The water consumption of plants is energy dependent. The energy comes from the sun, but solar radiation is difficult, and expensive to measure.
The temperature of the air reflects the solar energy and can be used as a measure of plant water consumption. In this test setup, an Arduino with data logger is used for measuring and calculating and controlling water pumps. The temperature is measured with DS18B20 sensors, resolution 0.06 degrees Celsius. Results are displayed on a 16 x 2 LCD display connected via I2C to Arduino.
In this setup, there are 2 irrigation groups that can be programmed independently. The number of such groups is 10-15 and functions other than watering can be switched on.The program calculates a temperature sum via several algorithms. When a certain value is reached, the plants are watered and the sum is reset.
The small video shows the Arduino in the upper, the temperature sensors to the right and the display in the middle. The temperature is measured in rapid succession, usually it will be measured every half hour.