STEM DEFORMITY IN PINUS-RADIATA PLANTATIONS IN SOUTH-EASTERN AUSTRALIA .2. EFFECTS OF AVAILABILITY OF SOIL-NITROGEN AND RESPONSE TO FERTILIZER AND LIME

Plantations of radiata pine (P. radiata D.Don) on soils previously und er legume based pastures have a high incidence of stem deformity compa red with forest soils. A comparison of soil properties and tree nutrit ion of 5 to 7 year-old radiata pine on former pastures in the first pa rt of the study showed that stem deformity was strongly correlated wit h mineralisation of soil N and in particular with nitrification. Other soil properties that have changed as a result of pasture improvement, e.g. pH, available P and Mn, were only partially correlated with stem deformity. In the second part of the study, the role of N availabilit y and other soil properties in the expression of deformity was further investigated in a separate field experiment on soils formerly under n ative eucalypt forest, tobacco cropping, and improved pasture. Young r adiata pine plantings were treated with lime, phosphorus, and nitrogen applied as urea and sodium nitrate. Liming increased soil pH by aroun d 1.5 units, raised exchangeable Ca2+ and decreased available Mn. Soil mineral N content was only marginally affected by liming. Superphosph ate increased soil available P and raised levels of P in foliage. Chan ges in soil pH, availability of P, Mn, and B did not affect growth or stem deformity at any of the sites. In contrast, application of N fert ilisers at 200 and 600 kg N ha(-1) increased mineral N content and sti mulated nitrification, particularly at the forest site. The high rate of N fertiliser increased basal area at the forest site by 45%, but al so raised the level of stem deformity from 12% to 56%. At the tobacco and pasture sites, this treatment did not increase growth and did not significantly raise stem deformity above the already high basic level of deformity (63%). Implications of stem deformity in young plantation s of radiata pine on potential utilisation later in the rotation are d iscussed.