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.