A low-cost portable system for on-site detection of soil pH and potassium levels using 3D printed sensors

Accurate data on the nutrient content of soil is essential for optimum fertiliser application in agriculture. Frequent and regular soil tests hold the key to mitigate difficulties that arise from lack of accurate information for soil and crop management, such as increased costs for fertilisers, and environmental degradation. Traditionally soil nutrient contents levels are measured from laborious methods which involves collecting field samples and returning to the laboratory for analysis. Laboratory analysis often requires sample pre-treatment, chemical extractants and expensive instrumentation. A low-cost on-site detection method for soil nutrients can increase data necessary for smart fertiliser application that can in turn increase farm profit and ensure environmental protection. Here we present a low-cost miniaturised multi-ion sensing system for on-site detection of pH and potassium. The sensing system consists of a PSoC4 microcontroller and novel 3D printed miniaturised ion selective electrodes for the simultaneous determination of potassium and pH. The 3D printed electrode's pH sensing capability and potassium ion sensing was validated using known pH and potassium ion concentrations, exhibiting high selectivity and excellent Nernstian sensitivities for pH (−61.05 mV/pH) and potassium (49.50 mV/decade). Soil pore water samples from various locations and depths were extracted using a MacroRhizon sampler and tested using the novel portable detection system. On-site pH and potassium determinations were acquired in extremely small volumes samples without the requirement of sample preparation.