Identifying eco-efficient year-round crop combinations for rooftop greenhouse agriculture

Abstract

Purpose: Rooftop greenhouses (RTGs) are agricultural systems that can reduce the food supply chain by producing vegetables in unused urban spaces. However, to date, environmental assessments of RTGs have only focused on specific crops, without considering more long-term impacts resulting from seasonality, combinations of crops, and non-operational time. We analyze the production of an RTG over 5 years to determine the crop combinations that minimize yearly environmental impacts while diversifying the food supply. Methods: The system study consists of an integrated RTG (i-RTG) with hydroponic irrigation in Barcelona (Mediterranean climate). By using life cycle assessment (LCA) with the ReCiPe hierarchical midpoint method, we evaluated the environmental performance of 25 different crop cycles and seven species cultivated during the 2015-2018 period. Two functional units are used: 1 kg of edible fresh production and 1 unit of economic value (€) in the wholesale market. The system boundaries consider two subsystems: infrastructure (greenhouse structure, rainwater harvesting system and auxiliary equipment) and operational (fertilizers and their emissions into water and substrate). In addition, we perform an eco-efficiency analysis, considering the carbon footprint of the crop cycles and their value at the wholesale market during their harvesting periods. Results and discussion: Spring tomato cycles exerted the lowest impacts in all categories, considering both functional units, due to the high yields obtained. In contrast, spinach and arugula had the highest impacts. Regarding relative impact, the greenhouse structure presented a large impact, while fertilizer production had notable relative contributions in tomato cycles. Moreover, nitrogen and phosphorus emissions from fertigation exerted the majority of the impact on freshwater and marine eutrophication. Growing two consecutive tomato cycles was demonstrated to be the best alternative with the functional unit of yield (0.49 kg CO 2 eq./kg), whereas a long spring tomato cycle combined with bean and lettuce cycles in the autumn was the best scenario with the functional unit of economic value (0.70 kg CO 2 eq./€). Conclusions:The present study has demonstrated that increasing the diversity of the system leads to better environmental performance of greenhouse urban agriculture if suitable crops are selected for the winter season. The functional unit involving the economic value and the eco-efficiency analysis were useful to demonstrate the capability of the framing system to produce added-value vegetables under harsher conditions, while categorizing and classifying the crops to select the most suitable based on economic and environmental parameters.

More than the sum of the parts: System analysis of the usability of roofs in housing estates

“…We calculated the human activity budget needed to maintain the new rooftop uses as well as the potential flow production (savings) for the roof mosaic scenarios (decentralized systems) for the same flows included in the end‐use matrix. The HA for rooftop use was retrieved from real data for the Barcelona region for open‐air farming (OAF) (11.55 h/m 2 /year) (Boneta et al., 2019) and rooftop greenhouses (RTGs) (6.72 h/m 2 /year) (Rufí‐Salís et al., 2020) and for companies specialized in the implementation and maintenance of remaining systems (PV) (2.77 E‐05 h/m 2 /year), green roofs (GRs) (0.24 h/m 2 /year), and rainwater harvesting (RWH) (44 h/tank/year). For GRs, we only consider the energy savings resulting from implementing them on roofs founded on 2% of energy savings (Sailor, 2008), and we also explore the increase of green spaces (m 2 /inhabitant) generated by new rooftop uses.…”

“…The most suitable systems for this area were, however, identified as PV panels, GRs, OAF, RTGs, and RWH. Vegetable crop yield was determined from real data of hydroponic crops (soilless system with perlite substrate) for the Barcelona region (10.6 kg/m 2 /year for OAF (Boneta et al., 2019) and 14.16 kg/m 2 /year for RTGs (Rufí‐Salís et al., 2020)). Electricity (PV) and water (RWH) outputs are based on our own calculations and measured at 75.8 kWh/m 2 /year and 0.52 m 3 /m 2 /year, respectively (see Supporting Information S2).…”

“…Upgrading strategies to implement in such areas should not only focus on climate change related strategies but also on providing well-being, urban equity, and economic benefits to these run-down areas (Ruth & Coelho, 2007;Solecki et al, 2011). Some examples include the general improvement of areas with high economic costs (Helleman & Wassenberg, 2004); the demolition of buildings with high environmental burdens (Arthurson, 1998); enhancing public spaces such as green spaces; or the creation of leisure and service facilities (Wassenberg, 2004;Wassenberg et al, 2010).…”

Assessing the environmental behavior of alternative fertigation methods in soilless systems: The case of Phaseolus vulgaris with struvite and rhizobia inoculation

“…The inventory data for the infrastructure and auxiliary equipment was compiled from Sanyé et al, 2012;Sanyé Mengual, 2015;Sanjuan-Delmás et al, 2018;Rufí-Salís, Petit-Boix, et al, 2020. For taking into account the emission factor of the total nitrogen and phosphorous in the applied quantity of struvite, even when not all struvite was dissolved.…”

Environmental and social life cycle assessment of growing media for urban rooftop farming

“…Nonetheless, the accumulation of populations, activities and resource demands triggers high pressures Communicated by Marzia Traverso regarding pollution, resource use, and land/space competition (Legner and Lilja 2010). Organisations, governments and academia have focused their attention on cities as high emitters but also because they offer potentials for multipurpose and easily replicable solutions for sustainability actions (Grimm et al 2008;Rosenzweig et al 2010). Many strategies for redressing the ecological problems associated with urban areas have emerged over the years.…”