Direct green waste land application: How to reduce its impacts on greenhouse gas and volatile organic compound emissions?

• The cumulative N2O emissions were greatly reduced by green waste soil incorporation.
• Green waste soil incorporation also reduced the cumulative CO2 and VOCs emissions.
• Application of green waste (GW) quickly consumed soil O2 within one day.
• GW soil incorporation is recommended to reduce emission from direct land application.

Direct land application as an alternative to green waste (GW) disposal in landfills or composting requires an understanding of its impacts on greenhouse gas (GHG) and volatile organic compound (VOC) emissions. We investigated the effects of two approaches of GW direct land application, surface application and soil incorporation, on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), and VOC emissions for a 12 month period. Five treatments were applied in fall 2013 on fallow land under a Mediterranean climate in California: 30 cm height GW on surface; 15 cm height GW on surface; 15 cm height GW tilled into soil; control + till; control + no till. In addition, a laboratory experiment was conducted to develop a mechanistic understanding of the influence of GW application on soil O2 consumption and GHG emission. The annual cumulative N2O, CO2 and VOC emissions ranged from 1.6 to 5.5 kg N2O-N ha−1, 5.3 to 40.6 Mg CO2-C ha−1 and 0.6 to 9.9 kg VOC ha−1, respectively, and were greatly reduced by GW soil incorporation compared to surface application. Application of GW quickly consumed soil O2 within one day in the lab incubation. These results indicate that to reduce GHG and VOC emissions of GW direct land application, GW incorporation into soil is recommended.