Large contribution of soil N₂O emission to the global warming potential of a large-scale oil palm plantation despite changing from conventional to reduced management practices

Abstract. Conventional management of oil palm plantations, involving high fertilization rate and herbicide application, result in high yield but with large soil greenhouse gas (GHG) emissions. This study aimed to assess a practical alternative to conventional management, namely reduced fertilization with mechanical weeding, to decrease soil GHG emissions without sacrificing production. We established a full factorial experiment with two fertilization rates (conventional and reduced fertilization, equal to nutrients exported via fruit harvest) and two weeding methods (herbicide and mechanical), each with four replicate plots, since 2016 in a ≥ 15-year old, large-scale oil palm plantation in Indonesia. Soil CO₂, N₂O, and CH₄ fluxes were measured during 2019–2020 and yield was measured during 2017–2020. Fresh fruit yield (30 ± 1 Mg ha⁻¹ yr⁻¹) and soil GHG fluxes did not differ among treatments (P ≥ 0.11), implying legacy effects of over a decade of conventional management prior to the start of experiment. Annual soil GHG fluxes were 5.5 ± 0.2 Mg CO₂-C ha⁻¹ yr⁻¹, 3.6 ± 0.7 kg N₂O-N ha⁻¹ yr⁻¹, and −1.5 ± 0.1 kg CH₄-C ha⁻¹ yr⁻¹ across treatments. The palm circle, where fertilizers are commonly applied, covered 18 % of the plantation area but accounted 79 % of soil N₂O emission. The net primary production of this oil palm plantation was 17150 ± 260 kg C ha⁻¹ yr⁻¹ but 62 % of this was removed by fruit harvest. The global warming potential of this planation was 3010 ± 750 kg CO₂-eq ha⁻¹ yr⁻¹ of which 55 % was contributed by soil N₂O emission and only < 2 % offset by soil CH₄ sink.