, Volume 13, Issue 3, pp 273-293
Date: 09 Jan 2010

Soil-atmosphere exchange of carbon dioxide, methane and nitrous oxide in urban garden systems: impact of irrigation, fertiliser and mulch

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Urban green spaces provide important ecosystem services, such as amenity, biodiversity, productivity, climate amelioration, hydrological and biogeochemical cycling. Intensively managed urban gardens can sequester carbon through vegetation growth and soil C increase, but may experience nitrous oxide (N2O) emissions and reduced soil methane (CH4) uptake from irrigation and fertiliser use. Soil atmosphere exchange of N2O, CH4 and carbon dioxide (CO2) was measured in lawn and wood chip mulched garden areas in Melbourne, Australia in winter, spring and summer under various water and fertiliser regimes. Gas exchange before and after lawn fertiliser application was measured continuously for three weeks using an automated chamber system. Applying fertiliser led to a peak N2O emission of >60 μg N m−2 h−1, but overall only weekly irrigation (10 mm) significantly increased mean soil N2O emissions above that in other treatments. Under mulch, mean soil N2O emissions (14.0 μg N m−2 h−1) were significantly smaller than from irrigated lawn (27.9 μg N m−2 h−1), whereas mean soil CH4 uptake under mulch (−30.7 μg C m−2 h−1) was significantly greater (p < 0.01) than in any lawn treatment. Lawns were either a weak CH4 sink or source. Soil C density (0–25 cm) under mulch (12.5 kg C m−2) was greater that under lawn (8.0 kg C m−2). On a carbon dioxide equivalent (CO2-e) basis, soil N2O emissions offset the benefits of soil CH4 uptake. Mulched garden areas provide greatest C sequestration potential in soil and vegetation and the smallest non-CO2 emissions, as soil CH4 uptake offsets a large fraction of soil N2O emissions. Results of this study suggest that reducing the irrigation and fertiliser application to lawns can help mitigate GHG emissions from urban garden systems, and increasing the area of mulched perennial garden beds can also provide net GHG benefits; however, this needs to be tested in other garden systems with different soil types and environmental conditions.