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w i n e G R O WIN G We believe the increase in N2O emission observed here was due to the pooling of water and organic matter in a plow-pan that developed in this treatment, aided by the soil's high clay fraction. If true, this would be an unintended, negative consequence of tillage. To describe and quantify the emissions from soil under the drip emitter required careful work that, to our knowledge, has not been approached by other researchers. Using smaller gas-collection chambers spaced at various distances from drippers, previous work in our laboratory found that emission "plumes" (emission patterns in 3-D around a point source) from drip fertigation could be described using two-dimensional Gaussian distribution patterns. In 2010, we observed that "chasing" N with irrigation water (a common practice) led to more complex emission patterns. In this case, the zone of major emissions took place on "shoulders" around the center of the drip zone, where a high-nitrate irrigation solution was present. Initially, emissions were lower directly under the dripper where chasing water had diluted applied NO 3-, but, over time, the plume became more even as NO 3- and water presumably diffused through the drip zone (Figure 7). Overall, our results have not suggested great opportunities to mitigate N2O emissions in wine grape vineyards with low N applications. However, vineyards with higher application of N may benefit in the future from more sophisticated N-fertigation practices, such as micro-sprinklers, or improved management of N-pulses and N-concentrations in fertigation. We are pursuing further research to describe how total N2O emissions from N-fertilization are affected by patterns of application. Applying N in lower concentrations at higher frequencies, or at earlier and cooler points in spring or summer when irrigation is not necessarily needed may result in lowered N2O emissions. Such investigation must also consider the potential for increased leaching of nitrates (NO3-) into groundwater. Methane fluxes Methane (CH4 ) is a major greenhouse gas, responsible for approximately 30% of radiative forcing, the driving mechanism behind global warming.2 Methane has a longer lifespan in the atmosphere than CO2, but a much shorter lifespan than N2O, partly because it is readily oxidized (consumed) by soil bacteria in many upland farming and natural ecosystems.1 Fostering CH4 oxidation may be possible in cultivated upland perennial crops like grapes. Two years of data indicated that a small amount of CH4 was oxidized in tractor rows. Treatment differences due to tillage were not apparent. Emissions are sometimes seen following rain, although they are difficult to predict or to model. We have seen consistent, high emissions of CH4 during KNO3 fertigation. Like N2O production, this may be related to the establishment of low-oxygen or anaerobic conditions, which is a requirement for methano enesis. g Vineyard operations A farm-gate carbon footprint for a vineyard must include tractor and other fuelconsuming operations. Table I (below) lists the CO2 equivalent production of each of the operations conducted in the field during the two years of interest when we were conducting intensive research on N2O and CH4 fluxes. The operations component of the GHG footprint was highly dependent on disease pressure (fungicide and sulfur dust applications) and cultivation practices of chopping, mowing and tillage. Conclusion We are close to achieving a total carbon footprint for a number of test case research vineyards. Once we have confirmed the carbon equivalent cost of the herbicides and fungicides used in this investigation the footprint should be 2009 Treatment CC min till CC + till no CC + till Herbicide x 1. . . . . . . . . . . . . . . . . . . . . . 4. . . . . . . . . . . . 4. . . . . . . . . . . . . . 4 Chop/mow x 1. . . . . . . . . . . . . . . . . . 43. . . . . . . . . . 43. . . . . . . . . . . . . 43 Till/cultivate soil x 2. . . . . . . . . . . . . . – . . . . . . . . . 44. . . . . . . . . . . . . 44 Sulfur dust x 5. . . . . . . . . . . . . . . . . . . 18. . . . . . . . . . 18. . . . . . . . . . . . . 18 Fungicide x 3. . . . . . . . . . . . . . . . . . . . 58. . . . . . . . . . 58. . . . . . . . . . . . . 58 Fall seed cc x 1. . . . . . . . . . . . . . . . . . 22. . . . . . . . . . 22. . . . . . . . . . . . . . . – Total.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146. . . . . . . . 190. . . . . . . . . . . 168 Primary sources of N20 from a Napa winegrape vineyard First Fall rains Seasonal rains and 48 hours after Tillage with rain Dry days Figure 8: Proportional sources of N2O emissions from the vineyard's soil, averaged across tractor rows and drip zones in 2009–10. "Seasonal rains and 48 hours after" include all rain events and the following two days, from the period after the first fall rainstorm and before the year's final rain event, which occurred after spring tillage. Although N-fertigation at 7.5–15 pounds per acre accounted for a small fraction of yearly N2O emissions, vineyards with higher application of N may benefit in future from more sophisticated N-fertigation practices such as micro-sprinklers, or improved management of N-pulses and N-concentrations in fertigation. forthcoming, but we are exercising caution in the reporting process. It has been important to investigate the capacity of a high C:N cover crop such as dwarf barley to sequester carbon when accompanied by minimum tillage practices (shallow tillage every other year). The use of the barley cover crop under conventional tillage practices (including an "extra" tillage pass for seeding bed preparation in the fall), did not lead to measurable carbon sequestration. Presumably the increased disturbance and aeration of the soil counterbalanced the higher inputs of organic carbon into the soil. 2010 Treatment CC min till CC + till no CC + till Herbicide x 1. . . . . . . . . . . . . . . . . . . . . . 4. . . . . . . . . . . . 4. . . . . . . . . . . . . . 4 Chop/mow x 1. . . . . . . . . . . . . . . . . . 43. . . . . . . . . . 43. . . . . . . . . . . . . 43 Till/cultivate soil x 2. . . . . . . . . . . . . . – . . . . . . . . . 38. . . . . . . . . . . . . 38 Sulfur dust x 3. . . . . . . . . . . . . . . . . . . 11. . . . . . . . . . 11. . . . . . . . . . . . . 11 Fungicide/insecticide x 7*. . . 135. . . . . . . . 135. . . . . . . . . . . 135 Fall seed cc x 1**. . . . . . . . . . . . . . . 44. . . . . . . . . . 44. . . . . . . . . . . . . – Total.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237. . . . . . . . 275. . . . . . . . . . . 231 Cover Crop (CC). *Insecticide passes were mandated this year due to European grapevine moth. **The soil was shallow-disked before seed drilling due to compacted soil. Table I: Kg of CO2 released per hectare in each vineyard management operation two years for three tillage systems. 92 p racti c al w i ne ry & v i n e yard NOVEMBER 20 13 N-fertigation