The bulk density of the soil will play an important role in determining if the soil has the physical characteristics necessary for plant growth, building foundations or other uses.
From the laboratory investigations you will obtain very high bulk densities for the Bt and sandy soil. The weight of the soil is important if you are going to be lifting it or hauling it long distances. One of the main reason for sod farms to be on organic soils is to reduce the cost of transportation because the organic soil is so much lighter than mineral soils. The organic sod is easier to handle. Most sod farms in Minnesota are on the peat soils north of the Twin Cities.
Volcanic ash also has a very low bulk density, and recently the soil order Andisols was established especially for those soils formed in volcanic ash.
For an example of a soil formed from volcanic ash, go to the Cody Lake soil. Or, to learn more about volcanic ash, go to What is Volcanic Ash.
Sometimes we are interested in the weight of an acre of soil for erosion
comparison purposes. Erosion of 5 tons per acre sounds like a lot. However the
weight of an acre furrow slice on average is 2,000,000 lbs., so 5 tons per acre
seems like a small amount. Five tons per acre is only about 34 thousandths of
an inch thick (.034 inches). However, many areas have lost 10 to 100 times that
amount. (Note: an acre furrow slice, or AFS, is a three-dimensional volume of
soil which is one acre in area and 7 inches deep.) 
Weight per AFS=BD × Volume
Example : Volume of soil=Soil depth × 43560 ft.² (area of 1 acre)
For conversion of g/cc to lbs/ft³, multiply BD × 62.4 lbs/ft³ (weight of ft³ water)
How many tons are lost if a soil with a B.D. of 1.2 g./ cm³ erodes 5 inches per acre?
answer : (1.2 × 62.4)=(weight in lbs/ft³) X Volume: (where Volume=(5 in. ÷12 in/ft) × 43560 ft)² or (74.88 lbs/ft³ ) × 18,150 ft³=1.3 million lbs or divide by 2000 lbs / ton or weight=679 tons
Another factor similar to carrying soil is its potential to be moved short distances, such as in plowing (see picture of plowing) or rototilling. The soil that is heavier will be more difficult to move. However, another factor is the ability of the soil to stick together, or the soil's consistence.
Clay soil is noted for its stickiness and large energy requirements in
tillage. Farmers refer to it as "heavy," but they really mean it is
difficult to plow, not that it has a high bulk density; clay soils generally
will have a lower bulk density than sandy soils (clay=1.3 g/cc vs
sand=1.6g/cc). Sandy soils have a higher bulk density, but are easier to
plow since they have weaker consistence. Thus they are often referred to as
"light soils." The lower B.D. of clays is due to their better
aggregation.
Rototilling the soil reduces the bulk density by "fluffing" the soil. For a look at tillage implements go to Tillage Implements
Soil consistence is the soil's ability to cohere or stick together. The soil's consistence may be evaluated at three moisture conditions: air dry, moist, and wet. Moist consistence is evaluated by placing the soil between the thumb and forefinger and gently applying pressure. The ease with which a ped can be crushed determines the consistency.
Terms commonly used to describe moist consistence are:
Loose- Non-coherent when dry or moist; does
not hold together in a mass.
Friable- When moist, crushes easily under
gentle pressure between thumb and forefinger and can be pressed together into a
lump.
Firm- When moist, crushes under moderate
pressure between thumb and forefinger, but resistance is distinctly noticeable.
Plastic- When wet, readily deformed by
moderate pressure but can be pressed into a lump; will form a "wire"
when rolled between thumb and forefinger.
Sticky- When wet, adheres to other material
and tends to stretch somewhat and pull apart rather than to pull free from
other material.
Hard- When dry, moderately resistant to
pressure; can be broken with difficulty between thumb and forefinger.
Soft- When dry, breaks into powder or
individual grains under very slight pressure.
Cemented- Hard; little affected by
moistening.
In air dry conditions, the resistance to rupturing when rubbed is measured. At intermediate moisture content, the soil's resistance to shearing forces by thumb and finger is noted. In the wet condition, its plasticity--ability to be molded and stickiness--are measured.
One significance of the B.D. of a soil is the amount of surface area a soil
has. The more surface area, the more ability to retain water and nutrients.
Notice that the two soils pictured below weigh the same, but are significantly
different in surface area. Which soil has the higher B.D.?
Lower bulk density implies greater surface area.
Bulk Density Chapter 1 Definition BD
Bulk Density Chapter 3 Compaction/Porosity and Soil Temp.........
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