Effects of Long-Term Nitrogen, Phosphorus, and Potassium Fertilization on Chenin blanc Vines. II. Leaf Analyses and Grape Composition

¹ Viticultural and Oenological Research Institute (VORI), Private Bag X5026, 7600 Stellenbosch, RSA.

The effect of N, P, and K fertilization on the nutrient concentrations in leaves and on grape and wine quality of Chenin blanc was followed over a period of 10 years. The levels of N were 16 (N₀), 56 ( N₁), and 96 (N₂) kg/ ha/yr; P applications were 0 (P₀), 9 (P₁), and 18 (P₂) kg/ha/yr; and K applications were 0 (K₀), 45 (K₁), and 90 (K₂) kg/ha/yr. Nitrogen fertilization caused only marginal increases in the N contents of both blades and petioles. For musts, however, the total N concentration in the case of the N₂ treatment was 50 mg/L higher than that of N₀. No consistent effect of N fertilization on either grape or wine quality could be detected, but during one season the occurrence of bunch rot was enhanced by the highest N application. The application of P fertilizer caused appreciable increases in the P levels of blades, petioles, and musts, with the most sensitive indicator of P nutrition. At veraison the deficiency level for P in petioles appeared to be around 0.08%. Furthermore, the K concentrations in both blades and petioles of the P₂ treatment was reduced, pointing to a P/K antagonism. Apart from this, P fertilization had little effect on either grape or wine composition. The K levels in blades, petioles, and musts of the K₁ treatment were increased significantly over that of K₀, while K₂ caused a further increase of K concentration in blades and petioles but not in the must. In addition to this, K fertilization also tended to reduce the N levels of the musts. Both acidity and pH of musts from the K₁ treatment were increased in comparison to that of musts from the K₀ treatments, while little further response was found for K₂. A petiole deficiency level of 1% for K seemed to be valid for South African conditions. Potassium nutrition was found to interact with arginine concentration in must, making the latter a doubtful indicator for N nutrition when levels of K in the soil are high.

Key words: nitrogen, potassium, phosphorus, mineral nutrition, fertilization, grapevines

Submitted on May 31, 1988

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