Life cycle assessment of rice production systems in different paddy field size levels in north of Iran.

Life cycle assessment (LCA) had proven to be an appropriate assessment tool for analysis of agro-ecosystems by identifying, quantifying, and evaluating the resources consumed and released into the environment. In order to assess the relevant environmental impacts of rice agro-ecosystems due to a specific process, using LCA method, two factors concerned with resource utilization and contaminant emissions were calculated in north of Iran during 2016 and 2017. All the management practices/inputs were monitored and recorded with the help of local experts without interference in farmer's practices. After preliminary evaluation, 100 paddy fields were selected in three planting systems (low input, conventional, and high input) which were predicted in two planting methods (semi-mechanized and traditional) in small, medium, and large farm size levels. Functional unit was considered as one ton paddy yield. The finding revealed that in both regions, all the impact categories and environmental pollutant were almost same and farmer's management practices are close to each other. Also, climate change (CC) in Amol and Rasht regions was 277.21 and 275.79 kg CO2 eq., respectively. The most CC, global warming potential (GWP 100a), and cumulative energy demand (CED) in both regions were observed in high-input system for semi-mechanized method. Furthermore, the result for the impact categories of terrestrial acidification (TA), freshwater eutrophication (FE), marine eutrophication (ME), agricultural land occupation (ALO), water depletion (WD), metal depletion (MD), and fossil depletion (FD) was similar to the CC, GWP, and CED where the highest amounts in both regions statistically went to high-input system, traditional planting method, and small farms. Moreover, in both regions, high-input and conventional systems emitted higher heavy metals than low-input system. Furthermore, the most heavy metal emission in the air was achieved in small farm, and medium farm got the next rank. Additionally, the high consumption of chemical inputs, such as fossil fuels and fertilizers, in the high-input and conventional systems led to an increase of environmental pollutant in comparison with low-input systems. Therefore, to increase the sustainability of agro-ecosystems, as well as to reduce the environmental impacts of pollutant, reforming the pattern of chemical input consumption and reducing the use of non-renewable energy sources are essential.