Investigating of energy consumption and global warming potential of direct rice cultivation under rain and drip irrigation systems

Introduction
Excessive consumption of energy, especially fossil fuels, in the agricultural sector has led to the release of greenhouse gases and environmental pollutants, the most important of which are global warming and climate change. Analyzing energy flow and greenhouse gas emissions in agricultural ecosystems can help reduce environmental impacts by optimizing production operations.Comparing the energy efficiency of crops is one of the methods that can be used in prioritizing the cultivation of different crops in each region. In this study, the energy flow and global warming potential of direct rice cultivation method in dry bed under rain and drip irrigation methods were investigated.

Materials and methods
In this research, by interviewing different farmers (by completing a questionnaire in Gorgan city), required data was collected for machinery and consumables including seeds, fertilizers, fuel and poisons during growing seasen in the year of 2020. The reason for choosing these two methods is several similarities (including similar planting dates, agricultural operations and consumption of inputs) that exist in these two irrigation methods and the largest area of ​​dry rice cultivation is done by these two methods. The variety cultivated in these farms was Fajr. To estimate the amount of energy consumption in consumables such as fertilizers, pesticides, insecticides, the amount of energy per gram of effective substance was multiplied by the relevant coefficients and their specific weight. Other calculations of energy consumption and global warming potential for inputs and outputs used in agricultural production and operations for each of the methods were done using coefficients obtained from different sources.

Research findings
The results of this study showed that the average input energy under rain and drip irrigation systems was 27.8 and 28.6 GJ per hectare, respectively. The highest percentage of input energy in the fields under rain and drip irrigation systems with 27 and 26.4% respectively was related to the use of nitrogen fertilizer and the lowest percentage in both irrigation methods was related to the use of fungicides with 014 percent. The amount of direct input energy in rain and drip irrigation methods was 7.2 and 8.8 GJ per hectare, respectively, while the share of indirect input energy in both irrigation methods (rain and drip) was order was 20.6 and 19.8 GJ/ha). Energy efficiency in rain and drip irrigation method was calculated as 7.3 and 9.2, respectively.Global warming potential was obtained from fields under rain and drip irrigation systems (1582.4 and 1764.7 kg CO₂ per hectare, respectively).

Conclusion
The results of the comparison between the input energy and global warming potential showed that there is a direct relationship between the input energy and global warming potential. The results indicated that the largest share of input energy in both irrigation methods was related to nitrogen fertilizer, irrigation and fuel consumption, which subsequently causes an increase in greenhouse gases. Based on the results of this research, it can be concluded that by reducing fuel consumption, increasing the efficiency of irrigation systems and optimal use of chemical fertilizers, energy consumption and greenhouse gas emissions can be reduced.