Nitrogen mineralisation indices in ferrosols under eucalypt plantations of North-Western Tasmania: association with previous land use

Abstract

Potentially mineralisable N was studied in the laboratory and in the held in ferrosols from eucalypt plantations and pastures in north-western Tasmania. The plantation sites previously supported either Pinus radiata plantations (ex-pine), mixed eucalypt-myrtle forest (ex-mixed), or open Eucalyptus delegatensis forest with a grass understory (ex-dele). Ranges of concentrations of organic C and total N, and C to N ratio, were 6.9-13.6%, 0.297-0.978%, and 10.3-30.4, respectively. The concentration of organic C was independent of previous land use, but rankings for total N, anaerobically mineralisable N, and extractable N in hot KCl were pasture > to ex-dele = ex-mixed > ex-pine. The ratio C:N in theex-pine group (23.6) was higher than ratios in other groups (13.1-15.6). Anaerobically mineralisable N ranged from 49 to 214 µg/g, and was highly correlated with total N and extractable N in hot KCl at 95°C for 16 h (r = 0.83 for both cases, P < 0.001). The C:N ratio was negatively correlated with total N and anaerobically mineralisable N (r = 0.56 and 0.70, P < 0.01). The results indicated that the pasture soils had greater availability of mineral N, and that total N, C:N ratio, and anaerobically mineralisable N may provide useful information for assessing N mineralisation in these soils.