Nitrogen mineralization potential in rewetted soils from a semi-arid stream landscape, north-west Australia

Abstract

Drying-rewetting pulses stimulate nitrogen (N) mineralization in semi-arid systems and enhance N availability. Intermittent stream landscapes encompass a mosaic of soils of different textures and composition, and may support intense N transformation after rainfall. We modelled N mineralization potential by measuring accumulation of inorganic N (KCl extractable NO3− and NH4+) in response to sustained flooding in soils from a small intermittent stream in semi-arid, north-west Australia. To test the relative importance of landscape position compared to flood pulse size, we incubated soils and sediments from six landscape positions, including three riparian vegetation types, rewetted to four different water potentials. Selected water potentials represented a light rain, heavy rain, single flood and successive flood event for the study site. The total amount of N mineralized was significantly affected by landscape position but not by saturation level. Riparian soils produced the greatest mineralization flush – over 70% of the total amount of N mineralized accumulated within 48h of rewetting – however there was no difference among riparian vegetation types in N mineralization potential. N mineralized was a half to two-thirds lower in channel, floodplain and bank soils in comparison with riparian soils. We conclude that in systems subject to prolonged drought, N mineralization is predominantly determined by soil characteristics rather than the size of the rewetting pulse.