Durbanville Hills Cellar News - November 2013

Tuesday, 3 December, 2013
Durbnaville Hills Cellar
In writing to you for the last time in 2013 I don’t know whether I should talk about what lies behind or predict what I believe lies ahead, particularly as far as the weather is concerned. In September I told you of tractors stuck in the vineyards; last month I shared my ideas on climate change.
In September I told you of tractors stuck in the vineyards; last month I shared my ideas on climate change. Now both seem to have come together in November with 60mm of rain caused by a Black South-Easter. In getting “only” 60mm of rain we seem to have been fortunate compared to some other areas of the Winelands where more than 200mm of rain fell in just two days.

The Cape Doctor, the strong south-easterly wind that normally blows during fair weather this time of year, helps to ensure that the vines stay healthy. Occasionally, in Spring and Autumn, it can be accompanied by a cut-off low-pressure system, bringing in heavy rain from the "wrong" side and causing flash floods and soaked vineyards so that locals then call it by the ominous name of Black South-Easter.

The Weather office, contrary to its usual pronouncement, did not state this phenomenon was "normal for this time of the year”, but issued timely warnings of potential flooding in certain areas, predictions which proved to be only too accurate. Friends from the rougher parts of the Winelands claimed they recorded 130mm halfway through the downpour. However, they couldn’t provide any subsequent information as their rain meters overflowed and they don’t like going out into the wet, not even in the interest of science.

Free fertiliser
Growth in the vineyards in our area tends to be somewhat vigorous and we strive to keep crop and vegetation in balance to help ensure grapes of good quality. To this end we have made numerous changes to trellis systems, vineyard practices, irrigation and nutrition in the past number of years.

So it was with some alarm that I heard thunder ahead of the rain because I knew the balance we nurture so carefully was about to be disturbed. I was in town when it happened and a passerby must have noticed my stricken look because he said: “You can be sure there’s a lot of rain on the way.” I don’t think he quite caught my drift when I added rather grumpily: “And a lot of fertiliser too.”

As you all know, air consists of a combination of gases of which by far the biggest component is nitrogen at slightly more than 78%, followed by oxygen at just under 21%. Nitrogen in its free form is of very little use as nutrition except when the enormous energy released by lightning breaks up nitrogen molecules enabling them to bind with oxygen to form nitrogen oxides that are soluble in rain water and can be utilised by plants. Green swimming pools after thunderstorms confirm this, as algae love this food from heaven. They produce their masses of green slime in even greater abundance when the ozone, which is also contained in the rain drops, depletes the chlorine.

In the vineyards we control exactly the amounts of fertiliser provided and prefer to do without any “freebies”. However, when we do end up with such an unexpected “gift” we very carefully remove the resultant exuberant growth to restore and maintain the balance.

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