Using a Soil Moisture Sensor with LawnCheck

[Jim]

Soil Moisture sensors have been proven to be effective in conservation-oriented irrigation systems.   Soil moisture sensors provide an indication of whether the growing soil has adequate moisture or not.   One might think that with the installation of a soil moisture sensor, one would not require further "smart" control.  But the fact is it is still very possible to over-water a landscape that is controlled by a soil moisture sensor. 

As the seasons change, the amount of water needed by the plant and the soil change - due to temperature related evaporation and relative plant growth rates.   Application of constant quantities of water throughout the year can result either in run-off or water that sinks in too deeply and does no particular good for the plant.   So the combination of a soil moisture sensor along with a seasonal ET related setback provides a very optimal system in terms of both water efficiency and cost for applying water on an annual basis. 

Another element to consider in maintaining plant health is the period of time between waterings.   Plants need time between waterings for their roots to dry out for a sufficient time to allow roots to get oxygen.   Daily waterings, for example, to keep the soil moisture sensor moist, would most likely result in over-watering and poor plant health because the roots would never be allowed to dry out.

See the Replies for continuation of this subject.

[Jim]

Continued:

Here's a recommended way to use a soil moisture sensor with LawnCheck.

First of all the type of soil moisture sensor recommended is the type that attaches directly to your sprinkler valves.  An example is  Irrometer's WEM.

The WEM attaches to either one valve or a cluster of valves that control irrigation of one area, like a front lawn for example.  WEM has a dial control that must be set for accurate moisture indication.  

To use LawnCheck and a WEM together a separate program must be dedicated to WEM controlled zones.  Lets call this program the "WEM" program.  The WEM program then should be scheduled to run on 3 or 4 of the seven days of the week.   Set the minutes per cycle so that anywhere from 1/4" to 1/2" of water is delivered in the cycle, depending on your soil type (less for light soils, more for heavier soils - use multi-cycle in heavier or parched soils to reduce or eliminate runnoff).

Next set up the months of the year that you wish to irrigate.  Assign 0% to the months where irrigation is off and 100% to the warmest months.   Many water districts publish seasonal ET setback data.  These setbacks can be used to automatically scale cycle run times to reduce usage during cooler months.

The combination of a soil moisture sensor and LawnCheck will provide optimized performance equal to or better than systems costing much more.   It is important however to make sure that the WEM dial is adjusted correctly.