Friday, February 27, 2015

Soil and the City

Typically we think of urban environments as a mixture of concrete sidewalks, buildings, and traffic lights. Soil for urban environments is referred to in a civil engineering sense; a medium that is a support system stabilizing these structures and walkways. However, recently there has been push to "unearth" this material and utilize it for supporting human life. The International Year of Soil's focus for February is "Soils Support Urban Life."

Urban farming has popped up in abandoned lots. City-dwellers lacking yards can rent plots of land to grow their own vegetables. Their is also a push to encourage people to have a better understanding of where their food comes from. Urban farms are popping up all over the United States. A summer program in Baltimore, Maryland helps kids develop urban farming skills. They learn how soil to prepare soil for planting, fertilize and irrigate soil, and harvest their hard work.

Photo courtesy of Ann Chen (2009).

Another area where soils are showing up in urban environments are roof top plantings or "green roofs." These gardens cover the roof of a building and grow plant in a special soil mixture. The establishment of more plant life in cities can be beneficial for air quality. Utilization of excess water  for plant growth diverts it away from stormwater systems and decreases stress on this system especially during heavy precipitation events. These gardens can absorb heat that would normally be reflected and contribute to the urban heat island effect during the summer. These systems also help to insulate buildings better for prolonged life of HVAC systems and decrease power demand for cities. Just think of what a city could look like with these on every roof!

This concept was translated to buses in New York City and Spain as well as food trucks in St. Louis! Traveling gardens can enhance urbanites daily life by helping reduce carbon dioxide concentrations.

As mentioned, the soil in green roof design is developed especially for this. Typically the soil is a shallow layer of light weight and well draining materials. A mixture of sand and compost can be a great place to start. The weight of the material when completely saturated with water (all pore spaces within the soil are filled with water) is crucial for decreasing chances of structural failure (i.e. roof collapse)! The soils is accompanied by a drainage system and other necessary components to allow for proper diversion of the water and support. Each green roof  design varies slightly, but the basic schematic and how it compares to common field soil can be seen below.

File:Typical native soil vs. Typical Green Roof Profile.jpg
Another installation where soil can be found in cities are wall gardens. Although not quite as grand as the hanging gardens of Babylon,  these green havens have also popped up all over cities. Wall gardens can range from small setups on your balcony using recycled materials to extensive designs that hang from parking garages. Landscape architects have created beautiful designs and work with soil specialists to determine the best growing media for these plants. The larger displays can often have complex setups with meticulously controlled fertigation (fertilization + irrigation) to provide the appropriated nutrients for growth.

This resurgence of soils in cities has been a fantastic way to connect humans back to the land. Improving air and water quality, bridging the gap between farm and food, as well as increasing the aesthetic value of cities are all ways soils support urban life. There is a hope for continued creativity and a strengthening of the relationship for soil and the city. Here's to urbanites getting their hands dirty!