Measuring soil pH at in situ like conditions using optical pH sensors (pH-optodes)

Soil pH is undoubtedly one of the key environmental parameters influencing soil biology and biogeochemistry. Nevertheless, measuring soil pH at in situ like conditions is not trivial. The current gold standard requires preparing a soil suspension with water or CaCl2, in which the soil pH can be assessed. Obviously, this is far from in situ conditions. In this study we evaluate optical pH sensors, so-called pH optodes, as an alternative technology to measure soil pH both in wet and dry soils. Our results indicate that pH optodes have the potential to sense soil pH in a wide range of soil water contents. We also compared our results to the standard slurry method and to measurements using a classical glass pH electrode.