Soil moisture measurements are important for a number of applications and for a number of different reasons. Applications include land slide studies, erosion, water shed studies, climate studies, predicting weather, flood warning, crop quality and yield optimization, irrigation, and soil remediation to name a few.
Measuring soil moisture is important in agriculture to help farmers manage their irrigation systems more efficiently. Not only are farmers able to generally use less water to grow a crop, they are able to increase yields and the quality of the crop by better management of soil moisture during critical plant growth stages.
In situ soil electrical conductivity monitoring is very important in agriculture because the salinity levels in soil moisture can have dramatic effects on crop health and yields. Agricultural soils over time may become sodic or saline and this may dramatically affect the health and yields of the crops. There are techniques that can remove the sodium to improve soil quality and increase crop production.
Time Domain reflectometry (TDR), Time domain transmissometry (TDT), Coaxial Impedance Dielectric Reflectometry (CIDR) and Frequency Domain Reflectometry (FDR) are the main methods used to measure soil moisture content and electrical conductivity. Most of the soil sensors use the SDI-12 serial protocol, allowing for multiple sensors to be connected to a data logger via a single cable.

ADU-500 Application

ADU-500, a D-size battery powered RTU/Data Logger, can address several SDI-12 soil sensors for a total of 48 measurement parameters (channels). Powered only by the internal 3.6V Lithium Thionyl battery, it can provide 12V excitation for all connected soil sensors. The restriction for the total current draw of the SDI-12 bus is:

(n-1)*I_IDLE+I_ACT < 250mA (at 12V)
where,
n: Nr. of sensors
I_IDLE: Sensor idle current (quiescent current)
I_ACT: Sensor active current (during measurement)