# Blockchain Applications in Agriculture: A Scoping Review
## 4 Discussion
### Summary of Evidence
#### 4.1.2 Data On-Chain and Off-Chain  
Blockchain technologies show the ability to handle various security issues. An important aspect in this direction was the identification of data stored on-chain and off-chain (RQ7 and RQ8). Based on the results of this scoping review, blockchain technology has been proposed more frequently for storing data by sensors and IoT devices in order to monitor specific aspects of the production process. This appears in 43 research papers (41%). These data are mainly used to monitor the process and, secondarily, used to manage information or the product. In addition to the above, there are four solutions that store access control and authentication policies, for IoT devices, on-chain [60; 61; 62] but also off-chain [63]. Some research papers suggest the periodical storage of data in the blockchain [64; 65; 66; 67; 68], so as not to unnecessarily burden the additional cost of storing and using the blockchain. In some cases, an external database is usually used to store the aggregate data [65; 66; 68]. In the corresponding category of solutions, there are also approaches that store only anomalies presented in the data from the IoT devices [65; 66; 69; 70; 71]. This is usually to ensure the integrity of the information and not to distort it. Almost all of these solutions that store only critical data in the blockchain have external storage. Both in the case of periodic storage and in the case of abnormal storage, all solutions use Ethereum, except one that uses Hyperledger Fabric. This makes sense because, in Ethereum, storage costs are taken into account when creating the architecture. Another common architectural scheme in creating decentralized applications is to store hashes in the blockchain and actual data in external storage. Most architectures use IPFS to store agriculture data and the blockchain stores either the IPFS hash [72; 73; 74; 75; 76; 77; 78; 79] or the data hash [58; 59; 80]. There is a study [58] that stores data from sensors in IPFS, then the hash of this data is stored in a private permissioned blockchain, while the block hash of this blockchain and the height of the block are stored in Ethereum. In the latter, an incentive mechanism is activated, through a smart contract, to reward the user who performed themining in the private permissioned blockchain. In this way, the authors achieve the security that a private permissioned blockchain would not have. As reflected in our research, a new trend in the blockchain is the digital representation of real-life assets through a digital twin. A digital twin is a virtual representation of a physical object or system, usually in multiple stages of its life cycle [81]. As [PERSON] et al. [82] point out, the use of digital twins could bring significant benefits to the agricultural process. The blockchain has also been proposed to represent digital twins using tokens. The research that has been conducted represents products as tokens (following the ERC20 token standard) that are indirectly related to the agricultural sector, such as water and energy that farmers need to share [54,83]. Their use as a currency for transactions between producers and buyers has also been suggested [84]. They can also be used as a reward system for the virtuous use of water [85], where the smart contract is a digital twin of an IoT device that monitors water consumption. Due to the lack of infrastructure, the researchers created a module for IoT devices to communicate directly with the smart contract [85,86]. According to our findings, no research has been conducted on the digital representation of the product, which would help in the certification and traceability of the product from the farm to the fork [87]. In addition to all the above data, we have an additional 42 different types of data stored in the blockchain.