# Blockchain Applications in Agriculture: A Scoping Review
## 3 Results
### Characteristics of Sources and Synthesis of Results
On the other hand, a large part of the solutions does not mention any specific blockchain technology (32%), while some have created a custom blockchain network (9%) which is either based on an existing framework (e.g., Ethereum) or not. Other blockchain frameworks used include Hyperledger Sawtooth, IOTA, NEO, Corda, and Multichain. There are also solutions that incorporate other blockchain-based technologies, such as BigchainDB and Polkadot. Regarding the types of blockchain (RQ6) utilized in the identified solutions, most of them (36%) use private permissioned blockchains, as shown in Figure 10. Moreover, a significant percentage of the papers (28%) use public permissionless blockchains, while 5% of the solutions use public permissioned blockchains. Most blockchain frameworks have a specific blockchain type; however, even if Ethereum is public permissionless by default, it is also used as a private permissioned or public permissioned. As we can see, no approach uses private permissioned blockchains, which are rarely used anyway. Finally, five research papers (5%) combine two different types, three papers (3%) combine public permissioned and private permissioned blockchain networks, and two papers (2%) use jointly public permissionless and private permissioned. Finally, in 28 research papers (27%), the type of blockchain is not mentioned. Figure 8: Countries for which the proposed solutions included in our scoping review were created or implemented. Figure 5.0 Blockchain technology frameworks considered in the papers included in our scoping review. The analysis of each source identified the data stored in the blockchain in agricultural applications (RQ7). These data vary, depending on the solution proposed by each paper, as shown in Figure 5.1 The most common type of stored data, as reported in 43 papers (41%) (Figure 11a), are data from IoT devices, such as temperature, humidity, etc. It should be noted that many sources do not constantly upload data to the blockchain but only do so when there are anomalies/invasions, something that occurs in six papers. In contrast, in another six solutions, the data are stored in the blockchain periodically during the day. The aggregate data are usually stored in external databases. It is also common in the identified applications to ask users to provide information about products (29%), farmers (4%), farmland records (3%), seeds (3%), animals (2%), machinery (2%), and ERP data (2%). Additionally, it is common practice to store data outside the blockchain, and its integrity is ensured by storing the hashes of this data in the blockchain. More specifically, we identified 8 papers (8%) that store IPFS files' hashes and 12 papers (12%) that store the hashes of data stored in external databases. It is essential to mention that, in recent works, the storage of tokens (4%) in blockchain has begun, while there are proposals for the storage of public keys of IoT devices (2%). In addition to all the above data stored in the blockchain, 34 other different data types have been reported in a single solution. Figure 11b shows a word cloud of all the different data types considered in the agricultural blockchain applications included in the scoping review for a visual overview. The data stored off-chain (RQ8) in the identified solutions are shown in Figure 5.2 From the 104 research solutions proposed, 37 of them (36%) mention at least one external storage. Most of the data stored off-chain are IoT data (13%) and product information (12%). Media files (6%), hashes (3%), RFID data (2%), and private data (2%) are also stored off-chain. Less common to be stored externally in research papers are reputation scores (2%), transaction logs (1%), GIS data (1%), and credentials (1%). In addition to the data stored externally, we present the storage technology used. No specific technology is mentioned in most of the external data storage solutions (13%). The most common technology used in conjunction with blockchain is IPFS (13%).