Get your macronutrients here.

The soil is not white in Oakville, these mounds are large piles of fertiliser heaped around the edge of the Opus One vineyard waiting to be applied and disked in.

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.

K Fertilisation.

No, this photograph isn't meant to be in soft focus, nor did I have too much to drink last night...it's just teeming down. 'Out of the Window' Vinogirl is sitting at the dining table with a cup of Earl Grey gazing out at a bleary, sodden vineyard. The Vinodogs curled up in their beds, periodically eye me askance, disapprovingly, like the rain is all my fault. They will be deprived of their walk today. Poor V2 hasn't had many instances of rain in her short life so she's a little confused.
What is not confusing is the propitious timing of Napa's first significant rainfall since February. Vinomaker and I have been busy out in the vineyard applying Potassium sulphate (K2SO4) around the vines. Placing the fertiliser near the root zone in large amounts, is the best means of overcoming soil fixation as Kalium, (K), is particularly immobile in the soil. It moves so slowly in fact that the results may not be seen until the second season after the application. Though it is an expensive procedure, it is an absolutely necessary one. The potassium needs of a grapevine are high, comparable to the demand for nitrogen, and a deficiency would result in poor vine growth and lower crop yields. However, one application will last at least 5 years.
So Mother Nature continues to smile on Vinogirl and Vinomaker, albeit in a different way, and helps move the fertiliser into the soil...next up, cover cropping.