Life cycle assessment of Iranian Rice cultivars production affected by NPK using management

The aim of present study was to investigate life cycle assessment of Iranian rice cultivars production affected by NPK chemical fertilizers using management. The experiment was conducted in farms located in Mazandaran province, Sari, during 2017 and 2018. The experiment was performed as split plot in a randomized complete block design with four replications. The different doses of fertilizer treatments at five levels including F1: 250 kg N ha-1 + 150 kg P ha-1 + 150 kg K ha-1 (N250P150K150), F2: 200 kg N ha-1 + 100 kg P ha-1 + 100 kg K ha-1 (N200P100K100), F3: 150 kg N ha-1 + 75 kg P ha-1 + 75 kg K ha-1 (N150P75K75), F4: 100 kg N ha-1 + 50 kg P ha-1 + 50 kg K ha-1 (N100P50K50), and F5: Control or no application of fertilizer treatments (N0P0K0) as main plot and local rice cultivars at two levels of Sang Tarom and Tarom Hashemi were considered as sub-plots. The results showed that an average amount of cumulative energy demand and cumulative exergy demand was 11549.78 and 13443.08 MJ, respectively that with increase of nitrogen consumption, both indices showed a decreasing trend. The average ecological footprint was 1190.80 m2a which CO2 emissions had shown the highest effect on the ecological footprint. The average of the impact categories of abiotic depletion was equals 12.44 kg Sb eq, acidification (3.15 kg SO2 eq), eutrophiction (2.33 kg PO4 eq), malodorous air (7295733 m3 air), freshwater sediment ecotoxicity (75.79 kg 1,4 DB eq), marine sediment ecotoxicity (116.11 kg 1,4 DB eq) that all of which decreased with increasing nitrogen consumption. The average global warming potential (GWP) 20a and GWP 500a were 399.20 and 382.97 kg CO2 eq, respectively. Two indicators of human toxicity and terrestrial ecotoxicity in the three periods of 20, 100 and 500 years shows increasing amounts equal 0.42% and 140.70% during 20a to 500a, respectively. All pollutants released into the air and the water demonstrated a decreasing trend with increasing nitrogen amounts. The emission of nitrate into soil, metals into the soil, and chemical oxygen demand showed a decreasing trend with increasing nitrogen levels. By group comparing between different levels of nitrogen at splitting levels, it can be stated that the main cause of variations in the amount of pollutants was the higher output (yield) compared to inputs. Indeed, nitrogen uptake in four developmental stages has resulted in maximum plant use, resulting in increased yield and emission reduction per unit area. Therefore, reducing the emission of pollutants by increasing nitrogen consumption can be due to increase of yield. According to the findings of this study, the application of N150P75K75 treatment is a better option to improving the yield of rice cultivars along with a decrease in chemical fertilizers and subsequent reduced fertilizers costs and environmental damages.