The effects of P and K levels on growth and yield of oil palm were studied at the Agricultural and Technology College Plantation in Trang province in October, 1993 using eight-year-old palms planted on the Natham soil series (fine loamy, mixed, isohyperthermic Oxic Plinthudults) at the spacing of 8.5 x 8.5 x 8.5 m. A factorial experiment in randomized complete block design with three replications was used. The four treatments consisted of the combinations of two fertilizers: P (2 levels; 0.4, 0.8 kg P2O5/palm/year) and K (2 levels; 1.2, 2.4 kg K2O/palm/year). All treatments were applied the same rate of N (0.8 kg N/palm/year). The growth and oil palm yield were recorded for 4 years. The results showed clear effects of high P and K levels on growth of oil palm. Although the number of fronds did not differ, leaf area, leaf dry matter weight and leaflets of 17th frond tended to increase. The high K level tended also to give an increased FFB yield in years 2, 3 and 4. However, the effect of P levels on FFB yield of oil palm varied over the years. Considering a suitable rate of fertilizer application in terms of economic return, the low fertilizer rate (P 0.4 kg P2 O5/palm/year, K 1.2 kg K2O/palm/year and N 0.8 kg N/palm/year) gave the highest profit, although it resulted in the lowest FFB yield.
