Richard E Marinos, Philip Conrad

Many cities demolish abandoned homes and create regreened vacant lots (RVLs), and an increasingly popular, high-intensity use of RVLs is as urban agriculture (UA) sites. UA may potentially result in higher nitrogen (N) runoff to aquatic ecosystems, but this potential has not been quantified. We examined the role that varying land reuse intensity plays in determining potential for N export via runoff or leaching, focusing on soil N availability and N removal capacity via denitrification. We contrasted three levels of land use intensity for vacant parcels: intact vacant properties, turfgrass RVLs, and regreened UA lots in Buffalo, NY. We examined soil N and C availability, denitrification potential, and isotopic evidence of denitrification.
Land use intensity only affected soil properties in surficial soil horizons. Total N was 2.5x higher in UA soils (mean = 0.51%) than non-UA (mean = 0.21%). Soil nitrate was 2.6x higher in winter (mean = 12.4 μg NO3--N g-1) than summer (mean = 4.7 μg NO3--N g-1) and was generally higher in UA soils. Despite higher soil N availability at UA sites, there were no differences in denitrification potential between UA and non-UA sites (mean = 620 ng N2O-N g-1 h-1). Isotopic evidence further confirms that denitrification was not a major sink of N. Although UA had high N availability compared to non-UA sites and low rates of denitrification, UA only has moderate potential for runoff-driven N export, as nitrate concentrations were substantially lower than values typical for conventional agricultural soils.