Effect of topography on N₂O and CO₂ emissions and dissolved N₂O in oil palm plantation in Riau, Indonesia

抄録

The oil palm plantations have been expanding into the different slope positions, through its association with deforestation and nitrogen fertilizer use and concerning emission of greenhouse gases. However the interactions of soil properties and topography influencing greenhouse gas fluxes are still poorly understood. Topography affects the movement of surface and subsurface water and causes the variability of soil processes, which makes the accurate estimation of greenhouse gas fluxes more difficult. This study aimed to assess N₂O and CO₂ emissions, measured by closed chamber method in upper, middle, and lower slope positions for a whole year from June 2012 to May 2013 in Tunggal sandy loam soil, Indonesia and to assess the dissolved N₂O concentration as source of indirect emission from oil palm plantation to the atmosphere, measured by headspace method in puddle, drain, and well. N₂O and CO₂ fluxes showed variability with seasons and slope positions. Cumulative N₂O fluxes were significantly higher in the lower position than upper and middle position, while cumulative CO₂ fluxes showed no significant difference among the slope positions. Dissolved N₂O concentrations varied by water sources and sampling time, sometime supersaturated than ambient equilibrated concentration. These results show that topography even in a short slope affected the spatial variability of N₂O and CO₂ emission, which may need to be taken into account in field measurements and estimating the whole emissions of these gases including the indirect emissions.