Short-term soil carbon accumulation following sustainable practices: A Life Cycle Assessment and carbon credit analysis

A 4-year on-farm experiment with a biennial maize-soybean rotation was conducted to assess whether soil organic carbon (SOC) sequestration in agriculture could be incentivized through the introduction of carbon credits. Ten different plots were managed with treatments involving two types of organic fertilizers (five with compost and five with digestate), three cover-crop (CC) management strategies (weedy fallow control, fixed CC species, and a succession of CC species), and two irrigation strategies (rainfed and drip irrigation). Carbon sequestration rates, obtained from a previous work on the same experiment, detailed emission factors and activity data allowed estimation of the carbon footprint of the ten treatments. Data from market operators, service providers and official regional price lists were considered for economic evaluation. Five treatments gave net negative carbon dioxide equivalent (CO2eq) emissions (-5.77 to -1.59 MgCO2eq ha- 1), but reduced maize yields (mean value: 6.1 Mg ha- 1) compared to business as usual management with mineral fertilizers (mean value: 15.9 Mg ha- 1). This translates into carbon storage costs of up to 6247.77 Mg CO2eq- 1 , which exceeds the pricing on the voluntary carbon credit market (typically 10-20 Mg CO2eq- 1 ). The experiment has shown that increasing the SOC is not enough to produce carbon credits, and if produced, their price is not enough to cover the direct and indirect cost increase due to the carbon farming techniques adopted.