A soil moisture sensor can be used to determine if landscape needs irrigation. To use a moisture sensor you need to set up your controller so that it works with the sensor. The controller should be set to irrigate on a daily basis at the minimum. When the controller sends the signal to turn the valve on, the moisture sensor will either block the irrigation or allow it to proceed, depending on the moisture content of the soil.
Moisture sensors that attach to the Rain Sensor input of a controller have a disadvantage in that they block the irrigation for all zones, even if only one zone in being monitored with the sensor. Conversely this type of attachment might apply too much water to other zones.
A moisture sensor that attaches directly to the valve actuators overcomes this disadvantage. The Irrometer WEM is such a sensor system
http://www.irrometer.com/landcat.htm#wem.
The benefit of using LawnCheck with a WEM sensor is that you can dedicate one program or cycle to the zones controlled by the WEM. You can set this cycle to irrigate once a day, and then let the WEM decide whether to allow the cycle. The LawnCheck cycle can also be set up to include weather data, for example to block if the temperature is cool, or to use seasonal scaling, so not as much is applied during different parts of the year.
If anyone knows of products like WEM please list them here.
