*4.2.1 Open-loop irrigation control*

A couple of irrigation decision support systems schedule irrigation at predefined intervals and apply predefined irrigation volumes [52]. These decisions are not based on any sensor feedback on plant status, soil moisture status, or weather parameters. The decision to initiate an irrigation action is largely dependent on historical data and heuristics. This irrigation control strategy is inefficient which may lead to over or under irrigation, thereby wasting valuable water and fertilizer.

#### *4.2.2 Closed-loop irrigation control*

Closed-loop irrigation control is a control strategy where a mathematical model is used to make predictions about the future output. This is aided by real-time feedback from sensors that monitor the process. The model of the plant can either be a physics-based or a data-driven model. Whereas physics-based models are derived from the laws of physics, such as (conservation of mass, gravity, etc.), data-driven
