ASSERT: A Platform Technology for Rapid Electrochemical Sensing of Soil Ammonium.

The world is facing a food shortage predicament largely fueled by inefficient, outdated farming conventions that are passed down from generation to generation. Overfertilization is one of the major byproducts of inadequate farming techniques. This leads to an imbalance in the soil ecosystem, affecting carbon sequestration, plant-available nutrients, and microorganisms. Sustainable agriculture, on the other hand, efficiently uses the soil with minimal fertilizer and crop rotation to prevent soil erosion. This method requires real-time information on the soil's health. An electrochemical ion-selective electrode (ISE) is presented to measure soil ammonium in situ. The sensor utilized electrochemical impedance spectroscopy for direct, continuous soil ammonium measurement without any soil pretreatment. The ISE is applied by drop-casting onto the working electrode. The sensor response was calibrated against the three main different soil textures (clay, sandy loam, and loamy clay) to cover the entirety of the soil texture triangle. The linear regression models showed an ammonium-dependent response with Pearson > 0.991 for the various soil textures in the range of 2-32 ppm. The sensor response was validated against the gold standard spectrophotometric method after KCl extraction showed a less than 20% error rate between the measured ammonium and reference ammonium. A 16 day in situ soil study showed the capability of the sensor to measure soil ammonium in a temporally dynamic manner with a coefficient of variance of 11%, showing robust stability for in situ monitoring.