Distinguishing urban soils with physical, chemical, and biological properties

Modifications associated with urban infrastructure directly impact soil properties. In particular, soil bulk density, microbial biomass and activity, and organic matter are impacted by anthropogenic activities. We proposed that urban soil properties are not only distinguishable from other systems, but also variable within types of landscapes in urban environments. We found soils from older urban landscapes (mean landscape age of 64 years) to be distinct from newer urban landscapes (mean landscape age of 9 years). Soil bulk densities were significantly greater in newer (1.73 g cm−3) compared to older urban soils (1.41 g cm−3). Older urban soils had significantly greater extractable phosphorous, weak Bray P (24%), strong Bray P (51%), and K (45%) than newer urban soils. Soil biological measures of nitrogen availability were significantly greater in old compared to new urban soils, microbial biomass N (71%), potential C mineralization (20%), and potential N mineralization (83%). We found exponentially decreasing metabolic quotient values, qCO2, suggesting the impact of site disturbance decreases rapidly with time, and older urban landscapes are closer to steady-state conditions relative to younger urban landscapes. Total soil organic matter was significantly greater (35%) in old urban soils. Fine POM was a larger contributor to total SOM in old compared to new urban soils. Particulate organic matter C/N ratios from older urban soils were less (coarse POM 14% less and fine POM 13% less) than newer urban soils. Of the soil forming factors, time played the most significant role in soil physical, chemical, and biological differences. We believe that as time since initial disturbance increases, the impacts of urbanization are reduced by processes improving physical, biological, and chemical soil properties.