All of the weather-based products reviewed operate on the principle of scheduling

irrigation as a function of weather conditions. Most of the products use real-time

or historical weather data to schedule irrigation based on evapotranspiration (ET),

which is a function of weather conditions and plant type. ET is defined as the

quantity of moisture that is both transpired by the plant and evaporated from the

soil and plant surfaces.  Thus, check the KC parameter fior the assigned crop(s), and by knowing the ET and other weather parameter you can determine the irrigation scheduale.

It depends on your soil moisture sensors- If you are using sensors that measure volumetric water content, then you need to know the soil type to estimate the available water holding capacity, and then you schedule your irritations based on an allowable deficit in the root zone. If you are using sensors that measure matric potential, then, assuming no salinity, you can irrigate at 40-50 centibars if you have sandy soils, and 60-80 if you have heavy soils.

Thanks Jafar and Khaled,

I am using sensors which gives % soil moiture. Can you also let me know about uppper and lower threshhold moisture conent for a given crop and a given soil type.

 The threshold depend on the sensor itself; what kind of wireless sensors are you using?

Manoj Gupta,

The upper and lower threshold moisture contents  for a given soil type have to be estimated at 0.1 to 0.33 bar and 15 bar pressure, respectively using pressure plates at laboratory  before  growing any type of crops. Then get the available moisture/water capacity (AW)  by subtracting lower limit(permanent wilting point) from upper limit of soil moisture content( Field capacity). Then the readily available /critical moisture (RAW) has to be determined based on management allowed depletion (MAD) for for the selected crop. For example,  MAD for vegetables is 25-30% of RAW. Therefore, your wireless sensor  should be able to get information about critical soil moisture content in order to commence irrigating, and about upper limit of soil moisture content ( field capacity) in order to terminate /stop irrigating for real-time irrigation scheduling. The soil moisture content between FC and  critical soil moisture content would not result in to a significant yield reduction of a crop.

Dear Guptaji

The irrigation controller based scheduling is good using timer control and automation of drip based on emitter discharge the time of irrigation operation can be fed to the controller and accordingly the irrigation.

Briefly, a hardware / software or app information acquiring sensors soil moisture (% or kPa) automatically, while having the ability to control irrigation valve and volumetric meter is required. The run time is determined by the speed of depletion soil water. Logically they must know the point of saturation, field capacity and minimum permissible moisture level for the culture substrate.

See:

"Precise sustainable irrigation: A review of the soil-plant-atmosphere system monitoring."