No abstract

Annual litter fait, nutrient concentrations in litter components and annual weight of nutrients in litter fall have been estimated for karri forest stands aged 2, 6, 9 and 40 years and in mature forest. The weight of litter falling annually increases with stand age, ranging from 1.13 tiha in 2-year-otd regeneration to 9.45 tIha in mature forest. This increase is due mainty to greater amounts of twigs, bark and fruit falling in older stands. Leaf fait is relatively independent of stand age once the canopy of regenerating stands closes and the understorey has developed.Concentrations of N, P, K, S and Mn in karri leaf litter differ significantly between sites and the differences appear to be related to stand age. Highest levets of these etements are found in karri leaf litter from the youngest stand and the concentrations decrease with increasing stand age. The amounts of annual litter fall and of nutrients cycling in litter are among the largest reported for Australian forests. In particular cycling ofCa, K and Mg in mature karri forest is greater than has been reported for any other eucalypt forest. Karri forest understorey ptays a key rote in nutrient cycting in these ecosystems, contributing 30-70% of the weight of many of the nutrients in the leaf component of titter. Understorey leaf material is particularly important in the cycling of N, S and the micro-nutrients Cu and Zn.

Sulphate a t concentrations of less than 30 mg 1-l of sulphur is determined on the AutoAnalyzer by reduction to hydrogen sulphide, distillation of the latter and its subsequent colorimetric determination.The method has been found to be suitable for aqueous solutions of sulphate, digests of leaf samples and animal faeces, and extracts of soils; it is applicable to a wide range of agricultural, biological and industrial materials.

Rates of weight loss and release ofN, P, K, S, Ca, Mg, Na, and Cl from litter of several species in jarrah (E. marginata Donn ex Sm.) forest were measured in relation to site fire history and soil type. Weight loss from leaf litter decreased in the order jarrah > marri (E. calophylla R. Br. ex Lindl.) > Banksia grandis Willd. After 18 months on the forest floor senesced leaves of jarrah, marri and Banksia had lost 45%, 42% and 19%, respectively, of their original weight. Although greatest rates of decomposition occurred on a site burnt 3 y previously by an intense autumn fire and slowest rates on a site which had not been burnt for 8 y, the differences between burn sites were small in comparison with the total weight loss from decomposing litter. The order of release of nutrients from decomposing eucalypt litter wasP dark sandy duplex soil > yellow gravels. These differences may be related to the higher nutrient status of the reddish gravel soils.

Automated procedures for the determination of ammonium and nitrate in soil extracts are described. Distillation of the extract with magnesium oxide, with subsequent determination of ammonia by the automated indophenol method, is used for ammonium. For ammonium plus nitrate, the nitrate is reduced with titanium( 111) sulphate during distillation with magnesium oxide, and ammonia determined as before. The method has wider application, for example, to the analysis of fertilisers and water samples.