Gypsum is useful during the establishment phase of a new vineyard and also for ongoing vine nutrition. It can be used to remedy certain local soil-quality problems caused by earth movement associated with contouring. In many situations, soil improvement will reduce vine establishment losses, encourage young vine growth and thus increase early vineyard production.
The production of premium quality wine usually requires that winegrapes be established on soils that limit vegetative growth and produce an open canopy. These soils are frequently very free-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.
In New Zealand, the rapid expansion of viticulture has meant that many new vineyards are being established in areas previously used for other purposes. Often these ‘ideal’ viticultural soils, as well as being free draining, are also low in organic matter.
Another feature of the soils of the new viticultural areas is that they are often prepared for planting by ‘contouring’ to remove the worst of the topographic irregularities so as to facilitate later 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 stony soil types that are easily leached. In some other 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 are a well-known and effective way to remedy many of these adverse soil conditions, especially in heavier soils with high clay contents. Here it encourages the formation of a better soil structure with better retention of organic matter resulting in better water drainage. 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. Gypsum can also help with compaction problems.
To gain the best benefit:cost in terms of soil remediation from applications of gypsum, it makes sense that the gypsum should be distributed in line with some assessment of the local soil problems. It should be deposited at the highest density (at rates up to 4,000 kg/ha) in areas where soil problems are perceived to be worst and at lower rates where they are less of an issue.
Stony soils tend to be easily leached and thus nutrient deficient. Grapevines, like other plants, require calcium and sulphur. Gypsum is a good source of both of these having the advantage that it is pH neutral so applications do not raise soil pH (grapevines do best in soils having pH values between 6 and 7). Winegrapes require around 250 kg/ha of calcium each year. A substantial part of this can be supplied in the form of gypsum. Gypsum applications can also be used to supply sulphur. They need about 120 kg/ha of sulphur annually and about one third of this will come from the organic sulphur cycle in the soil, one third from a base dressing of gypsum (40 kg/ha of sulphur requires 220 kg/ha of gypsum) and the balance from other sulphur containing fertilisers.
One of the, so-called, physiological disorders to which winegrapes are subject is ‘Shanking’ or ‘Bunch-stem Necrosis’. Typically a portion of the fruit stalk dies and the berries below this point in the cluster either drop off (yield loss) 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, for the seasonal effect implies a contribution from the weather (cold at bloom?), the variety effect a genetic predisposition (e.g. Reisling is particularly susceptible) and the vineyard effect possibly an ‘internal’ calcium deficiency.
There is not much that can be done about the weather or the variety responses but applications of gypsum (gypsum is one of the more soluble forms of calcium) so as to raise soil calcium to luxury levels in advance of Shanking symptoms becoming apparent may reduce the risk in vulnerable varieties following adverse weather. If soil calcium levels are on the low side anyway, gypsum applications would certainly be beneficial.