This paper investigates the blockchain technology and smart contracts integration within Agriculture IoT (Agri-IoT) systems to address key challenges in modern agricultural practices. As agriculture IoT systems often rely on centralized data management, traditional approaches face limitations such as single points of failure and vulnerabilities in data integrity. Blockchain technology provides a decentralized framework that enhances data security, transparency, and trust. Smart contracts further complement this by automating transactions and interactions among stakeholders. This paper starts with an introduction to the fundamental concepts of Agriculture IoT, blockchain, and smart contracts, then blockchain as a solution for Agri-IoT systems, practical use cases are presented to illustrate the applicability of blockchain and smart contracts in agricultural environments, along with the challenges involved in their implementation.