How does nitrogen application impact soil respiration and CH4 emissions? An experiment in an oil palm plantation on tropical peat.

Oil palm cultivation on peatlands causes severe environmental damage, yet its greenhouse gas (GHG) footprint and underlying biogeochemical drivers remain poorly quantified. This study assessed how nitrogen fertilizer application impacts soil respiration and CH4 emissions across spatio-temporal scales in a fertilization trial with three application rates: 0 (N0), 154.5 (N1) and 309 (N2) kg N ha-1 yr-1. Fluxes and environmental variables were monitored monthly over a year and daily for a month after two fertilizations. Measurements were taken close to palms (CP), where fertilizer was applied, and farther from palm (FP). Soil respiration (Mg CO2-C ha-1 yr-1) was high compared to the literature, with N0 and N2 (27.3 ± 2.8 and 28.5 ± 3.0) exceeding N1 (18.8 ± 2.5). Fertilization triggered short-lived respiration increases, without affecting annual rates. Treatment and spatial differences (FP > CP) aligned with soil temperature and soil N2O emission patterns, suggesting links to peat mineralization. CH4 emissions (kg CH4-C ha-1 yr-1) were greater in N0 (3.9±1.5) compared to N1 (0.7 ± 0.6) and N2 (1.0 ± 1.3), inversely mirroring soil nitrate distribution under unfertilized conditions. A transient fertilizer effect occurred, without affecting annual rates. Our findings highlight strong interactions between soil respiration, CH4 emissions and N cycling in drained tropical peatlands, warranting further investigation to constrain GHG process-based modelling.