A comparative study of irrigation techniques for energy flow and greenhouse gas (GHG) emissions in wheat agroecosystems under contrasting environments in south of Iran

摘要

The agriculture sector in general and irrigation, in particular, can be a major emitter of greenhouse gases and can contribute to global climate change. Most studies dealing with the evaluation of irrigation planning worldwide have not taken this aspect of irrigation into account, while it is of paramount importance to attach environmental assessment of irrigation programs, in particular their impacts on greenhouse gas (GHG) emissions, to any policymaking and development efforts for planning irrigation strategies. The present study aims at describing the energy flow and GHG emissions in wheat agroecosystems under different irrigation systems in Southern Iran. Three irrigation systems, including furrow irrigation (FI), sprinkler irrigation (SI) and drip irrigation (DI) were studied in two contrasting environments with regard to pedo-climatic conditions. The results indicated that environment and irrigation system remarkably affected energy input, energy output and GHG emissions. The highest energy input was observed in DI (75.59 GJ ha(-1)) followed by FI (62.67 GJ ha(-1)) and SI systems (49.81 GJ ha(-1)). In DI system, the main energy consumption item belonged to polyethylene (PE) pipelines (about one- third of total input energy), while in other two irrigation systems diesel fuel consumption was the main component of energy consumption (32.77% and 36.2% in FI and SI systems, respectively). Changing the irrigation method from furrow to sprinkler and drip reduced water requirement by 43.7% and 39.6% and electricity consumption by 36.5% and 25.2%, respectively. The highest output energy (averaged over both environments) was observed in DI system (154.52 GJ ha(-1)), although it was not considerably different from SI system (151.41 GJ ha(-1)). The environment that had more suitable environmental condition and longer growing season for wheat growth showed higher output energy (167.87 GJ ha(-1)) compared to a less favorable environment (125.57 GJ ha(-1)). Pressurized irrigation systems had priority over traditional irrigation practices in terms of energy efficiencies and global warming potential (GWP) and were more environment-friendly. SI system had the highest net energy and energy use efficiency (3.02 and 0.111 kg MJ(-)(1), respectively). Averaged over both environments, the highest direct energy, indirect energy, renewable energy and non-renewable energy consumptions were observed in FI (34.47 GJ ha(-1)), DI (49.26 GJ ha(-1)), FI (8.91 GJ ha(-1)) and DI (68.48 GJ ha(-1)) systems, respectively. Our results indicated that the total GWP on a hectare basis could be decreased by changing the irrigation system from FI (10886.1 kg CO(2)eq ha(-1)) to pressurized irrigation systems (8945.7 kg CO(2)eq ha(-1) and 8049.7 kg CO(2)eq ha(-1) for DI and SI system, respectively). In contrast to previous studies (which have mainly focused on methods of irrigation other than sprinkler), sprinkler irrigation was superior in these regards when compared to drip irrigation. The present study helps decision-makers to grasp a better understanding of the linkage between various methods of irrigation and the subsequent impact on GHG emissions, which is a prerequisite to any planning effort for future irrigation strategies at national and international levels.