Real-Time Soil Fertility Monitoring System Using RS-485-Based Electrochemical Sensors Module and NB-IoT Network

The development of precision agriculture requires real-time soil nutrient data to improve the effectiveness of fertilization and maintain optimal soil health. This paper presents the development of a real-time monitoring system for nitrogen (N), phosphorus (P), potassium (K), and soil pH levels, designed to analyze soil nutrient dynamics. The proposed system integrates RS-485-based electrochemical soil sensors with an Arduino Mega 2560 microcontroller and a SIM7000E module for cellular communication. Data is transmitted over GSM/LTE networks using the MQTT protocol, stored in an InfluxDB database hosted on a Virtual Private Server (VPS), and visualized via a web-based dashboard. Field testing was conducted over seven days with varied fertilization treatments. Validation results show sensor accuracies of 91.61 %(~N), 90.03 %(P), 91.95 %(~K), and 94.73 %(pH). The system achieved a 10 -second update interval with an application response latency of less than 500 milliseconds and an average network transmission delay of around two seconds. The system demonstrated consistent operation under GSM/LTE settings with a signal strength of - 7 0 ~ d B m. These outcomes show how effectively the technology facilitates real-time soil monitoring for agricultural decision-making.