A sequential soil coring and in situ soil exposure (incubation) technique was used to measure temporal fluxes of immobilisation, mineralisation, plant uptake and leaching of N in stands of Pinus radiata near Canberra, Australia. The stands had been subjected to the following treatments when 10 years old: (a) nil; (b) fertilised once with 400 kg N ha −1 in spring 1983; (c) irrigated to maintain the soil near field capacity; (d) irrigated and fertilised as in (b); (e) irrigated plus 300 kg N ha −1 year −1 (and other nutrients) added weekly in irrigation water during the growing season; (f) fertilised once with 13.3 t ha −1 of sewage sludge which added 176 kg N ha −1. The availability of water and N interacted positively to markedly increase tree growth during the 4 year (1983–1987) study period. In unfertilised soil, pools of mineral N were less than 10 kg ha −1 (0–40 cm), varied little with time, and were dominated by NH 4-N. Addition of 400 kg NH 4-N ha −1 increased pools of soil mineral N for about 15 months, and induced significant nitrification after 100 days. Approximately 70 kg N ha −1 were leached below 40 cm soil depth during four heavy rainfall periods in autumn and winter during the initial year after fertilisation, but no further leaching occurred. In unfertilised soil, net mineralisation rates were highest in spring and declined through summer and autumn to virtually zero in winter. In the untreated stand, annual totals of net mineralisation declined from 38 to 7 kg N ha −1 year −1 during the study period, indicating a gradual depletion of soil reserves of mineralisable organic N. Addition of sewage sludge had no significant effect on net N mineralisation, but irrigation initially accelerated it and led to the depletion of the pool of mineralisable N in the soil. After fertilisation with 400 kg N ha −1, marked (37% of added N) immobilisation was measured during the following 135 days. Net mineralisation commenced 9 months after fertilisation, at rates two- to three-fold greater than in unfertilised soil. Annual soil N mineralisation of the N-fertilised plots exceeded that of the control for the duration of the study. Estimated annual uptake of N from the soil by the vegetation ranged from 6 kg ha −1 (control) to 166 kg ha −1 (following fertilisation with 400 kg N ha −1, and a wet growing season). About 40% of the single application of fertiliser N was taken up during the initial 12 months. N uptake was approximately equivalent to N mineralisation, except during the initial year after heavy N fertilisation when