N fertilization effects on N2O fluxes from oil palm plantation on tropical peatland

Anthropogenic activities, and in particular the use of synthetic nitrogen (N) fertilizer, have a significant influence on soil nitrous oxide (N₂O) emission from oil palm plantation on tropical peatland. Finding a suitable N rate for optimum N uptake efficiency and yield with low environmental impact and production cost is crucial for the economic growth of Malaysia’s oil palm sector. However, studies on the impact of N fertilizers on N₂O emissions from tropical peatland are limited. Thus, long-term monitoring was conducted to investigate the effects of N fertilization on soil N₂O emissions. This study was conducted in an oil palm (Elaeis guineensis Jacq.) plantation located in a tropical peatland in Sarawak, Malaysia. Monthly soil N₂O fluxes were measured using the closed-chamber method in a control (T1, without N fertilization), and under three different N treatments: low N (T2, 31.1 kg N ha⁻¹), moderate N (recommended rate) (T3, 62.2 kg N ha⁻¹), and high N (T4, 124.3 kg N ha⁻¹), from January 2010 to December 2013 and from January 2016 to December 2017. The only N fertiliser rate to significantly increase (p<0.05) annual cumulative N₂O emissions was 124.3 kg N ha^-1 (T4). Increased in water-filled pore space (WFPS) (>70%) with a decrease in both N₂O flux and nitrate (NO₃⁻) implies that complete denitrification has taken place. Increased in NO₃^- uptake by oil palm with an increase in WFPS decreased NO₃^- concentration in soil, resulting in the reduction of N₂O emission. This study highlights the importance of WFPS on denitrification and N uptake by oil palm in tropical peatland. This needs to be taken into account for the accurate assessment of N dynamics in oil palm plantations on tropical peatland in order to enhance N fertilization management strategies and counteract anthropogenic activities that produce greenhouse gases.

Keywords: WFPS, oil palm yield, NO₃^-, N uptake