An inexpensive silver-silver chloride reference electrode

Simple, inexpensive, and rugged reference electrodes are essential for field applications. The objective of this study was to develop an inexpensive, field-worthy reference electrode. The electrode developed consists of a silver wire coated with AgCl held in a small glass tube filled with 4 M KCl gelled with agar. The glass tube assembly is fitted inside a larger polyvinyl chloride (PVC) tube filled with gelled (NH₄)₂SO₄ solution and capped with a fritted soil-contacting membrane. The millivolt output compared well (R² = 0.999) with predicted values and values from commercial reference electrodes when paired with pH and nitratesensing electrodes. Comparison of commercial and fabricated electrodes in two soils showed that the outputs were statistically the same, and that they were operational within a moisture range from saturation to 0.7 to 0.8 kg kg^{- 1}, depending on the soil texture. The fabricated electrodes are low cost, rugged, and stable for months when kept wet.