Soil Carbon Sequestration and Organic Wastes

In cities there is a special nexus between urban waste management, climate change mitigation, and urban agriculture. Urban areas contain under-utilized vacant land in a degraded state with poor topsoil, as for instance in a vacant lot. Urban soil improvements, to enhance the quality of public greenspace or to support urban agriculture, are often most quickly and dramatically achieved by adding significant amounts of organic soil amendments. Urban areas are also themselves the source of large amounts of organic residuals well suited for use as soil amendments: Biosolids from wastewater treatment, and compost derived from urban wastes such as yard- and garden wastes and pre- and post-consumer food wastes. Finally, activity in urban areas is a source of increasingly large greenhouse gas (GHG) emissions, and urban areas must also cope with increasingly large waste management demands (themselves a potentially large GHG source). As the following discussion will show, beneficially re-using urban organic residuals as soil amendments may allow urban areas to realize increased local food production along with greater soil carbon storage, while avoiding more GHG-intensive pathways for managing urban wastes.