Measuring Soil Redox Potential: Effects of Instrumentation.

Assessment of soil redox potential is commonly done in the field by measuring the voltage between Pt and reference electrodes.  Recent studies have shown that serious errors can result from using a multimeter to collect these data, because the input resistance of such instruments is low enough to permit substantial current flow during the voltage measurement.  This can be minimized by using a research grade instrument with a high input resistance, but the cost of such instruments is much greater. We will describe a low cost modification that can be applied to a standard multimeter which effectively increases the input resistance and allows the instrument to be used to collect reliable redox measurements.