Cover cropping affects soil N2O and CO2 emissions differently depending on type of irrigation

Agricultural management practices such as subsurface drip irrigation (SDI) and winter legume cover cropping (WLCC) influence soil water dynamics as well as carbon and nitrogen cycling, potentially changing emission rates of soil CO2 and N2O, principal greenhouse gases. A split plot tomato field trial in California's Central Valley was used to evaluate the use of SDI and WLCC on event-based CO2 and N2O emissions. SDI and WLCC were compared to the region's more conventional practices: furrow irrigation (Fl) and no cover crop (NCC). Our results indicate that SDI offers the potential to manage cover crops without the significant increases in greenhouse gas production during the growing season as seen under Fl cover-cropped systems. The highest N2O emissions occurred during the beginning of the rainy season in November in the Fl-WLCC treatment (5 mg m(-2) h(-1)) and the lowest in August in the SDI-NCC treatments (4.87 mu g m(-2) h(-1)). CO2 emissions ranged from 200 mg m(-2) h(-1) during the rainy season (winter) and >500 m(-2) h(-1) during the growing season. Though no differences were detected in CO2 emissions between irrigation practices, mean CO2 emissions under WLCC were 40% and 15% greater compared to NCC under Fl and SDI, respectively. The treatment with the greatest effect on CO2 and N2O emissions was WLCC, which increased average growing season N2O and CO2 emissions under Fl by 60 mu g N2O m(-2) h(-1) and 425 mg CO2 m(-2) h(-1) compared to NCC. In SDI there was no effect of a cover crop on growing season CO2 and N2O emissions. In the rainy season, however, SDI N2O and CO2 emissions were not different from Fl. In the rainy season, the cover crop increased N2O emissions in SDI only and increased CO2 emissions only under Fl. Subsurface drip shows promise in reducing overall N2O emissions in crop rotations with legume cover crops. (C) 2010 Elsevier B.V. All rights reserved.