Soil quality, carbon and nitrogen stocks across urban green spaces in rapidly expanding cities

Urbanization and population growth are exerting increasing pressure on urban soils, potentially affecting soil quality and soil carbon and nitrogen dynamics. Urban Green Spaces (UGS) can mitigate these impacts by enhancing carbon sequestration, nutrient cycling and overall soil health. However, the extent to which UGS types influence soil quality remains poorly understood in rapidly expanding metropolitan regions. The study evaluated soil organic carbon stock (SOCS), soil total nitrogen stock (STNS) and key physicochemical properties across five UGS classes in the Delhi Centralised National Capital Region (CNCR), India: urban forest (UF), parks (PA), roadside plantation (RP), urban agriculture (UA) and home lawns (HL). Soil samples were collected from two depths (0–10 cm and 10–20 cm). Soil pH at both depths was significantly higher ( p < 0.05) in UA and HL than in UF, PA, and RP. Similarly, soil moisture in the topsoil layer (0–10 cm) was significantly higher ( p < 0.05) in UA and HL than in the other UGS types. In the topsoil, the soil organic carbon to total nitrogen (SOC:TN) ratio followed the order UF > RP > PA > UA > HL, whereas in the subsoil, the order was UF > UA > HL > RP > PA. SOC and SOCS were significantly higher ( p < 0.01) in the topsoil layer than in the subsoil layer. TN concentration and STNS were also significantly higher ( p < 0.05) in the topsoil than in the subsoil. Overall, soil properties and carbon and nitrogen stocks varied considerably among UGS types, reflecting differences in vegetation characteristics and site management. These findings highlight the importance of maintaining diverse and appropriately managed Urban Green Spaces for sustaining soil quality and soil carbon and nitrogen storage in rapidly urbanizing regions.