THE EFFECT OF FERTILIZER APPLICATION ON DIPTEROCARP SEEDLING GROWTH AND MYCORRHIZAL INFECTION

In three independent experiments, application of fertilizers had no effect on the growth of dipterocarp seedlings. The experiments involved application of. (1) NPK at a rate of 10 g m-2 N, P2O5 and K2O to Shorea macroptera Dyer seedlings grown in pots of forest soil under nursery conditions in Penang, Malaysia; (2) N at a rate of 10 g m-2 and/or P at a rate of 5 g m-2 in a factorial design to 8-month-old Shorea curtisii Dyer ex King seedlings growing wild in coastal hill dipterocarp forest in Penang, Malaysia; (3) NKP at a rate of 10 g m-2 three times over 10 months to Hopea beccariana Burck seedlings growing wild in lowland mixed dipterocarp forest in Sabah, Malaysia. In Experiment 1, fertilizer application significantly increased the extent of ectomycorrhizal (ECM) infection of the S. macroptera roots, and unfertilized seedlings showed a closer correlation between extent of ECM infection and growth than fertilized seedlings. These preliminary results suggest that dipterocarp seedlings may only be responsive to fertilizer addition when grown at very low nutrient availabilities, and that ECM infection may be of great importance to seedling growth under such conditions.