ارزیابی تاثیر مدیریت کود و آب بر عملکرد برنج و شدت گاز گلخانه ای در شرایط فصلی مختلف در آب و هوای گرمسیری Evaluation of fertilizer and water management effect on rice performance and greenhouse gas intensity in different seasonal weather of tropical climate

1. Introduction Increased greenhouse gas (GHG) emissions have increased the global warming potential (GWP) in all regions of the world, resulting in elevated global average temperature near the surface of the Earth. Methane (CH4) and nitrous oxide (N2O) are two important greenhouse gases in agricultural soils that cause chemical changes in the atmosphere. Irrigated rice fields have the potential to emit both CH4 and N2O simultaneously, but the magnitude of these emissions depends on agricultural management systems (Linquist et al., 2012). Paddy field and irrigated lowland rice cultivation systems significantly affect the emissions of CH4 and N2O (Cai et al., 1997; Yao et al., 2012). Linquist et al. (2012) estimated that the aggregate emission of CH4 and N2O in rice production systems was approximately four times higher than that of either upland wheat or maize systems. Agricultural practices have the potential to mitigate GHG emissions. The most effective management practices to mitigate GHG emission for irrigated rice paddies, particularly to reduce CH4 emissions, are water management practices during the rice-growing season (Trost et al., 2013; Yan et al., 2005). Appropriate water management strategies can substantially decrease GHG emissions (Feng et al., 2013). The most effective practices include midseason drainage and intermittent irrigation, which aims to improve rice growth by controlling surplus tillering and supplying rice roots with molecular oxygen (O2) to prevent sulfide toxicity (Kanno et al., 1997). Another practice is alternate wetting and drying (AWD), which conserves water and reduces GHG emissions in rice cultivation while maintaining yields; AWD was developed by the International Rice Research Institute (IRRI) (Bouman et al., 2007). The AWD practice in Southeast Asia was adopted in rice cultivation during the dry season (DS) instead of the wet season (WS) because of water shortage in a rice–rice double cropping system. WS rainfall is typically sufficient to sustain rice crops, whereas additional irrigation is required for viable rice crops in the DS. The DS generally produces higher emissions than the WS due to high plant biomass (Sass et al., 1990; Ziska et al., 1998).