Bioenergy Feedstock Potential from Short-Rotation Woody Crops in a Dryland Environment †

Producing biomass from plantations of short rotations (3−10 years) of fast growing woody crops that are alternated with agricultural production, in a system termed phase farming with trees (PFT), could offer a range of advantages compared to the use of permanent coppiced plantings. These include providing landholders flexibility in land use and increasing the sustainability of farming systems by lowering water tables, removing excess nutrients, and improving soil quality. Disadvantages from permanent belts and blocks, such as competition with adjacent agricultural crops are reduced. PFT thus offers a method of producing both food and fuel from the same land, while increasing the sustainability of current agricultural systems. This paper describes the development of the PFT system in the dryland Mediterranean climate of southwestern Australia. Dry biomass yields of high-density (4000 trees/ha) plantings of Eucalyptus occidentalis of up to 22 tons/ha were achieved after 3 years and up to 54 tons/ha of Pinus pinaster (2000 trees/ha) after 7 years, in environments with only 300 mm of annual rainfall. Biomass yields of up to 31 tons/ha of E. occidentalis were achieved after 7 years on salinized soils, which had been effectively abandoned to agriculture. We describe the factors that affect yield in this water-limited environment, including the impact of initial planting density, rotation length, species, site selection (soils and landscape position), and fertilization and assess the impact of the system on sustainability in terms of removal of excess water and nutrients.