Soil moisture sensors are used to measure the water content, in the root-zones before planting takes place, as parts of the irrigation process. They are treated as rain shut off instruments very much like rain sensors, the difference being in the way they work.
While rain sensors ascertain the rates of evapo-transpiration , soil moisture sensors are engaged to ascertain real-time moisture in the soil. The main objective for using soil moisture sensors, is to regulate the present traditional timers of irrigation, which can bring about a lot of saving of water if they are properly installed and used in a proper manner.
They help the farmers to set up their own customized soil water content porch so that the condition of the soil, whether to be more dry or wet, can be planned. The function of these sensors is almost akin to rain sensors, which by pass irrigation activities when there is rain. In the case of soil moisture sensors, soil moisture is ascertained at the crops' root depth, which becomes very effective in controlling water expenditure.
The cost of building a soil moisture sensor is comparatively low, if you balance the potable quantity of water saved during the lifetime of the technology. Materials used for the making of a sensor and actual designing the final equipment will cost around US$400, while even cheaper systems can be built if the area is small. This is by far the most simple, economic and generally accepted system by people.
If a more complex system to measure water in different zones is needed, to ascertain water needs of plants, you may consider having more sensors which would of course increase costs. Let us remember that soil moisture sensors will be able to pay back within a time frame of 12 months after installation, through savings in water usage, which of course has to be calculated differently from water used for residential purposes and water costs paid to government.