Influence of Site and Fertiliser Addition on Nutrient Cycling in Eucalyptus globulus Plantations in Gippsland, South-eastern Australia. I. Foliage and Litter Quality

Abstract

The productivity of Eucalyptus plantations on many sites in south-eastern Australia is limited by nitrogen and phosphorus supply. Therefore, after canopy closure, nutrient return and decomposition are key processes maintaining productivity. To gain a better understanding of the effects of site and fertilisers on these processes, foliage and litter quality in E. globulus (Labill.) plantations in Gippsland, south-eastern Australia were characterised on three sites covering a range of soil types, inherent soil fertility and fertiliser treatments. Foliage and litter quality were estimated by sequential extraction of labile forms of N, P and C with cold, then hot, trichloroacetic acid (TCA). Selected treatments were sampled in N × P factorial fertiliser trials of 6-year-old trees where nutrients were added up to 2 years of age. Foliage and litter were categorised as recent or old depending on sampling position. Site significantly influenced concentrations of total and 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 greatest absolute and relative increases at the least fertile site (Glencoe). Inorganic P extracted by cold (4°C) TCA accounted for 30-55% of total leaf and litter P and was the fraction most responsive to P fertiliser addition. Total N concentration and N fractions in foliage and litter were not influenced by N fertiliser addition. Inorganic N extracted by cold and hot (90°C) TCA accounted for less than 2% of total N and was not significantly different among fertiliser treatments. Both sugar and phenol concentrations in foliage and litter varied significantly between sites, with the least fertile site showing significantly higher concentrations of phenols in recent litter. Sugars and phenols extracted in cold TCA decreased from old foliage to litter at all sites and were not influenced by N and P fertiliser addition. The results show that additions of 200 kg ha^-1 of P cause 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.