Evaluation of Global Warming and Toxicity Potentials from Chemical Fertilizer Application for Maize (Zea mays) Cultivation in Sri Lanka

Abstract

Maize is cultivated in Sri Lanka with an average yield of 3.52 tonne/ha which is adequate for 40% of the local demand. Cultivation yield improvement is essential to reduce future maize imports where chemical fertilizer application is a key factor at recommended rates, i.e., Urea: 350 kg/ha, Triple Super Phosphate: 100 kg/ha, and Muriate of Potash: 50 kg/ha. Chemical fertilizer application is associated with many environmental impacts due to direct/indirect emissions. A published study has not yet been reported in Sri Lanka with a proper evaluation of environmental emissions/associated impacts from fertilizer application for maize. Therefore, this study focused to evaluate the environmental emissions/associated impacts from fertilizer application for maize cultivation in Sri Lanka. The evaluation of emissions/impact potentials follows the life cycle approach which considered three main phases in the chemical fertilizer application process, such as chemical fertilizer production, fertilizer transportation, and fertilizer application. Emission calculations in fertilizer production and transportation phases were performed by obtaining emission factors from the Ecoinvent 3.0 database and necessary considerations. Airborne emissions (CO2, N2O, and NH3), groundwater leaching (heavy metals and nitrates), and soil deposition (heavy metals and phosphorous) due to the fertilizer application phase were calculated by using the standard Agri-footprint 4.0 methodology. Five impact potentials: climate change, human toxicity, terrestrial ecotoxicity, freshwater ecotoxicity, and marine ecotoxicity were evaluated and compared. Impact potentials were evaluated by using the ReCiPe world (H) V1.12 impact assessment method in the SimaPro Life Cycle Assessment software. Emission results showed that fertilizer production and transportation phases released lower pollutant levels, compared to the application phase. Impact results revealed that 92% of the climate change impact is contributed by the fertilizer application phase. Soil deposition from fertilizer application devotes the highest influences (above 98%) in human eco-toxicity and terrestrial eco-toxicity impacts. Freshwater eco-toxicity and marine eco toxicity impact results were 0.26 kg 1,4-dichlorobenzene eq and 0.22 kg 1,4-dichlorobenzene eq, respectively where groundwater leaching of heavy metals from fertilizer application contribute more than 80%. The findings from this study quantify the current levels of environmental impacts that support future decision making for environmentally-benign fertilizer application for maize cultivation in Sri Lanka.