Growth and nutrition of radiata pine on podzolised sands in response to phosphate fertilizer.  P. Hopmans, I. B. Tomkins and P. W. Geary.  April 1993.  25pp. (unpubl.)

SUMMARY

In 1970, a fertiliser trial was established at Rennick to evaluate the growth of radiata pine (Pinus radiata D. Don) on infertile deep sands in response to various rates of phosphate fertiliser at the time of planting and at age 9 years. The growth and nutrient status in the trial were monitored at regular intervals from 1972 to 1989.

Mortality of radiata pine was comparatively high (range 7% to 31%) following planting mainly due to inadequate weed control. In addition, mortality was also affected by the depth of sand to a humus pan. The applications of lime:superphosphate at planting did not affect survival.

Radiata pine was successfully established with lime:superphosphate at planting at rates of 227, 454, and 681 g tree^-1. There was little difference in height response to these rates of fertiliser at age 2 years. However, volume response of fertilised trees at age 9 years was estimated to be 39%, 49% and 89% higher respectively than control trees, clearly showing a significantly better long-term response to the highest rate of fertiliser.

Concentrations of P and Zn in foliage decreased to deficiency levels between 6 to 9 years after planting. Levels of N were marginal while those of other nutrients were generally satisfactory. Aerial application of zinc sulphate at age 7 years corrected Zn deficiency but foliar Zn again declined to deficiency levels 7 years later.

Broadcast application of single superphosphate at age 9 years at rates of 600 and 1200 kg ha^-1 increased volumes at age 19 years from 249 m³ ha^-1 in unfertilised trees to 376 and 395 m³ ha^-1 in fertilised trees, respectively. Average response to broadcast fertiliser was estimated at 56% of the volume increment of unfertilised trees over the 10 year period. There was little additional growth response to the higher rate of fertiliser. Both rates of fertiliser corrected P deficiency, but concentrations of P in foliage decreased again to marginal levels after 5 years indicating the need for further additions of fertiliser. Response to superphosphate was of short duration mainly due to the poor retention of applied P by these deep podzolised sands. Fertiliser increased site productivity from Site Quality (SQ) VI to SQ IV, however, foliar analysis indicates that regular applications of P and Zn would be required to maintain this increase in productivity over a full rotation. Results also showed potential for a response to N fertiliser from age 6 years onwards. It is expected that this would further enhance the productivity of these sites.