## 1 Introduction
### Incorporating Internet of Things to Optimize Agricultural Traceability Systems  
A large amount of data have to be gathered across the supply chain for traceability purposes. Early traceability systems used to rely on records kept by workers on the field and then manually entered in paper or computer-based systems. As a result, faulty information recording could be made. Following the rapid technological advancements associated with agriculture 4.0 [23; 24], especially with Internet of Things (IoTs) and machine learning [25; 26; 27; 28], more efficient and trustworthy gathering procedures have been utilized. Various sensor technologies, incorporated to IoT systems, support technologies involved in each stage of the food supply chain, hence, providing a more effective way for the purpose of recording and exchanging useful information. These technologies include, for example, barcodes, Radio-Frequency IDentification (RFID), Quick Response (QR) codes and Wireless Sensor Networks (WSN) [29; 30]. Regarding a QR code, it is a label that can be read, by a scanning device, a mobile phone for instance, and is made of a white background along with black squares arranged inside it. Although QR codes are similar in practice with barcodes, they encompass more information, since they can store information both vertically and horizontally; in contrast, barcodes contain only horizontal information. Hence, QR codes have a considerably higher capability of providing information, making them very popular in food industry. Furthermore, tagging food items with RFID enables the user to identify and track inventory problems as well as provide details on the overall performance of agri-food supply chain by emitting radio waves and receiving back signals from the tag [31]. RFID technology also offers real-time location tracking, condition monitoring, warehouse automation and transaction monitoring services. Compared with barcodes, RFID outperforms due to its capability to transmit precise information of high capacity with higher speed. Nevertheless, the foremost drawback in this technology is its relatively high implementation cost [2; 32]. As for WSNs, they refer to a variety of spatially distributed sensors with the intention of monitoring and recording the environmental conditions, including temperature, humidity, wind and pressure, by applying certain protocols and standards [33]. The low-power, small-sized, multipurpose and self-organized nodes are a scalable and cost-effective technology supporting WSN [34], rendering them essential tools towards automation of agricultural practices and enabling effective traceability. Various communication approaches can be implemented in traceability systems, depending on the degree of technology and standardization. According to [14], there are three indicative examples of communication approaches; (a) the \"One up-one down\" approach, that stores information concerning suppliers and customers, (b) the \"Pedigree\" approach according to which the product's history from all the previous process nodes is available, and (c) the \"Centralized\" approach, where a cloud-based centralized database exists that is managed by a third party. However, the centralized database is prone to get manipulated by enterprises [35]. In pursuance of increasing the reliability and security of information transmission between various stakeholders, blockchain has emerged, which can be simply defined as \"_a distributed ledger maintaining a continuously growing list of data records that are confirmed by all of the participating nodes_\" [36]. In practice, blockchain is a kind of decentralized tamper-proof database, which can be accessed by many parties, while any action must be consistent with agreed rules. Blockchain makes use of a cryptographic algorithm as a means of generating a chain comprising of data blocks in chronological order. A block is a record enclosing data along with information from the previous block's hash, which results in a value representing its own unique hash [37].