Adsorption of dissolved nitrogen by forest mineral soils

Dissolved nitrogen (N) species, including ammonium (NH4+-N), nitrate (NO3--N), and dissolved organic nitrogen (DON), are important nutrient sources in soils. The mobility of DON and NH4+-N in soil solutions is influenced by abiotic adsorption to mineral soil particle surfaces. We determined relationships between soil properties and their ability to adsorb NH4+-N, NO3--N, and DON, using batch experiments. A range of 41 mineral horizons was collected from across Canada, including Podzols, Brunisols, Luvisols, Gleysols, and an organic soil. The adsorption of DON and dissolved organic carbon (DOC) were positively correlated (R-2 = 0.86), and both were best explained by the amount of iron and aluminum associated with poorly crystalline phases. Adsorption of NH4+-N was strongest in Gleysols and Luvisols, while adsorption of NO3--N was weak in all soils. A reduction in the DOC:DON ratio was observed for most mineral horizons (89%) after equilibration from an original ratio of 35:1. Mineral horizons with a net desorption of DON had a significantly greater reduction in the final DOC:DON ratios than horizons with a net adsorption of DON. The results from this study found that while similar soil properties could predict DOC and DON adsorption, DON was slightly more mobile than DOC.