Life Cycle Assessment of NPK Fertilizers in Rice Production in Northern Iran

Life cycle assessment is an appropriate method to study the environmental impacts of producing a crop product throughout its cycle in a production system. Therefore, this research was conducted with the aim of evaluating the life cycle of paddy rice production under the effects of NPK fertilizers in Mazandaran province in northern Iran during 2017-2018. The different doses of nitrogen (N), phosphorus (P) and potassium (K) fertilizers were N250P150K150; N200P100K100; N150P75K75; N100P50K50, and control (N0P0K0). The results displayed that an average amount of cumulative energy demand and cumulative exergy demand was 11549.78 and 13443.08 MJ, respectively, that with increase of NPK consumption, both indices showed increasing trend. The average ecological footprint was 1190.80 m 2 a 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 enhanced with increasing NPK 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 enhancing trend with increasing NPK amounts. The emission of nitrate into soil, metals into the soil, and chemical oxygen demand showed enhancing trend with increasing NPK levels. Therefore, enhancing the emission of pollutants by increasing nitrogen consumption can be due to increase of yield.