Whilst vineyard managers are primarily concerned with all things harvest at this time of year, they must also consider whether an application of fertiliser is necessary. Apparently, the people at Opus One who are responsible for the health of this particular vineyard have decided that a good dose of potassium sulphate (K2SO4) is in order. I am assuming that it is K2SO4: potassium chloride (KCl) is another form of of potassium fertiliser that could be used, but it should not be used in a vineyard that may perhaps have an existing salinity condition.
Late autumn or early winter is a good time to treat a vineyard as full advantage can be taken of winter rainfall to move the fertiliser down into the soil and on into the root zone. Seeing as this vineyard was ripped out last spring, perhaps due to some unnamed creepy crawly, this empty field is a clean slate on which a new and improved, and fertilised, vineyard can be planted.