Hemstock, S. S., Quideau, S. A. and Chanasyk, D. S. 2010. Nitrogen availability from peat amendments used in boreal oil sands reclamation. Can. J. Soil Sci. 90: 165Á175. Following surface mining, peat is typically used as an organic amendment to cap reconstructed soils in the Athabasca oil sands region of Alberta. Yet, very little is known about its ability to provide available nitrogen (N) in these soils. Hence, the overall objective of this study was to measure soil nitrogen (N) availability throughout the year in five peat amendments. Specific objectives were: (1) to examine seasonal variability in soil labile N pool sizes (nitrate, ammonium, dissolved organic N, and microbial biomass N), and (2) to determine in situ net nitrification, ammonification, and mineralization rates using the resin-core technique. Results from this field incubation method indicated a strong seasonal variability in net mineralization rates, with maximum positive values in the fall, and low or negative rates in winter. Net ammonification rates, which were significantly correlated to soil moisture content, were significantly smaller and showed smaller seasonal fluctuations and fewer differences among peat materials than net nitrification rates. Furthermore, the contribution of net nitrification to total net mineralization rates was characteristically higher than what is typically observed in undisturbed boreal forest soils. Taken together, results indicate that net nitrification processes may control nitrogen availability in these reclaimed soils.Key words: Soil nitrogen, soil reclamation, nitrification, mineralization, boreal soils Hemstock, S. S., Quideau, S. A. et Chanasyk, D. S. 2010. Disponibilite´de l'azote dans les amendements de mousse de sphaigne employe´s pour restaurer les sables bitumineux dans les re´gions bore´ales. Can. J. Soil Sci. 90: 165Á175. Apre`s une exploitation minie`re a`ciel ouvert dans la re´gion des sables bitumineux de l'Athabasca, en Alberta, on restaure habituellement le sol en prenant de la mousse de sphaigne comme amendement organique. Pourtant, on en sait tre`s peu sur la capacite´d'un tel amendement a`renouveler l'azote du sol. Le but ge´ne´ral de l'e´tude e´tait de mesurer la quantite´d'azote disponible durant l'anne´e, pour cinq amendements a`base de mousse de sphaigne. Plus pre´cise´ment, on voulait : (1) ve´rifier la variabilite´saisonnie`re de la concentration d'azote dans les sols qui en renferment un bassin labile (nitrates, ammonium, azote organique dissous, et azote de la biomasse unicellulaire) et (2) e´tablir les taux de nitrification, d'ammonification et de mine´ralisation in situ par la technique d'incubation en carotte de re´sine. Les re´sultats issus de l'application de cette technique sur le terrain indiquent que le taux de mine´ralisation varie beaucoup avec la saison, la plus forte valeur positive survenant a`l'automne, tandis que l'hiver se caracte´rise par une faible mine´ralisation, voire une mine´ralisation ne´gative. Le taux d'ammonification net, qui pre´sente une importante corr...