Modern green roofs, which originated in Germany in the late 1800's, reduce energy use, mitigate urban heat island effects and reduce stormwater release. In recent years more attention has been turned to two additional potential benefits of green roofs; carbon sequestration and vegetable production. Although some work has been done on extensive Sedum spp. roofs, little has been done on carbon sequestration of other green roof types and other ornamental landscapes. Little literature also exists on the use of green roofs in urban agriculture.Urban agriculture has many benefits including increased economic and food security, job creation and community building, but is also faced with many challenges. The largest of which is land availability and competition with other forms of land development. The use of green roofs could eliminate this form of competition at some locations and help to alleviate other concerns surrounding urban agriculture such as health hazards associated with heavy metal contamination of food. It does however raise two other major concerns; how the added weight of the green roof and the weight load restrictions of most flat roofs will affect the scale at which it can be implemented and how higher nutrient requirements of vegetable and herb plants compared to most other green roof plants will affect runoff water quality. Four studies were designed to examine food production on extensive green roofs and the ability of extensive green roofs and other ground level ornamental landscapes to sequester carbon.Vegetable species selected for study were tomatoes (Lycopersicon esculentum), green beans (Phaseolus vulgaris), cucumbers (Cucumis sativus), peppers (Capsicum annuum), basil (Ocimum basilicum) and chives (Allium schoenoprasum). These were tested for their productivity on an extensive green roof, extensive green roof platforms and in ground. All plants survived and produced biomass at all three locations for three growing seasons. Use of three mulching strategies (no mulch, pine bark mulch, and a living Sedum mulch) and three fertilization regimens (25, 50, and 100 g/m2 of a 14-14-14 N-P-K slow release fertilizer applied twice during each growing season) were examined and the use of pine bark mulch and higher fertilizer application rates improved crop performance. Further research on other mulches and fertilizers is recommended to optimize vegetable and herb production. To examine effects of vegetable and herb production on the stormwater benefits provided by green roofs, stormwater runoff quantity and water quality were compared with more traditional extensive green roofs planted with a sedum mix and a native prairie mix. The prairie mix retained the most runoff and the vegetable and herb mix the least because of differences in plant density and morphology. Examination of runoff nitrate and phosphorus concentrations had mixed results with no differences among treatments for nitrate and higher phosphorus concentrations in the first 125 mL of runoff from the vegetable and herb green roofs. Further research into nutrient runoff is recommended. Finally the ability of nine in ground and four extensive green roof landscapes, including vegetable and herb gardens, to sequester carbon were compared. The in ground landscape systems sequestered more carbon than the corresponding green roof landscape systems. Most carbon was sequestered by landscape systems containing plants with large amounts of woody structures or high plant volumes, but more research on the effect of management practices is recommended.
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