GROWTH AND WOOD DENSITY RESPONSES TO LATER-AGE FERTILIZER APPLICATION IN PINUS RADIATA

Abstract

Growth or ring width responses to nitrogen, phosphorus and the two combined fertilizers were significant over five out of seven years that followed treatment (post-treatment period) in thinned, mid-rotation radiata pine ( Pinus radiata D. Don). Responses were similar between nitrogen and phosphorus treatments and largest in the nitrogen plus phosphorus (NP) treatment. Fertilizer increased the proportion of wood formed in mid-rotation relative to juvenile wood thereby increasing tree density in comparison to the control. Fertilizers, other than nitrogen, significantly lowered density compared to the control in the posttreatment period only. Density was higher in nitrogen than phosphorus and similar between phosphorus and NP. Density responses lasted for up to 5 years and were inconsistent between treatments. Ring width and density were weakly correlated. Ring width and density responded differently to climatic variables within and between sites, signalling independent physiological controls and highlighting the importance of site specific differences.