Growth responses of Eucalyptus regnans and soil changes following periodic fertilization

Increased demand for plantation hardwood production has resulted in the progression of Eucalyptus plantations onto soils of reasonable physical structure but low nutrient status. This study was undertaken to investigate the effects of periodic fertilization through 15 yr on stand growth and soil chemistry of a Eucalyptus regnans F. Mueller plantation on a high rainfall site in southern Tasmania. Substantial response to N fertilizer, applied as ammonium sulfate, were measured, but there was no response to P applied as single superphosphate, either alone or in combination with N. Annual applications of N fertilizer, for a period of 13 yr, at 100 kg N ha-1 yr-1 doubled volume growth from 125 to 281 m3 ha-1, at Age 19 yr. Long-term fertilization resulted in the accumulation of nutrients within the forest floor and surface soils. Significant reductions in soil pH, from 4.5 to 3.6 in the surface soil, were associated with the highest rate of fertilization. Reductions in pH occurred with both nitrogenons and phosphatic fertilizers. Substantial reductions in exchangeable Mg concentrations in surface soils, from 258 to 71 mg kg-1 were also measured. The research highlights the balance needed between obtaining growth response and causing detrimental soil effects from long-term fertilization. © Soil Science Society of America.