An Optical Soil Sensor for NPK Nutrient Detection in Smart Cities

An optical absorbance-based sensor designed to measure the concentration of vital Nitrogen (N), Phosphorus (P) and Potassium (K) nutrients in urban soil was developed. This device was characterized and tested in nine diverse green spaces around New York City’s Morningside Heights neighborhood, including street-tree pits and park spaces. The results show that the sensor can detect at minimum, a 1.4% change in nutrient concentration. Additionally, it was shown that the sensor can operate in various ambient light settings (indoor and outdoor) after calibration. A study of NYC’s green spaces shows that, on average, soil in street-tree pits that supports plant life has 54% more N, 34% more P, and 37% more K than park spaces, respectively. This new sensor technology will enable more detailed monitoring of soil nutrient conditions and thus help promote healthy green spaces in large urban environments.