ICT - Model MP306 - Soil Moisture Sensor

The MP306 can be used to take continuous measurements over time through permanent or temporary burial and connection to a SMM Soil Moisture Meter. The sensor has a compact body and the needles are arranged in a single plane making it ideal for use in soil columns, enabling measurement of discrete soil layers within the column. Similarly in soil profiles, narrow layers can be precisely measured.

The MP306 is also used to measure the moisture content in materials used in mining, roadway and buildings. The material that can be measured is often soil but can be any composition of non-metallic powdered, liquid or solid substance into which the needles are inserted. It is especially suitable for mineral stock piles, mine tailings and sand for batch mixing of concrete.

The MP306 Soil Moisture Sensor can also measure soil water potential via the SMM Soil Moisture Meter and a soil water characteristic curve.

MP306 uses the standing wave principle of measurement. It is equivalent to a Time Domain Reflectometry (TDR) sensor without the need for a complex and expensive pulse generator. MP306 is a high accuracy, precision sensor with 1% VWC accuracy following soil-specific calibration and 0.01% VWC resolution.

The MP306 is ideally supported by the SMM Soil Moisture Meter, a wireless, stand-alone logging instrument available from ICT International. With the SMM, MP306 sensors can be individually calibrated for maximum accuracy.

• The SMM can support up to 5 MP306 sensors.
• For complete monitoring solutions, the MP306 is used in combination with the MP406 soil volumetric moisture content sensor, tensiometers for soil water potential, ICTO2 soil oxygen sensor, or the ICT International automatic weather station.

MP306 Accuracy

The results from measurement of absolute volumetric soil water percent (VSW%) from prepared soil samples using the MP306 are given below (Figure 1). This result is typical of the results obtained from comparative testing of the MP306 in prepared soil samples, for a wide range of agricultural soils. Standing Wave Technology and hence the MP306 are not affected by changes in temperature or salinity of the soil or material being measured and hence the values of VSW% are equivalent to oven dried water content.

What is Standing Wave?

The standing wave technique uses an oscillator to generate an electrical field in order to detect the dielectric properties of a substrate of interest. The parallel needles of an MP306 act as a coaxial transmission line to generate a signal. The amplitude of the signal is related to the dielectric constant which in turn is directly related to moisture content.

Results

The results from measurement of absolute volumetric soil water percent (VSW%) from prepared soil samples using the MP306 are given below. This result is typical of the results obtained from comparative testing of the MP306 in prepared soil samples, for a wide range of agricultural soils. Standing Wave Technology and hence the MP306 are not affected by changes in temperature or salinity of the soil or material being measured and hence the values of VSW% are equivalent to oven dried water content.

Polynomial Look-up Table

Linearisation tables can be added to Data Loggers using the following data:
Converting Data Table for MP-306. From VSW% to mV & mA in mineral soil

• Volumetric Soil Water Content (%) or can simultaneously measure soil water potential
• Highly accurate and precise
• Robust, stainless steel needles and epoxy body
• Measures in saline, toxic and high temperature soils
• Rapid measurement
• Can be buried for up to 20 years