Effect of different agricultural practices on carbon emission and carbon stock in organic and conventional olive systems

Agricultural practices, particularly land use, inputs and soil management, have a significant impact on the carbon cycle. Good management of agricultural practices may reduce carbon emissions and increase soil carbon sequestration. In this context, organic agricultural practices may have a positive role in mitigating environmental burden. Organic olive cultivation is increasing globally, particularly in Italy, which is ranked first worldwide for both organic olive production and cultivated area. The aim of the present study was to assess the effects of agricultural practices in organic and conventional olive systems on global warming potential (GWP) from a life cycle perspective and to identify the hot spots in each system. The impacts assessed were associated with the efficiency of both systems at sequestering soil in order to calculate the net carbon flux. There was a higher environmental impact on GWP in the organic system because of higher global greenhouse gas (GHG) emissions resulting from manure fertilisation rather than the synthetic foliar fertilisers used in the conventional system. However, manure was the main reason behind the higher soil organic carbon (SOC) content and soil carbon sequestration in the organic system. Fertilisation activity was the main contributor to carbon emissions, accounting for approximately 80% of total emissions in the organic system and 45% in the conventional system. Conversely, given the similarity of other factors (land use, residues management, soil cover) that may affect soil carbon content, manure was the primary contributor to increased SOC in the organic system, resulting in a higher efficiency of carbon sequestration in the soil following the addition of soil organic matter. The contribution of the manure to increased SOC compensated for the higher carbon emission from the organic system, resulting in higher negative net carbon flux in the organic versus the conventional system (-1.7 vs -0.52 t C ha(-1) year(-)1, respectively) and higher efficiency of CO2 mitigation in the organic system.