Abstract
Short rotation energy crops have the potential to provide sustainable sources of biomass, but the efficient use of nutrients will be crucial to ensure that these systems are sustainable. In dryland environments 3- to 5-yr rotations of tree crops integrated with agriculture represent a major potential bioenergy feedstock and a means to restore landscape hydrologic balances, while maintaining food production. In soils with low natural fertility, the long-term viability of these systems is critically affected by site nutrient status and subsequent cycling of nutrients. A nutrient assimilation index (NAI) was developed to allow comparison of the nutrient assimilation between tree species and tree components, to optimise nutrient management, and to quantify different strategies to manage nutrients. Biomass, nutrient export, and nutrient use efficiency were assessed for three short rotation tree crop species (Eucalyptus globulus, E. occidentalis, Pinus radiata). Component NAI was generally in the order of leaf<twig<bark<root<twig<bark<root.