In situ efficiency of ion exchange resins in studies of nitrogen transformation

Mixed-bed ion-exchange resin bags have previously been used in studies of s oil N transformation rates with NH4-N and NO3-N being adsorbed From the sol ution percolating through the incubated soil core. An evaluation of the in situ adsorption efficiency of mixed-bed resin bags was performed by compari ng dissolved inorganic nitrogen (DIN, sum of NH4-N + NO3-N) accumulated in resins with DIN fluxes in throughfall (TF) and with DW concentrations in so il water. A significant correlation was found between DIN fluxes in TF and accumulated DIN in resins placed at the soil surface (r(2) = 0.92 for NO3-N , r(2) = 0.86 for NH4-N, P < 0.001). The ratio of accumulated DIN in resins to DIN flux in TF was significantly affected by season. A low but signific ant correlation was found between NO3-N concentrations in soil water and NO 3-N contents in resins deployed in the bottom of soil cylinders (r(2) = 0.3 4, P < 0.01), however, when only the winter periods were taken into account , the correlation improved (r(2) = 0.72, P < 0.001), As little water and fe w nutrients are removed from the soil water by the vegetation during the do rmant season, the conditions inside and outside the core were more comparab le, For NH4-N there was no correlation between accumulated amounts in the r esins and concentrations in soil water sampled at depths of 13 cm and 20 cm , respectively, probably due to the strong depth gradient in the NH4-N conc entrations of the soil, Although the resin bags were unable to adsorb all t he incoming DIN, they gave valuable information on smalt-scale input of N a nd on small-scale differences in NO3-N leaching.