Evaluation of energy indices and its impact on global warming potential for potato production: a case study, Golestan province

Nowadays, the agricultural sector is largely dependent on energy consumption due to response to increasing food requirements for the growing population of the earth and providing adequate and appropriate foods. Recently evaluation of input, output and global warming potential (GWP) have been applied in sciences of agriculture. Although, further crops production without considering the environmental issues and lack of evaluation the energy indices, do not seem logical. On the other hand, high price and limitation of energy resources used in the agricultural products is also other important reasons for energy analysis in agricultural ecosystems. Energy shortage and importance of agriculture in feeding the world oriented many studies to evaluating the quantities of fuel and energy in different products and different sites. Different quantities of energy are consumed per each hectare of potato production based on different inputs such as fertilizers, fossil fuels, electricity, seeds, pesticides and machinery that will lead to greenhouse gases emission including CO2, N2O and CH4. Increasing the concentration of such gases in the atmosphere can cause global warming. So serious attention to reducing energy consumption and greenhouse gas emissions seems to be necessary. For this purpose, fuel and energy consumption and greenhouse gas emissions were investigated in all potato fields in Golestan province. Finally, some strategies were presented for their consumption reduction. In order to determine the fuel and energy consumption and greenhouse gas emissions and how to reduce it, 95 potato fields in Golestan province were investigated through systematic random sampling. The amount of inputs, including fossil fuels was recorded and energy analysis was done based on the consumed inputs. Also, the greenhouse gases emission of carbon dioxide, nitrous oxide and methane derived from energy consumption for agricultural inputs and agronomic operations was calculated. Finally, energy efficiency, energy productivity, specific energy, net energy and total GWP, GWP in area unit, product weights, input energy and output energy were also calculated.  Results showed that total input and output energy were 30.8 and 79.2 GJ per hectare, respectively. In a study, the total input energy in potato fields in Ardabil province was 81.6 and 102.4 GJ.ha-1, respectively (Mohammadi et al., 2008). Also the most direct input energy from fuel in potato farms was 14.1 percent and the highest indirect input energy farms was 27 percent that related to fertilizers. The ratio of output to input energy, energy productivity and specific energy in potato farms were calculated 2.5, 0.71 and 1.4 respectively. Energy productivity in potato fields in Kurdistan province for commercial and traditional fields were calculated 0.38 and 0.39 respectively, which shows that energy productivity in Golestan province is higher than Kurdistan province.
The GWP observed in potato farms was 1350.2 (kg CO2.ha-1). For potato farms the highest GWP was related to nitrogen fertilizer and fuel consumption. Results indicated that consumption of fuel and fertilizers constitute the high percent of energy consumption and greenhouse gas emissions. Based on this study results, the use of devices that reduce fuel consumption is recommended, also need for research on crop rotation and nitrogen fixation plants in rotation were revealed. The use of Rhizobia bacteria and biological nitrogen fixation in rotation and organic fertilizers can be effective in reducing the use of nitrogen fertilizers and consequently, energy consumption and GHG emission. On the other hand, it can be said that increasing the yield along with reducing inputs consumption, especially fossil fuels and nitrogen fertilizer, can be effective in increasing energy efficiency.