Cover cropping affects soil N 2O and CO 2 emissions differently depending on type of irrigation

Abstract

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 CO 2 and N 2O, 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 CO 2 and N 2O emissions. SDI and WLCC were compared to the region's more conventional practices: furrow irrigation (FI) 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 FI cover-cropped systems. The highest N 2O emissions occurred during the beginning of the rainy season in November in the FI–WLCC treatment (5 mg m −2 h −1) and the lowest in August in the SDI–NCC treatments (4.87 μg m −2 h −1). CO 2 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 CO 2 emissions between irrigation practices, mean CO 2 emissions under WLCC were 40% and 15% greater compared to NCC under FI and SDI, respectively. The treatment with the greatest effect on CO 2 and N 2O emissions was WLCC, which increased average growing season N 2O and CO 2 emissions under FI by 60 μg N 2O m −2 h −1 and 425 mg CO 2 m −2 h −1 compared to NCC. In SDI there was no effect of a cover crop on growing season CO 2 and N 2O emissions. In the rainy season, however, SDI N 2O and CO 2 emissions were not different from FI. In the rainy season, the cover crop increased N 2O emissions in SDI only and increased CO 2 emissions only under FI. Subsurface drip shows promise in reducing overall N 2O emissions in crop rotations with legume cover crops.