Abstract:
This study introduces a portable soil nutrient meter utilizing light absorption and reflection principles to measure essential plant nutrients in soil. It includes an RGB LED light source, a TCS34725 color sensor, and a WIO Terminal microcontroller. Results show that nitrogen content in ammonium chloride solution notably affects blue light absorption, increasing with solution concentration. Ammonium chloride solutions absorb more light at 475 ± 5.00 nm compared to green and red light, with absorption rising alongside concentration. At 10.0 mg/L and 475 ± 5.00 nm, absorption peaks at 85.10 ± 1.68%, while at 2.00 mg/L and 630±5.00 nm, it's 3.94 ± 0.78%. Additionally, the study examines blue and green light reflection from soil mixed with nitrogen and phosphorus solutions (2.00 to 10.0 mg/kg). Reflection decreases with increasing nitrogen and phosphorus content. For every 1.00 mg increase in nitrogen, blue light reflection decreases by about 0.01% under blue and white light. Similarly, for phosphorus, green light reflection decreases by roughly 1.62% per 1.00 mg increase under green light. This portable meter offers accurate and user-friendly nitrogen and phosphorus measurements in soil, suitable for field applications.