-
Bulk Density of Soil - (mass
of soil)/(volume of soil) typically in g/cm3. The test is
performed by hammering a hallow steel cylinder into the soil
until its top is flush with the ground level. The soil is
removed from the cylinder, and weighed. The equations is
computed with the internal volume of the cylinder. The average density
of soil particles is 2.7g/cm3.
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Field Capacity - Is the
water content of the soil after it has been saturated, and excess
water has been drained away, and the rate of downward movement of the
water has decreased substantially.
-
Gravitational Water - The
water which runs out of the soil immediately after it has been
saturated.
-
Gravimetric Water Content (GWC) -
(moist weight - dry weight)/(dry weight)
-
Loam is a mixture of clay,
sand and/or silt.
-
Particle Density - Density
of a given mineral assuming no pore space.
-
| Mineral/Substance |
Density (g/cm3) |
Density (lbs/ft3) |
| Water |
1.0 |
62.5 |
| Quartz |
2.65 |
166 |
| Feldspars |
2.5-2.7 |
156-169 |
| Micas |
2.7-3.0 |
169-188 |
| Clay minerals |
2.0-3.0 |
125-188 |
-
Plant Available Water - This
is the amount of water in the soil which can be extracted by a
plant. It is calculated as the Field Capacity minus the Wilting
Point.
-
Porosity - BD%= (wet weight
(g)-dry weight (g))/(soil volume(cm3)). Or, BD%= (1- Bulk
Density/2.7)*100. 1 minus the bulk density divided by the
average density of soil particles.
-
Potentiometer - See
Tensiometer.
-
Resistance Blocks - Two
electrodes are embedded into a block of gypsum, fiberglass or other
material, and the resistance across the block is measured, as an
indication of soil moisture. The medium acts as a buffer to
salts and other chemicals. Unfortunately, the results of these
devices are greatly affected by salinity and other
chemicals.
-
Root Depth - Root depth is
important in calculating how much water is available to the
plant. The deeper the roots, the more available water.
-
Soil Particle Sizes
| Soil Particle Type |
UK |
US |
International System |
| Stones/Gravel |
>2.0mm |
>2.0mm |
>2.0mm |
| Coarse Sand |
2.0 to 0.2mm |
2.0 to 0.2mm |
2.0 to 0.2mm |
| Fine Sand |
0.2 to .06mm |
0.2 to .05mm |
0.2 to .02mm |
| Silt |
60 to 2 um |
50 to 2 um |
20 to 2um |
| Clay |
<2um |
<2um |
<2um |
-
Tensiometer - Acts like an
artificial root. It's a plastic tube with a vacuum gauge at one end
and a porous clay cup at the other end, and water inside the
tube. When inserted into the soil, water is pulled out through
the porous clay until an equilibrium is reached, at which point the
vacuum gauge can be read to indicate the moisture of the soil.
-
Tilth - How easy it is to
till a soil.
-
Water Content - (moist
weight - dry weight)/(dry weight)
-
Water Holding Capacity - The
amount of water that soil can hold, similar to the Field
Capacity.
-
Wilting Point - occurs with
the wter content of soil is so low that plan toots can no longer
adequate water to sustain life.
-
Volumetric Water Content (VWC) -
VWC= (Wet Soil Volume - Dry Soil Volume)/Dry Soil Volume. Or,
VWC= GWC*Soil Bulk Density/Water Density.
