Soil-less systems vs. soil-based systems for cultivating edible plants on buildings in relation to the contribution towards sustainable cities

Food production and consumption for cities has become a global concern due to increasing numbers of people living in urban areas, threatening food security. There is the contention that people living in cities have become disconnected with food production, leading to reduced nutrition in diets and increased food waste. Integrating food production into cities (urban agriculture) can help alleviate some of these issues. Lack of space at ground level in high-density urban areas has accelerated the idea of using spare building surfaces for food production. There are various growing methods being used for food production on buildings, which can be split into two main types, soil-less systems and soil-based systems. This paper is a holistic assessment (underpinned by the triple bottom line of sustainable development) of these two types of systems for food production on buildings, looking at the benefits and limitation of each type in this context. The results illustrate that soil-less systems are more productive per square metre, which increases the amount of locally grown, fresh produce available in urban areas. The results also show that soil-based systems for cultivation on buildings are more environmentally and socially beneficial overall for urban areas than soil-less systems.

Connecting the Water and Carbon Cycles for the Generation of Food Security and Ecosystem Services

Water scarcity and food insecurity are pervasive issues in the developing world and are also intrinsically linked to one another. Through the connection of the water cycle and the carbon cycle this study illustrates that synergistic benefits can be realized by small scale farmers through the implementation of waste water irrigated agroforestry. The WaNuLCAS model is employed using La Huerta agroforestry site in Texcoco, South Central Mexico, as the basis for parameterization. The results of model simulations depicting scenarios of water scarcity and waste water irrigation clearly show that the addition of waste water greatly increases the agroforestry system’s generation of crop yields, above- and below-ground biomass, soil organic matter and carbon storage potential. This increase in carbon sequestration by the system translates into better local food security, diversified household income through payments for ecosystem services and contributes to the mitigation of global climate change.

Recycling urban waste as possible use for rooftop vegetable garden

Urban authorities in Europe are confronted with increasing demands by urban dwellers for allotment gardens, but vacant urban soil tends to be scarce and/or polluted by past industrial activities. A possible solution for local authorities could therefore be to promote rooftop gardening. However little technical information exists on certain forms of rooftop urban agriculture, called Z-Farming. In 2012, a pilot experiment was run in Paris (France). Simple and cheap systems of rooftop gardening were tested on a rooftop using as crop substrates only local urban organic waste so as to contribute to the urban metabolism. Production levels and heavy metal contents in cropping substrates and edible vegetables were measured. Available results show (i) high levels of crop production with limited inputs compared to land professional gardening, (ii) low levels of heavy metal pollutants in the edible parts of the crops, especially for Cd and Pb with respect to EU norms for vegetables and (iii) positive influence on yields on organizing the substrate in layers and enhancing the biological activity through earthworm inoculation. These encouraging results allow us to consider that rooftop gardening is feasible and seem to have a great potential to improve urban resiliency. It will nevertheless be necessary to identify more precisely the types of roof that can be used and to assess more fully the generic result of the low level of pollution, as well as the global sustainability of these cropping systems.

The circular economy and the water-food nexus

The global economy is based on a take-make-consume and dispose model where natural resources are turned into products and the waste disposed of instead of being reused as a resource. In the Asia-Pacific region climate change along with rapid population and economic growth is resulting in increased demand for water and food, potentially leading to economic and political instability. Europe has developed policy and technological innovations that can facilitate the transition towards a circular economy where waste becomes a resource. By using existing instruments Europe can transfer its circular economy knowledge and technology to the Asia-Pacific region to increase security of supply of scarce resources. This can help ensure global security, influence climate change negotiations and create jobs in Europe.