Timing of nitrogen fertilisation and the effect of poultry manure on the performance of grapevines on sandy soil. II. Leaf analysis, juice analysis and wine quality.
Conradie, W. J.
South African Journal for Enology and Viticulture. Volume 22, Number 2, 2001 , pags. 60-68.
2001
บทคัดย่อ
The effects of timing of N application and of different N sources (organic vs. inorganic) on leaf composition, juice composition and wine quality of grapevines on a sandy soil with low organic material were investigated over a period of nine years (from 1981/82 to 1989/90) in Stellenbosch, South Africa. Two Vitis vinifera cultivars, i.e. Bukettraube (white) and Heroldrebe (red), both grafted onto Ramsey, were used. The control (N0) received no N, while three treatments each received 50 kg N/ha in inorganic form. The N was applied either as three equal installments, split between budbreak, fruitset and postharvest (N1), as a single application at budbreak (N2), or as a single postharvest application (N3). A fifth treatment (N4) received 50 kg N/ha at budbreak in the form of poultry manure. Total N in leaf blades and petioles, sampled at fruitset, tended to be highest for N2 and lowest for N0, but differences were relatively small. The NO3-N in petioles showed larger differences, with the value for N0 generally being significantly lower than that of inorganic N treatments. A single application of N at budbreak (N2), delayed maturity for both cultivars, while this was also the case for split applications (N1) for the more vigorous cultivar (Bukettraube). Total N in juice was lowest for N0 and N4, and higher for N1, N2 and N3, for both cultivars. In the case of Bukettraube, assimilable N was lowest for N0, while the other treatments did not differ. For Heroldrebe, with a lower sugar content, assimilable N was lowest for N0, N2 and N4, and higher for N1 and N3. Arginine was the predominant amino acid, constituting 61 and 40% of total amino-N for Bukettraube and Heroldrebe, respectively. Wine quality (Bukettraube only) was always lowest for N0 and higher for N1, N2 and N3. During most seasons, quality did not differ between the latter three treatments. However, with N2 being more prone to fungal diseases, wine quality was reduced for this treatment when climatic conditions favoured Botrytis cinerea infection. Wine from the organic treatment (N4) scored marginally higher than N1, N2 and N3. Under the conditions of this trial, split applications of N (budbreak, fruitset, postharvest) or a single application during the postharvest period, or application of organic N ensured highest wine quality. Reaction to N may be different for less vigorous rootstocks.