Nitrogen fluxes in surface soils of 1–2-year-old eucalypt plantations in Tasmania

Abstract

To improve our understanding of nitrogen (N) supply in eucalypt plantations in Tasmania, N fluxes were determined in surface soils (0–10 cm) at 4 sites supporting 1–2-year-old plantations of E. nitens. Net N mineralisation, nitrification, leaching, and uptake were measured by an in situ soil-core technique. Soils were derived from basalt (3 sites) or mudstone (1 site). Average rates of net N mineralisation ranged from 18 to 91 kg N/ha·year, and most mineralised N was nitrified and leached. There were significant linear relationships among net N mineralisation, nitrification, and leaching (r = 0·61–0·83). Annual rates of net N mineralisation varied as much within sites as between them, and rates in individual plots were significantly correlated with anaerobically mineralisable N (r = 0·82) or total N (r = 0·66), but were not correlated or only weakly correlated with C: N ratio, loss-on-ignition, organic C, water content, or temperature. Leaching was weakly correlated with effective rainfall (rainfall minus evaporation, r = 0·39). Soil contained most mineral N during February–April (i.e. late summer–early autumn) and least during October–November (i.e. late spring). We concluded that available N at these sites was highly variable spatially and temporally, and at a plot scale was closely related to concentrations of mineralisable substrate and not to soil water or temperature.