In virtually all European cities, urban food production faces stiff competition from other land-uses such as housing, commerce and industry, which often have a far higher profile and financial return. Overcoming this particular hurdle will significantly influence the development of urban food growing. There is no point in wishing economic obstacles away, but there is good reason to face them objectively. The biggest problem is the prevailing economic system, which only measures direct profits from the development of land. If the prevailing view regarding the comparative value of different activities changed, then planning regulations would follow, and development.
Brownfield versus greenfield
Brownfield sites, those that have had a previous industrial or commercial use, are one of the main sources of development land in existing cities. For CPULs and urban agriculture to become established in existing cities, some brownfield sites will need to be used. For this to happen, the benefits and drawbacks of their use as ‘landscape’ rather than ‘building site’ will have to be assessed. It may well be that environmental auditing of different forms of land-use can be used to assess the credits and debits associated with different activities, and so define environmental costs which need to be covered by development. There are now a few tentative moves in this direction in England, for example, the congestion charge in central London (making a charge for private cars entering the city centre) and policies which allow local authorities to take account of the environmental benefits of development and accept a lower price for selling land.
As long as development is concentrated in a few cities, these will almost inevitably need to expand onto greenfield sites, even if their density is increased. If the case for urban agriculture is, as we believe, convincing, then it has a place on brownfield and greenfield sites.
The first step in promoting urban agriculture is to increase the perceived value of development resulting in ‘Ecological Intensification’ and we hope that making a rational case for the varied benefits of urban agriculture will help to do this.
While a great deal of information describing the design of low energy buildings is available, including examples taking account of lifecycle impact due to embodied and operational energy (Viljoen, 1997), little literature is commonly available supporting the case for urban agriculture. Not surprisingly, therefore, built environment professions have traditionally had little to do with food issues. If planning is to be concerned with co-ordinating the use and development of land in the public interest, then the value of urban food growing will need to be publicised far more widely.
Examples of technical obstacles include land contamination, a particular feature of many inner city brownfield sites with long industrial histories. The introduction of organic urban agriculture requires that soils used for growing crops is tested for contamination, to establish if remedial measures need to be taken. Furthermore, hydrological investigations would be required to check that contaminants from adjacent non-organic or polluted sites are not carried by groundwater into organic fields.
Raised beds are often used as a means of limiting the amount of soil which has to be imported into food growing sites, on contaminated soil. The quantities of soil required for extensive urban agriculture sites can be large, and require transport for importation from
adjacent areas. Clearly this is a significant factor, which will need careful consideration when determining the viability of new urban agriculture sites. Similar issues exist if roads are to be converted into sites for market gardens; for example, the soil below roads will be heavily compacted by vehicular use, as well as being constructed from gravel and subsoil with all organic soils deliberately removed. Creating fields from roads also usually requires removal of large volumes of asphalt or concrete, but this material can find use as aggregate in general construction. The direct use of road materials to construct raised beds for food growing is not recommended, as leaching of toxic chemicals may occur from the aggregate.
These are some of the technical and environmental difficulties which will have to be addressed by a range of practitioners and professionals to achieve sustainable urban food production. Experiments are underway to ‘manufacture’ soil from recycled materials, for example, ground glass. The experiments of Phil Craul and much additional detailed information on repairing contaminated soil can be found in J. William Thompson and Kim Sorvig’s book, Sustainable Landscape Construction (Thompson and Sorvig, 2000). These issues will in certain instances act as limiting factors in the location of urban agriculture fields. A distinction should be drawn between the effect contaminated soil can have on the location of urban agriculture plots and the siting of CPULs. The spaces where CPULs contain circulation routes, parkland and playing fields may be suitable for soils which cannot support edible crops.
The argument that it may be expensive to purchase and prepare urban land for food growing is not sufficient to abandon the case for urban agriculture. After all, just think how expensive it must be for the Netherlands to make the very land on which they then construct towns. Certainly a proactive planning system will be required, allied with a clear presentation of the benefits associated with productive urban landscapes.