Energy Flow and GHG Emissions in Major Field and Horticultural Crop Production Systems (Case Study: Sharif Abad Plain)

Introduction

Energy use patterns and Green House Gas (GHG) emissions from agro-ecosystems vary depending on the farming system; cropping pattern; crop season; the level of technology; the size of the population engaged in agriculture; nature and amount of chemical fertilizer; harvesting and threshing operations; and ultimately yield levels. Worldwide, about 5% of the total energy is used in agriculture section that is directly linked to GHGs emissions. According to reports, agricultural GHG emissions account for 10–12% of all anthropogenic GHG emissions. Therefore, efficient use of energy in farming systems is one of the most important implications for decreasing GHG emissions and mitigating global warming. A good understanding of energy flow and GHG emissions in agricultural production systems will help to optimize crop management practices thereby reducing the environmental footprints of energy inputs and promoting sustainable agriculture. This paper describes the energy use patterns and global warming potential for major crop production systems in Sharif Abad plain located in Qom province, Iran.

The study area relates to the Sharif Abad plain, located in the Qom province in north-central Iran. The data were collected through face-to-face interviews with 183 farmers in the year 2018. A questionnaire form was designed to collect the required information related to various input uses (electricity, biocides, fertilizers, etc.), operation times, crop yields, etc. The selection of producers was based on cropping patterns and the fact that the farmers should be representative of the selected crops. The simple random sampling method was used to determine the survey volume. The studied field crops and horticultural crops were wheat (Triticum aestivum. L.), barley (Hordeum vulgare L.), alfalfa (Medicago sativa L.), corn silage (Zea mays L.), cotton (Gossypium hirsutum L.), canola (Brassica napus L.), pistachio (Pistacia vera L.), pomegranate (Punica granatum L.) and grape (Vitis vinifera L.). In the present study, input and output values for perennial crops (alfalfa, pistachio, pomegranate, and grape) are represented as averages of the crop production cycle.

Results showed that, in terms of total energy input, alfalfa (94,906 MJ.ha−1), pomegranate (79,696 Mj.ha−1), and grape (78,984 MJ.ha−1) production systems were more energy-intensive than other crops. Among the studied crops, the highest values of output energy were related to alfalfa (218,567 MJ.ha−1), corn silage (171,810 MJ.ha−1) and wheat (123,430 MJ.ha−1) production systems, respectively. Also, it was observed that the highest values of energy use efficiency and specific energy were related to barley (2.9) and cotton (72.7 MJ.kg−1), respectively. Among all the studied crops, the highest values of global warming potential were calculated to be 12,294 kg CO2eq ha−1 for the alfalfa production system followed by the pomegranate (10,484 kg CO2eq ha−1) and grape (10,085 kg CO2eq ha−1) production systems. In the average of all crops, electric power accounted for the greatest GHG emissions, followed by diesel and nitrogen fertilizer. The proportion of direct energy (human labor, diesel fuel, water for irrigation, and electricity) in the studied crops was greater than the indirect form (seed, chemical fertilizer, manure, pesticides, and machinery). Also, the amount of non-renewable energy (electricity, chemical fertilizer, diesel fuel, pesticides, and machinery) in all the investigated crops was higher than of the renewable form (human labor, seed, water for irrigation and manure).

It can be inferred from the present study that in all of studied crops, notable part of energy used and GHG emissions were related to electric power. In the study area, entire electrical power is consumed in irrigation practices. Therefore, optimal management of water and nitrogen in crop production systems are the ways that should be considered to improve energy performance and decrease the GHG emissions. Also, management of plant nutrients by renewable resources like farmyard manure and green manures would increase rate of renewable energy.