Short-term fates of high sulfur inputs in Northern California vineyard soils

The widespread application of elemental sulfur (S⁰) to vineyards may have ecosystem effects at multiple scales. We evaluated the short-term fates of applied S⁰ in a Napa Valley vineyard; we determined changes in soil sulfur (S) speciation (measured by X-ray absorption near-edge structure (XANES) spectroscopy), soil pH, extractable sulfate (SO₄ ²⁻), and total S to evaluate changes in acidity and soil S within the vineyard over time. Surface soil samples were collected immediately prior to and following two applications of S⁰ (6.7 kg S⁰ ha⁻¹), with weekly collections in the 2 weeks between applications and following the last application. XANES spectra indicated that the majority of soil S persists in the +6 oxidation state and that S⁰ oxidizes within 7 days following application. Soil pH and extractable SO₄ ²⁻ measurements taken at 30 min after S⁰ application revealed generation of acidity and an increase in extractable SO₄ ²⁻, but by 12 days after application, soil pH increased to approximately pre-application levels. These data suggest that the major consequence of reactive S applications in vineyards may be the accumulation of soil SO₄ ²⁻ and organic S during the growing season, which can be mobilized during storm events during the dormant (wet) season. In spatially-extensive winegrowing regions where these applications are made by hundreds of individual farmers each year, it will be important to understand the long-term implications of this perturbation to the regional S cycle.