Nitrogen dynamics in different types of pasture in the Austrian Alps

Soil N dynamics were compared in Alpine pastures on two mountains. N-pool s izes and N fluxes were measured relative to N losses via leaching and denit rification in summer. On each mountain, four types of pasture were studied: (1) forest pastures, (2) recently developed pastures formed by forest clea rance ("new pastures"), (3) older established pastures, and (4) pastures pl anted with clover. At both study sites (Scheuchegg and Teufelstein) we obta ined similar results. Compared with forest pasture soils, open pasture soil s were found to have greater microbial biomass and faster mineralisation po tentials, but net field mineralisation rates were slower. In the forest pas tures, highest N losses via denitrification were found. Higher potential le aching of NO3-, estimated by accumulation of NO3- on ion-exchange resins, i n the forest pasture soils suggests lower N uptake by microbes and herbaceo us plants compared with open pastures. N2O-production rates of the forest p asture soils at the Scheuchegg site (11.54 mug N2O-N m(-2) h(-1)) were of s imilar magnitude to those reported for spruce forests without pastures, but at Teufelstein (53.75 mug N2O-N m(-2) h(-1)) they were higher. However, if forest: pastures are not overgrazed, no elevated N loss through N2O produc tion and leaching of NO3- is expected. Denitrification rates in the open pa stures (0.83-7.50 mug N2O-N m(-2) h(-1)) were low compared with reports on lowland pastures. In soils of the new pastures, rates of microbial N proces ses were similar to those in the established pastures, indicating a were hi gh capacity of soils to restore their internal N cycle after forest clearan ce.