Management-Related N2O Emissions in a Mediterranean Vineyard.

The majority of global nitrous oxide emissions are from soils and agricultural activity through the processes of nitrification and denitrification. Knowing how different management events typically employed in agricultural systems influence these processes in terms of N2O produced is key to developing accurate greenhouse gas budgets. Consequently, there is an urgent need to quantify N2O emissions from Mediterranean agricultural systems as well as thoroughly understand the mechanisms responsible for these fluxes. Currently very little data exists on annual or seasonal N2O fluxes, especially within vineyards, as it is highly erratic and expensive to measure. The objectives of this study were thus to quantify annual and seasonal N2O emissions from a Mediterranean wine grape vineyard following conventional management events (i.e. tillage, fertilization, irrigation, etc) as well as to determine which events produced the highest fluxes over the longest time period. Throughout the year we measured N2O fluxes for a period of seven to ten days directly following management events using a closed-flux chamber method. The vineyard was divided into two functional locations: under the vine and in the tractor row, with four replications of each. Soil moisture, soil inorganic N content, air temperature, and soil temperature were also measured at each measurement point. Our results show that during the growing season, N fertilization had the largest influence on emissions under the vine and cover crop incorporation had the biggest influence in the tractor row. During the dormant season, precipitation events had the largest influence on emissions in both the vine and tractor row. Furthermore, the largest flux throughout the year for both the vine and tractor row resulted from the first major precipitation event in early fall. Total annual emissions ranged from 0.44 kg N2O-N ha-1 under the vine to 4.01 kg N2O-N ha-1 in the tractor row. The vines had similar emissions in both the growing season and the dormant season (0.16 kg N2O-N ha-1 from March 2009 through September 2009 and 0.28 kg N2O-N ha-1 from October 2009 through March 2010) while the tractor row had much higher emissions in the fallow season compared to the growing season (0.07 kg N2O-N ha-1 from March 2009 through September 2009 and 3.94 kg N2O-N ha-1 from October 2009 through March 2010). These results indicate that management events, especially in combination with climatic factors, do indeed play a significant role in total annual N2O emissions. However, they do not affect the vine and the tractor row evenly, which must be taken into account when calculating total GHG budgets. The presence of a leguminous cover crop in the tractor row drastically increased emissions over the dormant season due to increased inorganic N concentration and high water filled pore space when compared to the N fertilization event in the vine area. This clearly shows that management strategies to reduce N2O emissions need to consider climatic and seasonal events as equally as management events.