# A Survey of Blockchain Applications for Management in Agriculture and Livestock Internet of Things
## 2 Preliminaries
### Blockchain Technology in Agriculture and Animal Husbandry: An Overview
#### 2.2.3 Consensus Mechanisms for Agricultural and Animal Husbandry Networks  
Blockchain consensus mechanisms are frameworks devised to secure universal concord among all network participants regarding transactions and the blockchain's collective status. These algorithms are pivotal to blockchain technology, addressing critical issues like the double-spending problem (where the same digital currency could be spent twice) and ensuring data consistency across the decentralized network.  
Consensus algorithms ensure data integrity and consistency in distributed agricultural networks. For instance, in a network of smallholder farms, a Proof of Stake (PoS) mechanism can be used to validate crop growth data reported by various sensors, preventing any false data from entering the system. Similarly, in livestock management, a consensus algorithm can confirm accurate tracking of cattle movement across distributed nodes, such as those used in traceability systems for organic certification.  
Various blockchain platforms employ different consensus algorithms, each with unique features and mechanisms.  
Proof of Work (PoW) [65; 66]: Employed by Bitcoin and various other blockchain networks, PoW mandates that network nodes (miners) authenticate blocks through the resolution of intricate cryptographic challenges. The first miner to solve the challenge earns, necessitating extensive computational power and electricity.  
Proof of Stake (PoS) [67]: A node's eligibility to append new blocks is determined by its stake, often quantified by the volume of cryptocurrency it holds, in the PoS mechanism. Nodes with greater cryptocurrency holdings have a higher probability of validating transactions and creating blocks. PoS surpasses PoW by eliminating the need for extensive computational tasks, thereby enhancing energy efficiency.  
Delegated Proof of Stake (DPoS) [68]: In this consensus algorithm, cryptocurrency stakeholders vote to elect a select group of delegates or witnesses who are tasked with the validation of transactions and the creation of new blocks. This system enables quicker transaction confirmations and can process a larger volume of transactions, though it may lead to power centralization within the network.  
Practical Byzantine Fault Tolerance (PBFT) [69]: Designed to maintain system functionality even when some nodes fail (including malicious ones), PBFT reaches consensus through multiple rounds of communication among nodes. While effective in small to medium networks, PBFT's communication demands escalate with network growth, impacting scalability.  
Proof of Authority (PoA) [70; 71]: PoA entrusts transaction validation and block creation to a small number of trusted, publicly known, and verifiable validators. This system allows for rapid transaction processing and lower energy use but may compromise some decentralization due to its reliance on a limited number of validators.  
The blockchain field is marked by a multitude of consensus algorithm variations, each addressing specific challenges like energy efficiency, transaction speed, security, decentralization, and scalability. These adaptations are tailored to the unique requirements of different networks, striving for a balance between speed, security, decentralization, and other critical factors. As blockchain technology evolves, new and refined consensus algorithms are anticipated to emerge, further enhancing the capabilities and applications of this transformative technology.