Greenhouse gas emissions from conventional and organic cropping systems in Spain. I. Herbaceous crops

Abstract

Agriculture is a major driver of climate change, particularly when all indirect emission sources are accounted for. Mitigation options targeted on one process are often proposed, ignoring their secondary effects on the overall greenhouse gas balance. Integrative methodologies such as life cycle assessment (LCA) are often applied without adjusting emission factors to specific site characteristics. Here, we used LCA to calculate the global warming potential of 38 pairs of organic and conventional herbaceous cropping systems and products in Spain. Crop products included rainfed cereals and pulses, rice, open-air vegetables, and greenhouse vegetables. We used data from farmer interviews and published conversion factors. Our results show that the emission balances were dominated by fossil fuel use rather than by direct field emissions. Organic management reduced crop emissions by 36-65 %, with the exception of rice showing an increase of 8 % due to methane generation. Productbased emissions of organic crops were also lower by 30 % on average, except for rice.

Conservation Agriculture practices reduce the global warming potential of rainfed low N input semi-arid agriculture

“…As reported by previous studies (e.g. Aguilera et al, 2013aAguilera et al, , 2015Plaza-Bonilla et al, 2015;Abdalla et al, 2015), NT significantly increased the SOC content compared with CT (Table 3). This occurred despite the higher SOC content in the 15-30 cm layer in CT (as opposed to NT/MT), as suggested by Baker et al (2007).…”

“…The 'ASOC was the main cause of the differences between tillage and crop treatments (Fig. 4), while C02-eq emissions from inputs and operations were significant but less important, a finding which is consistent with Aguilera et al (2015) and Guardia et al (2016). Therefore, our results indicate that management practices which promote an increase in C stocks (e.g.…”

Greenhouse gas emissions in conservation and conventional agriculture systems under rainfed mediterranean agro-ecosystem

“…No tillage system increased significantly C sequestration, which caused a significant decrease in Net-GWP in comparison with other tillage systems (MT and CT), as CO 2 -eq emissions for inputs and operations in NT system were lowest than MT/CT and less important due to a reduction in the number of labour operations. This finding was in agreement with Guardia et al (2016a) and Aguilera et al (2015). Results from a recent meta-analysis (Abdalla et al, 2015) concluded that NT system significantly reduced CO 2 -eq emissions and increased soil C stock particularly under arid and sandy soil conditions with low SOC content, supporting our findings.…”

“…The 'ΔSOC' was the main cause of the differences between tillage and crop treatments (Fig. 5.4), while CO 2 -eq emissions from inputs and operations were significant but less important, a finding which is consistent with Aguilera et al (2015) and Guardia et al (2016a). Therefore, our results indicate that management practices which promote an increase in C stocks (e.g.…”

“…An adequate assessment of the effects of tillage and crop rotation on GHG balance require to estimate the global warming potential basis (CO 2 -equivalent emissions), particularly due to the relatively low weight of N 2 O losses in Mediterranean areas (Aguilera et al, 2015) in comparison to other climatic areas (Rees et al, 2013b), and the capacity of conservation tillage as a practice to mitigate GHG emissions through soil C sequestration. Moreover, the best way to evaluate if the conservation tillage can increase C stocks and its relative contribution to the GWP is through long-term experiments.…”