Short-term response of soil greenhouse gas fluxes to alfalfa termination methods in a Mediterranean cropping system

Soil acts as a natural source and sink for greenhouse gases (GHG) that are responsible for global warming and climate change. As the agricultural sector has an important impact on GHG (e.g., CO2, CH4, N2O) emissions, the definition of mitigation strategies is needed, especially for the Mediterranean climate areas that appear most vulnerable to climate change. The introduction of perennial legumes, such as alfalfa (Medicago sativa L.), falls within this scope, but it requires the application of a termination method aimed at reduction of GHG emissions. With the aim of assessing the short-term effects of two different alfalfa termination methods (Tillage vs No tillage plus herbicide), we defined the hypothesis that alfalfa termination by Tillage will increase soil GHG emissions compared to its termination by No tillage plus herbicide. Soil CO2, CH4 and N2O emissions were monitored over similar to 2 months (71 days; October-December, 2017) following alfalfa termination, using closed static chambers. The soil total GHG emissions after 71 days were significantly different for Tillage and No tillage plus herbicide: 311.90 +/- 21.21 versus 195.89 +/- 11.14 g CO2 equivalent m(-2), respectively. For both termination methods, CO2 (up to a maximum value of 1.24 +/- 0.18 and 0.65 +/- 0.07 kg C-CO2 ha(-1) h(-1), respectively) was the greatest contributor to the total soil GHG emissions (about 96%), compared to N2O (up to a maximum value of 0.37 +/- 0.13 and 0.31 +/- 0.10 g N-N2O ha(-1) h(-1), respectively) and CH4 (up to a maximum value of -0.01 +/- 0.03 and 0.07 +/- 0.03 g C-CH4 ha(-1) h(-1), respectively). These data suggest that over the short term, legume perennial crop termination by No tillage plus herbicide better supports the purpose of climate regulations.