EFFECT OF PHOTON IRRADIANCE AND FERTILISER LEVELS ON THE GROWTH OF <em>SHOREA</em> <em>LEPROSULA</em> STOCK PLANTS AND THE ROOTING ABILITY OF THEIR SUBSEQUENT STEM CUTTINGS

Abstract

Potted stock plants of Shorea leprosula raised under a high irradiance range of 0 to 722 (µrnol photons m^-2 s^-1 (nominally 30% full sunlight) produced better height and diameter growth than those grown under a low irradiance range of 0 to 325 µmol photons m^-2 s^-1 (nominally 10% full sunlight). An enhanced net photosynthesis (P_n) may be the cause of better growth rate in plants raised under high irradiance range. However, cuttings obtained from stock plants grown under low irradiance range were more inclined to root (78%;) and produced more roots per rooted cutting (4.8) than those from the high irradiance range (54% and 3.8 respectively). There was a negative correlation between rooting ability and stem volume of cuttings. Cuttings with high stem volume (2 to 3 cm³) tended to remain unrooted. In another experiment, height and diameter growth of S. leprosula potted stock plants were enhanced by the application of 1.5 g compared to 0.5 g per plant per two weeks of NPK fertiliser (12%N : 12%P₂O₅ : 17 % K₂O : 2%MgO + trace elements). However, rooting of subsequent cuttings was not affected by these fertiliser rates (73% and 70% for low and high fertiliser treatments respectively).