The effect of Nitrogen and Sulphur foliar applications in hot climates

Abstract

Vine nitrogen deficiency can negatively influence the aroma profile and ageing potential of white wines. Canopy management can alter vine microclimate, affect the nitrogen availability and influence the response of leaf senescence. Increasing the nitrogen availability to vines can increase the Yeast Assimilable Nitrogen (YAN) levels in harvested fruit and wine. Studies show that foliar nitrogen and sulphur applications at véraison, on low YAN Sauvignon blanc grapes have an effect on the level of amino acids (Jreij et al. 2009) and on S-containing compounds such as glutathione and thiols (Lacroux et al. 2008), which in turn can influence the formation of major volatiles and the aroma profile of the wine. The purpose of this study was to determine the effect of different foliar fertilization (spray applications) on the chemical and sensory composition of Vitis vinifera L. cv. Sauvignon blanc and Chenin blanc musts and wines. A Sauvignon blanc plot in the Elgin area and a Chenin blanc plot in the Somerset West area (Western Cape, South Africa), with naturally low nitrogen status, were sprayed three weeks and one week prior véraison. Urea (10 kg/ha) was used for the nitrogen application (N), elemental micronized sulphur (5 kg/ha) for the sulphur application (S), and combined urea (10 kg/ha) and elemental micronized sulphur (5 kg/ha) were used for the sulphur and nitrogen application (N+S). The applications were sprayed on the foliage of the vines and the control received no applications. Analysis of YAN, non-volatile and volatile compounds, namely volatile thiols, major volatiles, fatty acids, esters, alcohols, monoterpenes, and glutathione were done to evaluate the differences between the treatments. Sensory evaluation was performed by expert tasters using a free sorting method at two different stages of aging (3 months and 9 months after bottling). The YAN levels in the grapes were higher in the N and N+S applications compared to the control. The wines produced from the S and N+S applications contained more 3-mercapto-hexanol (3MH) and 3-mercaptohexyl-acetate (3MHA) compounds. Therefore with sufficient nitrogen and sulphur in the vines there may be an increase in aromatic quality and ageing potential of the Sauvignon blanc and Chenin blanc vines.

References
Jreij, R. et al., 2009. Combined effects of soil-applied and foliar-applied nitrogen on the nitrogen composition and distribution in water stressed Vitis Vinifera L. cv Sauvignon blanc grapes. J. Int. Sci. Vigne Vin, 43(4), pp.179–187. Lacroux, F. et al., 2008. Effect of foliar nitrogen and sulphur application on aromatic expression of Vitis vinifera L. cv. Sauvignon blanc. J Int Sci Vigne Vin, 42(3), pp.125–32.