Energy Flow and Global Warming Potential in Direct Seeded and Transplantation of Rice under Different Irrigation Systems

Energy efficiency is one of the most important factors for sustainable agriculture. This study explored the energy consumption and global warming potential for puddled transplanted (PTR), un-puddled transplanted, and direct-seeded rice (Oryza sativa L.) (DSR) production systems under sprinkler, flood, and drip irrigation systems in Gorgan City fields, Golestan Province, Iran. According to the results, the average energy input and output for different irrigation systems in puddled transplanted treatment was higher than the other treatments, while the highest input and output energy was related to drip irrigation system (36366 and 249971 MJ.h-1). The highest energy consumption in different irrigation and cultivation systems was related to water and nitrogen fertilizer. The results also showed that energy use efficiency for different systems ranged from 5.05 to 7.35 kg.MJ-1. Energy use efficiency for pressurized irrigation systems was higher in puddled transplanted treatment and for flood irrigation systems was higher in un-puddled transplanted treatment. Also, the energy productivities of different treatments were between 0.1 to 0.24 kg.MJ-1, while the mean energy efficiencies of PTR and un-puddled transplanted treatments did not differ significantly and were more than DSR treatment. The specific energy and net energy for different treatments ranged from 4.29 to 10.2 MJkg-1 and 112784 to 213825 MJ.ha-1, respectively. The puddled transplanted treatment had the highest GWP for all irrigation systems. The largest share of GWP in rice cultivation was related to the use of nitrogen fertilizers, fuels, and machinery. The results of mean comparison of GWP per unit area, weight, input energy, and output energy showed that modern pressurized irrigation systems with un-puddled transplanted cultivation method (due to less input and a yield similar to PTR) can be a suitable method for rice cultivation to reduce energy consumption and global warming potential.