Influence of site and fertiliser addition on nutrient cycling in Eucalyptus globulus plantations in Gippsland, south-eastern Australia. I. Foliage and litter quality

The productivity of Eucalyptus plantations on many sites in south-eastern A ustralia is limited by nitrogen and phosphorus supply. Therefore, after can opy closure, nutrient return and decomposition are key processes maintainin g productivity. To gain a better understanding of the effects of site and f ertitisers on these processes, foliage and litter quality in E. globulus (L abill.) plantations in Gippsland, south-eastern Australia were characterise d on three sites covering a range of soil types, inherent soil fertility an d fertiliser treatments. Foliage and litter quality were estimated by seque ntial extraction of labile forms of N, P and C with cold, then hot, trichlo roacetic acid (TCA). Selected treatments were sampled in N x P factorial fe rtiliser trials of 6-year-old trees where nutrients were added up to 2 year s of age. Foliage and litter were categorised as recent or old depending on sampling position. Site significantly influenced concentrations of total a nd labile N and P (P < 0.0001) in foliage and litter. Phosphorus fertiliser increased total P concentrations in old foliage at two sites, with the gre atest absolute and relative increases at the least fertile site (Glencoe). Inorganic P extracted by cold (4 degrees C) TCA accounted for 30-55% of tot al leaf and litter P and was the fraction most responsive to P fertiliser a ddition. Total N concentration and N fractions in foliage and litter were n ot influenced by N fertiliser addition. Inorganic N extracted by cold and h ot (90 degrees C) TCA accounted for less than 2% of total N and was not sig nificantly different among fertiliser treatments. Both sugar and phenol con centrations in foliage and litter varied significantly between sites, with the least fertile site showing significantly higher concentrations of pheno ls in recent litter. Sugars and phenols extracted in cold TCA decreased fro m old foliage to litter at all sites and were not influenced by N and P fer tiliser addition. The results show that additions of 200 kg ha(-1) of P cau se perturbations in P cycle that are bigger in magnitude and are sustained for longer periods of time compared to changes in N cycle with 400 kg ha(-1 ) of N additions.