When you think of cities, thoughts of cars, buses, people, skyscrapers and other concrete buildings might come to mind. But, below those concrete buildings, paved roads and high-traffic areas stands a foundation of one of the necessary components for life to exist—soil.
Soils in urban areas are often much different than farmland soils used to grow food or rangeland soils used to support essential ecology. Urban soils develop from soil material that has been disturbed, manipulated and transferred by various living creatures, said Ganga Hettiarachchi, a Kansas State University soil chemist.
Usually, urban soils are poor in physical, chemical and biological properties, she said, but this doesn't mean that urban soils should be regarded as dysfunctional.
"We always forget about the functionalities of urban soils," Hettiarachchi said. "Urban soils play a vital role in the livelihood of cities, biomass production, flood prevention, groundwater recharge, dust sequestration, carbon sequestration, as well as cooling and humidification. We should consider, especially during urban planning, urban soil as an important component in the planning process."
In 2015, people around the world are celebrating the International Year of Soils, which calls to mind the importance of soil in their daily lives. February's theme, "Soils Support Urban Life," helps paint a picture of how this sometimes overlooked natural resource is used to support life in cities and rural areas alike.
Food production in urban areas
According to the most recent U.S. census in 2010, more than 80 percent of the population lives in urban areas, and that percentage is expected to continue growing. Urban agriculture has also grown in popularity in recent years, as more people are interested in growing their own foods or buying foods grown locally by others.
"There has been a resurgence of urban gardening in the United States and elsewhere in the world," Hettiarachchi said. "The advance of urban agriculture activities can help low-income families and people who have no access to food—who are living in a food desert—to have access to healthy food."
Many challenges exist when trying to grow food in urban soils, however. Hettiarachchi said these might include soil compaction that causes poor drainage, and the presence of unwanted materials, such as debris from glass, plastic and other garbage.
Urban soils also face interrupted nutrient cycling and interrupted or modified microbial activities, she said. They may contain low levels of nutrients and contaminants such as lead, arsenic, cadmium and polycyclic aromatic hydrocarbons.
"Urban gardeners, when trying to garden in urban soils, face these additional challenges," Hettiarachchi said. "They need to make sure to follow common sense practices. Make sure that the soil nutrient levels are appropriate, and make sure to do things to enhance soil quality, such as get their soil tested for the common contaminants."
Although the contaminants will not transfer easily from the soils into fruit and vegetable plants, people should take precautions to prevent accidental ingestion of contaminated soil, she said. This could happen if the soil is not washed off fruits and vegetables properly, or if the soil is carried into the home.
"Use common sense practices, such as wash produce well, supervise children in gardens, make sure to remove dust before tracking it into the house on shoes and clothing, wash hands and keep soil moist to reduce the breathing it in during dry periods," she said.
In addition to gardens, urban soils help support other plant growth and trees, which are key components to bringing carbon dioxide back into soil, Hettiarachchi said. To enhance soil productivity for all of these plants, she recommended composting as a way to incorporate organic material back into the soil. Composting also helps reduce contaminant concentration in the soil through dilution.
Benefits of composting
DeAnn Presley, a K-State Research and Extension soil scientist, works in soil and water conservation in rural and urban areas. One of her areas of training is composting, and she works with cities and institutions, such as hospitals, to develop compost from food waste.
Presley said about one-third of waste in landfills comes from food.
"What's sad about that is food contains carbon, a soil amendment, and nutrients such as nitrogen, phosphorus and other nutrients needed for plant growth," she said. "We can divert that out of landfills where it is taking up space and producing methane, which is a powerful greenhouse gas. If we instead produce compost, we can then reapply that material which is great for two reasons—nutrients and organic matter, what gives soil its water-holding capacity."
Compost, Presley said, can be formed from anything that was alive, but it is usually vegetative matter decomposed in a controlled way.
"Put it in a pile, add water and turn it over two or three times," she said. "What a homeowner can do with that is add it to soils. You can put about 3 inches or less of compost on your soil, till that into a garden, or apply it on the soil surface in the fall and perhaps spade it in in the spring. Over time you can elevate the organic matter of that area."
Composting can also help reduce costs. Kansas State's dining facilities save food waste to create compost for research projects at the agronomy farm and other renewable products, such as biodiesel. Presley said this practice reduces fees the university would have to pay to place the waste in a landfill, while generating benefits for the environment.
For more information about soil quality, to have your soil tested, or to learn about urban gardening though the Master Gardener Program, contact your local extension office or visit the K-State Research and Extension website.
To watch a video interview with Hettiarachchi and Presley, log on to the K-State Research and Extension YouTube page. The Soil Science Society of America has resources for the public, teachers and children about soil and each monthly theme for the International Year of Soils.
Source: K-State Research and Extension