EFFECTS OF COMBINATIONS OF IRRIGATION AND FERTILIZATION ON THE GROWTH AND ABOVEGROUND BIOMASS PRODUCTION OF PINUS-RADIATA

Stand growth, associated biomass production and subsequent allocation were measured in a 10- to 14-year-old plantation of Pinus radiata treated with various combinations of fertilisation and irrigation. The study was carried out near Canberra, Australia as part of a major project which aimed to develop a mechanistic model of stand growth. Periodic annual increment in stem volume between 11 and 15 years of age was not affected by fertilisation alone (F) (20.5 m3 ha-1 year-1) but irrigation alone (I) increased it to 33.0 m3 ha-1 year-1. Irrigation in combination with solid (IF) or liquid (IL) fertilisation improved volume increment to 44.0 m3 ha-1 year-1 and 50.4 m3 ha-1 year-1, respectively, these increments being higher than reported for any other P. radiata stand in Australia. Total foliage mass in winter at the beginning of the experiment was 5 t ha-1. After 4 years it had increased to 11 t ha-1, 12 t ha-1 and 12.5 t ha-1 on control (C), F and I stands, respectively, while IF and IL stands carried 14 t ha-1. Total above-ground net primary production at this time was 17(C), 20(F), 22(I), 31(IF) and 39(IL) t ha-1 year-1. Annual production per unit foliage (foliar efficiency) declined with increased foliage mass but increased with fertilisation and with increases in available water (rainfall and irrigation). Fertilisation stimulated allocation to branches rather than to stems while irrigation promoted stem rather than branch growth. This resulted in marked changes in harvest index; the proportion of stem wood to total persistent above-ground biomass.