CHANGES CAUSED BY MID-ROTATION FERTILIZER APPLICATION TO THE FIBRE ANATOMY OF PINUS RADIATA

Abstract

Effects of nitrogen (N) and phosphorus (P) fertilizers on average fibre radial diameter, tangential diameter, wall thickness and number of fibres per unit area were studied over 7 years of growth in radiata pine. Stands were in mid-rotation, thinned and treatments replicated 4 times at 3 sites. Compared to a thinned, unfertilized control, N decreased and P increased fibre radial diameter. Only N decreased fibre radial diameter, thereby increasing the number of fibres per unit area. All fertilizer treatments decreased fibre wall thickness. Responses in ring width and fibre properties, other than fibre tangential diameter peaked 2 years following fertiliser application, before gradually disappearing after 4–5 years. Fertilizer effects on fibre properties diminished at different rates, causing significant interactions with time. Ring width had little effect on density. Changes in density and fibre coarseness were attributed to changes in fibre wall thickness more than fibre radial diameter and tangential diameter. The largest decrease in density and fibre coarseness in the combined N and P treatment was explained mostly by thinner walls.