Comparing organic and conventional olive groves relative to energy use and greenhouse gas emissions associated with the cultivation of two varieties

Highlights: • Multivariate statistical methods were applied to evaluate 88 olive groves. • Three main groups (high, medium, low energy inputs) were revealed. • The grouping was based on management practices and geographical location. • Best farming practices regulate the balance between environment and agriculture. - Abstract: Organic farming is applied in olive groves in Lesvos Island the last 20 years. "Kolovi" and "Adramitiani", two dominant varieties are cultivated. Since there is limited research for energy inputs in olive groves, 62 conventional and 26 organic farms were selected during 2011–2013 in order to (a) determine the differences in energy flow among farming systems and varieties, (b) group olive groves based on energy flow indicators, (c) compare the CO₂-equivalent emissions among farming systems and varieties. A combination of univariate and multivariate statistical methods was applied. Hierarchical Cluster Analysis (HCA) revealed three farm groups, all consisted of conventional and/or organic olive groves and included both varieties. Group 1 had the lowest energy inputs, while Group 3 the highest. Fuels and transportation, as energy inputs, had the highest contribution in farms' grouping. A large number of external variables was studied, most of which (fruit production, olive oil production, pomace production, shoot production, olive oil energy production, pomace energy production, shoot energy production, total energy inputs, total energy outputs, intensity, energy efficiency, and energy productivity) had statistically significant differences among the three Groups. Management practices along with geographical location could be a reasonable explanation for the differences between the groups of studied olive groves. Group 3 had the highest non-renewable energy inputs (14,683.5 MJ ha⁻¹) and consumption (2.4 MJ kg⁻¹) and gas emissions (1.27 Mg ha⁻¹ CO₂, 0.17 kg ha⁻¹ CH₄, and 10.31 g ha⁻¹ N₂O). Group 2 had the highest renewable energy inputs (7065.8 MJ ha⁻¹) and consumption (0.9 MJ kg⁻¹), and low CO₂-equivalent per fruit production (0.12 kg kg⁻¹). The above mentioned results show that best management farming practices introduce the use of renewable energy inputs and lead to lower gas emissions