Evaluating the Sustainability Indices for Rapeseed (Brassica napus L.) Production Systems Using Emergy Analysis (Case Study: Kalaleh County, Golestan province)

Sustainability in agriculture at regional scale is about balancing food security with maintaining environmental health. Therefore, agricultural operations are sustainable when they maintain the health of the environment, the interaction between plant and animal production, social acceptance and economic benefits (Kumaraswamy, 2012). Excessive use of environmental resources and excessive consumption of chemicals in agriculture have caused environmental problems and reduced sustainability (Quintero-Angel & Gonzales-Acevedo, 2018). Therefore, it is necessary to study the patterns of energy consumption and efficient use of energy in agriculture, which is one of the basic principles in sustainable agriculture. Emergy analysis, as suitable tool for this purpose, is used in the various ecosystems (Odum, 2000; Brown & Ulgiati, 2004). Emergy analysis is able to determine the degree of sustainability of connected ecological and economic systems. Emergy indices are effective tools for integrating ecological-economic systems and make it possible to measure and compare all aspects of these ecosystems (Patterson et al., 2017). The purpose of this study was to evaluate sustainability indices for rapeseed (Brassica napus L.) production systems using emergy indices and provide suggestions for sustainable product of the crop in Kalaleh county. 

In this study, production systems of rapeseed were evaluated using emergy sustainability indices in Kalaleh County (Golestan province), during the period of 2018-2019. For this purpose, 50 rapeseed fields were selected as Cochran equation. First, the spatial and temporal boundaries of the system were defined (Odum, 1996; Odum, 2000) and resources were divided into four categories: renewable environmental resources, nonrenewable environmental resources, purchased renewable resources and purchased nonrenewable resources (Amiri et al., 2019). Emergy flow for each input was multiplied by their transformities in joules and grammes (Odum, 2000). Finally, emergy indices such as renewability, emergy yield ratio, emergy self-support ratio, environmental loading ratio and emergy sustainability index were calculated and evaluated in rapeseed production systems. 

Total emergy input for the rapeseed production was estimated as 1.64E+16 sej ha-1 year-1. In rapeseed production, dependence on environmental and nonrenewable inputs was higher than purchased and renewable inputs. Soil erosion emergy was the largest emergy inputs of the total in rapeseed production system with share of 47.31%. Also, fossil fuel emergy was the largest emergy inputs of the purchased with share of 38.41%. In this research, we calculated the transformity equal to 2.59E+05 sej j-1, specific emergy equal to 7.33E+09 sej g-1, emergy renewability equal to 8.16%, emergy yield ratio equal to 2.17 and emergy investment ratio equal to 0.85. Also, emergy self-support ratio, standard environmental loading ratio, modified environmental loading ratio, standard emergy sustainability index, and modified emergy sustainability index were estimated 0.54, 13.81, 11.27, 0.16 and 0.19, respectively. Despite the higher contribution of environmental resources in the rapeseed production system, the high share of soil erosion as a non-renewable input along with the unreasonable consumption of some nonrenewable purchased inputs, such as fossil fuels, led to a decrease in renewability and an increase in environmental load. Based on evaluation of emergy indices, rapeseed ecosystem had the high production efficiency and resource consumption efficiency and it had the great potential to increase economic productivity. However, rapeseed production in Kalaleh county had low environmental and economic sustainability. The implementation of conservation tillage methods and the modernization of machinery can contribute to a reduction in the consumption of nonrenewable and economic inputs in rapeseed production ecosystems. This reduction in input consumption not only alleviates environmental pressure but also enhances sustainability. By prioritizing the use of renewable environmental inputs and minimizing the utilization of nonrenewable and economic inputs, the emergy sustainability index can be improved.

The rapeseed ecosystems exhibited high production efficiency and resource consumption efficiency, along with significant potential for increasing economic productivity. However, despite the substantial contribution of environmental resources in these systems, the prevalence of soil erosion as a significant portion of the total emergy input resulted in a decline in renewability, an escalation in environmental burden, and ultimately a decrease in sustainability. It appears that enhancing management methods to minimize the consumption of nonrenewable and economic resources would be effective in bolstering the environmental and economic sustainability of rapeseed farming ecosystems in Kalaleh county.