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| Crop | Year and season of research | Country of research | Objective | Major findings | Conclusion | References |
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| 22 crop species were planted (top five: tomato, chard, lettuce, pepper, and eggplant) | 2015–2017 | Barcelona, Spain | The objective of this research was to experiment the yield potential of the green roof under soil less polyculture | The experiment was conducted on 18 m2 soil with less polyculture, found productivity of 10.6 kg/m2/year, and reported that 5.3 m2 of area is required to feed one person annually | The productivity of soilless urban agriculture is high and cucurbitaceous crop had low yield compared to others. There should be cultivation-based trial on urban RTG helping to meet the market demand | [11] |
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| Tomato and lettuce | 2013–2015 | AgroParis Tech university | The purpose of this study was to access the rooftops productivity using organic waste having the potential to generate many urban ecosystem services | The result is high levels of food provision with acceptable food quality in terms of contaminants, important runoff mitigation, and use of a local organic waste, but with a negative effect on runoff water quality in terms of carbon | The foods are of acceptable quality and urban organic waste has huge production potential in rooftop garden | [12] |
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| Tomatoes (Solanum lycopersicum), beans (Phaseolus vulgaris), cucumbers (Cucumis sativus), peppers (Capsicum annuum), basil, and chives | 2010-2011 | United States of America | The purpose of this study was to explore three mulching strategies (pine bark, living sedum, and no mulch) and three fertilization regimens (25, 50, and 100 g·m−2 of 14-14-14 N-P-K slow release fertilizer applied twice each growing season) over two growing seasons to determine their benefits to rooftop agriculture | Tomato and cucumber have a positive response to fertilizer and under intensive management yield of tomato, bean and cucumber were comparable to that of conventional agriculture | More research must be conducted to access the alternative local mulching material and source of nutrients for organic production | [13] |
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| Pepper and lettuce | June to September (2020) | | To examine production systems by testing struvite solubility and uptake in granular form for two different crops: pepper plants (a highly P-demanding crop with a long growth cycle) and lettuce (shorter cycle) | The three cycles of lettuce treated with 20 g of struvite had the highest and most sustained overall yield, although such a high struvite concentration resulted in very slow dissolution. However, no signs of P deficiency can be seen in the pepper plants; even when obtaining a greater production, the P content was regarded as very low due to the slow struvite solubility | The use of struvite in hydroponic production due to the capacity of sustained production of shorter and longer cycle crops as well as the reduction of the environmental impacts compared to mineral fertilizer | [14] |
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| Lettuce and leafy vegetables on hydroponics: tomato, chili pepper, eggplant, melon, and watermelon on soils | 2012–2014 | Bologna, Italy | Assessing the sensitivity of the results to the availability of reused materials and the use intensity of the community rooftop garden for producing various crops | The best techniques of lettuce cultivation to address global warming were floating in the summer, with 65–85% less environmental impact per kilogram than nutrient film, and soil production in the winter, with 85–95% less environmental impact | In the design of rooftop gardens, soil production and fruit vegetables might be prioritized to achieve higher levels of ecoefficiency. However, leafy production using the floating technique is recommended for areas where water scarcity is an environmental issue, as it is the most water-efficient option | [15] |
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