عنوان مقاله [English]
Life cycle assessment (LCA) is a common tool for environmentally assessing various agricultural systems based on type and quantity of input consumption and emissions generated during the production. LCA is a method assessing the environmental performance of a given production. The method has been recently developed, providing some detailed information on how to mitigate environmental impacts as well as how to improve sustainability of existing agricultural systems. The aim of this study was to compare environmental impacts of four major crops of wheat, barley, seed water melon and alfalfa in Belherat Rural District of Neyshabur.
Materials and Methods
Using the LCA, four steps including goal definition and scoping, inventory analysis, life cycle impact assessment and integration and interpretation were taken. The system boundary contains production processes, chemical fertilizers, manure, herbicides, pesticides, irrigation (electricity), seed, fuel and other inputs. Functional unit was equivalent to one ton of economic yield, and all inputs, pollutants and average of economic yields were quantified based on one ton of economic yield. Global warming, acidification and aquatic and terrestrial eutrophication were considered as three important impact categories. The coefficient factors (CF) and weighting factors were used to calculate the environmental index (Ecox). A higher Ecox score represents a higher environmental impact.
Results and Discussion
Average economic yields of wheat, barley, seed water melon and alfalfa in Belherat Rural District of Neyshabur were 2.9, 3.1, 0.6 and 5.2 t.ha-1, respectively. The results showed that the global warming potential was a high environmental impact for all four crops including wheat (with 869.4 kg CO2-equiv. per one tonne economical yield), barley (with 694.3kg CO2-equiv. per one tonne economical yield), seed watermelon (with 4947.1 kg CO2-equiv. per one tonne economical yield) and alfalfa (with 2678.9 kg CO2-equiv. per one tonne economical yield), and the aquatic eutrophication potential was the lowest environmental impact such as wheat (with 3.08 kg PO4-equiv. per one tonne economical yield), barley (with 2.4 kg PO4-equiv. per one tonne economical yield), seed watermelon (with 11.1 kg PO4-equiv. per one tonne economical yield) and alfalfa (with 3.3 kg PO4-equiv. per one tonne economical yield), respectively. Among the three emissions of CO2, CH4 and N2O generating the global warming potential, the CO2 had the highest proportion. Fossil fuels and nitrogen-based fertilizers are the main sources of the CO2 emission. Among the four crops, seed water melon generated the highest amount of CO2 – almost five times more than other crops- due to the high use of chemical fertilizers. In general, between these four crops, seed watermelon (Ecox 1.14 per tonne of economical yield) and barley (Ecox 0.07 per tonne of economical yield) were created the highest and lowest environmental impacts, respectively. In producing seed watermelon, acidification potential – with 0.58 ECOX for one tonne of economic yield- was found as the highest environmental impact. This environmental impact of seed watermelon was seven times more than wheat and barely a long with about two times more than alfalfa. Among the three emissions of SO2, NH3 and NOX associated with creating acidification potential, NH3 comprised the largest proportion followed by SO2. Nitrogen- based fertilizers were found the major source of NH3 and SO2 emissions. The high environmental impact of seed watermelon is due to its low economic yield that does not cover its input consumption.
Considering the high contribution of the global warming potential to environmental impacts for these production systems in Belherat Rural District, it is recommended for the study area to manage the use of chemical fertilizers. It is also suggested that effective extension approaches such as conservation agriculture by reducing the consumption of fossil fuels, sustainable nutrition strategies aimed at replacing organic fertilizers with chemical fertilizers are provided to farmers to justify the harmful effects of pollutants on the environment.