Smart agriculture (SA), which combines the Internet of Things (IoT) with a variety of smart devices including unmanned aerial vehicles (UAVs), unmanned ground vehicles (UGVs), and computing systems, is an emerging technology that shows how far the agricultural sector has progressed. Usage of edge computing devices on farms has been growing in the past decades for increasing the yields by improving resource use efficiency through the utilization of temporal, spatial, and individual farm data. With the growing adoption of digital technology, the agricultural sector now offers tools and services for retaining, storing, and analyzing the vast amounts of data produced by Smart Agricultural systems. However, this industry is more vulnerable to cyber security risks due to its growing reliance on technology. This article presents a comprehensive assessment of the state-of-the-art consequences of SA and current cyber security concerns. In addition, this article delves into the structural framework of SA, thoroughly addressing the major security threats at each layer. This study also provides a complete overview of major developments and future research directions in agricultural cyber security for SA. These valuable insights into cyber security will encourage cyber security researchers to suggest more creative and innovative ideas in the future.