Purpose Rooftop greenhouses (RTGs) are agricultural systems that can improve 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 the impacts resulting from seasonality, combinations of crops and nonoperational time. We analyze vegetable production in an RTG over 4 years to determine the crop combinations that minimize yearly environmental impacts while diversifying food supply. Methods The system under study consists of an integrated RTG (i-RTG) with a hydroponic system in Barcelona, in the Mediterranean region. By using life cycle assessment (LCA), we evaluate the environmental performance of 25 different crop cycles and 7 species cultivated during the period 2015–2018. Three functional units are used: 1 kg of edible fresh production, 1 unit of economic value (€) in the wholesale market and 1 kcal of nutritional value. The system boundaries consider two subsystems: infrastructure (greenhouse structure, rainwater harvesting system and auxiliary equipment) and operation (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 exert the lowest impacts in all categories, considering all three functional units, due to the high yields obtained. In contrast, spinach and arugula have 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 are the main causes of freshwater and marine eutrophication. By combining the most eco-efficient cycles, we can see that growing two consecutive tomato cycles is 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/winter is the best scenario when using market (0.70 kg CO 2 eq./€) and nutritional value (3.18·10 −3 kg CO 2 / kcal). Conclusions This study shows that increasing the diversity of the system leads to better environmental performance of greenhouse urban agriculture if suitable crops are selected for the autumn/winter season. The functional unit involving the economic value and the eco-efficiency analysis are useful to demonstrate the capability of the growing system to produce added-value vegetables under harsher conditions while categorizing and classifying the crops to select the most suitable combinations based on economic and environmental parameters.

中文翻译：

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为屋顶温室农业确定生态高效的全年作物组合

目的 屋顶温室 (RTG) 是一种农业系统，可以通过在未使用的城市空间生产蔬菜来改善食品供应链。然而，迄今为止，RTG 的环境评估只关注特定作物，没有考虑季节性、作物组合和非操作时间造成的影响。我们在 RTG 中分析了超过 4 年的蔬菜生产，以确定在使食品供应多样化的同时最大限度地减少年度环境影响的作物组合。方法 所研究的系统由位于地中海地区巴塞罗那的带有水培系统的集成 RTG (i-RTG) 组成。通过使用生命周期评估 (LCA)，我们评估了 25 个不同作物周期和 2015-2018 年期间种植的 7 个物种的环境绩效。使用了三个功能单元：1 公斤可食用的新鲜产品，批发市场的 1 单位经济价值 (€) 和 1 大卡的营养价值。系统边界考虑两个子系统：基础设施（温室结构、雨水收集系统和辅助设备）和操作（肥料及其排放到水和基质中）。此外，我们还进行了生态效率分析，考虑了作物周期的碳足迹及其在收获期间在批发市场上的价值。结果和讨论 考虑到所有三个功能单元，由于获得的高产量，春季番茄周期在所有类别中的影响最小。相比之下，菠菜和芝麻菜的影响最大。在相对影响方面，温室结构的影响较大，而肥料生产在番茄周期中具有显着的相对贡献。此外，施肥造成的氮和磷排放是淡水和海洋富营养化的主要原因。通过结合最具生态效率的周期，我们可以看到连续种植两个番茄周期是产量功能单位（0.49 kg CO 2 eq./kg）的最佳替代方案，而长春番茄周期与豆类和生菜相结合当使用市场（0.70 kg CO 2 eq./€）和营养价值（3.18·10 -3 kg CO 2 / kcal）时，秋/冬周期是最佳方案。结论 本研究表明，如果为秋/冬季节选择合适的作物，增加系统的多样性会导致温室都市农业更好的环境绩效。