This paper presents the design and validation of a pH measurement IoT system for Precision Agriculture applications. The system is based on an IoT architecture which consist on: data acquisition and processing, information, centralization and access to users. The design process of each module is reported as well as its experimental validation process. With a -0.058V slope for pH measurement and RMSE of 0.037 for the calibration model, we demonstrated the capability of the system to perform measurements at multiple points in large areas.