Geoscience Reference
In-Depth Information
Salinity
The total soluble salt (dissolved electrolyte) concentration in a soil. High salinity levels in
soil can adversely affect plant growth and land use. Salinity is typically determined by the
electrical conductivity measurement of a solution extracted from a saturated soil paste.
Sand
Soil particles with an equivalent diameter ranging from 0.05 to 2.0 mm.
Self-Potential Methods
From an operational standpoint, self-potential methods are probably the
simplest geophysical methods, requiring only the measurement of a naturally occurring elec-
tric potential difference between two locations on the ground surface. Essentially, a voltme-
ter is used to measure the electric potential difference between two nonpolarizing electrodes
placed at the ground surface that are connected to the voltmeter via electric cable. Naturally
occurring electric potential differences in the subsurface are often caused by electrokinetic,
electrochemical, or ore body oxidation and reduction processes.
Seismic Adsorption Coefficient
A constant value used in the calculation of seismic wave attenua-
tion that accounts for elastic energy loss due to frictional dissipation.
Seismic Methods
Geophysical subsurface investigation methods employing explosive, impact,
vibratory, or acoustic energy sources to introduce elastic (or seismic) waves into the ground.
The seismic waves are timed as they travel via direct, reflected, or refracted paths through
the subsurface from the source to the sensors, which are called geophones. Information
on the timed arrivals and amplitudes of the seismic waves measured by the geophones is
then used to determine below-ground conditions or to locate and characterize subsurface
features.
Seismic Waves
Elastic vibrations capable of propagating through Earth materials such as soil and
rock.
Silt
Soil particles with an equivalent diameter ranging from 0.002 to 0.05 mm.
Site-Specific Management
The use of spatially governed agricultural practices to manage crops,
soil, pests, and so forth, based on information obtained regarding variable conditions within
a farm field.
Sodium Adsorption Ratio (SAR)
A quantity used as an indicator of the exchangeable sodium
percentage (ESP), which is the percentage of the soil cation exchange capacity occupied
by sodium ions (Na
+
). Both SAR and ESP are used to gauge soil sodicity that reflects not
only the amount of sodium present but also its impact on plant growth. The value of SAR is
commonly determined from the calcium ion (Ca
2+
), magnesium ion (Mg
2+
), and sodium ion
(Na
+
) concentrations in a solution extracted from a saturated soil paste, and it is calculated
using the following equation:
+
Na
SAR
=
+
2
+
2
+
Ca
Mg
2
where the values in brackets represent ion concentrations in meq/L.
Soil Drainage Class
A soil can be assigned to one of seven drainage classes based on the fre-
quency and duration for periods of water saturation or partial water saturation.
Soil Gravimetric Water Content
Weight amount of water per unit weight of dry soil.
Soil Organic Carbon (SOC)
The amount of carbon contained in organic matter that is present
within a soil. Soil organic carbon is usually expressed as a fraction of total soil weight.
Soil Organic Matter (SOM)
The amount of plant and animal material at various stages of decom-
position that is present within a soil. Soil organic matter is usually expressed as a fraction
of a total soil weight.
Soil Particle Size Distribution
(Also referred to as
soil texture.
) The relative proportions of a soil's
sand-, silt-, and clay-sized particles.
