Land use legacies and nitrogen fertilization affect methane emissions in the early years of rice field development

Methane (CH₄) emissions are critical to greenhouse gas (GHG) management in agriculture, especially in areas growing rice (Oryza sativa). However, studies on CH₄ emissions and the nitrogen (N) fertilization effect in new rice fields in subtropical regions are still scarce. In this study, we designed a split-plot field experiment in Jiangxi Province, southern China, to examine whether land-use legacies and N fertilization would influence CH₄ emissions. Using static chambers and gas chromatography, we measured CH₄ fluxes in a newly developed rice paddy and a 10-year-old rice paddy. We also measured climatic factors and soil chemical and physical properties to match the flux measurements. The results showed that annual CH₄ emissions in the new rice plots were significantly lower than in the old rice plots regardless of N fertilization. Annual CH₄ emissions increased with the land-use years of rice paddies, following the order of 1 year < 2 years < 3 years < 10 years. N fertilization significantly decreased CH₄ emissions by 36.9% in the first year after the new rice plots were developed, whereas it had no significant effects on CH₄ emissions in the old rice plots or the new rice plots in the second and third years. The results suggest that land-use legacies have significant effects on CH₄ emissions and may influence the N fertilization effect on CH₄ emissions in rice fields in subtropical regions. The findings suggest that land-use legacies should be considered in managing and estimating GHG emissions in rice-growing regions.