Wine Grapes

Grapevines do best growing in soil with a pH range 6 -7. The production of premium quality wine usually requires winegrapes to be established on soils that limit vegetative growth and produce an open canopy. These soils are frequently freely draining and often have a high stone content. While, in mature vines, the reduced vegetative growth achieved with these soils is highly desirable, it is a different matter with young vines during establishment. The young vines require good access to water and nutrients in the upper soil layers to encourage root establishment, good vine health and vigorous growth. These factors will minimise vine deaths and vineyards will also come into production as early as possible.

Another feature of soils in new viticultural areas is that they are often prepared for planting by ‘contouring’ to remove the worst of the topographic irregularities to facilitate access by vineyard machinery (harvesters etc). These soils are also often subject to deep ripping and surface cultivation. These practises tend to lead to the presence of stripes of different soil types running across the vineyard with some of these (especially those where subsoil has been exposed by topsoil removal) being particularly low in organic matter and nutrients. The problem is made worse on stoney soil types that are easily leached and can be nutrient deficient. In some areas, depending on the nature of the subsoil that has been exposed, poor drainage can also be a problem.

Although the ideal soil types for viticulture are more resistant to compaction than other soils, the increase in mechanisation in modern vineyards can still lead to compaction problems.

 

Soil structure improvement

Applications of gypsum can be an effective way to remedy many adverse soil conditions, eg. compaction, especially in heavier soils with high clay content. With regular annual applications Gypsum can improve soil structure, retention of organic matter, drainage of water through the soil profile and reduce surface water pooling. Moreover, gypsum also helps to reduce wind and water erosion that can be a problem in freshly prepared and exposed soils during the early years of vineyard establishment.

To gain the best cost: benefit ratio in terms of soil remediation, gypsum should be distributed in line with an assessment of the local soil issues and based on a recent soil lab test result. Gypsum can be applied up to 3,000kgs/ Ha in areas where soil problems are perceived to be worst and at lower rates where they are less of an issue.

 

Nutrition

Grapevines, like other plants, require calcium and sulphur. Winegrapes require around 250 kg/Ha of calcium each year, a substantial part can be supplied in the form of gypsum. They also require about 120 kg/Ha of sulphur annually, about one third will come from the organic sulphur cycle in the soil, one third from a base dressing of gypsum ( 220 kg/Ha of gypsum supplies 40 kg/Ha of sulphur) and from other sulphur containing fertilisers. Gypsum is pH neutral so applications do not raise soil pH.

 

Bunch-stem necrosis

One of the physiological disorders of winegrapes is ‘Shanking’ or ‘Bunch-stem Necrosis’ where a portion of the fruit stalk dies and the berries below this point in the cluster either drop off or are retained but fail to sweeten (reduced juice quality). This condition can be particularly serious in some seasons, and in some vineyards, and with some varieties. Shanking probably has a multiplicity of causes, the seasonal effect implies a contribution from the weather, the variety effect (e.g. Reisling is particularly susceptible) and the vineyard soil effect possibly causing an ‘internal’ calcium deficiency.

Applications of gypsum (gypsum is one of the more soluble forms of calcium) to raise soil calcium to luxury levels in advance of Shanking symptoms may reduce the risk in vulnerable varieties following adverse weather. If soil calcium levels are on the low side, gypsum applications would certainly be beneficial.

An application of gypsum will depend on soil type and results from a recent soil lab test.

 

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