FERTILISER GUIDELINES FOR THE WINE INDUSTRY

amounts of S can vary between 1-100 kg/ha -1 j -1 and is often enough to meet the nutritional needs of plants. A considerable amount of S is also found in the organic fraction of the soil, with N:S-ratios that vary between 10:1.2 and 10:1.5. This S is released through mineralisation. Sulphur deficiencies are generally not expected in grapevines due to Scon taining fungicides commonly being used in the past, and fertilisers like su perphosfate containing much S in the form of gypsum. Conditions favourable for Sdeficiencies include i.a. high rainfall, regions located far from industries or the sea, lightly textured soils, excessive cultivation which accelerates the breakdown of organic material, the use of S-free fertilisers and the cultiva tion of legumes with a high S-requirement. The amounts of S contributed by fungicides are nowadays negligible, and fertilisers are increasingly higher concentrated, S-free compounds or mixtures, making the S-requirements of grapevines an increasingly important consideration. Recently, a Sdeficiency was indeed identified in grapevines under the abovementioned conditions, and where neither S-containing fungicides or fertilisers were used. In grapevines Sdeficiency symptoms are also nonspecific. It exhibits a light yellowing of leaf edges, bush-like growth, shoots that curl back, cracks in the bark of shoot bases, red petioles, tendrils and bunch stems in the case of Cab ernet Sauvignon and the angle between the petiole and main vein shrinking. In rootstocks the leaves fold upwards, together with clear leaf edge chlorosis and necrotic specks, especially on the back of the leaves, while shoots of certain cultivars show red colouration (Fig. 17 & 18). Gypsum application is the most practical and costeffective solution for Sdefi ciencies, but recovery takes place gradually over more than one season. The annual S-requirement of a grapevine is comparable to that of P and an applica tion of 1 ton/ha -1 gypsum should be sufficient for the lifetime of the grapevine. According to local norms for the sulphur content of soils, a value of 0-4 mg kg -1 is considered “low”, against “slightly low” for 46 mg kg -1 , “satisfactory” for 6-8 mg kg -1 , “good” for 812 mg kg -1 and “high” for >12 mg kg -1 .

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