انرژی غیرمستقیم

Energy flow is one of the most important issues in agroecology. The amount of energy that is consumed in different agroecosystems not only depends on the type of crop but also on the material and methods that is used in its production. Potato plants are one of the most important crops that is produced in Torbat Heidarieh region, Khorasan Razavi Province of Iran. Different irrigation methods influence the energy consumption and production. Thus, the aim of this study is to compare energy efficiency of potato with different irrigation methods.

In order to evaluate and compare the efficiency of energy consumption in potato production based furrow,  sprinkle and drip irrigation methods, a study was carried out at 11 fields in the Jolgeh Rokh Torbat Heidarieh region in 2013- 2014 . The comparison was performed using a completel randomized, unbalanced design. In which the type of irrigation system was considered as the treatment and fields that were matched to each irrigation system as a replication. The studied traits included the amount of input and output energy, the equivalent energy of all inputs, and energy use efficiency, net energy, energy production and specific energy.                                                                                                                                         

The largest amount of energy consumed by the human labor was due to furrow irrigation. The highest average of fossil fuel consumption was due to furrow irrigation method followed by sprinkle and drip irrigation. The amount of electricity consumed in the drip irrigation method had the highest amount compared to the other two methods. The most energy consumed by nitrogen fertilizers was related to furrow irrigation method, and the methods of irrigation of droplets and sprinklers in this regard were ranked in the following order, respectively. The amount of energy consumed by phosphorus fertilizers in irrigation was the least amount of droplets. This amount was in sprinkler irrigation and furrow irrigation respectively, although there was no significant difference between the two methods. The energy of using potassium fertilizers in the highest irrigation system was similar to the other irrigation systems. The energy consumption of herbicides was highest in drip methods and furrow irrigation was in the next category. Energy consumption of machinery was highest in sprinkler irrigation method. In the recent method, energy consumption of machinery was about half of the energy consumption of the total inputs. Indirect energy consumption for drip irrigation system was 6868 MJ.ha-1 and in sprinkle irrigation 2756 MJ.ha-1. Energy produced by seed was highest in drip irrigation method and the lowest in sprinkle irrigation. The total amount of input and output energy in sprinkler irrigation method was the highest (106674.24 and 162000 MJ.ha-1), followed by drip irrigation (97807.82 and 151000 MJ.ha-1) and furrow irrigation (92539.61 and 139000 MJ.ha-1) were placed in the following categories. The energy use efficiency of the drip irrigation method 1.6 was more than other irrigation methods. Production energy in terms of amount of drip and furrow irrigation was the highest 0.44 and in sprinkle irrigation 0.41. Net energy was the highest in sprinkler irrigation (53392.18 MJ.ha-1) and the lowest in furrow irrigation (46660.38 MJ.ha-1). Production energy was highest in drip and furrow irrigation (0.44 and 0.43) and lowest in sprinkle irrigation (0.41). The specific energy in furrow irrigation (2.36) was higher than the other methods and in the drip irrigation with the lowest (2.32).                                                                               

According to the results of the present research, in spite of higher yield of potatoes under sprinkle and drip irrigation systems, there were not significant differences among the energy indices; energy efficiency, energy productivity, and special energy; of three systems. This was due to more total input energy in the sprinkle and drip systems. Because the machinery and installations energy input in furrow irrigation system were lower than two other systems.

Cheap and plentiful fossil energy causes human’s life welfare to improve and increase food production, but today, major problems have been created in fossil fuels. These problems include: scarcity of fossil fuels for future generations, increase in energy prices, and the most importantly, greenhouse gas emissions (such as carbon dioxide, nitrous oxide and methane) from the use of fossil fuels to the atmosphere.
Energy productivity is one of the most important factors for sustainable agriculture. The use of fossil fuels and chemical fertilizers are threatening the environment. The comparing energy consumption by crops is one of the ways to prioritize various agronomic productions in each area.
To conduct this study, two crops (silage corn and sorghum) were selected. The reason for this choosing was the numerous similarities of these two plants (including similar planting date, farm operation and consumptions). Accordingly interviews with various farmers (15 and 20 farmers was selected to filling in questionnaire for silage corn and sorghum in Gorgan suburb, respectively) required data of machinery and consumables inputs, including seeds, fertilizers, fuel and pesticides were collected.
To estimate the energy consumption of inputs such as fertilizers, pesticides, insecticides amount of energy per gram of active ingredient was multiplied in related coefficients and their density. Other input and output calculations of energy used in production and field operations for each of the methods was calculated using coefficients obtained from various references. After that it was analyzed in three parts, fuel consumption, and consumed fuel and global warming potential based on the carbon dioxide equivalent.
The most input energy in silage corn and silage sorghum was 23.2 and 24.7 percent respectively based on fertilizer consumption. Also, the highest direct input energy in corn silage and forage sorghum was 27.3 and 31.4 respectively, related to fuel. The output energy in silage sorghum was more than silage corn, such that the output energy in forage sorghum was 315.56 GJ/ha more than silage corn. The main reason for this observation was the high yield of forage sorghum fields. The ratio of output to input energy in spring corn and forage sorghum were calculated 4.3 and 15.6 respectively. In other words, energy efficiency was higher in silage sorghum farms and this was due to the higher yield and lower inputs in the crop. The energy efficiency in corn silage was less than silage sorghum, the reason was low yield per unit area (12.500 kg of dry matter per hectare) and more energy input in silage corn farms. In both crop the highest global warming potential (GWP) was related to nitrogen fertilizer and fuel consumption. The highest and the lowest global warming potential respectively observed in silage corn and forage sorghum (with 1845.9 kg CO2/ha and 1729 kg CO2/ha). Consumption of agricultural inputs such as herbicides and pesticides was lower in silage sorghum farms. In both the least amount of greenhouse gas emissions related to fertilizer potassium was 39.5 kg CO2 equivalent.
The energy input and greenhouse gas emissions in spring corn were higher than forage sorghum due to more agricultural operations (such as herbicides and pesticides consumption), in this respect the cultivation of forage sorghum had minimal environmental impacts. In both crops the consumption of fuel and fertilizer constitute the high percentage of energy consumption and greenhouse gas emissions. Therefore, the use of devices that reduce fuel consumption is recommended, also need for research and investigation on crop rotation and nitrogen fixing plants was revealed. Comparison of the global warming potential (GWP) based on the unit weight yield per hectare of silage sorghum and silage corn showed that there are very significant differences between the two crops, so that global warming potential of the spring corn planting was 12.1 times higher than that of silage sorghum.