LONGEVITY OF RESPONSE IN PINUS RADIATA FOLIAR CONCENTRATIONS TO NITROGEN, PHOSPHORUS, AND BORON FERTILISERS

In the winter of 1972, a fertiliser trial was established in recently thinned (740 stems/ha) 4- to 5-year-old Pinus radiata D.Don regeneration in Harakeke Forest, Waimea County. In a factorial design experiment, nitrogen, phosphorus, and boron were variously applied as urea (168 kg N/ha), superphosphate (112 kg P/ha), and * 'fertiliser borate 65 " (22 kg B/ha). Foliage samples were collected at monthly intervals for the first 3 years, and then about quarterly for 2 more years. Soil samples (0-10 cm) were collected at quarterly intervals and analysed for total nitrogen, Bray-2 phosphorus, Olsen phosphorus, and hot-water-soluble boron. The concentration of all three nutrients in foliage increased steeply within a few weeks of application, reached a peak in the spring, and declined during the summer. Phosphorus levels then stabilised and remained consistently higher than in the controls for at least 5 years. Nitrogen and boron continued to decline, though at different rates; for nitrogen, the response lasted about 11 months, and for boron about 5 years. Increased levels of extractable phosphorus and boron persisted in the soil for the duration of the trial but appeared to be declining. The applied nitrogen had no obvious effect on soil total-nitrogen status. Tree growth data suggest ( D a positive effect of phosphorus on basal area increment lasting the full 5 years, (2) an effect of nitrogen on diameter increment lasting 1 year, and (3) no effect of boron