Nitrogen leaching from agricultural soils represents a significant environmental concern, contributing to groundwater contamination and eutrophication of surface water bodies. This research presents the development and field validation of an Internet of Things (IoT)-based monitoring system employing subsurface electrochemical probes for continuous nitrogen leaching detection. The system integrates ion-selective electrodes, soil moisture sensors, and temperature monitors connected via LoRaWAN communication protocol to a cloud-based analytics platform. Field trials conducted across three agricultural sites over eight months demonstrated measurement precision with correlation coefficient r=0.96 when compared against standard laboratory methods. The system achieved temporal resolution of 10-minute intervals, successfully identifying leaching events associated with rainfall and irrigation activities. Peak nitrate concentrations reached 82.3 mg/L, exceeding regulatory thresholds by 64%. Data analysis revealed strong correlations between soil moisture content and nitrate mobility (r=0.89, p<0.01). The IoT monitoring framework reduced operational costs by 58% compared to conventional sampling approaches while providing actionable insights for precision fertilizer management. This technology offers transformative potential for sustainable agricultural practices and environmental protection strategies.