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78 P R A C T I C A L W I N E R Y & V I N E YA R D May 2015 78 P R A C T I C A L W I N E R Y & V I N E YA R D May 2015 G R A P E G R O W I N G S everal decades of research have characterized the ecological effects of fossil fuel-derived sulfur depo- sition on temperate forests in the northeastern United States and Europe. These studies demonstrated that high sulfur loads in acid rain cause soil and surface water acidification, 4,5 base cation depletion in soils, 13 changes to forest struc- ture and function, 12,16 and production and bioavailability of other elements including methyl mercury. 6,7 In agricultural systems, sulfur is pur- posely applied as a fungicide, pH regula- tor and vital plant nutrient. 15 Unlike in forested ecosystems, there has been little research to examine the pathways and ecological consequences of its use within and downstream of agricultural systems; most research to date has focused on crop sulfur requirements, 1,2,9,14 the rela- tive efficacy of sulfate (SO 4 2- )-supplying fertilizers 17 and the effect of elemental sulfur oxidation on soil pH and SO 4 2- availability. 8,18 In vineyard agriculture, application of elemental sulfur is a common prac- tice for controlling powdery mildew. In the Napa Valley of Northern California, 810.5 Mg of elemental sulfur are applied to the region's 47,980 acres of vineyards each year. 3 During the growing season, which coincides with the dry season in Northern California (April through October), grow- ers broadcast-spray sulfur by tractor frequently (every seven to 14 days) at low doses (often approximately 5 to 12 pounds per acre) targeting vines but also dusting the soil between trellises. On average, these applications add up to 100 to 300 kg (220 to 661 pounds) of sulfur per hectare per year and are made in wettable or dust form, depending on the vineyard's individual sulfur program. The potential environmental conse- quences of sulfur in major winegrowing regions have been largely unexplored. More broadly in the agricultural sec- tor, many believe that sulfur is inert in the environment. Researchers have not investigated whether targeted applica- tions of sulfur may have consequences for soil and water quality locally within vineyards, or the timing and fate of sulfur moved by water off-site. The eco- logical consequences of applied sulfur in vineyards may be similar to historic, inadvertent sulfur deposition to temper- ate forested ecosystems. In this research, we evaluated the major chemical transformations of elemental sulfur occurring during the growing and dormant seasons in vineyards, and the patterns of sulfur application, storage in soils and export in water flow paths that determine the annual sulfur cycle. Two vineyard locations in Napa Valley, Calif., were used by our research group to evaluate the immediate fate of applied sulfur on the soil surface and sulfur retention within and loss from vine- yards. We hypothesized that growing season conditions favored rapid chemical Eve-Lyn S. Hinckley, Institute of Arctic & Alpine Research, Boulder, Colo. BY Fate of sulfur fungicide in the vineyard and beyond Figure 2. Sulfur transformations and flows in a Napa Valley vineyard. (a) The growing season, showing drip irrigation, elemental sulfur application and leachate; (b) the dormant season, showing cover crop, and lateral transport of sulfur and water caused by large storm events. Size of arrows and text indicates the relative magnitude of each pool and pathway. Dashed arrows depict inferred pathways. In the study vineyard, a clay hardpan was present below the rooting zone of the vines. S 0 H S 2 EXPORT vola za on leachate leachate plant uptake mineraliza on S 0 organic S S 0 Drip irriga on line Drip irriga on line a. precipita on Clay hardpan b. SO 4 2 - r oo t ex uda o n est e ri fic a on li e rf a ll root exuda on plant uptake SO 4 2 - organic S EXPORT soil water mvmt soil water mvmt Clay hardpan Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec Feb 0 20 40 60 80 100 120 Dissolved sulfur (mg L −1 ) 5 15 25 35 45 Water inputs (mm) Sulfate S Total S 2005 2006 Figure 1. Sulfur in precipitation, irrigation, leachate and soil water during the period of study. Precipitation and irrigation water are represented by bars, and elemental sulfur inputs are shown with arrows. Leachate draining from vineyards was measured during irrigation events in the growing season (shaded panels), and soil water was measured below the rooting zone during the dormant season (white panels). Note three long (more than 8 hours) irrigation events on Sept. 25, 2005, Aug. 1, 2006, and Oct. 10, 2006. Values are the average of more than 16 measurements from unique instruments per sample date, ± 1 SD. (Data originally appeared in reference 20.)