Factors Influencing the Relationship of Ion Exchange Membrane (PRSTM Probe) Measurements and Soil Extractable Concentrations for Secondary and Micro Nutrients.

Plant Root Simulator (PRS) probes are widely used for in situmonitoring of soil nutrients in a wide range of ecosystems. Although PRS-probe measurements are often strongly correlated to extractable soil nutrient measurements, the relationship is not constant or linear due to the different factors that influence these two types of measurement.  Comparisons were conducted to elucidate controlling factors and facilitate appropriate comparisons between measurements for secondary and micro nutrients.

The main factor contributing to differences between PRS probe and extraction measurements is soil ion mobility.  Short-term PRS-probe measurements of sulfate are hgihly correlated to extraction measurements, but the quantitative relationship varies with soil moisture and duration of PRS probe exposure.  In contrast, PRS-probe measurements of immobile nutrients such as Ca, Mg and micro nutrients are less sensitive to duration of burial but more sensitive to ion interactions and soil redox.  The two methods of monitoring soil nutrients often complement each other, and can often be compared with appropriate consideration of method and context.