Carbon sequestration and greenhouse gas emissions in urban turf

Undisturbed grasslands can sequester significant quantities of organic carbon (OC) in soils. Irrigation and fertilization enhance CO 2 sequestration in managed turfgrass ecosystems but can also increase emissions of CO 2 and other greenhouse gases (GHGs). To better understand the GHG balance of urban turf, we measured OC sequestration rates and emission of N 2 O (a GHG ∼ 300 times more effective than CO 2 ) in Southern California, USA. We also estimated CO 2 emissions generated by fuel combustion, fertilizer production, and irrigation. We show that turf emits significant quantities of N 2 O (0.1–0.3 g N m −2 yr −1 ) associated with frequent fertilization. In ornamental lawns this is offset by OC sequestration (140 g C m −2 yr −1 ), while in athletic fields, there is no OC sequestration because of frequent surface restoration. Large indirect emissions of CO 2 associated with turfgrass management make it clear that OC sequestration by turfgrass cannot mitigate GHG emissions in cities.