It is well known that agricultural production contributes to global warming through the release of greenhouse gases CO2, N2O, and CH4, the most potent of which is N2O. However, most N2O emission studies focus on intensively managed, annual cropping systems. Few have documented greenhouse gas production in perennial crops, which often have substantially different agricultural management practices and growth patterns compared to annual crops. Hence, the objectives of this study were to (1) quantify seasonal and annual direct N2O emissions from a Mediterranean vineyard and (2) determine how conventional management practices such as irrigation, fertigation, cover cropping and tillage affect the magnitude and duration of N2O emissions. This study took place in a wine grape vineyard (Vitis vinifera)in Arbuckle, CA over a two-year period using closed-flux chamber measurements. Annual emissions totaled 3.92 kg N2O-N ha(-1) the first year, when a leguminous cover crop was planted in the alleys, while emissions in the second year when the alleys were fallow showed a 7-fold reduction, reaching only 0.56 kg N2O-N ha(-1). During the growing season of both years, fertigation events in the crop rows produced slightly increased emissions, ranging from 11 to 23 g N2O-N ha(-1) day(-1) and lasting less than one week, compared to the low background values of 0.5 g N2O-N ha(-1) day(-1). The largest fluxes occurred during the dormant season in response to the first precipitation event of the year, especially in the alleys. Nitrous oxide emissions following precipitation events in the second year, when the alleys were fallow, did not follow the same pattern, indicating the significant influence of cover crop-derived N (and C), when coupled with precipitation events, on annual N2O emissions. The results of this study indicate that the effects of individual management practices such as cover cropping may not be seen immediately, but instead act in sequence with other events when conditions are favorable for N2O production. Hence, when determining specific management practices to employ, it is important to recognize the interaction between management, climatic events, and time as important drivers in total N2O production.
