Nutrient cycling, nutrient use efficiency and nitrogen fixation in an age series of Alnus–cardamom plantations were studied in the eastern Himalaya. The impact of stand age (5, 10, 15, 20, 30 and 40 years) on the nutrient dynamics of mixtures of N2‐fixing (Alnus nepalensis) and non‐N2‐fixing (large cardamom) plants was assessed. Foliar nutrient concentrations ofAlnus decreased with advancing age groups of plantations and showed an inverse relationship with stand age. Annual N fixation increased from the 5‐year‐old stand (52 kg ha–1), peaking in the 15‐year‐old stand (155 kg ha–1) and then decreased with increasing plantation age. Nitrogen and phosphorus uptake was lowest in the 40‐year‐old stand, and highest in the 15‐ and 5‐year‐old stand, respectively. Nutrient storage in understorey cardamom was very high: up to 31 % N and 59 % P of the stand total in the 15‐year‐old stand. Nutrient use efficiency was higher (with faster turnover times) in younger stands and decreased (with slower turnover times) in older plantations. Nitrogen retranslocation showed a strong positive relationship with stand age, while that of P was inversely related to stand age. Nutrient standing stock, uptake and return were also highest in the 15‐year‐old stand. Nitrogen and P cycling in Alnus–cardamom plantations was functionally balanced. Nutrient cycling and dynamics indicated thatAlnus–cardamom plantations performed sustainably up to 15–20 years. The management practice should be altered to incorporate replantation after this age.
