Mid-rotation response to fertilizer by Pinus radiata D. Don at three contrasting sites

Mid-rotation responses to fertilization of Pinus radiata D. Don plantations after the first or second thinning have been observed in research experiments in many regions where the species is grown. The practice is not however common in commercial plantations. This is probably because the effects of soil-site conditions on the magnitude and duration of tree and stand growth responses are not well understood. The effects of nitrogen (150 and 300 kg N · ha -1 ) and phosphorus (0, 20 and 40 kg P· ha -1 ) including common base fertilization of boron (8 kg B· ha -1 ) and potassium (65 kg K · ha -1 ) were evaluated in three mid-rotation P. radiata plantations after thin- ning. The plantations were located on sites with contrasting nutrient and water availability, sandy, granitic and red- clay sites, in south-central Chile. The magnitude and duration of growth response was site specific. After 8 years, the growth response to the highest dose of fertilization relative to the control was 57 m 3 · ha -1 (16%) at the granitic and 24 m 3 · ha -1 (14%) at the sandy site. No response to either nitrogen or phosphorus fertilizer was observed at the red-clay site. Nitrogen and phosphorus were limiting at both granitic and sandy sites, and high fertilization doses considering 300 kg N · ha -1 plus 40 kg P · ha -1 would ameliorate nutrient resource limitations and yield a cost-effective increment in stand volume.