Soil extraction, ion exchange resin, and ion exchange membrane measures of soil mineral nitrogen during incubation of a tallgrass prairie soil

Two commercially available ion exchange resin (IER) devices - Unibest resin capsules (Unibest, Inc., Bozeman, MT) and Plant Root Simulator (PRS) probe-ion exchange membranes (Western Ag Innovations, Inc., Saskatoon, Canada) - for measuring soil nutrient availability were compared to traditional soil NH4+ and NO3- measurements during incubation of an Oklahoma tallgrass prairie soil at two temperatures (16degrees and 25degreesC) and two moisture contents (15 and 25% by weight). Nitrate dominated the soil mineral N pool in soils and in both IER devices. Soil extractable and resin capsule mineral N showed significant responses to both temperature and moisture whereas PRS probe mineral N showed responses to moisture only. Both devices were more sensitive to moisture than soil mineral N was. Neither device related well to N mineralization or the patterns of extractable mineral N over time. Possible reasons for the differences include the integration of soil mineral N over time in the IERs as opposed to snapshots in time for soil mineral N, spatial variation within the incubated soils, and the importance of solution contact with IERs.