Nitrogen mineralization assessment using PRS™ probes (ion-exchange membranes) and soil extractions in fertilized and unfertilized pine and spruce soils

Several assay approaches that measure mineralizable nitrogen (N) have been used, with varying success, to assess the N supply power of soil. We compared Plant Root Simulators (PRS (TM) probes, Western Ag Innovations, Inc., Saskatoon, SK) with chemical extractions in an incubation to evaluate how these methods quantify N-mineralization activity of forest soils. Nitrogen mineralization was compared in spruce- and pine-forest soils that had varying N status and had been subjected to 14 yr of N-based fertilization. We paired the assays to determine how the measures co-varied after 1, 2, 4, 6, 8, 10 and 12 wk of incubation. Significant correlations existed between PRS probes and extractable ammonium (NH 4) in the spruce (r =0.567, P <0.001) and pine (r =0.730, P <0.001) soils, although trendlines differed by soil type. Nitrate (NO3-)- PRS relationships were evident only in the spruce soils (r =0.916, P <0.001), as the pine soils produced minimal NO3-. Both assays provide opportunities for assessing N-mineralization processes in forest soils and differences between assays appear to be related to soil N availability. The PRS probes responded primarily to factors affecting ion mobility because of the cumulative nature of the PRS probes; whereas the static soil extractions were more sensitive to variations in mineralization and immobilization fluxes.