fine textured soils because particles of sandy soils are more closely packed, resulting in lower total porosity.
• Bulk density (Db) is defined as the mass of a unit volume of dry soil, which includes both solids and pores.
• If all the solids of 1 cm3 of soil could be compressed to the bottom, the cube would look like.
• Bulk density is a measure of the degree of compaction of the soil and an indicator of its porosity.
• Bulk or total volume refers to the combined volume of the soil solids and pore space.
• A special soil sampler designed to remove a cylindrical core of soil without causing disturbance or compaction is known as a bulk density sampler.
• Volume total is equal to the volume of solids and volume of pores.
• Mathematically, the bulk density is determined by the formula : Bulk Density (BD) = Ws Vt = Oven dried weight of soil (g) (Ws) Total volume of soil clod (cm3) (Vt).
• The sampler head of a bulk density sampler contains an inner cylinder and is driven into the soil with blows from a drop hammer.
• High bulk density indicates limited soil aeration, very slow water movement, poor drainage, impedance to root growth and critically retards seed germination.
• In the field, 1 cm3 of a certain soil appears as … Total volume of soil (solid + pore spaces) (Vt) = 1 cm3 Weight (Ws) = 1.33 Mg.
• Bulk density is calculated by the formula : Bulk Density (BD) = Ws Vt = Weight of soil in Mg (Ws) Volume of soil solids in cm3 (Vt) = 1 cm3.
• The inner cylinder of a bulk density sampler containing an undisturbed soil core is then removed and trimmed on the end with a knife to yield a core whose volume can easily be calculated from its length and diameter.
• The weight of this soil core is determined after drying in an oven.
• High bulk density becomes a major advantage in flooded paddy soils where the hardpan prevents water from percolating into the deeper layers.
• Particle Density (Dp) is defined as the mass (dry weight) per unit volume of soil excluding the pore spaces within that soil volume.
• Particle density is essentially the same as the specific gravity of a solid substance.
• The chemical composition and crystal structure of a mineral determines its particle density.
• In typical soils where quartz and feldspars prevail, the particle density may range from 2.60 to 2.75 g/cm3.