Interaction of site, spacing, weed control and fertiliser in Pinus radiata plantations in southeast New South Wales

Two trials addressing soil preparation, weed control, fertiliser application and planting density were established on dry, high-elevation sites as part of a program to develop site-specific management. The sites differed in soils and the level of pasture improvement. The objectives included identifying treatment combinations that had greatest productivity and best stem and branch form, considering that poor stem form is an issue on pasture sites. The trials were assessed at 13 years of age. Volume production was high compared with a plantation established earlier on a native forest site, but it was not possible to determine whether this was a result of higher survival, higher nutrition, improved weed control or improved genetics. There was little difference in the effects of soil preparation treatments, and there was no effect at 13 years of the small early-fertiliser application. Weed control was important, with effects on volume production varying between sites and having a greater effect on the highly improved pasture site. Increasing stocking from 1000 stems ha(-1) to 1500 stems ha(-1) increased volume production by about 24% where weed control was applied. There were differences in stem and branch form between sites, and the highly improved pasture site had a higher level of multi-leaders, probably attributable to low boron. The study shows the value of small, standardised silvicultural trials in the development of site-specific management.