Carbon footprint of hemp and sunflower oil in southern Italy: A case study

The proteoleaginous plants demand has seen significant growth, leading to an expansion of the sunflower (Helianthus annuus, L.) and industrial hemp (Cannabis sativa, L.) cultivation area in Italy. However, by-products obtained during seed oil extraction and agricultural residues are often unused due to the absence of a receptive market and nearby processing centers. The carbon footprint (CF) methodology was used to compare the two supply chains considering the soil incorporation of all crop residues and by-products. The boundary of the supply chains analyzed includes all the agricultural processes that occur during cultivation and the subsequent oil extraction phase. Furthermore, research explored the direct and indirect environmental benefits of incorporating by-products into the soil, in terms of reducing the need for mineral fertilizers to restore soil fertility due to the nutrients contained in the buried biomass, and the potential carbon sequestration achievable. Results show that 1 kg of sunflower and hemp oil release 4.49 kg CO2-eq and 23.34 kg CO2-eq, respectively. Agriculture represents the most impacting phase and, in particular, fertilization, tillage and harvest are responsible for high emissions. The different results between the two supply chains can be attributed mainly to yield and extraction efficiency. The use of by-products as amended in the soil (avoided fertilizers) contributes to a reduction of greenhouse gas (GHG) emissions by -0.53 kg CO2-eq and -7.87 kg CO2-eq per kg of sunflower and hemp oils, respectively. Additionally, the sequestration of carbon in biomass can result in a further reduction of -1.16 and -33.6 kg CO2eq per kg of sunflower and hemp oil, respectively. In summary, sunflower oil production emits 74 % less CO2 than hemp oil. However, if all crop biomass is buried, hemp has the potential to be more sustainable. This phenomenon depends on many factors such as soil type, climate, and farming practices. The study outcomes can aid policymakers, farmers, and the agribusiness to make informed decisions on promoting and expanding sustainable sunflower and hemp cultivation in Italy.