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Soil moisture sensor | Wikipedia audio article

Soil moisture sensors measure the volumetric
water content in soil. Since the direct gravimetric measurement of
free soil moisture requires removing, drying, and weighing of a sample, soil moisture sensors
measure the volumetric water content indirectly by using some other property of the soil,
such as electrical resistance, dielectric constant, or interaction with neutrons, as
a proxy for the moisture content. The relation between the measured property
and soil moisture must be calibrated and may vary depending on environmental factors such
as soil type, temperature, or electric conductivity. Reflected microwave radiation is affected
by the soil moisture and is used for remote sensing in hydrology and agriculture. Portable probe instruments can be used by
farmers or gardeners. Soil moisture sensors typically refer to sensors
that estimate volumetric water content. Another class of sensors measure another property
of moisture in soils called water potential; these sensors are usually referred to as soil
water potential sensors and include tensiometers and gypsum blocks.==Technology==
Technologies commonly used to indirectly measure volumetric water content (soil moisture) include) Frequency Domain Reflectometry (FDR): The
dielectric constant of a certain volume element around the sensor is obtained by measuring
the operating frequency of an oscillating circuit. Time Domain Transmission (TDT) and Time Domain
Reflectometry (TDR): The dielectric constant of a certain volume element around the sensor
is obtained by measuring the speed of propagation along a buried transmission line. Neutron moisture gauges: The moderator properties
of water for neutrons are utilized to estimate soil moisture content between a source and
detector probe. Soil resistivity: Measuring how strongly the
soil resists the flow of electricity between two electrodes can be used to determine the
soil moisture content. Galvanic cell: The amount of water present
can be determined based on the voltage the soil produces because water acts as an electrolyte
and produces electricity. The technology behind this concept is the
galvanic cell.==Application=====Agriculture===
Measuring soil moisture is important for agricultural applications to help farmers manage their
irrigation systems more efficiently. Knowing the exact soil moisture conditions
on their fields, not only are farmers able to generally use less water to grow a crop,
they are also able to increase yields and the quality of the crop by improved management
of soil moisture during critical plant growth stages.===Landscape irrigation===
In urban and suburban areas, landscapes and residential lawns are using soil moisture
sensors to interface with an irrigation controller. Connecting a soil moisture sensor to a simple
irrigation clock will convert it into a “smart” irrigation controller that prevents irrigation
cycles when the soil is already wet, e.g. following a recent rainfall event. Golf courses are using soil moisture sensors
to increase the efficiency of their irrigation systems to prevent over-watering and leaching
of fertilizers and other chemicals into the ground.===Research===
Soil moisture sensors are used in numerous research applications, e.g. in agricultural
science and horticulture including irrigation planning, climate research, or environmental
science including solute transport studies and as auxiliary sensors for soil respiration
measurements.===Simple sensors for gardeners===
Relatively cheap and simple devices that do not require a power source are available for
checking whether plants have sufficient moisture to thrive. After inserting a probe into the soil for
approximately 60 seconds, a meter indicates if the soil is too dry, moist or wet for plants.==See also==

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