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

Compared with CO(2), methane (CH(4)) and nitrous oxide (N(2)O) 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 CH(4) and N(2)O fluxes. The effects of converting double rice cropping to vegetables on CH(4) and N(2)O fluxes were examined using a static chamber method in southern China from July 2012 to July 2013. The results indicate that CH(4) fluxes could reach 31.6 mg C m(−2) h(−1) under rice before land conversion. The cumulative CH(4) 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 CH(4) emissions were −0.4 and 1.4 kg C ha(−1) yr(−1) for the fertilized and unfertilized vegetable fields, respectively. Similarly, the cumulative N(2)O 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 CH(4) emissions increased GWP under rice compared with vegetables with non-fertilization, but increased N(2)O emissions compensated for similar GWPs with fertilization under rice and vegetables.