Residue management effects on soil carbon and nutrient contents and growth of second rotation eucalypts

Abstract

We examined tree growth and dynamics of organic matter and soil nutrient pools annually for 7 years under contrasting harvest residue management treatments in south-western Australia. Two second rotation Eucalyptus globulus sites were established on soils of contrasting fertility and productivity. Harvest residues were either (i) burnt, (ii) removed, (iii) retained, or (iv) retained at double the normal quantity. More than 31 and 51 Mg ha −1 of harvest residues resulted from harvesting of 8-year-old first rotation stands at a low fertility Grey Sand site, and a higher fertility Red Earth site, respectively. Harvest residue retention increased tree growth at the lower fertility Grey Sand site, but had no effect on plantation productivity at the Red Earth site up to 7 years. Burning resulted in a direct loss of most of the organic material, and up to 200, and 350 kg ha −1 of N at the Grey Sand and Red Earth sites, respectively. Significant quantities of organic material in harvest residues (>50 Mg ha −1 C in the double residues treatment at the Red Earth site) had a limited effect on soil C pools during the 7 years of this study. Retention of residues limited immediate losses of nutrients, and resulted in higher quantities of soil exchangeable K, Ca and Mg during the 7 years after establishment. However, the content of soil exchangeable cations, especially K, decreased during the first 4 years of establishment in all treatments, including those where residues were retained. After 4 years, cation quantities in soil started to increase again, probably due to the decomposition of leaves and twigs from litterfall.