Transformations transport and potential unintended consequences of high sulfur inputs to Napa Valley vineyards

摘要

Unintended anthropogenic deposition of sulfur (S) to forest ecosystems has a range of negative consequences, identified through decades of research. There has been far less study of purposeful S use in agricultural systems around the world, including the application of elemental sulfur (S⁰) as a quick-reacting fungicide to prevent damage to crops. Here we report results from a three-year study of the transformations and flows of applied S⁰ in soils, vegetation, and hydrologic export pathways of Napa Valley, CA vineyards, documenting that all applied S is lost from the vineyard ecosystem on an annual basis. We found that S⁰ oxidizes rapidly to sulfate () on the soil surface where it then accumulates over the course of the growing season. Leaf and grape tissues accounted for only 7–13% of applied S whereas dormant season cover crops accounted for 4–10% of applications. Soil S inventories were largely and ester-bonded sulfates; they decreased from 1,623 ± 354 kg ha^-1 during the dry growing season to 981 ± 526 kg ha^-1 (0–0.5 m) during the dormant wet season. Nearly all S applied to the vineyard soils is transported offsite in dissolved oxidized forms during dormant season rainstorms. Thus, the residence time of reactive S is brief in these systems, and largely driven by hydrology. Our results provide new insight into how S use in vineyards constitutes a substantial perturbation of the S cycle in Northern California winegrowing regions and points to the unintended consequences that agricultural S use may have at larger scales.