Estimation of net carbon sequestration potential of citrus under different management systems using the life cycle approach
A study was conducted to determine the net carbon sequestration potential of citrus to mitigate climate change. Perennial crops such as citrus have the potential to absorb and sequester carbon dioxide from the atmosphere, save for the carbon released back through the application of agro-chemical inputs and use of fossil fuels in running farm machinery in the management of citrus production systems. The main objective of this study was to determine the net carbon sequestration potential of sweet orange (Citrus sinensis (L.) Osbeck), orchards under different management systems. The biomass densities and the carbon stocks (carbon sequestration) of citrus trees were determined and orchard carbon emissions estimated and converted to carbon equivalents. Carbon stocks were estimated using standard carbon inventory methods. Allometric equations were used to transform citrus tree diameter into biomass. Farmers from the ten fields used in this study analysis were asked over input application history to the orchards. Life cycle assessment based carbon foot-printing methods were used to determine citrus orchard carbon emissions. The carbon emission factors were calculated in conformity with PAS 2050. Results obtained showed that citrus trees carbon sequestration in biomass ranged from 23.99 Mg CO2e/ha for young trees to 109 Mg CO2e/ha for mature trees. The carbon emissions from fertilizer, pesticides, water, electricity and fuels production, delivery and use was estimated to range from 0.22 Mg CO2e/ha for low input orchards to 4.28 Mg CO2e/ha for high input management. The net carbon sequestration potential were calculated to be between 15.35 Mg CO2 eq/ha and 95.14 Mg CO2 eq/ha for input application ranging from two years to 16 years. Continous application of agro-chemical inputs beyond the optimum fruit bearing age could result in net carbon emissions and is not justified. The carbon sequestered (biomass accumulation) in trees was observed to increase with age (r2 = 0.55) and was not seen to increase directly with the increase in carbon emissions (r2 = 0.44), but it was apparent that increase in inputs especially fertilizer, pesticides and electricity resulted in increased greenhouse gas emissions. An opportunity exist in the growing of citrus especially with low input management and under well managed high input management systems to mitigate climate change by reducing CO2 from the atmosphere through carbon sequestration in citrus biomass.
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