Recently there has been an excessive groundwater pumping and seawater intrusion in the costal aquifers of Oman. To deal with this problem, a fully automated and wireless irrigation control system that avoids subjective decisions about irrigation volumes and timing was developed. All fields in the farm are accessible via TCP/IP protocol. Each farm has a Single Collecting Node for data collection connected to a host computer. All nodes in a crop are connected to Xbee network and considered as Slave Nodes except one termed Master Node. The Master Node includes two sensors and a solenoid valve. The Master Node controls the irrigation of the field with a same crop sequentially using slave nodes. Both the Xbee network and the solenoid valves are powered by a lithium battery with photovoltaic charging panels. The irrigation control and monitoring program is implemented in the host computer in the farm, which monitors the states of all crops and controls the valves using a threshold and timers. The smart irrigation system has been installed in 14 farms.