Effects of weed control, fertilization, and soil cultivation on the growth of Pinus radiata at midrotation in Canterbury, New Zealand

Two factorial experiments examining effects of weed control, fertilization, and soil cultivation on Pinus radiata D. Don growth were established in the Canterbury region of New Zealand during 1983. The experiments were measured every year for the first 5 years, during which effects of both weed control and fertilization were detected. Midrotation measurements of height and diameter at breast height were taken. Growth in subplot mean height and basal area per unit area over 3 years in one case and 4 years in the other, up to ages 13 and 14, respectively, was analysed. Results showed that the initial time gain due to weed control and fertilization was preserved at midrotation and that there was no continuing divergence between treated and untreated subplots after weed control. There was, however, continuing divergence after fertilization on one site where topsoil had been shifted into heaps during land clearing. Modelling revealed that effects of weed control and fertilization on basal area growth and yield of stands could be represented by the same difference equation with an additive term to represent the effects of treatments. On the other hand an existing regional growth and yield model failed to represent these effects properly.