Effects of Land-Use Conversion from Double Rice Cropping to Vegetables on Methane and Nitrous Oxide Fluxes in Southern China.

Compared with CO₂, methane (CH₄) and nitrous oxide (N₂O) are potent greenhouse gases in terms of their global warming potentials. Previous studies have indicated that land-use conversion has a significant impact on greenhouse gas emissions. However, little is known regarding the impact of converting rice (Oryza sativa L.) to vegetable fields, an increasing trend in land-use change in southern China, on CH₄ and N₂O fluxes. The effects of converting double rice cropping to vegetables on CH₄ and N₂O fluxes were examined using a static chamber method in southern China from July 2012 to July 2013. The results indicate that CH₄ fluxes could reach 31.6 mg C m⁻² h⁻¹ under rice before land conversion. The cumulative CH₄ emissions for fertilized and unfertilized rice were 348.9 and 321.0 kg C ha⁻¹ yr⁻¹, respectively. After the land conversion, the cumulative CH₄ emissions were −0.4 and 1.4 kg C ha⁻¹ yr⁻¹ for the fertilized and unfertilized vegetable fields, respectively. Similarly, the cumulative N₂O fluxes under rice were 1.27 and 0.56 kg N ha⁻¹ yr⁻¹ for the fertilized and unfertilized treatments before the land conversion and 19.2 and 8.5 kg N ha⁻¹ yr⁻¹, respectively, after the land conversion. By combining the global warming potentials (GWPs) of both gases, the overall land-use conversion effect was minor (P = 0.36) with fertilization, but the conversion reduced GWP by 63% when rice and vegetables were not fertilized. Increase in CH₄ emissions increased GWP under rice compared with vegetables with non-fertilization, but increased N₂O emissions compensated for similar GWPs with fertilization under rice and vegetables. [ABSTRACT FROM AUTHOR]