EFFECTS OF CONTROLLED RELEASE NITROGEN FERTILIZER ON VEGETATIVE GROWTH AND LEAF NITROGEN OF IMMATURE OIL PALM PLANTED ON TROPICAL PEATLAND

摘要

The objective of this study was to compare the effects of controlled release urea fertilizer (CRUF) and conventional urea on vegetative growth and leaf nitrogen (N) of oil palm cultivated on tropical peatland. The study was conducted in a young oil palm plantation on tropical peatland in Sarawak for four (4) years. The treatments included without N fertilizer (Control) (Tl), 100% conventional urea (T2), 50% CRUF (T3) and 100% CRUF (T4). Vegetative growth parameters such as number of pinnae, pinnae length, pinnaewidth , petiole width and petiole depth , were measured and recorded. Leaf samples were collected from the midsections of themiddle leaflets, oven-dried and ground for total N analysis. No statistically, significant difference in number of pinnae, width of pinnae or leaf N was observed between conventional urea and CRUF, regardless of rate of application of N. However, pinnae length, petiole width and petiole depth were significantly higher in palms treated with 100% urea than those treated with 100% CRUF. This might be due to the lack of adequate release of the substantial N from CRUF to fulfil the requirements of the oil palm, especially during its rapid growth, possibly resulting in the palms absorbing the N from peat mineralization rather than from the fertilizers. Leaf N concentration from fertilized palms (T2, T3 and T4) demonstrated an obvious increasing trend for the first three (3) years after planting and thereafter decreased to a constant phase. A decrease in the leaf N concentration to deficiency level (<2.5%) in the control plot in March 2012 may due to high rainfall during that period, causing more N leaching and dilution in both soil and plant tissue. Long-term measurements are still needed to evaluate the efficiency of CRUF on oil palm growth and productivity on tropical peatland.