Hanna Petroski,
Assessing Soil Health and Lead Contamination in Chicago Urban Gardens: A Collaboration with Contemporary Farmers Inc. and SOUL
Project Goals
This project partnered with David Toledo of Contemporary Farmers Inc. and southside organization South Siders Organized for Unity and Liberation (SOUL) to test soil nutrient levels and lead contamination in Chicago urban farms and gardens. Sites tested for Contemporary Farmers Inc. included vegetable beds at DePaul Community College Prep and at Otis Farms, which is an urban farm in Back of the Yards. The site tested for SOUL was Come Unity Joy Garden, a community garden located in a former vacant lot on the far south side. The goals of this project were two-fold. The first was to increase access to and education about soil testing in Chicago community gardens. The second was to specifically look at gardens treated with compost tea to see if compost tea application improves soil health for agricultural purposes.
As the importance of access to green space and healthy food in urban areas has become more well-known, more and more city governments and community members have turned to urban farming or community gardens. Community gardens and urban farms in cities in general and Chicago specifically face certain challenges not found in gardens outside of urban areas. Urban soil is often heavily compacted and nutrient-poor, requiring applications of compost or capping with new soil in order to be able to support crops. The biggest issue facing urban gardens, however, is contamination with lead and other heavy metals. Many urban gardens take advantage of vacant lots or other open areas which are not attractive to developers but are walkable for community members. However, many times these vacant lots are the former sites of old buildings or of industrial activity. Old buildings were often painted with leaded paint, and manufacturing processes often produce chemical or heavy metal byproducts. While lead paints and leaded gasoline are no longer used, and while industry may not have been active on a particular site for decades, contaminants such as lead leach into the soil. Lead holds tightly to soil and is not easily washed out, and so can stick around in soil for decades after contamination. While lead rarely enters into the edible portions of fruits/vegetables, contaminated soil can be blown by wind or moved by water onto the surface of crops. Urban gardeners who are unaware of contamination may handle contaminated soil with their bare hands. Children are especially vulnerable to the effects of lead, and if they don't wash their hands thoroughly before eating, they may be consuming lead-contaminated soil.
Contaminated soil can be dealt with in a number of ways. The most simple and cost-effective is to cap contaminated soil with clean soil or compost, in order to prevent direct contact. Very high levels of phosphorus can lead to lead combining with phosphorus to form lead phosphaets, which are not bioavailable and so not absorbed by the human body. Because of this, capping contaminated soil with high-phosphorus compost is especially useful. However, if urban gardeners are not aware of high lead levels, then they may not be aware of the need to cap contaminated soil and to thoroughly clean any produce grown in contaminated lots. Access to lead and soil testing is key to ensuring not only that healthy food is available to urban residents, but also that urban residents are able to spend time gardening or otherwise
Accomplishments of the project
Composite soil samples were collected from each individual bed at each site, as well as from native soil, in order to compare how soil which has been amended and used for crops compares to soil which has not received any treatment. Composite samples were dried and sieved to remove non-soil material, and then analyzed for pH, phosphorus levels, bioavailable nitrogen levels, microbial community mass, microbial community fungus:bacteria ratio, and lead levels.
Most soils among sites were found to have neutral to slightly alkaline soil pH. Phosphorus and nitrogen levels were, as a whole, very high. As expected, lead levels were low in constructed beds, moderate in beds which have received some compost/compost tea treatments, and high in native, untreated soil. Microbial biomass tended to be higher in treated areas, though not significantly; fungus:bacteria ratios also tended to be higher in treated soils, which indicates a better growing environment for most agricultural crops.
Project impacts
Unfortunately, without clear documentation on which beds had received compost tea treatments and in what amounts, it was impossible to come to any firm conclusions about how compost tea treatments affected soil microbiomes. Part of my contribution to the project was helping to revamp the spreadsheet used by citizen scientists to track compost tea use. I also suggested leaving some areas without compost tea treatment, in order to have a control which future grad students on this project might use to do a more thorough statistical comparison of nutrient and microbiome levels between sites that do or don't receive compost tea.
The biggest impact of this project was that it made lead testing possible for some of these sites. Through conversations with community garden leaders, it became apparent that community gardeners are invested in their garden sites and aware of the importance of regular testing, but also that they have minimal trust in and access to the sort of soil testing that would be able to determine if contamination is present. It was important to not only extend my knowledge of soil science, but also to listen to community gardeners about the story behind their gardens and their concerns about and plans for the spaces. While this project had a direct impact on individual garden spaces, in that I was able to recommend some treatments, such as capping contaminated soil and planting clover cover crops to improve nitrogen levels in beds which were lacking, my hope is that performing these tests and engaging respectfully with urban gardeners provided one more link in the possibility of a partnership between DePaul and more urban farming organizations. Urban green spaces such as community gardens are key to both ecological and human health within cities, and urban residents are aware of their importance and enthusiastic about being able to create their own green spaces. Scientific support that encourages these sorts of projects without overwhelming them will be key to the future of urban conversation.