Design and Development of Colorimetry based Optical Soil pH Meter

Soil pH is a vital characteristic as it directly affects the accessibility of vital nutrients in the soil. Measuring and managing soil pH is fundamental for creating an environment that supports overall plant health. In this research work, different methods of measuring soil pH are discussed along with their pros and cons. This paper aims to develop a cost-effective and portable pH meter prototype based on the colorimetry principle using soil test kit reagents. TCS3472 color sensor is used for sensing RGB Color component of the solution under test which is interfaced with Node MCU (ESP8266). Trials are conducted to obtain the true color response of the reactants, which will be utilized as color benchmarks. The mathematical model is developed based on the analyzed data. The system is calibrated and validated using Prerana Laboratories Soil Test kit. The device is tested using 10 soil samples collected from different states of India with different pH levels. By using the standard deviation method system performance is analyzed. The system accuracy is found to be 99.30%. The values obtained from the sensors are displayed in a user-friendly embedded web server application without Internet as well as on system LCD. Based on the pH level system also classifies soil samples as acidic, neutral, and alkaline. To facilitate the measurement of Soil pH for farmers from rural areas where Soil testing labs are not easily available, this non-contact type portable pH meter will play an important role to periodically test soil pH to improve soil fertility where accuracy, speed, non-destructive testing and reduced maintenance are critical factors.