Repeated harvest residue removal reduces E. globulus productivity in the 3rd rotation in south-western Australia

Abstract

The use of biomass for energy is becoming increasingly popular, with many plantation forestry growers considering selling or using the biomass to generate renewable energy. It is known that this may lead to a net export of nutrients from the site, but the capacity of plantation sites to buffer this and sustain yield has not been quantified. In 2 long-term experiments, we explored the impact of repeated residue removal, retention, or retention of double the quantity of residues over 2 rotations of Eucalyptus globulus in south-western Australia. The 2 sites that we used had contrasting soil types, and we previously reported differential responses of plantation productivity to residue manipulation in the 2nd rotation. In this study we have shown that removal of harvest residues (and litter) into a 3rd rotation of E.globulus resulted in a significant impact on plantation productivity at both sites. It is important to note that a response to residue removal occurred even at a site that was highly productive in the first and second rotations, and which did not respond to residue removal or N fertilizer addition in the 2nd rotation. Retention of harvest residues and litter resulted in a significant increase in soil exchangeable cations at the higher productivity site, but the impacts on total soil C and N stocks were not as clear cut, with no significant changes to either of these, although a trend in the means for increased soil C under the residue retained treatments at the Red Earth site should be monitored into the future.