Greenhouse gas emissions and financial analysis of rice paddy production scenarios in northern Iran

Adopting environmentally and economically sustainable rice production systems is essential to achieve better results in terms of yield, financial profitability and eco-efficiency. This study compares the GHG emissions and the financial analysis (based on both costs and gross return and some financial indicators) in eight rice paddy production systems in northern Iran, under the combination of three factors: two water irrigation sources (groundwater by wells and surface water by rivers), two groups of rice cultivars (low-and high-yielding), and two transplanting methods (traditional and mechanical). The average total GHG emissions were 117.6% higher in groundwater than surface water systems, 12.4% higher in mechanical than traditional systems and 20.8% higher in high-yielding than low-yielding rice cultivars. The highest GHG share in groundwater systems was as average for electricity (52.2%), while in surface water systems was diesel fuel (51.0%). The best option for higher and more profitable yields among the studied rice production scenarios was the use of the surface water source for irrigation that, however, implies a higher water use. Considering irrigation water productivity, traditional cultivation and high-yielding rice cultivars coupled with irrigation from the surface water source could be preferred. In terms of yield profitability, that is summarized by the benefit/cost ratio and the productivity index, the best combination is irrigation with surface water, mechanical cultivation and high-yielding cultivars (1.99 and 1.36 kg US$-1, respectively). However, net return in relation to global warming potential (GWP) indicated that irrigation with surface water source systems, traditional cultivation and high-yielding rice cultivars proved more eco-efficient. Therefore, policies should give priority to surface water use and high-yielding cultivation.