Urban agriculture is enjoying a renaissance in many cities in the US, including Indianapolis. Urban agriculture provides the potential to alleviate food insecurity in communities with little or no access to grocery stores and to restore ecosystem services to urban systems. However, since most research connecting agriculture to ecosystem services has focused on rural areas there is little understanding of how urban agriculture can help restore ecosystem functions. In addition, many urban farms are established on soils with industrial or commercial histories, which can lead to legacy contaminated soils that must be modified before they are suitable for food production. The goal of this project was to survey several farms within Indianapolis to examine if there are legacy contaminant concerns for conducting agriculture within the city limits and if soil modification strategies have been successful in addressing the contaminants and improving overall soil health. We examined farms that either used a raised bed system, wood chip barrier and soil mounds, or directly planted in native soil. Soils from both inside and outside the growing bed were analyzed for heavy metals, total and extractable nutrient metals, organic matter, and soil physical characteristics.
Across seven urban farms, soils outside of growing beds revealed that several sites within Indianapolis did have legacy contamination with heavy metals such as lead, arsenic, and zinc. Several of those sites had soil levels above recommendations for human or plant health. However, both methods for addressing contaminated soils (raised bed and wood chip barrier plus soil mounding) reduced levels below health thresholds. However, there were some indications of potential dry deposition of contaminated soils in growing beds within several years of construction. Not surprisingly, the raised bed and barrier and mound systems had much higher levels of calcium, magnesium, and potassium, but in several sites, phosphorus was excessively high. P levels were high enough to be a concern for runoff and potential waterway contamination. These P levels suggest a disconnect between application guidelines and needs of this type of urban agriculture. Additionally, native soil based farms had a small increase in soil organic matter and protein while soil aggregate stability and waster holding capacity remained stable suggesting that this type of management might provide long-term stable and productive agroecosystems.