Establishing Wireless Sensor Networks (WSN) for precision agriculture has become need of time now but few challenges like energy, reliability, cost etc. need to overcome and serve the application in most efficient manner. Considering advantage of open space i.e. Line of Sight (LOS) in agriculture fields and solar presence this paper proposes the novel architecture of WSN which uses existing Radio Frequency/ Free Space Optical (RF/FSO) link model and hybrid energy source for base station for precision agriculture. Randomly deployed sensors consume more energy than organized sensor deployment hence positioning of sensor is critical factor for energy efficiency of WSN. this paper also proposes sensor positioning method for agriculture fields which covers maximum area and minimum energy. Use of available best routing protocol in the application will add more energy efficiency to the system. Reduction in number of sensor nodes to maximum area will also optimize the cost of project. Overall creating win-win situation to establish WSN for precision agriculture is the objective of this paper. Copyright 2012 ACM.