Methane oxidation potential of soils in a rubber plantation in Thailand affected by fertilization

Abstract. Forest soils, as crucial sinks for atmospheric methane in terrestrial ecosystems, are significantly impacted by changes in ecosystem dynamics due to deforestation and agricultural practices. This study investigated the methane oxidation potential of rubber plantation soils in Thailand, focusing on the effect of fertilization. The methane oxidation activity of the topsoils (0–10 cm) in the dry season was extremely low and increased slightly in the wet season, with lower activity for higher fertilization levels. The methane oxidation potential of the topsoil was too low to explain the in situ methane uptake. Soils below 10 cm depth in unfertilized rubber plantations showed higher activity than the surface soils, and methane oxidation was detected down to, at least, 60 cm depth. In contrast, soils under the high-fertilization treatment exhibited similarly low activity of methane oxidation up to 60 cm depth compared to surface soils during both dry and wet seasons, indicating that fertilization of para rubber plantations negatively impacts the methane oxidation potential of the soils over the deep profile without recovery in the dry (off-harvesting) season with no fertilization. Methane uptake per area, estimated by integrating the methane oxidation potentials of soil layers, was comparable to the field flux data, suggesting that methane oxidation in the soil predominantly occurs at depths below the surface layer. These findings have significant implications for understanding the environmental impacts of tropical forest land uses on methane dynamics and underscore the importance of understanding methane oxidation processes in soils.