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

Harrison, D. J. and D. Maynard. 2014. Canadian Journal of Soil Science


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® 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 years of N-based fertilization. We paired the assays to determine how the measures co-varied after 1, 2, 4, 6, 8, 10 and 12 weeks. Significant correlations existed between PRS® probes and extractable ammonium (NH4 ) in the spruce (r = 0.567, p = 0.000) and pine (r = 0.730, p = 0.000) soils, although trendlines differed by soil type. Nitrate (NO3-2013) 2013 PRS® relationships were evident only in the spruce soils (r = 0.916, p = 0.000), as the pine soils produced minimal NO3-2013. 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 nature of the soil extractions were more sensitive to variations in mineralization and immobilization fluxes.

Key Words

Ammonium, forest soils, inorganic N, laboratory incubation, nitrate