Distributable screen-printed soil pH sensor demonstrates robust response across variable soil conditions

Management of soil pH is critical for maintaining crop productivity, but high-spatiotemporal measurement of pH in soils can be a challenge due to sampling methods, recalibration requirements, and instrumentation costs. To address these limitations, a distributable, screen-printed carbon-alizarin-based soil pH sensor designed for long-term continuous operation in soils was studied. Square-wave voltammetry is employed to determine the alizarin redox peak position in a current-voltage scan, which is proportional to pH and is relatively invariant over time. The printed sensors were tested across varying soil moisture content, compaction levels, and soil types, confirming robustness over different environmental and installation conditions without the need for recalibration. Integration of the electrodes onto a printed circuit board addressed with a custom low-cost, low-power, weatherized potentiostat enabled autonomous data logging and continuous operation for months under field conditions, demonstrating reliable in situ pH sensing. These results highlight the suitability of this approach for use in collecting spatiotemporally dense pH data directly and continuously in soils.