Low-cost precision agriculture for sustainable farming using paper-based analytical devices.

The United Nations estimates that by 2030, agricultural production must increase by 70% to meet food demand. Precision agriculture (PA) optimizes production through efficient resource use, with soil fertility being crucial for nutrient supply. Traditional nutrient quantification methods are costly and time-consuming. This study introduces a rapid (15 min), user-friendly, paper-based platform for determining four essential macronutrients-nitrate, magnesium, calcium, and ammonium-using colorimetric methods and a smartphone for data reading and storage. The sensor effectively detects typical soil nutrient concentrations, showing strong linearity and adequate detection limits. For nitrate, the RGB method resulted in an of 0.992, a detection range of 0.5 to 10.0 mmol L, and an LOD of 0.299 mmol L. Calcium quantification using grayscale displayed an of 0.993, a detection range of 2.0 to 6.0 mmol L, and an LOD of 0.595 mmol L. Magnesium was best quantified using the hue color space, with an of 0.999, a detection range of 1.0 to 6.0 mmol L, and an LOD of 0.144 mmol L. Similarly, ammonium detection using the hue color space had an of 0.988, a range of 0.5 to 2.5 mmol L, and an LOD of 0.170 mmol L. This device enhances soil fertility assessment accessibility, supporting PA implementation and higher food production.