Tuesday, 15 January 2013

Hydroponics vs Vosne

Reading a recent article about grape growing in Santa Rita, I was struck at the fine line between irrigation and hydroponics. Without their weekly fix of water, vines grown on Santa Rita’s sandy valley floor would die. Albert Hammond’s contralto has familiarised us to the fact that it never rains in Southern California, and the limited capacity of their soils to hold onto water only intensifies the problem.

Water enters the vine primarily through the roots.  Up until veraison, the xylem conducts water around the vine unimpeded, to the leaves, stems and bunches. Easy access to water at this vegetative stage of growth influences vine vigour and berry size, and red wine grapes in particular are thought to benefit from a measure of early season stress. Skins become thicker, and the berries are better exposed to light; the two processes reinforce each other.

After veraison, the picture becomes more confused. The xylem flow into the berries becomes severely disrupted, and the direct link between soil moisture and berry-size is broken. The continued swelling of berries after veraison presented something of a conundrum to researchers, but recent investigations in Germany have shown how water also enters the grape clusters through the skins, rachis and pedicles. Rain falling on the berries is absorbed through the skins (though this movement also declines with maturity), yet even without rainfall, grapes will normally continue to expand as they ripen. Just why they do this continues to be the cause of speculation, but one plausible account suggests that bunch closure creates a cylinder around the stem tissues of the bunch. Fluctuations in ambient temperature will cause water to condense onto the interiorised rachis and pedicles, which then wicks into the berries, causing them to swell. If this is the case, then one can easily imagine a feedback mechanism in which large berries pre-veraison result in tight clusters, leading to water condensation and more rapid enlargement post veraison.

One of the significant differences between the vineyards of the Côte de Nuits is their underlying pedology and geology; climatically they are near-identical. The best soils shed water rapidly, but their depth and structure facilitates the vertical movement of water from the underlying limestone during periods of drought. They are precisely irrigated, if you like, though the pipes and pumps are in this instance of a geological origin. The berries remain relatively small in humid years; while in drought years, like 2005, the top vineyards can still access sufficient water to maintain metabolic function. Of course, the best vineyards will still be subjected to the climatic trends of a particular vintage, but they will be buffered in a way that the lesser vineyards are not.

All this is fascinating because it suggests that if irrigation can be precisely controlled, then grape quality can be favourably manipulated.  In a hydroponic system, watering could be tailored precisely to the qualitative needs of production, keeping berries small and clusters open, whilst the berries could simultaneously be protected from the effects of deluge and damaging water absorption through their skins. Of course, you would need climatic control, but this is the same for hydroponically grown tomatoes and peppers as well.

If this is all starting to sound expensive, you are right. But at the end of a week in which mediocre Burgundies were  offered at £thousands a case (and knowing there are Grands Crus coming through that will make these prices look like pocket money), how long can it be before somebody takes a punt on creating their own minutely managed terroir?

Sunday, 13 January 2013

Spur Pruning Tixover Vineyard

Shoots of even vigour and length, carrying similar crop loads is the aim of most viticulture. Some people achieve this with cane pruning, but we prefer spur pruning.

On a low vigour site like Tixover, spur pruning requires patience.Try and elongate cordons by more than four buds at a time, and they suffer from acrotony: the canes shoot at their ends, but not in their middles, so that the distance between renewal points the following year is too great. Likewise, lay down canes that are too long, and already established spur positions further down the cordon will fail. Normally 10cm is a sufficient distance between shoots, but inour damp and sunless climate we look to achieve 15cm of separation between 1 bud spurs.  

Each Cordon will eventually carry 6-7 spurs, with a renewal spur just above the rootstock graft. This basal renewal spur gives us an option to replace and rebuild the vine’s aerial structure if the vine becomes diseased, or we start to drop spur positions along the cordon. Secateurs are a useful measuring tool in the vineyard. The gap between single-bud spurs needs to be less than the length of the secateurs, and cordon extensions again run the risk of acrotony if they are longer than the secateurs.

One unanticipated consequence of spur pruning is improved frost resistance. When we have suffered frost damage, shoots on spurs seem a degree or two hardier than shoots on canes.