California is the second largest U.S. state emitter of greenhouse gases, of which 8% of total state carbon dioxide (CO₂) and 59% of nitrous oxide emissions (N₂O) are from agriculture related activities. However, some alternative agricultural management practices such as subsurface drip irrigation (SDI), conservation tillage (CT) and winter legume cover cropping (WLCC) have the potential to reduce the rate of soil CO₂ and N₂O evolution.
A split-split plot tomato field trial in California’s Central Valley was used to evaluate system differences in CO₂ and N₂O emissions among different types of irrigation, tillage and cover cropping. SDI, CT, and WLCC were compared in all combinations with the region’s more conventional practices: furrow irrigation (FI), standard tillage (ST) and no cover crop (NCC). Annually, the SDI treatments had a CO₂ emission rate 4% lower than that of the FI treatments. During the growing season, total CO₂ flux was lower in the SDI treatments than in the FI treatments where the winter season showed no significant differences in total CO₂ flux between irrigation treatments. The effect of tillage on gas emissions was dependent on irrigation and tillage events, with higher CO₂ rates in CT following irrigation but lower compared to ST following field operations.   Preliminary N₂O results show that SDI had lower total N₂O emissions compared to FI during the growing season.  The highest N₂O emissions were found in the FI-WLCC treatments in the furrow (813.60 øg m^2- h^-1) where the lowest N₂O emissions tended to be in the SDI treatments, also in the furrow (4.87 øg m^2- h^-1).