Fluxes of methane and nitrous oxide in water-saving rice production in North China

Lowland rice production is currently facing serious water shortages in numerous Asian countries. In the North China Plain water limitations are severe. Water-saving rice production techniques are therefore increasingly searched for. Here we present the first study of trace gas emissions from a water-saving rice production system where soils are mulched and are kept close to field capacity in order to compare their contribution to global warming with traditional paddy rice. In a two-year field experiment close to Beijing, CH4 and N2O fluxes were monitored in two forms of the Ground Cover Rice Production System (GCRPS) and in traditional paddy fields using closed chambers. With paddy rice the observed CH4 emissions were very low, about 0.3 g CH4 m(-2) a(-1) in 2001 and about 1 g CH4 m(-2) a(-1) in 2002. In GCRPS, the CH4 emissions were negligible. N2O fluxes in GCRPS were similar, 0.5 to 0.6 g N2O m(-2) a(-1) in 2001 and 2002, and emission peaks mainly followed fertilizer applications. In paddy rice, N2O fluxes were unexpectedly low throughout the year 2001 (0.03 g N2O m(-2) a(-1)), and in 2002 larger emissions occurred during the drainage period. So with 0.4 g N2O m(-2) a(-1) the cumulative flux was similar to emissions in GCRPS. Total CO2 equivalent fluxes calculated according to IPCC methodology were tenfold higher in GCRPS compared to paddy in 2001. In 2002, fluxes from both systems were similar with 175 and 141 g CO2 equivalents m(-2) a(-1) from GCRPS and paddy.