Alternate wetting and drying (AWD) is a water-saving irrigation technique in a paddy field that can reduce the emission of methane, a potent greenhouse gas (GHG). It is being adopted to Asian countries, but different results are reported in literatures on methane, nitrous oxide emission, and rice productivity under AWD. Therefore, the local feasibility needs to be investigated before its adoption by farmers. The current study carried out a 3-year experiment in an acid sulfate paddy field in Prachin Buri, Thailand. During five crops (3 dry and 2 wet seasons), three treatments of water management were compared: continuous flooding (CF), flooding whenever surface water level declined to 15 cm below the soil surface (AWD), and site-specific AWD (AWDS) that weakened the criteria of soil drying (AWDS). Methane and nitrous oxide emissions were measured by a closed chamber method. Rice grain yield did not significantly (p < 0.05) differ among the three treatments. The amount of total water use (irrigation + rainfall) was significantly reduced by AWD (by 42%) and AWDS (by 34%) compared to CF. There was a significant effect of treatment on the seasonal total methane emission; the mean methane emission in AWD was 49% smaller than that in CF. The seasonal total nitrous oxide emission and the global warming potential (GWP) of methane and nitrous oxide did not differ among treatments. The contribution of nitrous oxide to the GWP ranged 39-62% among three treatments in dry season whereas 3-13% in wet season. The results indicate that AWD is feasible in terms of GHG emission mitigation, rice productivity, and water saving in this site, especially in dry season.
ARTICLE HISTORY
Water regimes play a central role in regulating methane (CH 4 ) and nitrous oxide (N 2 O) emissions from irrigated rice field. Alternate wetting and drying (AWD) is a possible option, but there is limited information on its feasibility under local environmental conditions, especially for tropical region. We therefore carried out a 3-year experiment in a paddy field in Central Java, Indonesia to investigate the feasibility of AWD in terms of rice productivity, greenhouse gas (GHG) emission, and water use both in wet and dry seasons (WS and DS). The treatments of water management were (1) continuous flooding (CF), (2) flooding every when surface water level naturally declines to 15 cm below the soil surface (AWD), and (3) site-specific AWD with different criteria of soil drying (AWDS) established to find out the optimum for GHG emission reduction. Gas flux measurement was conducted by a static closed chamber method. Rice growth was generally normal and the grain yield did not significantly differ among the three treatments both in WS and DS. AWD and AWDS significantly reduced the total water use (irrigation + rainfall) as compared to CF. As expected, the seasonal total CH 4 emission was significantly reduced by AWD and AWDS. On average, the CH 4 emissions under AWD and AWDS were 35 and 38%, respectively, smaller than those under CF. It should be noted that AWD and AWDS were effective even in WS due partly to the field location on inland, upland area that facilitates the drainage. The seasonal total N 2 O emission did not significantly differ among the treatments. The results indicate that AWD is a promising option to reduce GHG emission, as well as water use without sacrificing rice productivity in this field.
ARTICLE HISTORY
Indirect emission of nitrous oxide (N 2 O), associated with nitrogen (N) leaching and runoff from agricultural lands is a major source of atmospheric N 2 O. Recent studies have shown that carbon dioxide (CO 2 ) and methane (CH 4 ) are also emitted via these pathways. We measured the concentrations of three dissolved greenhouse gases (GHGs) in the subsurface drainage from field lysimeter that had a shallow groundwater table. Aboveground fluxes of CH 4 and N 2 O were monitored using an automated closed-chamber system. The annual total emissions of dissolved and aboveground GHGs were compared among three cropping systems; paddy rice, soybean and wheat, and upland rice.The annual drainage in the paddy rice, the soybean and wheat, and the upland rice plots was 1435, 782, and 1010 mm yr À1 , respectively. Dissolved CO 2 emissions were highest in the paddy rice plots, and were equivalent to 1.05-1.16% of the carbon storage in the topsoil. Dissolved CH 4 emissions were also higher in the paddy rice plots, but were only 0.03-0.05% of the aboveground emissions. Dissolved N 2 O emissions were highest in the upland rice plots, where leached N was greatest due to small crop biomass. In the soybean and wheat plots, large crop biomass, due to double cropping, decreased the drainage volume, and thus decreased dissolved GHG emissions. Dissolved N 2 O emissions from both the soybean and wheat plots and the upland rice plots were equivalent to 50.3-67.3% of the aboveground emissions. The results indicate that crop type and rotation are important factors in determining dissolved GHG emissions in the drainage from a crop field.
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