FERTILISER GUIDELINES FOR THE WINE INDUSTRY

• What is a fact however, is that any condition that can negatively affect the photosynthetic capacity/working of the leaves, can lead to an increased K-movement from the leaves/petioles to the bunches/berries. The most important factors involved here are a lot of wind, dense canopies and water deficiency in especially the ripening period, which leads to increased K in the bunches and must. • Agenbach (2001) found that the seasonal climate has the greatest influence on K-levels. Canopy management and even the fertilisation treatment were not meaningful factors. However, the soil’s potassium content before veraison, shoot growth (and of course canopy qualities) at and after veraison as well as water stress during the ripening period, did impact on the K-accumulation in the berries. • Wooldridge (2012) further found that the higher natural K-levels of shale soils do not necessarily contribute to higher K-levels in the grapes and must compared to the naturally lower levels in granite soils. The K“pool” and potential for translocation to the bunches can be greater, but there are other factors that determine the ultimate K-levels in the grapes and wine. • If high K-uptake and movement do occur due to the above-mentioned fac tors, the potential is higher that the K-cations can bind with the malic acid and can crystallise as potassium bitartrates. This can happen in the berry or after crushing and can cause a decline in the total acidity. The pH however, may increase, decrease of remain the same depending on the value. Calcium and Mg • Many local as well as European winemakers argue that grapes that originate from lime-rich soils (with a high Ca-content) yield wines with low pH and good fixed acids which in particular lead to young white wines with a lively, refreshing palate with lime flavours. These wines also have a very good maturation potential, but it has not yet been scientifically proven that these characteristics can indeed be attributed to a high Ca-content in the wine. • Different practices, like for example Ca and Mgfertilisation and various canopy management practices, have been used in an attempt to reduce the K-uptake of granite-rich vineyards (Engelbrecht & Saayman, 2007). It has been found that Ca- and Mg-fertilisation can decrease the juice pH, but the reason for this was unclear. A soil application of Mg-sulphate resulted in the best reaction, but excessively high applications of Mg-salts can be harmful to the soil structure.

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